≡ Menu

A SETI Search of Earth’s Co-orbitals

One objection to SETI is that it is not falsifiable — there is no point at which a lack of signals can prove that extraterrestrial civilizations do not exist. But there are some aspects of SETI that can be falsifiable. Consider a class of objects near enough for us to investigate not only with listening efforts but with probes, one small enough to be thoroughly covered, and one most people know almost nothing about. Could these offer a listening post for ‘Bracewell probes,’ a way of watching the development of our culture and reporting home to ETI? And if so, could we combine SETI with METI to advance both disciplines without compromising our own security?

If the idea of nearby probes seems far-fetched today, it was even more so when Ronald Bracewell advanced his ‘sentinel hypothesis.’ Bracewell took the question of SETI and stood it on its ear. That was no mean feat in 1960, for SETI was just being born in that year through the efforts of Frank Drake at the Green Bank instrument in West Virginia. While Drake was, reasonably enough, asking whether we might pick up signs of an extraterrestrial civilization around another star, Bracewell had begun to wonder whether there might be a different way to study an alien culture. A long-lived probe could be planted in any system under investigation.

Image: Stanford’s Ronald Bracewell, who in 1960 advanced the idea of long-lived probes investigating other planetary systems. Credit: Stanford University.

Add Von Neumann-style self repair and such an object might stay on sentry duty for millennia, for aeons, all the while returning useful data about the changes occurring on an interesting habitable planet. And if a civilization arose on that planet and reached the level of electromagnetic communications, then the probe could be programmed to make contact, at whatever threshold its builders chose.

Jim Benford has been thinking about Bracewell probes and their possibilities of late because they offer advantages over traditional forms of SETI. For one thing — and this is a huge advantage — a contact once made with a local probe could initiate dialog in more or less real time, without interstellar lightspeed delays, although of course we would be querying an intelligence that was itself subject to those delays if it communicated with its home world.

Image: Plasma physicist Jim Benford (Microwave Sciences).

The question is interesting enough that is has inspired some top-notch science fiction, in particular David Brin’s novel Existence, where the idea is extended to not one but a series of different probes at work in Earth orbit and in the asteroids. But it would be Michael Papagiannis who in 1978 wrote seriously about the asteroid belt as a possible venue for such ‘lurkers,’ (to use Benford’s term). Benford is not sold on the asteroid belt as a target.

For we also have an all but undiscussed body of targets that can be called co-orbital objects with Earth. These small objects approach the Earth closely and on an annual basis, for they have the same orbital period as Earth. We might study them for signs of artificiality through spectroscopy in the visible or near-infrared as well as pinging them with radar or other signals.

What strange orbits these objects occupy, with some in so-called ‘horseshoe’ orbits — these can actually become quasi-satellites for a time before returning to earlier orbital parameters. Have a look at a horseshoe orbit.

Image: A horseshoe orbit. No wonder these objects took so long to find. Credit: James Benford.

And from another view:

Image: Plan showing possible orbits along gravitational contours. In this image, the Earth (and the whole image with it) is rotating counterclockwise around the Sun. Credit: Wikimedia Commons.

As Benford explains, think of a quasi-satellite as an object in a 1:1 orbital resonance with a planet, so that the object stays close to the planet over many orbital periods. Outside the Hill sphere (that region where an astronomical body dominates the attraction of satellites), quasi-satellites cannot be considered true satellites. Instead, while their period around the Sun is the same as the planet, they seem to travel in an oblong retrograde loop around it.

Beyond horseshoe orbits we also find ‘tadpole’ and ‘quasi-satellite’ orbits as shown in the figure below. Here we find stable orbits for centuries and possibly longer, much longer. Co-orbitals include Cruithne (3753), a 5-kilometer object with closest approach to Earth of 0.080 AU — interestingly, this one experienced a close encounter with Mars in historical timescales, around the time of Periclean Athens. Another is Earth Trojan 2010 TK7, which oscillates around the Sun-Earth Lagrangian point L4, and 2016 HO3, which Benford describes as “currently the smallest, closest, and most stable (known) quasi-satellite of Earth,” with a minimum distance of 0.0348 AU. A number of other quasi-satellites are known.

Image: Three types of co-orbital orbits. Credit: James Benford.

How might we investigate these objects with the tools of SETI, and why? Benford calls for a multi-year program of observations in radio and optical wavelengths as well as planetary radars, with the main burden of the work falling upon the Lick Observatory and other platforms involved in the Breakthrough Listen project. Here we’re looking for size, shape, rotation periods and spectra. At the same time, he urges SETI observations of this range of objects.

Planetary radar also comes into play, and with an interesting consequence. From the paper:

These objects have not been pinged or imaged by any planetary radar as yet. Recent developments in planetary radars have shown they can detect the presence and trajectories of spacecraft in lunar orbit, even though their size is a few meters. Whether these radars are sensitive or powerful enough to get a return signal from any of the presently known co-orbital objects requires analysis. In any case, they can ‘ping’ the objects, meaning that a signal reaches there but the return signal may be too weak to detect at Earth.

Here the Bracewell idea comes into full view:

If there is an ET probe there, it might sense that it had been noticed by us.

What an interesting campaign Benford has in mind. It includes simultaneous use of planetary radar on the target and SETI observations. Readers at this point may be recalling that Benford is on the record with strenuous objections to METI, the idea of Messaging to Extraterrestrial Civilizations, given the limits on what we know about what is around us in the cosmos, and the need for international agreement on how to proceed, as opposed to sending signals to the stars in random bursts of activity and with wildly varying content.

Yet here we are talking about an activity that, in the unlikely event there is a probe in our own Solar System, could conceivably activate it and cause it to respond. The Bracewell probe is front and center here, recalling Duncan Lunan’s 1974 proposition that a Bracewell probe could be the cause of long-delayed echoes of radio transmissions heard in the 1920s. Benford notes that the phenomena Lunan identified have subsequently been explained as unusual propagation patterns in Earth’s magnetosphere. But it’s interesting to see Benford’s response to the idea of METI in this new context:

This would be ‘Active SETI’, which could solicit a response from a hypothetical probe. This does not incur the objections to sending interstellar messages, messaging to ETI (METI), because any such alien lurkers would already know we are here. Of course, this is at very short range compared to the interstellar ambitions of METI enthusiasts. We presume that Lurkers already know that we have radar, but might not respond to a single radar painting such as we have done to many asteroids. If we want to send a message, as Paul Davies suggested for the LaGrange points in 2010, how would a signal be designed to elicit such a response?

An interesting question indeed, and as the author points out, actually working on a near-term use of METI at a nearby target could benefit research into message creation and drive the field forward. The problem is an easy one to state: What kind of message would one send to a lurking probe that would ‘awaken’ it to the possibility of communicating with us?

As to falsification and SETI:

In my view SETI has suffered from being seen as somewhat nonscientific. That’s because it doesn’t offer itself as a study with falsifiable propositions, which is the very definition of science, as Popper said.

I advance a falsifiable proposition: “There exist in near-Earth space extraterrestrial probes which are observing Earth and it may be possible for us to find and contact them.

This proposition can be disproved. We can observe them, ping them with radar, transmit messages to them, send robotic probes to them and visit them with human spacecraft missions.

What a lively concept. We blend SETI’s listening to the stars with astronomical imaging and spectroscopy, while simultaneously turning METI into what Benford calls a ‘local experiment.’ And as we do this, our efforts at studying co-orbital objects advance the cause of astronomical science, which is engaged in the great process of mapping the entire Solar System.

The paper is Benford, “Looking for Lurkers: Objects Co-orbital with Earth as SETI Observables,” submitted to the Astrophysical Journal. I’ll have a link to the preprint as soon as it goes live.

tzf_img_post

{ 11 comments }

Working with the Unexpected at Asteroid Bennu

We know by now to expect surprises when we do something for the first time with a spacecraft. The latest case in point is OSIRIS-REx, which has revealed multiple unexpected facets of the asteroid Bennu, near which it has been operating since December. Consider the surface of the asteroid, a key factor in how the mission goes forward since this is a sample return mission, and that involves finding a place relatively free of surface debris from which to take the sample.

The problem: This smallest body ever to be orbited by a spacecraft turns out to be strewn with boulders. The original sample collection plan — christened Touch-and-Go (TAG) — will have to be altered, for it was dependent on a sample site with a 25-meter radius free of hazards. The OSIRIS-REx team has been unable to identify any site that meets those requirements. A new type of candidate site will have to be found, demanding higher performance using an updated sampling approach called Bullseye TAG that will be tailored for smaller sample zones.

Nonetheless, the OSIRIS-REx team remains optimistic:

“Throughout OSIRIS-REx’s operations near Bennu, our spacecraft and operations team have demonstrated that we can achieve system performance that beats design requirements,” said Rich Burns, the project manager of OSIRIS-REx at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Bennu has issued us a challenge to deal with its rugged terrain, and we are confident that OSIRIS-REx is up to the task.”

Image: Bennu’s surface is rockier than expected, creating challenges for the team whose mission is to scoop up a sample of pristine material and return it to Earth in 2023. Credit: NASA/Goddard/UA.

The larger issue facing asteroid investigations is the question of computer modeling. The reason scientists have assumed that Bennu’s surface would be generally smooth is that observations from Earth of the object’s thermal inertia and radar measurements of its surface roughness have been integrated into computer models that made this prediction. We now learn that the interpretation of these models was not correct. Indeed, data from Bennu should help us refine such models to better predict what we’ll find on the rocky surfaces of small asteroids.

A suite of papers covering the Bennu findings has appeared in Nature following presentations at the recent 50th Lunar and Planetary Conference in Houston (citations below). On the matter of Bennu’s boulder strewn surface, a team from SwRI presents results showing that the surface geology of the asteroid is between 100 million and 1 billion years old. That too can be considered a surprise, to judge from the remarks of SwRI’s Kevin Walsh:

“We expected small, kilometer-sized NEAs to have young, frequently refreshed surfaces,” said SwRI’s Dr. Kevin Walsh, a mission co-investigator and lead author of a paper outlining the discovery published March 19 in Nature Geoscience. “However, numerous large impact craters as well as very large, fractured boulders scattered across Bennu’s surface look ancient. We also see signs of some resurfacing taking place, indicating that the NEA retains very old features on its surface while still having some dynamic processes at play.”

Some of Bennu’s boulders are larger than 45 meters (150 feet) in size, much larger than earlier observations had predicted, and according to Walsh, they are simply too big to be the result of cratering. Instead, the scientist believes they date back to the formation of the asteroid.

But OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer — I have to untangle the acronym once in each post on the mission) continues to seize our attention long before the sample return with the news that particle plumes are erupting from its surface. This one caught everyone by surprise as well when, on January 6, the science team discovered the plumes while the spacecraft was about 1.6 kilometers away, with further detections in the ensuing months. Some of these particles were ejected from Bennu entirely, while others returned to the asteroid. None are thought to pose a danger to the spacecraft.

“The discovery of plumes is one of the biggest surprises of my scientific career,” said Dante Lauretta, OSIRIS-REx principal investigator at the University of Arizona, Tucson. “And the rugged terrain went against all of our predictions. Bennu is already surprising us, and our exciting journey there is just getting started.”

Image: This view of asteroid Bennu ejecting particles from its surface on January 19 was created by combining two images taken on board NASA’s OSIRIS-REx spacecraft. Other image processing techniques were also applied, such as cropping and adjusting the brightness and contrast of each image. Credit: NASA/Goddard/University of Arizona/Lockheed Martin.

We’ve already talked about the change in Bennu’s spin rate as an apparent result of the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect (see Asteroid Bennu: Changes in Rotation Rate), a fascinating find in itself, but it’s also encouraging in terms of understanding asteroid composition to learn that the MapCam color imager and the OSIRIS-REx Thermal Emission Spectrometer (OTES) have detected magnetite on Bennu’s surface, which points to rock and liquid water interactions on the asteroid’s much larger parent body.

Learning about the sources of organic molecules and water on Earth may be enhanced by our analysis of such asteroids, and we’re also beginning to learn what resources will be available in near-Earth space. Bennu truly offers us a window into the early days of the Solar System.

The papers are Lauretta et al., “The unexpected surface of asteroid (101955) Bennu,” Nature 19 March 2019 (abstract); Barnouin et al., “Shape of (101955) Bennu indicative of a rubble pile with internal stiffness,” Nature Geoscience 19 March 2019 (abstract); Walsh et al., “Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface.” Nature Geoscience 19 March 2019 (abstract); Hamilton et al. “Evidence for widespread hydrated minerals on asteroid (101955) Bennu.” Nature Astronomy 19 March 2019 (abstract); Hergenrother et al., “Operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations,” Nature Communications 19 March 2019 (abstract); Scheeres et al., “The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements,” Nature Astronomy 19 March 2019 (abstract); and DellaGiustina et al., “Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis,” Nature Astronomy 19 March 2019 (abstract).

tzf_img_post

{ 26 comments }

Carbon Monoxide as Biosignature?

Biosignature gases are those that can alert us to the possibility of life on a planet around another star. We’re moving into the era of biosignature observation by studying the atmospheres of such planets through instruments like the James Webb Space Telescope, and the effort to catalog the combinations of atmospheric gases that point to life is intense and ongoing.

One gas has turned out to be controversial. It’s carbon monoxide, which in some quarters has been considered to be the opposite of a biosignature, a clear sign, if detected in sufficient abundance, that a planet is not inhabited. Edward Schwieterman (UC-Riverside) begs to disagree, and a team led by Schwieterman has produced its modeling of biosphere and atmosphere chemistry to focus on living planets that nonetheless support carbon monoxide at levels we should be able to detect. The work appears in the Astrophysical Journal.

Interestingly, the paper harks back to our own planet’s deep past. We don’t expect to see high levels of carbon monoxide on life-giving planets because the gas is so quickly destroyed by chemical reactions on our oxygen-rich world. Go back several billion years, however, and Earth was a place whose oceans carried an abundance of microbial life, with an atmosphere that was at the same time all but devoid of oxygen, all under a surface lit by a much dimmer Sun.

The researchers found through their modeling that a world like this could support carbon monoxide levels of about 100 parts per million, several orders of magnitude higher than the traces we find of the gas in the atmosphere today. To co-author Timothy Lyons (UC-Riverside), that result carries a clear signal:

“That means we could expect high carbon monoxide abundances in the atmospheres of inhabited but oxygen-poor exoplanets orbiting stars like our own sun. This is a perfect example of our team’s mission to use the Earth’s past as a guide in the search for life elsewhere in the universe.”

Useful information indeed, but the findings go beyond worlds around G-class stars to include possible habitable planets around M-dwarf stars like Proxima Centauri, already known to host an Earth-sized planet in its habitable zone. Here the team found that a living world rich in oxygen could support high carbon monoxide levels from hundreds of ppm to several percent.

Image: A rocky planet orbiting Proxima Centauri might sustain liquid water (artist’s depiction). Credit: NASA, ESA, G. Bacon (STSc).

Astrophysical context is all, even if microbial biospheres with high levels of carbon monoxide, as Schwieterman says, “would certainly not be good places for human or animal life as we know it on Earth.” Photochemistry around such stars tells the tale. From the paper:

…the sequence of reactions that ultimately result in tropospheric OH is mediated by NUV radiation that is substantially less plentiful from M-stars such as Proxima Centauri because of lower photosphere blackbody temperatures, with the result that OH production is much less favored and consequently the sinks for CO and CH4 are much less efficient…

which leads to this:

Our results introduce some important caveats to previous suggestions for interpreting CO in planetary atmospheres, particularly for planets orbiting M dwarfs. For example, our demonstration that high CO may be achieved on inhabited planets means that while simultaneously high CO2 and CH4 with little CO is still a compelling biosignature, ambiguous scenarios with high levels of all three gases also exist, and these are mostly relevant for transit transmission observations of habitable zone planets orbiting M dwarf stars. Arguments regarding threshold CH4 levels that are incompatible with abiotic CH4 outgassing rates are in principle still valid (Krissansen-Totton et al. 2018b), but the proposal that CO provides a check on abiotic versus biological origins of CH4 is weakened by our results given likely near-future capabilities.

The ongoing examination of biosignatures is critical, for we could be looking at atmospheric analysis within a few short years. The challenge will be not only to hunt for reliable biosignatures but to avoid overlooking potentially habitable worlds. This paper indicates that two types of living world, one similar to our early Earth, the other around red dwarf stars, are able to support both life and the ready accumulation of carbon monoxide. The reminder that the photochemistry around M-dwarf stars allows substantial buildups of CO while supporting an inhabited world helps to clarify our range of interpretations.

Image: Carbon monoxide features prominently in oxygen-rich atmospheres in the habitable zone of a red dwarf star like Proxima Centauri. Credit: Schwieterman et al.

Ten years from now, will we have identified unmistakable signs of life around another star? I seriously doubt it. My guess is that many of our early efforts will turn up results that are ambiguous enough to allow for a range of conclusions. Thus the need to continue cataloging alternative biosignature gases and to fine-tune the spectral capabilities of the instruments we will use to survey these atmospheres. Also in play, according to the paper, are “…searching for biogenic seasonality” and “advanced methods for calculating atmosphere-surface disequilibria.”

The paper is Schwieterman et al., “Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System,” Astrophysical Journal Vol. 874, No. 1 (15 March 2019). Abstract / full text.

tzf_img_post

{ 19 comments }

Exploring our System’s Dust Lanes

Dust rings in the Solar System are of interest because they offer clues about the formation of the planets, as well as allowing us to contrast our own circumstellar dust with what we see around other stars in varying stages of planetary development. Recent work out of NASA’s Goddard Space Flight Center offers a dust ring with a difference from others we’ve found in our own system. Scientists have traced a dust ring near the orbit of Venus, and it’s one with origins different than the dust that occurs in Earth’s orbit as well as dust found near Mercury.

Explaining what is going on in Earth’s orbital path has us resort to the asteroid belt between Mars and Jupiter, where the collisions of small objects create a steady source of dust. The material drifts gradually toward the Sun, but some of it, moving near the Earth, is drawn into our planet’s orbit. A surprising amount of dust falls to Earth each day (one recent estimate is fully 60 tons of the stuff), and the mechanism seems a natural explanation for what we see at Venus.

But the explanation fails. The problem is that simulations of dust moving toward the Sun undertaken by GSFC astrophysicist Petr Pokorný produce a dust ring around the Earth but fail to generate one as dusty as the one around Venus. That sets up a series of simulations that Pokorný, working with colleague Marc Kuchner, have recently discussed in the Astrophysical Journal Letters. Their hypothesis: There exists a group of still undetected asteroids that orbit the Sun co-orbitally with Venus. Collisions between these over time account for the added dust.

Image: Asteroids represent building blocks of the Solar System’s rocky planets. When they collide in the asteroid belt, they shed dust that scatters throughout the system, which scientists can study for clues to the early history of planets. Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab.

A new population of asteroids offers an interesting observational challenge, but the dust ring involved is known to be large, about 26 million kilometers (16 million miles) thick and 10 million kilometers (6 million miles) wide. Even so, this is fairly diffuse material, only about 10 percent denser with dust than surrounding space, and accounting for it has been a challenge. The researchers tried modeling everything from long-period comets to main belt asteroids to explain it.

If asteroids move co-orbitally with Venus, perhaps in its orbit but often on the other side of the Sun, they may have gone undetected because of the difficulty in observing objects this faint so close to our star. Modeling different potential resonances, Pokorný and Kuchner find only a group of asteroids matching Venus’ orbits one for one would reproduce the dust ring.

The researchers work from the premise that this hypothesized group of asteroids has been there since the beginning of the Solar System. Modeling this scenario with a starting group of 10,000 asteroids produced a present-day population of fewer than a thousand, enough to explain the dust ring we see today. Finding such survivors will take an instrument like Hubble, but it will help us nail down the size of the population as well as its physical characteristics.

Dust rings seem to be common, given that we also have strong evidence of a dust ring around Mercury, as demonstrated by Guillermo Stenborg and Russell Howard (Naval Research Laboratory, Washington DC), who present evidence of cosmic dust in a ring some 15 million kilometers (9.3 million miles) wide over Mercury’s orbit. In a region presumed to be free of dust because of its proximity to the Sun, this ring was found using data from the STEREO satellite (Solar and Terrestrial Relations Observatory) and has implications for data gathering by the Parker Solar Probe, now operating in a highly elliptical orbit around the Sun.

“It wasn’t an isolated thing,” Howard said. “All around the Sun, regardless of the spacecraft’s position, we could see the same five percent increase in dust brightness, or density. That said something was there, and it’s something that extends all around the Sun.”

Image: In this illustration, several dust rings circle the Sun. These rings form when planets’ gravities tug dust grains into orbit around the Sun. Recently, scientists have detected a dust ring at Mercury’s orbit. Others hypothesize the source of Venus’ dust ring is a group of never-before-detected co-orbital asteroids. Credit: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk-Keith.

So the solar wind and magnetic forces from the Sun have failed to sweep away the dust found at Mercury’s orbit. As we work to refine our dust models, distinguishing between coronal light and light reflecting off dust in space (which is some 100 times brighter), we’re learning how to separate out the dust signature, which is how the researchers made their unexpected discovery. “It wasn’t an isolated thing,” says Howard. “All around the Sun, regardless of the spacecraft’s position, we could see the same five percent increase in dust brightness, or density. That said something was there, and it’s something that extends all around the Sun.”

Is there a zone of dust-free space close to the Sun, as originally assumed? If so, its boundary will tell us something about the dust’s composition, with implications for early planet formation. Learning how dust near the Sun behaves should occupy scientists with the Parker Solar Probe mission as they witness first hand the environment through which their spacecraft moves.

The papers are Pokorný & Kuchner, “Co-orbital Asteroids as the Source of Venus’s Zodiacal Dust Ring,” Astrophysical Journal Vol. 873, No. 2 (12 March 2019). Abstract; and Stenborg et al., “Evidence for a Circumsolar Dust Ring Near Mercury’s Orbit,” Astrophysical Journal Vol. 868, No. 1 (21 November 2018). Abstract.

tzf_img_post

{ 10 comments }

Spacefaring Mythologies

I became fascinated with Scandinavian mythologies in grad school and wound up doing a deep dive into early Icelandic literature. Heroic tales from a worldview long superceded proved a rich source of materials, but is myth always a thing of the past? Joseph Campbell would speak about ritual as the only way to participate in mythologies that were essentially over, but perhaps, as Nick Nielsen argues below, there is a mythology of the future that is being born right now. If humanity succeeds in expanding to the stars, how will our descendants look back upon the early age of space? Perhaps the things we do today turn into the far future’s own mythologies, particularly if waves of star travel lead to speciation or post-human outcomes. Nielsen probes cultural and philosophical aspects of an interstellar future in Grand Strategy: The View from Oregon, and Grand Strategy Annex, where as in the essay below, the outcomes of the choices we make today propel the discussion.

by J. N. Nielsen

1. Two Forms of Spacefaring Mythology
2. Two Ways of Living Mythologically
3. Origin Myths and the Beginning of History
4. Origin Myths of Spacefaring Civilizations: Three Scenarios
5. Our Hour of Need in Civilizational Crisis
6. A Naturalistic Account of Mythic Archetypes
7. Of Axial Ages and Archetypal Ages
8. Crises and Effacement in the History of Western Civilization
9. Future Crises and Effacement in Civilization
10. A New Axial Age of Spacefaring Civilization
11. A New Archetypal Age of Trans-humanity or Post-Humanity
12. Human Archetypes and Their Successors
13. The Branching Bush of Cognitive Speciation
14. Deep Cognitive Homology
15. A Naturalistic Scenario for Future Cognitive Speciation

1. Two Forms of Spacefaring Mythology

A spacefaring mythology might be the mythologized recollection of the recent past since the beginning of human spacefaring, or it might be the mythology that some future spacefaring civilization evokes in order to orientate itself in relation to the cosmos. These two distinct conceptions of spacefaring mythology are not necessarily mutually exclusive, although either could obtain in the absence of the other. Let us begin by briefly summarizing the two cases yielded by the method of isolation.

In the first of the two senses taken in isolation, the mythologization of the recent spacefaring past could be a myth for contemporary civilization only, if civilization comes to an end in the near future, or if it does not project itself into the cosmos and establish itself as a mature spacefaring civilization (in both of these cases, the early spacefaring era is followed by no consummation, no spacefaring civilization). In the latter scenario, one could even imagine a future human history in which this mythology of the early spacefaring era remains as a touchstone even after any spacefaring capability has lapsed, much as peoples of the early medieval period marveled at the great works of classical antiquity, which were far beyond their means to build. [1]

In the second of the two senses above taken in isolation, the mythology of a spacefaring civilization would be a myth or set of myths that serve several functions within spacefaring civilization, but it would not be a mythology of the early spacefaring era. That is to say, in this scenario, as a contingent matter of fact, the spacefaring civilization in question takes its mythology from some source other than its early spacefaring history. This would be easy to understand if the progenitors of such a civilization reached further back into their past for their sustaining mythology, or if they needed a mythology less directly entangled with the ordinary business of life. Since mythology often involves defamiliarization, having too familiar a mythological context could render a myth less effective in fulfilling the social functions it typically serves.

The two senses distinguished above would come together in the case of a mature spacefaring civilization that takes as at least a part of its mythology its early spacefaring era. If this were to occur in the human future, we would today be living in a mythological age, creating the myths of the early spacefaring era that would go on to inspire and to drive forward an ongoing spacefaring civilization. What does it mean to be living in a mythological age? Are we, today, equal to the challenge of establishing a heroic model that can serve as a model for a civilization much larger and much older and much more advanced than our own? What can the future take from our struggles today to project our civilization beyond Earth?

Mythology scholar Joseph Campbell once urged his listeners to “live mythologically,” and we may need to live mythologically, or, at least, attempt to live mythologically, if we are to inspire future generations. I was old enough to have watched and to have been impressed with the Bill Moyers’ interviews with Joseph Campbell (in which he made this statement about living mythologically) during their original airing on PBS (1988), and I remember how this advice was sometimes appreciated but more often misunderstood (seemingly intentionally) by the press at the time. Though Moyers was clearly out of his depth in these interviews, he at least appreciated what Campbell was saying and was inspired by it, even if he didn’t understand all of it. Moyer’s amiable incomprehension was of great value to me, however, as this served as my introduction to mythology scholarship. [2]

2. Two Ways of Living Mythologically

In regard to living mythologically, again, we have a bifurcation (as with the bifurcation between spacefaring mythologies that could be the mythologized recent past or the mythology of a mature spacefaring civilization), and, again, either of the alternatives of the bifurcation can be entertained in isolation. I will discuss this bifurcation in terms of embodiment and exemplification. Mythological embodiment in isolation is when the individual lives out a mythological role in one’s own life, modeled on past exemplars, but, in living out this role, does not (necessarily) serve as a mythological model for others to follow. [3] Mythological exemplification in isolation is when the individual lives out a mythological role based on no model other than mythological archetypes, and in so doing fashioning a myth for others to embody.

In each case the individual is living mythologically in the sense of living in reference to mythic archetypes, while one is a reenactment of the past and the other is a model to the future. Both of these cases taken in isolation are exceptions; mostly the difference between mythological embodiment and mythological exemplification is a difference of emphasis. Much of the time, the archetypal torch is passed from one age to the next, with each mythic figure both referring to the past and serving as a model to the future. An example of this is the “Golden Chain” of Platonic succession at the Academy—the more than nine hundred years of successors to Plato at the school founded by Plato in Athens.

Embodiment through participation in a myth is by far the most common way of living mythologically, not only because it requires less imagination, but also because this way of living mythologically admits of indefinite iteration, whereas mythological exemplification is much rarer. It is extraordinarily difficult to forge a new myth, or even variations on the theme of an old myth, from raw, archetypal material, but it is not impossible. Most of the time the result is a variation on the theme of a familiar myth, but sometimes this little variation makes all the difference. When an individual has the right instincts and intuitions to tap into archetypes, the likelihood is that such an individual will spontaneously produce a variation on the theme of a familiar myth, as there are only a limited number of narratives that can coherently link together the archetypal material; archetypes leave us very little wiggle room, but they are neither absolute nor absolutely incorrigible.

3. Origin Myths and the Beginning of History

One might plausibly claim that it is not easy to live mythologically in modern times, that our times, modern times, are decisively removed from the mythological times — mythological times proper being the Axial Age, as Karl Jaspers styled it  [4]— in which the great traditions of our civilizations were laid down. The origins of human civilization are long past, according to this way of understanding history, and they will not return. We have the civilizations we have because of the origin myths that made us what we are today, but the times in which the origin myths came about (no less than the mythologized events themselves, I might add) are long gone. This, however, is not my interpretation of history.

I regard the past ten thousand years as the infancy of human civilization, and we ourselves as constituting an infancy that is only now on the cusp of coming into the earliest stages of maturity. If we could be said to be located anywhere in history, I would say that we are near the end of the beginning, still working through the earliest stages of the development of civilization. I have presented this interpretation in Where wast thou when I laid the foundations of the earth? or, What it means for us to be living near the beginning of history.

Near the end of the beginning of history, there is still plenty of time to make and to participate in the origin myths of the future civilization that is to come. But what the origin myth from our times will be will depend upon the mature form of future civilization, looking back over history to find inchoate and embryonic forms of itself in the past. If the mature form of human civilization takes nothing from our era, we will be not so much forgotten as effaced from history. For in order to construct a narrative of the convergence of human civilization on a particular mature state, it will be necessary to parse the past and to preserve only those moments that contribute to the narrative.

In our own time, there are several different historical threads that might someday become the basis of the origin myth (also known as a foundation myth or etiological myth) of spacefaring civilization, if that is the mature form that our civilization eventually takes, but we cannot yet speak of the foundation myth of spacefaring civilization because nothing yet is settled. Not only is there not a single origin myth for spacefaring civilization, but if mature human civilization turns inward rather than outward, those stages in the progress of spacefaring will count as dead ends in the branching bush of civilization.

4. Origin Myths of Spacefaring Civilizations: Three Scenarios

Since I am especially interested in spacefaring civilization as the destiny of humanity, I will focus on this particular mature state of civilization. One could just as easily consider the origin myth possibilities for other forms of mature civilization. The only limitation here is that, if our present stage of civilization is close enough to the beginning of time that we are today participating in the origin myth of civilization, that civilization must be exceptionally long-lived by contemporary standards. The civilization for which we, and our activities, can provide an origin myth would be something like a million-year-old supercivilization. This may not be the destiny of human civilization, but it could be, and, if it is, this million-year-old supercivilization will have plenty of history on which to draw for its origin myths.

At the fine-grained extreme of origins myths for spacefaring civilization, we have the ongoing efforts in our time to create a space industry — the origins of rocketry, the Space Race, the contemporary privatization of space industry and technology, and so on. This sequence of events may be continued into the future with further triumphs and tragedies until the fulfillment of a spacefaring destiny allows civilization new worlds and new opportunities for human achievement. Industrialized civilization has presented us with a suite of heroic roles specific to a technological economy—the heroic financier, the heroic businessman, the heroic scientist, the heroic inventor, and the heroic engineer. All of these can be mythic figures woven together into one narrative of striving to raise humanity to its next stage of development. This is an inspiring mythology of human effort in the face of an indifferent universe, punctuated by great successes and devastating failures, all of which contribute to the poetic possibilities of mythology. The dialectic of triumph and tragedy is always great source material for mythology.

In the middle ground of history and human activity, an origins myth for spacefaring civilization might focus on the development of the political, social, and economic institutions and wherewithal that make a spacefaring industry possible. This would be a more troubling mythology than the straight-forward inspiring vision of relentless human toil as in the fine-grained account. There would be Machiavellian plotting both to bring about great enterprises, and no less in the attempt to sabotage great enterprises. In the middle ground account, there would be villains, and an encounter with malevolence, perhaps a great struggle and a great moment of decision when the turning point in the struggle is realized. Probably we have not yet even approached that moment and the turning point, which has yet to develop out of the tensions of the present.

In the most expansive vision of a spacefaring future for humanity, we would look back to the origins of civilization, the origins of humanity, and indeed the origins of the universe, and we would see these successive origins of great new possibilities as ontological novelties that are revealed in and through history. David Christian regularly presents Big History as an origins myth of contemporary civilization [5], and we could well see this tradition and method extrapolated into the future, in which our present civilization, on the cusp of true spacefaring civilization, was a threshold of this emergent complexity that we are struggling to bring into being, perhaps to be followed by no less consequential thresholds of emergent complexity as yet unknown. The cosmogonic myth of a spacefaring civilization could reach into cosmology itself as its affirmation of itself as an extension of the natural processes of the cosmos. This would be a less anthropocentric myth, but also the most comprehensive and holistic myth to which human beings could aspire, being less about the human struggle for attainment than about the universe itself giving birth to a new period of its development. (It is also interesting to note that this would constitute an origins myth for spacefaring civilization that did not explicitly evoke the early spacefaring era, as in the second of the two alternatives considered in isolation, with which we began this exposition in section 1.)

In the very long view of history — perhaps the view of history that a million-year-old supercivilization might possess — in which our ten thousand years of civilization to date is merely the preparation for the true beginning of history, when humanity is a spacefaring and multi-planetary civilization, it may be one of these three scenarios that furnishes the origins myth, or all three of them woven together, or something else yet that I have not considered. In so far as our lives and our struggles can contribute to the development of any of these narratives implicit in the present, or to all of them, we are living mythologically. To be equal to the task of living mythologically is to live up to a heroic role in laying the foundations of a future worth having—in a other words, a future worth living for, and a future worth giving one’s life to create.

5. Our Hour of Need in Civilizational Crisis

Joseph Campbell not only said to live mythologically, he also said that a ritual is an opportunity to participate in a myth. In other words, the mythological age is over (i.e., the view I rejected above in section 3 when I said we are living near the beginning of history), and our only hope to participate in the mythological age is through the ritualized reliving of a myth. [6] But if we are today creating the myth of tomorrow, we can participate in mythology in a much more robust form than a vicarious ritualized rehearsal of a long past mythology. By living mythologically today we can create a myth upon which the future will look back for the source of their being. They will seek to replicate our experiences, and in the ritualized celebration of our present as a past myth, they will participate in our world in order to participate in a myth.

We are, then, both living a myth and creating a myth as we live; we both embody and exemplify mythic archetypes. This is at least part of what it means to live mythologically. But, again, the question with which we began was whether it is possible to both live a myth and to create a myth today, in the 21st century. This, I think, is the wrong way to frame contemporary mythology. Mythology is inevitable and unavoidable because of who and what we are. It is an instinctive response of human nature to orientate itself in the world with reference to familiar myths, as myths are narrative formulations of the archetypal material we carry within ourselves by dint of our evolutionary psychology, and these narratives allow us to manage, and sometimes even to master, the forces that well up from within ourselves. No one chooses to respond to archetypal material; one responds, if one responds at all, spontaneously and instinctively. [7]

We tap into mythological archetypes in living our own lives even if we are also at the same time creating a myth based on the same archetypes. Archetypal images and stories and situations resonate almost universally among human beings; we respond to them instinctively, without any preparation or education in them. Mythological narratives offer us an intuitively accessible guide by which to navigate the storms of life when all else seems to have failed us. In our hour of need, we reach down into the depths of the mind and drawn on the deep sources of our being in order to have the strength to carry on. And the great transitions in the history of civilization are usually times of crisis when we seek for guidance at the deepest levels because ordinary precedent has failed us.

6. A Naturalistic Account of Mythic Archetypes

From a naturalistic point of view, the deep resonance of mythology is due to the fact that archetypal elements evoke central features of human evolutionary psychology. The formative period of human evolutionary psychology is what evolutionary biologists call the environment of evolutionary adaptedness, or EEA. [8] The EEA is the period in which we truly became what we are. The speciation of humanity in terms of anatomical modernity took place on the plains of Africa, which was, then, the EEA of our anatomical modernity. I argue that cognitive modernity (in contradistinction to anatomical modernity) occurred later, and that it occurred separately in different geographical regions after anatomically modern human beings had already spread themselves to the four corners of the world. [9] If I am correct, cognitive modernity in each geographical region took place in the context of a slightly different EEA in each case, which then accounts for the slight differences in the characters of the regional civilizations that eventually supervened upon these populations. [10]

Joseph Campbell wrote The Hero of a Thousand Faces to demonstrate the universality of the hero myth and the hero as archetype. This is fundamental to human evolutionary psychology, and represents a cross-cultural manifestation of an archetypal theme. However, there are also archetypal themes that are more restricted (though not completely restricted) to particular geographically regional traditions. For example, metempsychosis, or the transmigration of the soul, and the archetypes associated with this idea, is much more common in the Indian subcontinent than it is elsewhere. On the other hand, complex symbols can have different significations in different civilizations. Dragons, for example, have a different significance in East Asia than they have in Western Europe. The dragon comes from deep in our evolutionary psychology, being a patchwork of many fear- and awe-inspiring properties, but it is woven into distinct narratives in distinct cultural regions.

Some archetypes, then, are truly universal (the hero), and some are universal but interpreted in importantly different ways (the dragon), while still other archetypes resonate much more in one cultural region than another (metempsychosis). I assume that this variance follows from the differences in evolutionary psychology from cognitive modernity occurring independently in different geographical regions, each of which regions constituted the EEA of the particular occurrence of the cognitive modernity that it shaped. With these considerations in mind, I hold that, from a mythological or psychological standpoint, one might also call the EEA the Archetypal Age. The EEA is when the archetypes of the human collective unconscious were laid down (and they are with us still), and these archetypes vary slightly from region to region. Human beings ultimately have more in common with each other than they have fundamental differences, but the differences remain and they are important.

7. Of Axial Ages and Archetypal Ages

The Axial Age is to be distinguished from the Archetypal Age. While the Archetypal Age was about the formation of human nature (our psycho-social makeup, as selected by evolutionary pressures), the Axial Age was that time in human history when a macro-historical division of human experience reached a mature mythological expression, and this occurred tens of thousands of years after the Archetypal Age. The selective forces that resulted in the Axial Age were primarily social, and have not continued for a period of time sufficient to change human nature. In other words, the Axial Age was not an environment of evolutionary adaptedness for new cognitive archetypes.

The Axial Age identified by Karl Jaspers was the Axial Age of agricultural civilizations. I have speculated that there was an earlier Axial Age when our Paleolithic ancestors produced a distinctive culture that was the mature mythological expression of the Paleolithic human world (cf. Axialization of the Nomadic Paradigm), and that there could be another Axial Age (cf. The Next Axial Age) when the mythological framework of industrialized civilization is brought to its mature expression. Indeed, this axialization of industrialized civilization could coincide with the origin myth of spacefaring civilization, if the mature form that industrialized civilization takes is that of a spacefaring civilization.

The transition from hunter-gatherer nomadism to agricultural civilization involved a loss of the entirety of human prehistory—a history that only relatively recently has been recovered with the advent of scientific historiography, which reconstructed prehistory from archaeological evidence, because no human memory of it remains. Prior to the recovery of human prehistory, everything before agricultural civilization was history effaced—the slate wiped clean and humanity starting over again from scratch, except for the mute and unconscious evolutionary psychology retained from our environment of evolutionary adaptedness. [11]

It is said that nature abhors a vacuum. Whether or not this is true of nature, it certainly is true of the human mind (hence Viktor Frankl’s conception of the “existential vacuum” as a pathological condition of human consciousness [12]). The void of effaced prehistory was filled with mythologies that peopled the nothingness before civilization with meanings, values, and personalities that provided a surrogate content for an actual past than had been lost. Thus foundational myths are interpolations that fill a collective existential vacuum—the existential vacuum of effaced history.

8. Crises and Effacement in the History of Western Civilization

If we return to the foundational myths of Christian civilization, of which our civilization is the direct descendant, we find a conflicted evaluation of mythic prehistory. Before the Fall of Man, Adam and Eve found themselves in Eden, where they neither had to work nor to die. When expelled from paradise, life in agricultural civilization is made to sound harsh: “…cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life; Thorns also and thistles shall it bring forth to thee; and thou shalt eat the herb of the field; In the sweat of thy face shalt thou eat bread.” However, after Cain has killed Abel, God says to Cain, “When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a vagabond shalt thou be in the earth.”

Thus the already hard lot of agricultural civilization outside Eden can be made even more difficult; Cain is demoted from agricultural labor, earning his bread in the sweat of his face, to being a mere vagabond—a nomad. Cain responded, “I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that findeth me shall slay me.” I see in this a distant echo of our nomadic prehistory, that condition that Hobbes famously described as a war of all against all, in which life is, “solitary, poor, nasty, brutish and short,” [13] and which contrasts sharply with the paradisiacal prehistory of Eden. The agricultural civilization described in the Old Testament had blotted out all but the faintest traces of the nomadic condition that had preceded agriculture, but which was lost with the advent of agriculture and settled civilization.

The next great transition in human history, the passage from agricultural civilization to industrial civilization, effected less severe absolute historical losses—the intellectual superstructure of agricultural civilization had created a system of record keeping (writing) that preserved a significant portion of the past—but the loss of human experience was almost as extreme. Most alive today would have no idea whatsoever what to do if they found themselves on a farm, or on a sailing ship, so that even if they possess an abstract knowledge of what came before, this knowledge is not internalized (i.e., it is knowledge without lived experience) and the practical link with the experience of our ancestors has been sundered as completely as the practical link between hunter-gatherer nomadism and settled agriculture.

As an industrial civilization today, in possession of a reconstructed past but cut off from the experiences of our ancestors, we may stall and stagnate, remaining a planetary civilization for hundreds or thousands of years. If at some point humanity moves beyond exclusive reliance on Earth, then this story will have further episodes; if not, planetary civilization will eventually be extinguished by the natural processes of our homeworld and our solar system. In other words, the entirety of humanity and our civilization will be wiped away by a planetary scale historical effacement, and the universe will not notice our passing from the scene. (This is the first of the two scenarios noted in the opening of this essay.)

9. Future Crises and Effacement in Civilization

In the scenario in which humanity has (or our descendents have) a cosmological destiny beyond our homeworld, we will build upon industrialized civilization and transform it into a spacefaring civilization, and the story continues, for a time at least. There will be a transition from human beings being a majority terrestrial species, to a time in the distant future when human beings are a minority terrestrial species, i.e., more human beings will reside away from Earth than on Earth, and this demographic transition will mean that the fate of human beings and our successor species will not be determined on Earth, but by hundreds or thousands of human populations maintained elsewhere, on planets, moons, generational starships, or artificial habitats.

For any species to leave its homeworld will involve a radical loss of its direct contact with its own historical antecedents, beyond that loss experienced by refugees and colonists who leave the lands and homes of their forefathers to establish themselves at distant outposts on Earth. These losses we have experienced to date from historical effacement—the destruction of humanity’s historical legacy due to war, neglect, and iconoclasm—will be small in comparison to the losses entailed by spacefaring and world-spanning civilizations, which may lose the records of entire planets.

Our descendents will have the abstract knowledge of the meaning of planetary endemism, and what it meant for our species to be entirely confined to the surface of Earth, with spacefaring a rare and prohibitively expensive undertaking. They will not have the lived experience of planetary endemism; the actual practice of planetary constraints will not define the human condition in their time. And when human beings find themselves on far-flung worlds or vessels throughout the universe, it may happen again that the past is lost, and these beings, human or otherwise, will feel cut off from their roots in the cosmos. With their natural history effaced, and unable to bear an infinitude of nothingness before themselves, they may fill the void with meanings, values, and personalities that help to sustain them in the cosmological circumstances in which they find themselves. Again there will be historical effacement, and, again, the human mind (or the post-human mind) will transform the existential vacuum into an existential plenum with mythology.

The more successful and wide the dispersion of terrestrial life in the cosmos, the more likely that some of these communities ultimately derived from Earth will forget their origins, or those origins will be otherwise effaced, and the void of their prehistory will be filled by an etiological myth that explains that people’s origin and destiny. Indeed, under the conditions of the end of cosmology there will be a greater existential void than ever before that any intelligent agent would feel the need to fill, whether these agents are our distant descendants or those of some other civilization. These mythologies to come of spacefaring civilizations may depart significantly from the mythologies of planetary endemism, but they will likely serve the same soteriological and eschatological functions, albeit under changed circumstances. [14]

10. A New Axial Age of Spacefaring Civilization

It must be emphasized that we do not yet know in what direction contemporary planetary civilization is headed, but a spacefaring civilization is among the possibilities. Industrialized civilizations following the industrial revolution are still very young in historical terms. There are some who argue that there have been two or three or even four distinct industrial revolutions. Certainly we can distinguish finer-grained periods within industrialization, but in the big picture the changes to human society and civilization since the industrial revolution is one continuous movement of change for the past two hundred years, approximately. This is, as I said, a very recent phenomenon. It took thousands of years for settled civilizations all over the planet to displace hunter-gatherer nomadism as the primary pattern of human activity. It will take at least hundreds of years more for the changes begun by the industrial revolution to be consolidated and brought to social maturity. We should not wonder at this; we should expect it.

As noted above (in section 7), the axialization of industrialized civilization could coincide with the origin myth of a mature spacefaring civilization if this is the trajectory of the development of civilization today. This would be another Axial Age and not another Archetypal Age, because we would still be bringing our hunter-gatherer evolutionary psychology with us as we make the transition to a spacefaring civilization (something that I wrote about in Hunter-Gatherers in Outer Space). Transitions from one stage in the development of civilization to another stage are messy rather than neat affairs, and we tend to bring a lot of baggage along with us from the past.

For example, we have preserved Axial Age religions into the early stages of industrialized civilization, but this cannot be satisfying to the soul of man. We see this in the nihilism and anomie (manifestations of the existential vacuum) that characterize the industrialized peoples, who feel cut off from their history and traditions, and have nothing (as yet) to replace them. It is this kind of social tension that is a catalyst for myth-making efforts, in the attempt to fill a void left by the tightly-coupled relationship between mythology and civilization in the now-lapsed paradigm of a social order that no longer exists except in cultural memory.

11. A New Archetypal Age of Trans-humanity or Post-Humanity

All of the foregoing about mythology is concerned with Axial Ages that bring our older Archetypal Age evolutionary psychology into some kind of workable relationship with the social order in which we find ourselves. All of these myths reach down into the same collective unconscious and dredge up the same (or nearly the same) archetypes. However, there could be another Archetypal Age if there were to be another environment of evolutionary adaptedness, i.e., another period during which evolutionary changes were being shaped by the environment in a decisive way, i.e., in a way that shaped a new (or, more likely, altered) human nature based on a new (or altered) evolutionary psychology, with the latter shaped by a new (or, again, altered) EEA.

Archetypal Age evolutionary psychology is incomprehensibly old on a human time scale, but according to the scale of time by which we must measure the evolution of life and mind on Earth, the Archetypal Age (understood as the most recent human EEA) was a recent development. The brain and the central nervous system (CNS) have a deep history in the biosphere as revealed in the fossil record. [15] While it might be too much to attribute consciousness to panarthropoda, at some point in the history of life on Earth, brains and CNSs became sufficiently complex that rudimentary forms of consciousness and cognition emerged. With consciousness and cognition comes the possibility of what I called cognitive speciation. [16] The cognitive speciation that is cognitive modernity also results from a distinctive period in the formation of human minds, our EEA.

Evolution, of course, continues for us following such a distinctive period—an EEA in which an Archetypal Age takes shape—but does not play the same constitutive role as it did during the Archetypal Age. Evolution has not come to an end with human beings or indeed with any species currently in existence. A species only stops evolving when it goes extinct. [17] However, the speciation and stabilizing selection of a species within a given environment constitutes a distinctive period in the evolution of an organism.

By building civilizations and growing them to planetary scale, human beings have in fact created a new environment that is selecting for fitness differently than the way in which nature prior to civilization selected for fitness. If civilization continues for long enough, and human beings live in a civilized state for a period of time during which differential survival and differential reproduction result in speciation, whether anatomical or cognitive, then civilization would be the EEA of a new species of human being or a new kind of human mind. This is already happening very slowly and gradually — but not at a rate rapid enough or consequential enough at this time to result in speciation. This could yet happen, but it is not happening now. At the current rate of human evolution within civilization, any changes to human nature as a result of civilization could still be derailed or redirected by some other force that acted more rapidly or which impacted humanity more dramatically.

If, however, we began to alter ourselves at the genetic level, becoming trans-human or post-human — i.e., becoming something other than what humanity has been to date — the environment in which this took place would then be the EEA of this new trans-human or post-human species. However, for the environment to play the role it has in the past in terms of EEA, this process of human change would have to take place over a considerable period of time so that the environment had an opportunity to act as a selective pressure on differential survival and differential reproduction. The kind of sudden and radical change made possible by technology could result in a disconnect with the environment as it is usually understood, so that the real selection pressure is the technological milieu within which these changes take place. If reproduction were to be dominated by technology (e.g., ectogenesis), differential reproduction would be a function of the technological environment narrowly conceived, and not the environment we equate with a particular ecosystem.

Here, then, is a little recognized risk of transhumanism: that the formation of both mind and body of the transhuman individual, and any group of transhuman individuals taken together, would occur under unprecedented evolutionary conditions, which could result in unprecedented selection pressures upon the human organism undergoing such change. (This is an instance of a technological scenario for future cognitive speciation; a naturalistic scenario for future cognitive speciation will be given below, in section 15.) Can the human organism be changed in this way and still retain its integrity as a living being? We do not yet know the answer to this question, and finding out the answer to this question could be unpleasant.

12. Human Archetypes and Their Successors

However the next change in humanity takes place, whether by nature or my technology, and whether it goes well or badly, this kind of change would be a change in human nature rather than a change in human culture. In other words, it would be an archetypal change and not an axial change, a biological change rather than a social change. The conditions under which an archetypal change came about — the EEA of the archetype — would shape that archetype, and the new successor species would respond to different archetypal symbols, and different narratives would resonate in the psyche of such a being.

In actual practice, it would be a little more complex than this. It is not likely that there would be a sharp break with the human archetype, but rather there would be an overlap between the human archetype and the transhuman or post-human archetype, so that some aspects of human depth psychology would carry over to our successors, some aspects would not carry over, and some aspects would be carried over but substantially modified by the transition. (This is treated in more detail in sections 13 and 14 below.) Almost certainly this is what happened when homo sapiens speciated from human ancestors, but at that time the development of the mind and the capacity of thought on behalf of the genus homo was at a much lower level than it is now, so that a change in conceptual framework would have been less in evidence. Archetypal change after cognitive modernity will be a different matter.

13. The Branching Bush of Cognitive Speciation

Cognitive modernity is a particular instance of what I call cognitive speciation. This is not the only form of cognitive speciation, however. Cognitive speciation can be found throughout the biosphere. In so far as the biological individuality that characterizes the terrestrial biosphere entails individual organisms with individual brains and central nervous systems, and, when these become sufficiently complex, individual minds and consciousness supervene upon these biological structures, to the extent that mind corresponds with these biological structures, the branching bush of species coincides with a branching bush of cognition. [18]

Both our anthropocentric conception of cognition and our human exceptionalism have, in the past, militated against recognizing mind as it has appeared in other species, but there has been a sea change in this area and it is no longer considered unspeakable, much less eccentric, to attribute mind and consciousness to other species. [19] In so far as non-human species have minds, they engage in cognition, and this implies that these other species have concepts that they employ to organize their cognition.

Needless to say, human cognition is much more advanced and abstract than that of other species in the terrestrial biosphere, especially in regard to the human ability to use grammatically structured languages to structure their thoughts and formulate their conceptual frameworks. Language is a networking tool for minds, and by networking their minds through the use of language human beings have exponentially augmented their cognitive abilities.

Even if the concepts employed by other species are impoverished in comparison to the human conceptual framework, non-human conceptual frameworks are the ultimate source and origin of later human cognition. Once we accept this, we can see that different minds would have different conceptual frameworks populated by different sets of concepts. We would expect that the set of concepts employed by human beings is absolutely larger than the set of concepts employed by other species, but we would also expect that these sets of concepts overlap and intersect with the sets of concepts employed by other species.

Where the set of concepts employed by human beings and another species overlap but to not coincide, human beings will employ concepts not employed by the other species, and vice versa. For example, there are parts of the killer whale (Orcinus orca) brain that correspond with areas of the human brain that are responsible for emotions. In the killer whale brain the cingulate gyrus of the limbic lobe has grown in structure and complexity in a way not reflected in the human brain [20], so that it is likely that killer whales experience at least some emotions that human beings do not experience. In this sense, their cognition may be richer than ours in at least one way, which points to a conceptual framework populated by emotional concepts we do not possess.

This and similar arguments would probably encounter less resistance if it were confined to more-or-less immediate human ancestors and near relatives in the human tree. I doubt many would strongly object that Neanderthals had some form of cognition, and that it differed to some degree, but not absolutely, from that of homo sapiens. The same proximity would be operable if we consider human descendants that would differ from us if we were to speciate rather than to go extinct. It would be expected that some future transhumans or post-humans would possess a conceptual framework that overlapped with the human conceptual framework but which did not perfectly coincide.

14. Deep Homology of Cognition

As any human being—or, for that matter, any biological individual with a brain in the terrestrial biosphere—is inseparably both mind and body, with each acting upon the other, cognitive speciation as represented in cognitive modernity cannot be cleanly separated from corporeal speciation, and vice versa. We see this clearly, for example, in sexual selection, when a mate is selected for reproduction on the basis of a judgment made by one or both of the parties involved. Mind can impact the development of our bodily evolution, and the body can impact the development of our minds.

And our minds are not blank slates, but are related to the previous minds that preceded it in those organisms from which we inherit that which we are, both bodily and cognitively. While the blank slate doctrine has come in for considerable criticism and is today widely viewed as untenable, I don’t think that we have fully drawn the conclusions that we need to draw if the human mind is not a blank slate.

It is a contemporary commonplace that the human brain consists of a reptilian hindbrain, a mammalian mid-brain, which includes the limbic system, and the neocortex, which in large mammals like human beings, whales, and elephants has grown exponentially, and it is this development of the neocortex that is primarily responsible for human intelligence, hence human cognition. This is, of course, a bit of an oversimplification, but it gets the point across that the brain evolves, and especially the brain grows by adding on to itself, and by adding to itself and increasing its capacities, it does not rid itself of older brain structures, which continue to be inherited by subsequent descendants. We forget, and we gloss over, past brain structures and past behaviors rooted in these brain structures, but neither the anatomical structures or the behaviors are entirely effaced.

I argue that it is not merely older brain structures that are inherited from our ancestors, but also the cognition associated with these brain structures. This is widely recognized in regard to instinctual behaviors, which we understand can be traced into the deep past of life on Earth, but it is less widely recognized when we place these behaviors in relation to conscious and explicit cognition. If we understand behaviors and cognition to be related (and this relation in itself is the hoary philosophical question of the mind-body problem), then inherited behaviors also mean inherited forms of cognition.

What evolutionary developmental biology (more commonly known as “Evo-Devo”) has taught us, inter alia, is that there is often a deep genetic homology that drives the repetitive appearance of structures in terrestrial life across apparently diverse clades. This deep genetic homology ultimate goes back to the last universal common ancestor (LUCA), which contained within it the seeds of all later life on Earth. Might this homology also extend to the cognition that supervenes upon homologous brain and CNS structures? Is there a deep cognitive homology in the terrestrial biosphere? Should there be an evolutionary developmental psychology?

15. A Naturalistic Scenario for Future Cognitive Speciation

With further changes to the human brain and CNS, humanity could experience further changes in cognition. [21] Suppose some mutation in ARHGAP11B (the human-specific gene responsible for neocortex expansion), or in some related gene, led to further neural proliferation and neocortex expansion. It is because the neurons that are responsible for our higher executive functions are in the outer layer of the neocortex that the deep convolutions of the neocortex give more surface area of the brain, hence more neocortex, within the confined space of the human skull. If some mutation allowed for a thicker and larger neocortex, or greater cortical density, or both, the brain that resulted might considerably out-perform the human brain as we know it today.

Given what we know about the inherited structures of the brain and the deep history of mind in the biosphere, we can say with some confidence that any human beings that were to inherit such a mutation, or post-human beings as the case may be, however great their executive functions in comparison to ours, would still be human, all-too-human in the sense that they would still have the drives of the reptilian hindbrain and the emotions of the limbic system. They would not be Apollonian and god-like beings, pure spirits possessing a higher form of consciousness; they would be recognizable human beings, or mostly recognizable human beings.

We could, however, formulate scenarios in which the recognition would not be so obvious or immediate. It would be possible, though not likely, that a future mutation could both expand the neocortex while shrinking or disabling the limbic system, which would result in the kind of mind of science fiction nightmares: a highly-intelligent, relentlessly rational, unemotional mind—“intellects vast and cool and unsympathetic.” There is only so much room inside our skulls, the argument could run, so that more neocortex eventually would mean less hindbrain and less limbic system. Here the cognitive speciation would be more apparent, and the conceptual frameworks of human beings and post-humans would overlap less and contrast more. However, there would still be many concepts in common, if not most concepts in common.

I have here described a naturalistic evolutionary scenario in which human beings could be cognitively surpassed and our descendants would experience cognitive descent with modification, that is to say, cognitive speciation. Further above (in section 11) I mentioned the possibility of technological interventions that could result in a new Archetypal Age. The evolutionary scenario I have described in this section could also result in a new Archetypal Age, so that the cognition of our descendants could involve novel or modified archetypal material, to which they would respond as we respond to the archetypal material within our subconscious. There would no doubt be significant overlap between human and post-human archetypal material, but the two may not perfectly coincide, and could diverge over time, exemplifying what Alfred Russel Wallace called, “The Tendency of Varieties to Depart Indefinitely from the Original Type.” [22] As future archetypes diverged, relevant mythologies would diverge, and each distinct species would look to separate destinies for themselves. [23]

Notes

[1] An early Anglo-Saxon poem, The Ruin, depicts the broken buildings of classical antiquity as the work of giants.

[2] I have since listened to all of Campbell’s available recorded lectures, and I can definitely say that his lectures are superior to his conversations with Moyers, as in his lectures he is free to communicate his ideas on his own terms; however, it was Moyers who made me aware of Campbell. Everyone has to start somewhere.

[3] Campbell in his lectures liked to mention how Jung had asked himself at one point in his life—“What is the myth by which I am living?”—and in asking the question Jung realized that he didn’t know the answer and that, moreover, he needed to know. This is the question of mythological embodiment.

[4] “An axis of world history, if such a thing exists, would have to be discovered empirically, as a fact capable of being accepted as such by all men, Christians included. This axis would be situated at the point in history which gave birth to everything which, since then, man has been able to be, the point most overwhelmingly fruitful in fashioning humanity; its character would have to be, if not empirically cogent and evident, yet so convincing to empirical, insight as to give rise to a common frame of historical self-comprehension for all peoples—for the West, for Asia, and for all men on earth, without regard to particular articles of faith. It would seem that this axis of history is to be found in the period around 500 B.C., in the spiritual process that occurred between 800 and 200 B.C. It is there that we meet with the most deepcut dividing line in history. Man, as we know him today, came into being. For short we may style this the ‘Axial Period’.” Karl Jaspers, The Origin and Goal of History, Yale University Press, 1968, p. 1.

[5] “Maps of Time attempts to assemble a coherent and accessible account of origins, a modern creation myth.” Christian, David, Maps of Time: An Introduction to Big History, University of California Press, 2004, p. 2.

[6] In the language of Nick Bostrom’s simulation hypothesis, this is an ancestor simulation. For those who are attracted to technocentric reinterpretations of tradition, the project of mythology might be understood as an attempt to provide a simulacrum of an ancestor simulation before this is technically possible. Once it becomes technically possible, the appeal of the simulacrum of an ancestor simulation will disappear. I am not advocating this interpretation, but it is worth mentioning because it structurally resembles the idea that traditional religious belief often (though not in all traditions) offers the individual immortality prior to the technological ability to secure individual immortality. This observation is usually followed by broad hints about traditional religious belief disappearing when technological immortality becomes possible. Such an account of religious belief elides the role of mythological archetypes in religious belief.

[7] If you have been told that something is a myth, but it leaves you cold and stirs no feelings within you, then this myth has no connections to the sources of your being and the archetypes buried in your subconscious. For you, this myth is dead. But you will almost certainly find other aspects of the world, and stories about these aspects of the world, that excite and inspire you. N.B.—I feel the need to add this note because a number of those who read this essay will have a background in the sciences and technology, and they will likely see much of what I am writing here as pure “woo woo,” but this is largely because the institutionalized myths of our time are walking zombies that no longer move us, and we often fail to recognize the contemporary myths that do in fact move us. Campbell often addressed this in his lectures.

[8] I have written about this previously in Survival Beyond the EEA and Existential Threat Narratives.

[9] Cf. Multi-Regional Cognitive Modernity; I do not know of anyone else who holds this view, so the reader should understand that I am putting myself out on a limb by taking this position.

[10] This is not unlike the native ability that all human beings have for language, but many different languages of different structures are to be found in different geographical regions. Analogously, I hold that cognitive modernity was a potential in all human populations, differently realized in different regions.

[11] The loss of prehistory with the advent of agriculture is a particular instance of what I call historical effacement. I previously introduced the idea of historical effacement in History Effaced, and further developed the idea in A Brief History of the Loss of History and The Effacement of Being. This was in part inspired by Krauss and Sherrer’s thesis on the end of cosmology, which I applied to archaeology in The End of Archaeology. Effacement is an ongoing process, the result of the gnawing tooth of time. We cannot perceive historical effacement any more than we can perceive the ongoing processes of erosion or gravitational mass wasting, but it is always there in the background, slowly eroding the distant past, until that past ceases altogether to exist.

[12] “Ever more patients complain of what they call an ‘inner void,’ and that is the reason why I have termed this condition the ‘existential vacuum.’ In contradistinction to the peak-experience so aptly described by Maslow, one could conceive of the existential vacuum in terms of an ‘abyss-experience’.” Viktor Frankl, The Will to Meaning, Penguin, 1988, p. 83. Rather than employing the locution of “abyss experience,” Maslow contrasts peak experiences to nadir experiences—same idea, different terminology. Frankl also devotes a section of his Man’s Search for Meaning to the existential vacuum.

[13] Hobbes, Thomas, Of Man, Being the First Part of Leviathan, Chapter XIII, “Of the Natural Condition of Mankind as Concerning Their Felicity and Misery.”

[14] This transition in the form of religious experience from planetary endemism to spacefaring civilization is something I previously explored in Religious Experience and the Future of Civilization and Addendum on Religious Experience and the Future of Civilization, but which deserves much more careful and detailed study at some future time.

[15] I have previously discussed the deep history of the brain and the central nervous system (CNS) in How Early a Mind? and A Counterfactual on Central Nervous System Development. These posts were inspired by the discovery of early fossilized CNSs, specifically, by two papers discussing such discoveries, “Fuxianhuiid ventral nerve cord and early nervous system evolution in Panarthropoda” and “Brain and eyes of Kerygmachela reveal protocerebral ancestry of the panarthropod head.”

[16] I previously discussed cognitive speciation, which implies mechanisms of cognitive selection, in The Overview Effect over the longue durée.

[17] This can be shown by the Hardy-Weinberg equilibrium. The conditions that would have to obtain in order for evolution to cease acting upon gene flow in a given population (i.e., for that population to be in equilibrium, meaning that the distribution of allele frequencies in a given generation are the same as in the previous generation) never in fact obtain in nature.

[18] I have here adopted the metaphor of the “branching bush” to describe evolution, following the use of this metaphor by Stephen Jay Gould, who was at pains to deny that evolution is a ladder of progress. Gould wrote: “…evolution is a copiously branching bush with innumerable present outcomes, not a highway or a ladder with one summit.” (Full House: The Spread of Excellence from Plato to Darwin, p. 21) I am less concerned about the conflation of evolution and progress (more on that another time), but I like the sense of proliferation in all directions that we get from the branching bush metaphor.

[19] The denial of consciousness and cognition to other species may be understood as a distinctively modern idea, probably largely due to Descartes. Medieval thought did not follow this particular research program in the philosophy of mind. Cf. “Why is the Sheep Afraid of the Wolf? Medieval Debates on Animal Passions,” by Dominik Perler, in Emotion and Cognitive Life in Medieval and Early Modern Philosophy, edited by Martin Pickavé and Lisa Shapiro, Oxford University Press, 2012.

[20] Cf. “Neuroanatomy of the killer whale (Orcinus orca) from magnetic resonance images” by Lori Marino, Chet C. Sherwood, Bradley N. Delman, Cheuk Y. Tang, Thomas P. Naidich, and Patrick R. Hof (The Anatomical Record. Part A, Discoveries in Molecular, Cellular, and Evolutionary Biology, 281, 2, 1256-63.) For an overview of this material cf. “Killer Whales are Non-Human Persons” by Lars Crawford. One of the authors of the paper, Lori Marino, said the following in an interview: “There’s some parts of the limbic system of dolphins and whales that have changed and actually gotten smaller, but there are other parts of it that are adjacent areas that are much larger and more elaborate than in the human brain. That area is called the paralimbic region. So they have like an extra lobe of tissue that sort of sits adjacent to their limbic system and their neocortex… That lobe has something to do with processing emotions, but also something to do with thinking. It’s very highly elaborated in most cetaceans and not at all or not nearly as much in humans or other mammals, so it suggests that there’s something that evolved or adapted in that brain over time that did not occur in other mammals, including humans.” Cf. Inside the mind of a killer whale: A Q+A with the neuroscientist from ‘Blackfish’

[21] A good review of neurophysiology is Evolution of the neocortex: a perspective from developmental biology by Pasko Rakic. There is an embarrassment of riches when it comes to neuroscience papers, but I will also mention the article Researchers find DNA mutation that led to change in function of gene in humans that sparked larger neocortex by Bob Yirka, which led me to the paper Human-specific gene ARHGAP11B promotes basal progenitor amplification and neocortex expansion by Marta Florio, et al., which discusses neural proliferation in primates.

[22] The title of Wallace’s “Ternate Essay” (1858) in which he independently proposed evolution by natural selection was “On The Tendency of Varieties to Depart Indefinitely from the Original Type.”

[23] This coupling of anatomical and cognitive speciation would result in what I have called the “Great Voluntaristic Divergence” in an earlier Centauri Dreams post, Transhumanism and Adaptive Radiation.

tzf_img_post

{ 50 comments }

Asteroid Bennu: Changes in Rotation Rate

Tuesday’s post on asteroids and what it would take to deflect or destroy one has been usefully reinforced by a new paper from Mike Nolan (Lunar and Planetary Laboratory, University of Arizona) and colleagues, who discuss their findings in Geophysical Research Letters. Here we’re looking at observations of the near-Earth asteroid (101955) Bennu, both archival (extending back to 1999) and current, drawing on the OSIRIS-REx mission.

You’ll recall that OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) is in operation around the asteroid, its observations helping us understand the object’s rotation, structure and composition, with a sample return planned for 2023. The Nolan paper fills us in on observed changes in rotation, which are apparent on the order of about 1 second per century. The asteroid’s rotation is speeding up.

Exactly what’s going on here is something we can hope OSIRIS-REx can help nail down. One possibility is a process like the Yarkovsky‐O’Keefe‐Radzievskii‐Paddack effect (YORP), by which asteroids are known to be affected because of the uneven distribution of solar heating across their surfaces. The effects of YORP depend on the shape and orientation of the individual asteroid and can cause either a slowdown or uptick in the object’s spin rate.

Or are there other processes at work here? Even boulders on the surface and their relative positions can play into changes in asteroid spin. It’s important to find out because over astronomical time periods, a faster spinning asteroid could eventually shed some of its mass. One thing, then, that OSIRIS-REx will be looking for is the presence of landslides or other surface evidence of such changes. Nolan points to the possibilities:

“As it speeds up, things ought to change, and so we’re going to be looking for those things and detecting this speed up gives us some clues as to the kinds of things we should be looking for. We should be looking for evidence that something was different in the fairly recent past and it’s conceivable things may be changing as we go.”

Image: This series of MapCam images was taken over the course of about four hours and 19 minutes on Dec. 4, 2018, as OSIRIS-REx made its first pass over Bennu’s north pole. The images were captured as the spacecraft was inbound toward Bennu, shortly before its closest approach of the asteroid’s pole. As the asteroid rotates and grows larger in the field of view, the range to the center of Bennu shrinks from about 11.4 to 9.3 km (7.1 to 5.8 miles). This first pass was one of five flyovers of Bennu’s poles and equator that OSIRIS-REx conducted during its Preliminary Survey of the asteroid. Credit: NASA/Goddard/University of Arizona.

We’re fortunate in having data from ground-based telescopes as well as Hubble to study the object over time. 110 million kilometers from Earth, the spinning Bennu completes a full rotation every 4.3 hours. The Hubble data on rotation rate showed a slight mismatch with the predictions of the earlier observations. And while Nolan and team point out that a change in the asteroid’s shape could account for its change in rotation, they clearly favor the YORP hypothesis. Having OSIRIS-REx at Bennu offers the opportunity to put YORP ideas to a close-up test.

The increase in Bennu’s rotation over the past two decades does not fit some earlier analyses of the YORP effect, making the spacecraft’s work all the more important. As the paper notes:

The OSIRIS-REx science team will independently measure the rotational acceleration during its 2-years of proximity operations. The precise shape determination, surface boulder distribution, gravity measurements, and thermal property determinations will allow for a better connection between the dominant drivers of the YORP effect (if confirmed) and their relative importance. The OSIRIS-REx team can measure the stability of the rotation state, to confirm whether this acceleration is a steady increase due to the YORP effect, or some other (likely episodic) process such as mass movement. Thus, our observations form a critical baseline for future work.

Within two years, we should have the OSIRIS-REx data independently providing Bennu’s rotation rate, which should help to identify the cause. We’ll also be looking at Bennu with other instruments for the next several decades to see whether further changes in rotation rate, consistent with YORP or not, emerge. Usefully, work like this allows us to compare and contrast in situ measurements with ground-based observations, giving us the chance to hone our skills at asteroid analysis for application to the larger population.

The paper is Nolan et al., “Detection of Rotational Acceleration of Bennu Using HST Light Curve Observations,” Geophysical Research Letters 31 January 2019 (abstract).

tzf_img_post

{ 10 comments }

A Biosignature Plus for K-Class Stars

Kepler-62 is a reminder of how interesting K-class stars (like Alpha Centauri B) can be. Here we find two worlds that are conceivably in the habitable zone of their star, with Kepler 62f, imagined in the image below, orbiting the host star every 267 days. Kepler-62e, the bright object depicted to the right of the planet, may orbit within the inner edge of the habitable zone. Both planets are larger than Earth, Kepler 62f about 40 percent so, while Kepler-62e is 60 percent larger.

Image: The artist’s concept depicts Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. Credit: NASA Ames/JPL-Caltech/Tim Pyle.

We actually have five planets here, all known thanks to Kepler to transit their star. The two of habitable zone interest may or may not be solid planets — their masses are not well constrained through either radial velocity or transit timing methods, so we are a long way from knowing whether life might actually form on either. Kepler-62e may well turn out to be a gaseous mini-Neptune, based on its radius. As for the host, Kepler-62 is a K-class main sequence star approximately 70 percent the mass of the Sun, and about 7 billion years old.

K-class stars, particularly those closer than Kepler-62, are seeing a flurry of interest as potential homes for life. In fact, Giada Arney (NASA GSFC) sees them as “in a ‘sweet spot’ between Sun-analog stars and M stars,” for reasons that become clear when you compare them to their smaller and cooler cousins. M-dwarfs are ubiquitous, comprising perhaps 80 percent of all stars in the galaxy, but they’re also given to severe flare activity especially in their early years, enough so that there is a real possibility of damage to the atmosphere and loss of liquid water on the surface.

Add to this problems like tidal locking that could afflict planets in the close-in habitable zone around a cool M-dwarf and by comparison, K-class stars have particular advantages. Arney’s analysis of K star habitability and biosignatures appears in Astrophysical Journal Letters, and it makes the case that a biosignature like the simultaneous presence of oxygen and methane will likely be stronger around a K star than a star like the Sun.

To examine the issue, the scientist developed a computer model simulating planetary atmospheres that could be subjected to conditions around a variety of host stars. Simulations of planetary spectra from these atmospheres could then be produced for analysis. Arney’s work shows that a habitable zone planet circling a K star is one that allows methane to build up in the atmosphere because the host star’s ultraviolet does not generate the highly reactive oxygen that destroys methane as quickly as a star like the Sun. With methane lasting longer within an oxygenated atmosphere, our chance of detecting disequilibrium between the gases increases.

We can add in another factor (one that also favors M-dwarfs): The contrast in brightness between the Sun and our Earth would, to a distant observer, be about 10 billion times, making Earth a very tricky world to observe. Whereas the contrast between a habitable zone planet and a K star is closer to 1 billion. That makes nearby K stars interesting places for future biosignature searches, allowing shorter observing times to achieve a given signal to noise ratio. The author thinks we should keep these advantages in mind as we plan future exoplanet observatories.

The paper lists some interesting targets:

These simulations suggest that nearby mid-to-late K dwarfs such as 61 Cyg A, and 61 Cyg B, Epsilon Indi, Groombridge 1618, and HD 156026 may be particularly excellent targets for biosignature searches on exoplanets. In addition to the “K dwarf advantage” for biosignatures, these stars can offer access to a wide range of wavelengths for HZ planets even with IWA [Inner Working Angle] constraints. 61 Cyg A, 61 Cyg B, Epsilon Indi, and Groombridge 1618 provide higher or comparable S/N to Tau Ceti, the closest G dwarf other than the Sun and Proxima Centauri A. In particular, 61 Cyg A and 61 Cyg B, which are at a similar distance as Tau Ceti (3.6 pc), offer S/N that is 1.6–1.7 times better in the same integration time. HD 156026 is at a similar distance as 82 Eridani (6 pc), and it offers 1.4 times better S/N compared to this G6V star.

But there is this challenge, as alluded to above: Habitable zone planets around K stars will orbit closer to their host than comparable planets around G-class stars like the Sun. That could mean that such planets fall inside the Inner Working Angle (IWA) of future observatories. The IWA defines the smallest separation between planet and star at which the planet can be resolved. Direct imaging telescopes, including the future LUVOIR and HabEx may not, then, be able to see the planet at the needed wavelengths. The paper considers starshade and coronagraph designs that could solve this problem.

The paper is Arney, “The K Dwarf Advantage for Biosignatures on Directly Imaged Exoplanets,” Astrophysical Journal Letters Vol. 873, No. 1 (6 March 2019). Abstract / full text.

tzf_img_post

{ 30 comments }

Asteroids in Collision: A New Model

If we were to find an asteroid on a trajectory to impact the Earth, what strategies would we use to stop it? Recent work from Johns Hopkins University shows that there is a wide range in our thinking on what happens to asteroids under various mitigation scenarios. Much depends, of course, on the asteroid’s composition, which we must account for in our models. A good thing, then, that we are supplementing those models with sampling missions like OSIRIS-REx and Hayabusa-2.

Let’s look at the JHU work, though, which updates earlier results from Patrick Michel and colleagues, reported in a 2013 paper; the latter had considered the 5 km/s head-on impact of a 1.21 km diameter basalt impactor on a 25 km diameter target asteroid, with a model varying mass, temperature and material brittleness. Michel’s work showed evidence that the asteroid being targeted would be completely destroyed by the impactor. What Charles El Mir and colleagues at Johns Hopkins have been able to show is that other outcomes are likely.

“We used to believe that the larger the object, the more easily it would break, because bigger objects are more likely to have flaws,” says El Mir. “Our findings, however, show that asteroids are stronger than we used to think and require more energy to be completely shattered.”

Using essentially the same scenario as Michel, El Mir, K. T. Ramesh (JHU) and Derek Richardson (University of Maryland) have created a new model that offers a more detailed look at the smaller-scale processes that take place during such a collision. “Our question was, how much energy does it take to actually destroy an asteroid and break it into pieces?” adds El Mir.

Discussing methods, the authors note their model’s calculation of the first tens of seconds following impact, with transition to computer code integrating longer-term effects. From the paper:

The multi-physics material model is centered around the growth mechanism of an initial distribution of subscale flaws. Rate effects in the model are a natural outcome of the limited crack growth speed, which is explicitly computed based on the local stress state. In addition, porosity growth, pore compaction, and granular flow of highly damaged materials are captured at the material-point level. We validated the model’s predictive capability by comparing the dynamic tensile strength with high-strain-rate Brazilian disk experiments performed on basalt samples.

Image: A frame-by-frame showing how gravity causes asteroid fragments to reaccumulate in the hours following impact. Credit: Charles El Mir/Johns Hopkins University.

The first phase of the scenario is shown in the video below, available at https://www.youtube.com/watch?time_continue=1&v=Vt_xwQYafOY for email subscribers who would like to follow it up in their browsers. What emerges is that millions of cracks form in the asteroid as the crater is created, with the asteroid surviving the hit rather than being shattered, while the surviving core then has sufficient gravitational pull to act on the fragments swirling around it.

In the second phase, available at https://www.youtube.com/watch?time_continue=1&v=ZjBgljnCtWk, what we have left is not a rubble pile held loosely by gravity, but rather a surviving core whose fragments have been redistributed. Can we, then, hope to break an asteroid into small pieces, or is it best to find ways to nudge the entire object onto a new trajectory? The latter still involves the question of asteroid survivability, as we need to move it without breaking it into smaller impactors.

The paper shows the capability of the parent asteroid to withstand huge shock:

The collision imparted substantial damage onto the target, with most of the damage localized under the impact site, resulting in a heavily fractured but not fully damaged “core”. The material points were then converted into soft spheres and handed over to pkdgrav [the modeling software] in a self-consistent manner to calculate the gravitational interaction of the ejected material. We observed substantial ejecta fallback onto the largest remnant of the parent body, with a recovered mass of the largest remnant being 0.85 that of the parent body, indicating that the disruption thresholds for such targets may be higher than previously thought.

Thinking ahead to asteroid mitigation strategies is simple prudence, and requires continuing study of how asteroids respond to the various methods now under consideration to destroy them or change their trajectory. This paper gives us a glimpse of the changing parameters of research on the matter, a window into the ongoing analysis that will refine our planning.

The paper is El Mir et al., “A new hybrid framework for simulating hypervelocity asteroid impacts and gravitational reaccumulation,” Icarus Vol. 321 (15 March 2019), pp. 1013-1025 (abstract). The Michel paper is “Collision and gravitational reaccumulation: Possible formation mechanism of the asteroid Itokawa,” Astronomy & Astrophysics 554, L1 (abstract).

tzf_img_post

{ 13 comments }

A Sparse Population of Small Kuiper Belt Objects?

One problem with learning about the Kuiper Belt is that objects out there are small and details from Earth-based imaging all too sparse. New Horizons yielded up a world of wonders with Pluto, showing us nitrogen glaciers, and mountains fully 4 kilometers tall. But even relative proximity doesn’t help us in some areas. Pluto’s surface has seen enough geologic activity that evidence of its impact history is sparse. Where to turn to learn what has hit it, and when?

The large moon Charon may provide some answers. Unlike Pluto, its surface is relatively stable, giving us insights deep into the past. And we learn from a new paper by Kelsi Singer (SwRI) that there is a surprising lack of craters here nonetheless. The craters we do see on the two worlds were, according to the paper, formed by objects with diameters ranging from ~40 kilometers to ~300 meters, making them smaller than most KBOs we can observe with our telescopes.

Thus a measure of how much in the dark we are about the nature of KBOs. Even Pluto, with resurfacing at work through geological processes, should show more signs of small craters of 13 kilometers or less in diameter. Their lack seems to make small KBOs — ≲1 to 2 kilometers in diameter — very sparse. The work, which appears in Science, implies that there are major differences between the Kuiper Belt and the closest analogue in our system, the main asteroid belt. Says Singer:

“This surprising lack of small KBOs changes our view of the Kuiper Belt and shows that either its formation or evolution, or both, were somewhat different than those of the asteroid belt between Mars and Jupiter. Perhaps the asteroid belt has more small bodies than the Kuiper Belt because its population experiences more collisions that break up larger objects into smaller ones.”

Image: An SwRI-led team studied the craters and geology on Pluto and Charon and found there were fewer small craters than expected. This implies that the Kuiper Belt contains relatively small numbers of objects less than 1.6 kilometers in diameter. Imaged by New Horizon’s LORRI camera, the smooth, geologically stable “Vulcan Planitia” on Charon illustrates these findings. Credit: Courtesy of NASA/JHU/LORRI/SwRI.

We’re still early in the analysis of data from the Ultima Thule flyby, so we don’t want to read too much into this, but it does appear that Ultima supports the same lack of cratering. That’s intriguing because we’re dealing with formation models of the Solar System, which can produce different outcomes and hence populations of objects depending on their inputs. We’re thus homing in on information about the early formation of the Solar System as we analyze the differences between the two belts of debris in their respective positions around the Sun.

Sorting this out will be a lengthy process, dependent upon leveraging data on the three surfaces we’ve been able to study up close through New Horizons, and future data from continued observation (and, let’s assume, additional space missions, including a New Horizons flyby in a future extended mission). Remember that some of the surfaces we’ve seen on Pluto and Charon are likely to be over 4 billion years old, making this analysis of the size and frequency distribution of KBOs provocative.

Interestingly, the paper speculates that if the lack of smaller KBOs is primordial (as opposed to being the result of, say, structural properties of KBOs themselves), this may be consistent with “dynamical models of gravitational instabilities causing rapid growth to larger objects.” Such models produce fewer small bodies and fewer collisions overall. The paper concludes:

There may be more than one combination of processes that can produce the observed KBO SFD [size-frequency distribution]. If there are fewer small objects in the outer Solar System, the probability of collisions is lower, and comets such as 67P/Churyumov–Gerasimenko are less likely to be affected by many catastrophic collisions throughout their lifetimes… By providing constraints on a size range of KBOs not currently accessible by telescopes, the New Horizons crater data can help discriminate between models of accretion, evolution, and/or emplacement of the Kuiper belt.

And dropping back to 1990, we might note another surface, this one of a likely captured KBO, that we viewed from Voyager. I’m pointing to a paper from Robert Strom (Lunar and Planetary Laboratory, University of Arizona) and colleagues on impact cratering on Neptune’s large moon Triton. The scientists found few impact craters on Triton thanks to recent resurfacing from icy melts, with the most heavily cratered surfaces, found on the leading hemisphere in Triton’s orbit, having a crater density about the same as the lunar maria. The scientists argue that some of the craters in Triton’s so-called ‘cantaloupe’ terrain may well be the result of volcanic activity.

The paper is Singer et al., “Impact craters on Pluto and Charon indicate a deficit of small Kuiper Belt objects,” Science Vol. 363, Issue 6430 (01 March 2019), pp. 955-959 (abstract). The Strom paper is “The Impact Cratering Record on Triton,” Science Vol. 250, Issue 4979 (19 October 1990), pp. 437-439 (abstract).

tzf_img_post

{ 5 comments }

A planet designated Kepler-1658b is, after a good deal of investigation, demonstrated to be a ‘hot Jupiter,’ orbiting a star that is 50 percent more massive and three times larger than the Sun. The sizzling world is close enough to its star that were you to look into its sky from near the planet, the star would be 60 times larger than the Sun as seen from Earth. And while none of this makes Kepler-1658b unique in our catalog, what does stand out is how we learned all this.

For we are talking about the first planet candidate ever uncovered with the Kepler Space Telescope. Recall that for any transiting planet to be considered confirmed, we need a second kind of detection. The reason: Various astrophysical processes can mimic transit activity. Prudence dictates the backup, and in the case of Kepler-1658b, both the initial estimate of the star’s size and the size of the planet were underestimated. The result was that the putative world became thought of as a false positive whose numbers didn’t check.

Three of the stars in the Kepler field were already known to have planets from ground-based transit observations when the mission launched in 2009, and these three targets became the first designated Kepler Objects of Interest (KOI). What would be labeled KOI 4.01, Kepler’s first new planet candidate, was given a stellar radius of 1.1 times that of the Sun, with an initial transit depth implying that the star was orbited by a Neptune-class planet. A new paper on Kepler-1658b goes through the history of its description and subsequent catalog listings.

The detection remained a false positive, though, until a graduate student at the University of Hawai’i named Ashley Chontos reanalyzed the problematic find:

“Our new analysis,” says Chontos,” which uses stellar sound waves observed in the Kepler data to characterize the host star, demonstrated that the star is in fact three times larger than previously thought. This in turn means that the planet is three times larger, revealing that Kepler-1658 b is actually a hot Jupiter-like planet.”

Armed with that information, Chontos contacted Dave Latham (Smithsonian Astrophysical Observatory), whose team went to work culling the needed spectroscopic data to make a radial-velocity call on the planet. Newly confirmed, Kepler-1658b turns out to orbit at a distance only twice the diameter of the host star, making its orbit one of the closest we’ve found to an evolved star (one that has exhausted the hydrogen fuel in its core and, drawing on nuclear reactions outside the core, is passing through the subgiant phase and swelling into a red giant).

Image: Artist’s concept of a Kepler-1658-like system. Sound waves propagating through the stellar interior were used to characterize the star and the planet. Kepler-1658b, orbiting with a period of just 3.8 days, was the first exoplanet candidate discovered by Kepler nearly 10 years ago. Credit: Gabriel Perez Diaz/Instituto de Astrofísica de Canarias.

This is an interesting find for more than its significance as the first Kepler exoplanet. We know of few planets orbiting stars of this class, a deficit not yet understood. From the paper:

Systems like KOI 4.01 are interesting because giant planets at short orbital periods (P < 100 days) are rare around subgiant stars (e.g. Johnson et al. 2007, 2010; Reffert et al. 2015; Lillo-Box et al. 2016; Veras 2016), although the reason for this is still a topic of debate. On one hand, this may be related to the stellar mass. Subgiant host stars are thought to be more massive than main sequence stars targeted for planet detection. A higher mass could shorten the lifetime of the protoplanetary disk and lead to fewer short-period giant planets orbiting these type of stars (e.g. Burkert & Ida 2007; Kretke et al. 2009). Other authors have suggested that subgiants have fewer short-period planets because these objects may get destroyed by tidal evolution, which is likely stronger for more evolved stars (e.g. Villaver & Livio 2009; Schlaufman & Winn 2013). Distinguishing between those scenarios is further complicated by the fact that it is challenging to derive stellar masses of evolved stars (Lloyd 2011, 2013; Johnson et al. 2013; Ghezzi et al. 2018).

Thus Kepler-186b is a useful outlier that helps us put constraints on what happens as planets approach a death spiral into their star. And another exoplanet mission may provide a useful cross-check:

The Kepler field will be observed by the Transiting Exoplanet Survey Satellite (TESS; Ricker et al. 2015) in mid-2019. Extending the baseline of transit observations to over a decade for Kepler-1658 will allow for a stronger constraint on orbital period decay in more evolved systems. Extrapolating our period decay analysis to the time Kepler-1658 would be observed by TESS would rule out another order of magnitude for the tidal quality factor in subgiant stars.

The paper is Chontos et al., “The Curious Case of KOI 4: Confirming Kepler’s First Exoplanet Detection,” accepted at the Astronomical Journal (preprint).

tzf_img_post

{ 14 comments }