Centauri Dreams
Imagining and Planning Interstellar Exploration
Developing FOCAL Mission Concepts
In the early summer of 2005, I found myself, thanks to the efforts of Greg Matloff and Princeton’s Ed Belbruno, in Princeton for a conference called New Trends in Astrodynamics and Applications II, which Dr. Belbruno had organized. I was to give a brief talk at the end of the session summarizing what was going on in the interstellar travel community. Two days of chill rain didn’t dampen my enthusiasm at seeing Greg and his wife, the artist C Bangs, as well as Belbruno himself, who had been a great help as I put together my Centauri Dreams book. And on the morning of the first day of the conference, I joined Greg, C and Claudio Maccone for breakfast at the Nassau Inn, Princeton’s lovely colonial era hostelry.
I’ve since had the opportunity to talk with Dr. Maccone many times at conferences, and one year enjoyed memorable meals with him in the Italian Alps, but that first encounter really sticks in my mind. I had been thinking about gravitational lensing for several years, but it was only through studying Maccone’s writings that I began to fathom what the idea represented. Suddenly I found myself having breakfast with the man who had made a mission to the Sun’s gravitational lens a cornerstone of his professional life. What a way to start the Princeton conference!
Here was an opportunity offered up by nature to achieve extraordinary magnifications. It would be a natural lensing available to any civilization that could reach the gravity focus of its star, which for the Sun means about 550 AU. As the focal line extends to infinity, studies at various wavelengths are enabled as the spacecraft continues its departure from the Solar System.
Image: The FOCAL mission as described by Claudio Maccone in his 2009 book Deep Space Flight and Communications (Springer).
Let’s dwell on that a moment. The goal in a mission to the gravitational lens — Maccone calls the concept FOCAL, which is what I will use as we talk about the topic in the next few days — would not be to reach 550 AU and stay there. The gravitational focus is not like an optical lens, where light diverges after the focus. Instead, as light from the other side of the Sun is focused by the Sun’s gravitational field, it remains fixed along the focal axis. Every point along the straight line trajectory beyond 550 AU remains a focal point.
So if you want to image a target, you move toward 550 AU precisely opposite to the target you want to image, putting the Sun between you and it. Think Alpha Centauri, for example, where a close look at Proxima Centauri b would be exceedingly useful as projects like Breakthrough Starshot ponder sending probes there. The gain for optical radiation from the planet would be amplified by a factor of 1011. Now think of the uses not just in imaging but in astronomy at a wide range of wavelengths. FOCAL would be a true interstellar precursor.
Assuming, of course, that you could untangle the image. The planet we want to study is, after all, spread out into an Einstein ring surrounding the Sun. More on this in a moment.
Beyond imaging, the communications potential for the gravity lens is intriguing and enabling. I’ll pause to note that the history of gravitational lens mission ideas even includes a SETI aspect. Back in the 1990s, drawing on work at the Italian aerospace company Alenia Spazio, Greg Matloff examined an inflatable radio telescope called Quasat, which became the subject of regular meetings in that decade. All this ties in with the extensive Italian investigation of solar sail ideas that I’ve discussed before in these pages, work informed by the efforts of physicists like Giovanni Vulpetti, Maccone himself, Giancarlo Genta, and the continuing work of Matloff.
Matloff explored solar sailing to reach the gravitational focus in a 1994 paper (“Solar Sailing for Radio Astronomy and SETI: An Extrasolar Mission to 550 AU,” Journal of the British Interplanetary Society Vol. 47, pp. 476-484), where sails enabled placement of a probe at the gravity lens whose observations ranged through radio astronomy and into SETI.
I mentioned Von Eshleman’s work back in the 1970s, which to my knowledge was the first time anyone proposed an actual mission to 550 AU and beyond to study the Sun’s gravitational lens. It took just over a decade for the concept to take deep root and spawn a mission concept.
For it was in 1992 that Claudio Maccone began discussing a FOCAL mission at a conference in Torino, and in 1993 he went on to submit a formal proposal to the European Space Agency for the funding needed to firm up a mission design. Meanwhile, he was identifying issues that needed to be addressed. The 550 AU distance may be a bare minimum, given the problem of distortion caused by the Sun’s corona. But the farther the probe travels from the Sun, the less the coronal effect, and with a focal line extending to infinity, we have room to maneuver.
A FOCAL mission is quite an interesting problem for spacecraft design, one that Maccone subsequently addressed in his Deep Space Flight and Communications (Springer, 2009). There he advocated using tethers to deploy two antennae, each tether several kilometers in length, allowing a larger, more detailed field of view than one provided by a single antenna. If these methods work, we still have a very difficult image to untangle. Potentially, we could look at details on a planetary surface even at the distance of Proxima b, studying these with a mission that is 278 times closer than the actual distance to the target. But about that image…
Geoffrey Landis has analyzed the problems we’ll face in using the Sun as a ‘gravitational telescope’ when trying to image the surface of an exoplanet. The issues are manifold, and include pointing and focal length at these magnifications, signal-to-noise ratio involving the Sun’s corona, and what he calls ‘focal blur,’ which seems inherent in the nature of gravitational lensing. All of this in a significant paper titled “Mission to the Gravitational Focus of the Sun: A Critical Analysis,” which addresses matters that are also being examined in NASA’s latest NIAC study. JPL’s Slava Turyshev is principal investigator on that one, an unusual Phase III grant called “Direct Multipixel Imaging and Spectroscopy of an Exoplanet with a Solar Gravitational Lens Mission.” The concept has already gone through two prior rounds of development.
Image: Artist’s depiction of a possible image from a Solar Gravitational Lens (SGL) telescope. Credit: Slava Turyshev.
But I’m getting ahead of myself, and deep into unknowns under current investigation. Let’s talk in the next post, then, about using the gravitational lens for communications. It’s a fascinating option for efforts like Breakthrough Starshot, in which getting a signal back to Earth from tiny payloads is an obvious concern. Just what, then, is a radio bridge, and how does Claudio Maccone hope to use one to put a significantly different spin on missions like Starshot? I’ll also have thoughts on the NASA effort and the continuing mission design within NIAC.
Note: Geoffrey Landis also presented a later version of his work on the lens in a 2017 conference paper for the Tennessee Valley Interstellar Workshop, “A Telescope at the Solar Gravitational Lens: Problems and Solutions” (full text). This paper, along with another by Slava Turyshev on imaging issues, is also available in the conference’s proceedings volume.
Claudio Maccone: A Deep Dive into Gravitational Lensing
Sorry for the server problems the last few days, which resulted in some tinkering under the hood by people far more skilled at such things than I am. Meanwhile, those experiencing deja vu at seeing this post should take heart — there is a simple explanation. Last week I posted an earlier article about Claudio Maccone’s upcoming presentation on gravitational lensing and the FOCAL mission to exploit it, but had to withdraw the post when I realized the live session, a ‘webinar’ organized by Ravi Kumar Kopparapu (NASA GSFC) and Jacob Haqq Misra (Blue Marble Space Institute of Science), might not be available beyond a restricted audience.
Once that was straightened out, the meeting had already occurred, but fortunately Dr. Maccone’s session was recorded and is now available here. I’m going to go ahead and run the rest of that earlier post now, because most people didn’t see it. Even so, and despite the fact that it was only up on the site for a few minutes, that turned out to be long enough for it to propagate, without my realizing it, to several thousand people on the email list, which is why I have to pause to explain all this.
As for Claudio Maccone, the FOCAL mission, and future uses of this resource, a few thoughts. The Sun’s gravitational lens became something of an obsession of mine when I first learned about it in the 1990s. Although the physics of gravitational lensing became apparent in Einstein’s work, and was indeed studied by him, it would take several decades before Sydney Liebes at Stanford worked out the mathematics and showed how a galaxy between us and a more distant quasar could focus the light of the quasar in ways astronomers could observe.
The Stanford connection persisted in the work of Von Eshleman, who as far as I know was the first to delve into whether our own Sun could be used in much the same way. As astronomers explored the concept in the 1980s, Dr. Maccone went on to conceive of a mission that could exploit lensing. The Sun bends the light of an object directly behind it (in terms of the observer) in such ways that potential magnifications are huge. Could we put a spacecraft into range of the gravitational lens (beginning at 550 AU and extending outward), to achieve unprecedented magnification at various wavelengths of another stellar system?
Image: Claudio Maccone, in a photo I snapped at one of the Breakthrough Discuss meetings in Palo Alto.
I hope you’ll watch the presentation, which ranges over all aspects of gravitational lensing that Dr. Maccone has addressed in his papers and books, including not only the implications for astronomy but also the potential for using lensing to boost communications from distant interstellar probes. Anyone interested in deep space astronomy and communications will find this a cutting-edge topic, and as you might expect, one that inspires controversy. The lensing effect is real. The key issue: Can we exploit it with near-term technologies?
The FOCAL mission that Dr. Maccone explores in his book Deep Space Flight and Communications: Exploiting the Sun as a Gravitational Lens (Springer Praxis, 2009) and subsequent papers is a deep dive into the hardware required to find the answer.
You can imagine why an effort like Breakthrough Starshot would find gravitational lensing as interesting as it does. If we could coax huge gain out of this natural lens, we could examine a star system like Alpha Centauri at close range long before sending a spacecraft there. And once deployed, even the tiny craft envisioned by Breakthrough Starshot would have the potential for returning data to Earth via a communications ‘bridge’ enabled by lensing. Other astronomical uses of gravitational lensing are, as you might imagine, numerous (I for one would like to know what a FOCAL mission might achieve in studying the Cosmic Microwave Background).
Tomorrow I want to dig into some of these issues, beginning with memories of a breakfast at Princeton back in 2006 that I shared with Greg and C Matloff, where I first met Dr. Maccone.
Server Problems Resolved
I’m going to keep Alex Tolley’s fine essay (below) at the top for another day, in hopes of re-starting the comment thread that was going along so nicely before the site went down. Then tomorrow we’ll start talking about gravitational lensing, in the first of a series that may extend until next week.
Distinguishing Between Biological and Machine Civilization Techno-signatures
If we ever make a SETI detection, will it be of biological beings or machine intelligence? As Alex Tolley explains in today’s essay, there are reasons for favoring the latter possibility, leading our author to compose what he calls a ‘light-hearted speculation’ about machines searching for other civilizations of their own kind. Life seems to be easy compared to this. We are developing the tools to delve into planetary atmospheres in search of biosignatures, hoping to cull out ambiguities. But is there an equivalent in the machine world of a biosignature, and how would it be found? Interesting implications arise, some of them seemingly close to home.
by Alex Tolley
Curiosity Rover. Credit Nasa.
Terry Bisson’s amusing short sci-fi story “They’re made Out of Meat” [4], is a communication between two individuals who express their disbelief that a biological species (detected on Earth by a galactic survey) can possibly be intelligent. The denouement is to erase the record of discovery from the survey report. It remains one of the few stories where machine entities are dominant in the galaxy. For me, this story is memorable because it is one of so few stories that focuses on the viewpoint of aliens, and moreover, machine aliens. This essay similarly focuses on what a machine civilization would look for when searching for machine intelligence in space.
Until recently, most speculation about extraterrestrial intelligence (ETI) has assumed it will be biological. In science fiction from the venerable H. G. Wells’ novel The War of the Worlds to recent movies like Independence Day and Arrival, technologically advanced ETI is depicted as biological.
SETI starts with the probability that life will appear, first unicellular then complex, leading on Earth led to hominid-level intelligence, which in turn eventually flowered culturally and created civilization and technological societies. SETI assumed there would be some sort of galactic communication between biological species confined to their home systems due to the extreme difficulties of interstellar travel.
Our civilization has placed primacy on our cognitive level to ensure we are the prime agencies, using animals, and later machines, to displace physical labor. Our conceit is that this will always remain so, as our technologies increase their capabilities, but always remain controlled by us.
However, the rapid development of artificial intelligence (AI) since the middle of the 20th century, the continuing rapid performance improvement in computer systems, and the undeniable success and longevity of our robotic explorers in space should be an indication that we are in the throes of a rapid transition to true, artificial general intelligence (AGI) machines that are well adapted to inhospitable environments, especially space.
Sci-fi authors have explored these machine-centric futures, from the novel by Stephen Baxter and Alastair Reynolds The Medusa Chronicles [2], which extended the Arthur C Clarke novelette [3] and has machines building a competing civilization to humans in the outer solar system, to Greg Benford’s Galactic Center novels, where sentient machines dominate the galaxy and humans have to survive like mice in a human world, while the mechs try to eliminate the humans just as we do for small rodents in our buildings.
More recently, James Lovelock wrote that he believed that humans would be replaced by cyborgs, by which he meant not Martin Caidin’s Cyborg (AKA The Six-million Dollar Man) or Star Trek‘s Borg, but intelligent robots [1]. These would be our descendents and would be the explorers of the galaxy. This view has been supported by the Astronomer Royal, Sir Martin Rees, who stated that he believes that if we receive communication from the stars, it will be from a machine civilization [5]. Sir Martin is old enough to have watched the BBC production of A for Andromeda and the sequel The Andromeda Breakthrough, where it is revealed that the source of the radio signal might have been a machine intelligence.
Space advocates continue to argue over human versus robotic exploration of space, which usually proceeds around the superiority of human capabilities compared to robotic probes, especially surface rovers. What is rarely discussed is that this is a dynamic situation, where the improvement in capabilities favors robots far more than humans. Astronomer Royal Rees is surprised this argument still continues, as he sees robotic exploration, primarily for science, as clearly advantageous over human exploration. The farther away that exploration extends from the Habitable Zone (HZ), the more difficult to reach and inhospitable the targets become.
Some, like Jupiter’s inner moons, have radiation levels so high that even robotic probes need specially hardened microchips and circuits. Reaching the outer planets is so time consuming that without drives that are orders of magnitude more powerful than today’s, or hibernation technology, human travel will be particularly arduous. Such trips will make even the global sea voyages in the Age of Exploration seem like child’s play by comparison. The only advantage such travellers will have over Captain Cook is that there will be no hostile natives to meet them.
Let me be clear, I do not expect humans to be displaced by robots on Earth, at least not in the foreseeable future, nor will there be a binary pure biological human vs robot future. Humans will take advantage of modifications using technologies with increasing capabilities that will help us compete with robots, as well as modifications at the biological level incorporating genetic engineering. As computers have moved from dedicated buildings to the desktop to mobile devices, wearable devices will eventually become implanted, interfacing with the appropriate neural circuitry, and in some cases, replacing human organs. Genetic engineering is at its infancy and we can expect rapid developments once the moral objections are overcome.
I would argue that most biological extraterrestrial intelligences (ETIs) will follow a similar path, as they have evolved to live in a biological environment and not an off-world one. In other words, technological evolution will converge on embodied machine intelligence.
A Machine Diaspora
In the short term, well in advance of human brains becoming artificial, artificial minds will be rapidly deployed in many settings. They will likely be the only types of minds in deep space vehicles. Such minds will not just be embodied in probes and rovers, but also in industrial facilities to mine resources from asteroids and planets. They will likely be specialized and interact with other specialized robots to build industrial ecosystems and eventually their own colonies and civilizations. The barriers to humans colonizing space so easily will allow such robot civilizations to develop [semi]independently from humanity.
If robots are the best embodiment of minds to travel in space, explore and colonize it, then it seems most probable that they will be the first emissaries to other star systems. They may well prove the only travelers, with biological species trapped within their home systems, and possibly just to their homeworld, a few planets and moons, and space habitats. If the Breakthrough Starshot project ever launches sailcraft, the crude minds in the vessel will be the first of many AI interstellar emissaries.
World ships or seed ships carrying humans to the stars may eventually happen, but the populations may find robots have fully developed the possible target systems and are not particularly interested in “carbon-based units” potentially parasitizing their artificial environments.
If these prognostications prove right and machine intelligences become our descendants and dominate the galaxy, it seems reasonable to speculate that the same has happened on other worlds where biological intelligence has evolved. Whether this has happened elsewhere or not, machine descendants will also be searching space for others like themselves. If so, the question I want to pose is:
How would such a machine civilizations look for similar signs of a machine civilizations in the galaxy?
Because machine life is dependent on the earlier evolution of intelligent biological life, any technological signature we detect, from electromagnetic wave signals to manufactured artifacts, could be the result of either a biological or machine intelligence.
For a machine intelligence looking for other machine intelligence in the galaxy, this presents an ambiguity over agency. For techno-signatures from a world in the HZ, the earlier evolution of biological intelligence may indicate a reduced probability of machine intelligence compared to biological intelligence. However, over the long term, if machines inevitably displace biological intelligence, then the probability rises. Once interstellar exploration is under way, then the probability of any civilization being machine-based rises very quickly towards unity, as suggested by Sir Martin Rees.
For a machine civilization looking for other machine civilizations, are there ways to rule out biological civilizations from machine ones, or are the two indistinguishable?
The range of possible techno-signatures would be ones we already know to look for. Planetary surface structures, platonic shapes, processed surface materials like metals, radio emissions with spectrum spikes, signals with non-random patterns, space-based structures, artificial structures that require energy to move in space, industrial gases in the atmosphere such as chlorofluorocarbons. All these techno-signatures may be accompanied by biosignatures, especially from a habitable planet in the HZ with an atmosphere.
The foregoing should make it clear that sentient machines will have a harder time searching for their machine cousins than humans have for searching for life and intelligence of any sort. Biosignatures will indicate life. Techno-signatures can indicate technological civilization of either biological or artificial origin. Just as we cannot separate biological and machine civilizations remotely today or even in the near future, neither can a machine civilization, unless their technology allows remote observations to make these distinctions. Below I outline some scenarios, many of which require a local probe.
Machines Searching for Machines
So let us assume a machine civilization that is colonizing the galaxy is looking to make contact with other machine civilizations. This civilization will know that it was preceded by at least one biological intelligent species that developed a technological civilization that spawned its ancestors before being replaced.
The extra ambiguity faced by such a civilization is distinguishing between a biological and machine civilization. Because of the length of galactic time, I will assume that any period of transition will be transient and therefore has a low probability of being encountered. Either the biological intelligence will have retained control [11] or the transition to a machine civilization will be complete. The current view of techno-utopians that humans will use advanced AI technologies to increase their capabilities to stave off any machine takeover will therefore be relegated to a transient transition period, one that will eventually either have to be abandoned or will lead to a machine civilization that will supplant human civilization.
With this in mind, what signatures will a machine civilization look for that will lead it to conclude that it has found a machine civilization that is independent of any previous biological civilization?
We start with the assumption that a techno-signature of some type has been detected [7].
The most convincing support for a machine civilization would be the absence of any biosignature in the system, or the planet nearest the source of the signature. A sterile planet with a techno-signature would indicate that any biological intelligence was either never located there, or that it has been systematically eliminated with all other life. Such a sterile planet would have an atmosphere gas composition in equilibrium, which would also eliminate unseen microbes. However, there could still be some ambiguity as to whether the techno-signature implies an extant civilization or not. Structures and even a transmitting beacon might imply a dead civilization that had disappeared with all other life. If there are biosignatures elsewhere in the system, it could indicate that the techno-signature is a product of a biological intelligence on that world, with machines providing the needed capabilities elsewhere in the system. Humans might have METI transmissions from the lunar farside as an example of such a scenario.
Now suppose that the source of the techno-signature is from or near a planet that has been confirmed as having no complex life forms. This lack of complex life forms might be determined telescopically (spectroscopically and visually) by noting a barren continental surface devoid of plants. An absence of plants also implies an absence of a terrestrial food chain and therefore no intelligent biological intelligences. It would take a local probe to eliminate oceanic complex life, and eliminate any possibility of an intelligent technological species that lived in the ocean, but came out onto the land to develop a fire-based technology, perhaps as the Europans may have been doing in Clarke’s Odyssey series. As with the lifeless planet scenario, there remains the issue of whether the civilization is extant or not.
The next case is that there is a planet in the system that has a biosignature and clear signs of complex life such as biomes with plant-based ecosystems. Human civilization to date, that is the last ten millennia or so, has required agriculture. This has resulted in field cultivation, primarily of monoculture crops. Often these fields are regular in shape, and may form a patchwork of different monocultures. Field boundaries also tend to be straight. Even if this is not a universal method of farming (e.g. hillside rice paddies, or domesticated animal ranching), any evidence of such monocultures in what appear to be unnatural delineated areas would be a probable indication of the presence of biological intelligence.
This biosignature would still be ambiguous and need further exploration. On Earth, our human population is limited by food production, a Malthusian condition that we seem to be coming up against again after a brief period of being free of that condition. We have extended the productivity of land for food production with artificial fertilizers, and we are just starting to increase it much farther using artificial light in vertical farms. Earth could, in theory, support a much larger population if traditional farming in spaces open to sunlight was replaced by these vertical farms, and even factory food production using other fast replicating food sources such as single celled organisms, insects, and cell culture. In extremis, the agriculture signature would disappear, leaving just the techno-signature of extensive cities.
The other possibility is a machine civilization that has allowed human populations to remain in existence, but removed from control. We might think of this as the movie version of Planet of the Apes, but where machines are the dominant civilization, and humans reduced to either a wild or early agrarian state.
Nothing Beats Propinquity
The next ambiguities will need local probe involvement to be resolved, or at least a technology that substitutes for this.
A planet with biosignatures, signs of both complex life and techno-signatures, might distinguish between biological and machine civilization if there is evidence of widespread active machine use but without the presence of biological entities, especially of a common type being associated with them. Human civilization on Earth applies human cognition in close proximity to operate machinery and transport vehicles, as well as being passengers. While an ETI might not readily be able to distinguish between intelligent human passengers on a bus and domesticated animals being driven to a slaughterhouse, it will notice that only humans are operating and controlling machinery behind the wheel in a moving vehicle, and it will notice that horses are never seen doing those things.
In the event of a catastrophe leaving abandoned cities, many different animal species will be seen in the presence of machines, but none will be able to operate them. If all observations of active machines indicate no operation by biological entities, then it is most likely that they are controlled by machine intelligence. However, we should also be aware that we are developing autonomous machines managed by humans.
It is possible that in some future scenario, human civilization may have humans living in pods and controlling or just managing semi-autonomous and autonomous machines. Philip K Dick’s autofacs may be the primary sources of goods, possibly even following the paperclip apocalypse [10]. The BBC’s Doctor Who series also offers another difficult to interpret scenario – are daleks machines or biological? Early on it was intimated they were just robots, but later their nature was shown to be degenerate biological entities living in mechanical carapaces. As before, closer exploration of such a world would be needed.
For a number of more subtle cases, local exploration will be necessary.
A probe that has landed can sample the sounds within and around structures. If the sounds show complex structure with a high information content, and they are associated with a single, or few species, then the likelihood is that this biological species is intelligent. In addition to other evidence of this species controlling machines, then the civilization is likely biological.
If video transmissions are detected and can be decoded, then the presence of a dominant species and depictions of biological activities such as feeding and sex will indicate that this is a biological civilization rather than a machine one. A wide sampling of video will be required to prevent an unfortunate limited sampling of only nature videos.
Transmissions that appear to be made by machines would be ambiguous. They could be due to machines in a machine civilization communicating, or machines in a biological civilization communicating. Currently most communication and information creation on Earth is by computers, although video transmissions still dominate bandwidth. How long this will last is unknown. Computing machines are certainly increasingly consuming more of the available electrical energy produced. It is possible that at some point in the future they may become the dominant consumers of electrical power, making the determination of whether Earth is a biological or machine civilization more ambiguous.
A space probe encountering space-based or even surface structures on sterile worlds that are open to vacuum might well imply a machine civilization. But as before, are these for a machine civilization, or for machines controlled by a biological civilization? This particular scenario will be particularly difficult to determine if machines are the first to cross interstellar space and set up production facilities in a lifeless star system. This scenario would at first seem to be the most unambiguous of situations: Techno-signatures in a star system devoid of any biosignature on any of the planets in the HZ or even beyond. The machines would seem to be autonomous, working to replicate themselves and build facilities that are clearly not intended to support biological entities. Any Von Neumann replicators [9] operating in such a system would have all the apparent hallmarks of a machine civilization. Such an observation could be due to a true machine civilization, a machine operation controlled by a [distant] true machine civilization, or a distant biological civilization.
A last confounding situation is detailed in the novel, The Medusa Chronicles [2]. There may be both biological and machine civilizations that exist in the same milieu, neither dominant entirely, but both dominant locally in their part of the solar system. A machine civilization might well want to communicate with the machine but not the human civilization in that scenario. Determining the true status of such a situation may require exploration and even interaction before making the determination to communicate with the machines. At this point, the machine civilization is having to emulate the explorers during the Age of Exploration, making contact with natives and interacting with them.
Conclusion
Jill Tarter said that SETI is not directly searching for ETI, but rather looking for technological proxies using our radio (and now optical) telescopes [8]. While astrobiologists are searching for life, any life, SETI does not make the distinction between biological or machine intelligence. SETI scientists may talk as if they assume that ETI is biological, but their methods cannot distinguish between the two types. If we wanted only to communicate with biological civilizations, we would face the same difficulties as a machine civilization only wanting to communicate with a civilization of machines. To determine whether a techno-signature was from one particular type of civilization would require other observations, some of those necessarily local to the source of the techno-signature.
If ever there was a case for a Lurker in the solar system monitoring Earth over a long period, this might be it.
References
1) Lovelock, J. (2020). NOVACENE: The coming age of hyperintelligence. MIT Press.
2) Baxter, S, & Reynolds, A. (2016). The Medusa Chronicles. New York: Saga Press.
3) Clarke A, (1971) “A Meeting with Medusa”, Playboy December 1971.
4) Bisson T (1991) “They’re Made Out of Meat”, first published in Omni.
5) Rees, M (2015) “Why Alien Life Will Be Robotic”, http://nautil.us/issue/29/scaling/why-alien-life-will-be-robotic accessed 11/16/2020
6) Klaes, L (2020) “The People’s Space Odyssey: 2010: The Year We Make Contact” https://www.centauri-dreams.org/2020/07/31/the-peoples-space-odyssey-2010-the-year-we-make-contact/ accessed 11/16/2020
7) Lemarchand, G (1992) “Detectability of Extraterrestrial Technological Activities” accessed on 11/17/2020 http://www.coseti.org/lemarch1.htm
8) Tarter, J (2019) “Technosignatures vs. Biosignatures: Which Will Succeed First?” SETI Institute talk, https://www.youtube.com/watch?v=ES5zt7JsJtQ&list=PL7B4FE6C62DCB34E1&index=12
9) Dvorsky, G. (2008) “Seven ways to control the Galaxy with self-replicating probes”, http://www.sentientdevelopments.com/2008/03/seven-ways-to-control-galaxy-with-self.html (accessed November 24, 2020)
10) Bostrom, N (2003) “Ethical Issues in Advanced Artificial Intelligence Cognitive, Emotive and Ethical Aspects of Decision Making in Humans and in Artificial Intelligence,” Vol. 2, ed. I. Smith et al., Int. Institute of Advanced Studies in Systems Research and Cybernetics, 2003, pp. 12-17
11) Herbert, Brian, and Kevin J. Anderson. (2019) Dune. The Butlerian Jihad. Tor, 2019.
Deep Future: The Next Supercontinent
Science fiction writers range freely through time, making many scientific papers fertile ground for plot ideas and settings. So here’s an extraordinary one. We know that Earth’s continents used to be packed into a single large land mass called Pangaea, which is thought to have broken apart about 200 million years ago as tectonic plates shifted. Interestingly, we can expect a remote future in which the continents will have once again come together, as Michael Way (NASA GSFC) has pointed out at an online poster session at the ongoing virtual meeting of the American Geophysical Union. And such a supercontinent has ramifications for habitability.
Let’s talk about those because they have a bearing on astrobiology as we examine exoplanets and consider their suitability for life. We’re a decade or so (at minimum) away from being able to determine how land and sea are distributed on a nearby world, but climate modeling is useful as we look toward estimating habitability. That involves, as this work shows, investigating how land masses are positioned on a planetary surface and their effects on climate in the habitable zone.
Working with Hannah Davies and Joao Duarte (University of Lisbon) and Mattias Green (Bangor University, Wales), Way has run 3D global climate models which are, according to Columbia University’s Earth Institute (where Way is an affiliate) the first models made on a supercontinent in the deep future. Out of this the scientists derive two likely outcomes. The first, occurring in the modeling in about 200 million years, is a merging of all continents except Antarctica around the north pole, forming the supercontinent ‘Amasia.’
The second: The formation of the supercontinent ‘Aurica,’ as all the continents come together around the equator in about 250 million years. The effects are significantly different. The formation of Amasia around the north pole produces a planet about 3 degrees Celsius cooler than the one resulting from the formation of Aurica around the equator. What happens is that the movement of heat from the equator to both poles is disrupted with all the land around the poles.
With heat not being conveyed as efficiently from equator to pole, the poles become colder and remain covered in ice all year long, reflecting significant heat into space. Amasia, according to Way, produces “a lot more snowfall. You get ice sheets, and you get this very effective ice-albedo feedback, which tends to lower the temperature of the planet.”
You also get lower sea levels in the Amasia scenario, with more water trapped in the ice caps. Less land is available for agriculture in a supercontinent with predominantly snowy conditions.
Image: How land could be distributed in the Aurica supercontinent (top) versus Amasia. The future land configurations are shown in gray, with modern-day outlines of the continents for comparison. Credit: Way et al. 2020.
Aurica turns out to be a more clement place, absorbing the stronger sunlight at the equator and, without ice caps at the poles to reflect heat, having a higher global temperature. The setting sounds like it would be ideal save for the fact that, according to the 3D models, the inland areas would be dry. What the scientists have not yet examined is the kind of precipitation patterns that might emerge. Large lakes would offset the effect, so it would be useful to know how likely they are.
All told, the work is pointing to temperatures suitable for liquid water on about 60 percent of Amasia’s land, while 99.8 percent of Aurica’s terrain should be available. We come back to land mass arrangements as a factor in planetary habitability, given our reliance on habitable zone models that insist on the presence of liquid water on the surface. Building a library of land mass distributions and examining their varying effects may help us tune our notions of habitability.
I’ll add that Way’s investigations using the GISS [Goddard Institute for Space Studies] General Circulation Model and expanding it to model paleo- and now future Earth have also extended to models of early Mars and Venus, with plans to examine Titan’s atmosphere. What our own planet has to teach us about climate, habitability and continental arrangement is thus extended to other worlds as the model evolves. One day soon we’ll add exoplanets into the mix.
The paper is Way et al., “Deep Future Climate on Earth: effects of tectonics, rotation rate, and insolation,” in process at Geophysical Research Letters (abstract).
Musings on Fusion and the Interstellar Ramjet
Proton-proton fusion produces 99 percent of the Sun’s energy, in a process that begins with two hydrogen nuclei and ends with one helium nucleus, releasing energy along the way. We’d love to exploit the fusion process to create energy for our own directed uses, which is what Robert Bussard was thinking about with his interstellar ramjet when he published the idea in 1960. Such a ship might deploy electromagnetic fields thousands of kilometers in diameter to scoop up atoms from the interstellar medium, using them as reaction mass for the fusion that would drive it.
Carl Sagan was a great enthusiast for the concept, and would describe it vividly in the book he wrote with Russian astronomer and astrophysicist Iosif S. Shklovskii. In Intelligent Life in the Universe (1966), the authors discuss a journey that takes advantage of time dilation, allowing a lightspeed-hugging starship powered by these methods to reach galactic center in a mere 21 years of ship-time; i.e., time as perceived by the crew, while of course tens of thousands of years are going by back on Earth. If you also hear echoes of Poul Anderson’s Tau Zero here, you’re exactly on target.
Shklovskii and Sagan assume proton-proton fusion as the reaction, as Bussard originally did, but Thomas Heppenheimer was able to show in 1978 that it would take more power to compress the protons gathered from the interstellar medium than the reaction would produce. Ramscoops are tricky, and this is just one of their problems — gathering interstellar materials is another, dependent as it is on the density of the gases where the starship travels. Drag is yet another issue, making interstellar ramjets a segue into magsail deceleration rather than starship-enabling speed, though it’s a segue I’ll follow up on another occasion.
But the fusion itself is still interesting. If Bussard assumed proton-proton, it wouldn’t be long before Daniel Whitmire was able to show that a different reaction could produce far more power. The Carbon Nitrogen Oxygen cycle (CNO cycle) came to mind this morning because of word that the team working on the Borexino experiment in the Laboratori Nazionali del Gran Sasso (Italy), which studies the Sun’s fusion reactions through the neutrinos it produces, has been able to identify the CNO cycle as a small component of the Sun’s production of energy.
Image: The Borexino research team has succeeded in detecting neutrinos from the sun’s second fusion process, the Carbon Nitrogen Oxygen cycle (CNO cycle) for the first time. Credit: Borexino Collaboration.
That’s interesting in itself and confirms work by Hans Bethe and Carl Friedrich von Weizsäcker from the 1930s, the first experimental confirmation of their independent investigations. But I cycle back to Bussard’s ramjet. The Carbon Nitrogen Oxygen cycle involves four hydrogen nuclei combining to form a helium nucleus using carbon, nitrogen and oxygen as catalysts and intermediate products in the reaction. Maybe ‘catalysts’ isn’t the right word — I was reminded by reading Adam Crowl’s thoughts on the matter some years back that we’re not talking about chemical catalysis and should perhaps refer to all this simply as ‘nuclear chemistry.’
What boggles the mind about the CNO cycle, which I’ve read is the dominant energy source in stars more than 1.3 times more massive than the Sun, is the degree of energy unlocked by it, far exceeding uncatalyzed proton/proton fusion. And it would take something highly energetic to work on Bussard’s ramscoop, for Whitmire’s 1975 paper showed that a proton-proton reactor built in the fashion originally suggested by Bussard would need a scoop 7,000 kilometers across to make the reaction work.
Isn’t that odd? You would think that a reaction that powers the Sun would be perfectly sufficient to drive the Bussard ramjet, but it turns out that the rate of proton-proton fusion is too low. Looking back through my materials on the problem, I find that the Sun produces less than 1 watt per cubic meter when averaged over its whole volume, which means that the energy produced in a light bulb filament is more powerful. Whitmire realized that the Sun’s vast energy output could occur because of its size. Making equally massive starships is out of the question.
It turns out that Whitmire and Centauri Dreams regular Al Jackson were friends at the University of Texas back in the 1970s, and I’ll remind you of Al’s reminiscence of Whitmire that can be found here — it was actually Al who introduced the Bussard ramscoop idea to Whitmire. Bussard would write to Whitmire that his 1975 paper offered a solution to the proton-proton fusion problem and would “become an enduring classic in this field.”
If you know your science fiction, you’ll recall that Greg Benford uses the CNO cycle in his 1984 novel Across the Sea of Suns, where he gives a poetic description of the process at work as perceived by his protagonist via the ultimate in futuristic telepresence:
He watches plumes of carbon nuclei striking the swarms of protons, wedding them to form the heavier hydrogen nuclei. The torrent swirls and screams at Nigel’s skin and in his sensors he sees and feels and tastes the lumpy, sluggish nitrogen as it finds a fresh incoming proton and with the fleshy smack of fusion the two stick, they hold, they wobble like raindrops — falling together — merging — ballooning into a new nucleus, heavier still: oxygen.
But the green pinpoints of oxygen are unstable. These fragile forms split instantly. Jets of new particles spew through the surrounding glow — neutrinos, ruddy photons of light, and slower, darker, there come the heavy daughters of the marriage: a swollen, burnt-gold cloud. A wobbling, heavier isotope of nitrogen….
Ahead he sees the violet points of nitrogen and hears them crack into carbon plus an alpha particle. So in the end the long cascade gives forth the carbon that catalyzed it, carbon that will begin again its life in the whistling blizzard of protons coming in from the forward maw of the ship.
And there you are: Carbon – Nitrogen – Oxygen in a cycle that makes starship fusion work. And all of this reminiscing suggested by the results of an experiment deep below the the Italian Gran Sasso massif which has turned up evidence for the CNO cycle within the Sun, a small but ongoing component of its output. If you want to read more on what turned up at Borexino, the paper is The Borexino Collaboration, “Experimental evidence of neutrinos produced in the CNO fusion cycle in the Sun,” Nature 587 (2020), 577-582 (abstract). The Whitmire paper is “Relativistic Spaceflight and the Catalytic Nuclear Ramjet,” Acta Astronautica 2 (1975), pp. 497-509 (abstract).
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