Looking for ‘Technosignatures’

by Paul Gilster on November 22, 2016

We speculated yesterday that categorizing civilizations on the basis of their power use may not be a given, though it is the basis of the familiar Kardashev types. It seems natural to a rapidly changing technological society like ours that the trend is always upward, a clear path toward harnessing the energies of the home planet, then the Sun, then the galaxy.

That this may not be the case seems to go against the grain of ‘Dysonian SETI,’ which looks for, among other things, artifacts as large as Dyson spheres and other astro-engineering projects on massive scales. Or maybe not, for some engineering involving adjustments to planetary environments may well produce observables. We just have to be aware of the range of possibilities here, and recognize our own limitations in trying to figure them out.

For we’ve learned something else from technology, and that is that its components grow ever smaller. Working at nanotech scales to create things from the ground up isn’t beyond the imagination, and engineering that recedes into the background so as not to be visibly apparent is even now gaining traction. The kind of voice recognition and rudimentary intelligence built into my Google Pixel hides its complexities in a small package. I speak into the air and tap the resources of computer clusters that are located who knows where.

What would a stable, space-faring civilization that has gone through its own version of the Anthropocene and reached a societal maturity look like when viewed from afar? Working these themes in Earth in Human Hands (Grand Central, 2016), David Grinspoon is anxious to reconcile our human activities through technology with the long-term survival of the planet, an outcome he believes, with a refreshing optimism, is likely to occur.

As we’ll see, it’s also an outcome made possible by going off-planet, for we cannot turn our back on the technologies that have the power to transform and heal our world. These invariably involve studying our globe with new space-based tools and analyzing other planets to understand what can go wrong and right about planetary evolution. So the question becomes, how does a civilization get through its early stages to harmonize its technologies with the planet that gave it birth, becoming a ‘planetary intelligence’? And from the SETI perspective, how would we go about finding a civilization that had succeeded?

A Different Kind of Biosignature

We’re entering the era when space-based resources will be able to analyze the atmospheres of exoplanets, looking for the kind of imbalances that suggest constant replenishment in a life cycle of some kind. The same technologies allow us to look for what we can call ‘technosignatures,’ which are signs not just of life but of a civilization. One way to look at this is through terraforming, the adaptation of a planet to make it hospitable for living beings. Grinspoon believes that we will eventually be terraforming our own world, in the sense that we will acknowledge the need to engineer and reverse ecological damage and emissions.


Image: Can we detect not just biosignatures but signs of technological civilizations through analysis of an exoplanet’s atmosphere? Credit: IAU/L. Calçada

One thought is to look for signs of imbalance suggestive of technologies like ours, producing air pollution that can be measured by spectroscopic analysis. Because we don’t know what we may eventually stumble across, it makes sense to study the potential signatures of a planet in transition. I can point you, for example, to Henry Lin (Harvard), who in collaboration with Gonzalo Gonzalez Abad and Abraham Loeb has produced “Detecting industrial pollution in the atmospheres of earth-like exoplanets,” a paper published in the Astrophysical Journal Letters (Volume 792, Number 1 — preprint here).

The authors of the Lin paper are interested in anthropogenic pollution as a technosignature (though they don’t use the term), a marker of intelligent life and technology. It turns out that the James Webb Space Telescope will be capable of picking up atmospheric tetrafluoromethane and trichlorofluoromethane, which are the easiest to detect chlorofluorocarbons produced by industrial activities. But Lin et al. are talking about detections involving Earth-like planets transiting white dwarfs and levels of pollution ten times as strong as Earth’s.

Even so, this gets intriguing. One thought is that a civilization in a highly polluted environment is transitory — it is either going to solve its contamination problems or else go under, and this must occur in a tiny window on the scales of astronomical time. But perhaps there is another possibility, as the paper argues:

Coupled with the fact that the half-life of CF4 in the atmosphere is ∼ 50, 000 years, it is not inconceivable that an alien civilization which industrialized many millennia ago might have detectable levels of CF4. A more optimistic possibility is that the alien civilization is deliberately emitting molecules with high GWP [global warming potential] to terraform a planet on the outer edge of the habitable zone, or to keep their planet warm as the white dwarf slowly cools.

Now we’re hunting a terraforming signature, an environment being deliberately manipulated. David Grinspoon points to this kind of signature as a more enduring observable:

If we find an exoplanet with a strange climate that is being controlled by unexpected atmospheric compounds such as chlorofluorocarbons, that should get our attention. Or if we find a world with a suspiciously unusual pattern of albedo (reflectivity) or day/night pattern of brightness, we might suspect planetary engineering with mirrors or surface alteration. We should take notice if such a world seems to be in a climate state that preserves or extends an early evolutionary stage, stabilizing against the aging of its star.

Global engineering on a scale that would ward off, say, a runaway greenhouse should throw a signature; it’s our job to figure out what it would be, on the off chance that we someday see it. It’s clear enough, and Grinspoon makes the point repeatedly, that we can’t anticipate what advanced alien societies are going to do, so maybe the best approach is to be on the lookout for what we can call ‘unnatural’ planetary states that tip us to some kind of management. This theme — that we have to avoid being doctrinaire because we are bringing all too human judgments into matters that involve aliens, about whom we know nothing at all — is significant not just for analyzing our SETI observables but for extending SETI into other arenas.

Signaling to the Stars

There is a photo in Earth in Human Hands that shows author David Grinspoon standing with Alexander Zaitsev, who was chief scientist at the Russian Academy of Science’s Institute of Radio Engineering and Electronics, and whose name has become synonymous with broadcasting to the stars. Zaitsev has, in fact, been the driver behind several messages beamed from Earth as a deliberate attempt to raise the interest of any nearby civilizations. In 1999, the first Cosmic Call message was transmitted to four different stars, with a second Cosmic Call sent out in 2003 to five Sun-like stars between 30 and 45 light years away.

Long-time Centauri Dreams readers know that Dr. Zaitsev was a frequent contributor to the comments in these pages as the discussion over so-called METI (Messaging to Extraterrestrial Intelligence), also known as Active SETI, flared into life. And I do mean ‘flared’ — nothing polarizes people more than the question of whether or not we should deliberately brighten our radio signature with such targeted messages, given that we know absolutely nothing about what kind of alien civilizations may exist. It’s ‘shouting into the dark,’ at a time when we don’t have a clue what may be out there.

David Brin was also a frequent participant in those discussions, which often referred to the 1983 Brin paper “The Great Silence” and speculated on reasons why advanced civilizations might want to keep a low profile. While METI proponents argue that reaching out to announce our presence is a means of exploration, and one that is necessary because if all civilizations are listeners, there will be nothing to receive, the Brin contingent argues that inclusive international discussions are needed so that we make this decision by consensus.


Image: At the heart of the Messier 13 globular cluster in Hercules, toward which a simple pictorial message was sent from Arecibo in 1974. Credit: Credit: ESA/Hubble and NASA.

This is a serious debate with a history that I don’t have time to get into this morning other than to say that Grinspoon’s book presents the background. There is plenty to talk about — the development of guidelines for Earth broadcasts at Valencia in 2006, a strong editorial response in Nature, the resignation of Michael Michaud and John Billingham from an IAA SETI study group because of changes to the Second SETI Protocol, the AAAS session in San Jose in 2015 — and the often acrimonious debate continues to flourish.

Brin has often held up the ‘Asilomar process’ as a model. The reference is to the agreements within the DNA research community to work out voluntary guidelines for experiments and containment procedures, while banning particularly dangerous experiments involving hard to contain pathogens. The Asilomar guidelines became incorporated into laboratory practices as the field of biotechnology began its growth. It was a form of self-policing that effectively kept research alive while minimizing associated risks. Can we adapt such a process to METI?

METI is filled with arguments and counter-arguments, most of which have been rehearsed in these pages many times over. But I found Grinspoon’s take on the matter refreshing because he’s one of the few involved in the debate who have actually changed sides over time. Beginning with a position not so far from Alexander Zaitsev’s, that SETI demanded both a listening and a sending component, Grinspoon now says he is swayed by those who advocate caution and a moratorium on broadcasts until the matter can be fully assessed.

I’m taken with the fact that the author stresses how much we don’t know. It’s easy to use our human experience to generalize about what aliens might do, something that occurs all the time in discussions on METI. How likely is it that an alien culture would see us as a threat? How reasonable is it to assume that an advanced civilization will have given up war? Shouldn’t we expect a species more advanced than us scientifically to be morally advanced as well? Wouldn’t they, in fact, be inclined to help us elevate our own society to their level?

Grinspoon has been down this road, and he goes through these are other reasons why broadcasting to the stars could be beneficial. But the reasons simply aren’t enough:

Still, I must also admit that these are just my opinions, semi-informed at best. We absolutely can’t know any of this. Maybe it’s all wishful thinking. There certainly are logically valid arguments for the possibility of great dangers. So how do we proceed, if the risks seem absurdly low, but the cost of being wrong is everything we have, everything we love?

Which means that the author remains in favor of active SETI but only with appropriate precautions, and supports a voluntary moratorium. His thinking ties in with the long-term perspective — a millennial outlook — that informs his discussion of geoengineering. We have vast amounts to learn, in other words, about climate before we ever think of active terraforming, either here or somewhere else. Similarly, we need global buy-in to a project like METI that, to be successful, will doubtless also need to operate on long timeframes.

…I would submit that lack of self-knowledge is an existential risk. It may well be that the greatest value of METI will come not from anything we learn in response to a message we send, but from what we learn about ourselves in the process of attempting to reach some common ground and find our global voice. If we decide to send a message to possible extraterrestrials, we are also sending a message to our descendants. We are gifting them with possibilities of both benefit and harm. Such an endeavor requires us to form an alliance with future generations, to enter into a common project with them. That is clearly something we need to learn how to do. So, then, starting the conversation about whether to broadcast, the effort to have a globally inclusive process, becomes a worthwhile goal in itself.

Tomorrow I’ll wrap up this discussion of Earth in Human Hands with the question of sustainability in the context of space. Is a civilization that is working long-term in ways that are hard to spot by our SETI methods one that is invariably planet bound? The answer is no, and we’ll talk about this in terms of interstellar travel. Also in coming days, I want to look at Caleb Scharf’s thoughts on how alien life may prove indistinguishable from physics. More anon.



SETI in the Anthropocene

by Paul Gilster on November 21, 2016

Have we, as some have argued, entered a new ‘age of humanity,’ the so-called Anthropocene? The notion is controversial in many quarters, but it addresses the growing concern about our human influence on the Earth and the nature of planetary change. David Grinspoon’s new book Earth in Human Hands (Grand Central Publishing, 2016) has much to say about the Anthropocene, but as anyone who has read the work of this canny scientist knows, he’s not one to let facile assumptions get by unquestioned.

For if the activity of humans is now emerging as an agent of geological change, then we are discussing our civilization in the same terms we talk about planetary forces like tectonic movement and the carbon cycle. This makes us major players whose effects we can begin to chart in terms of the effects of our technology on Earth’s living systems. If the Anthropocene is happening, it presents us not only with danger but the prospect of a long-term future. And its implications take in not just our movement into space but our search for other civilizations.


Hence Grinspoon’s view that while we are leaving an unmistakable footprint on our planet’s living substrate, this is not something to be deplored as much as understood and put to good use, the theory being that living things have always shaped the world around them, in ways as profound as the Great Oxygenation Event of 2.5 billion years ago. Earth in Human Hands is rich in discussion of what it would be like to enter what Grinspoon calls the ‘mature Anthropocene,’ in which humans acting wisely and with long-term horizons learn to use technology to repair past damage and introduce a new era of planetary stability.

In this view, our current dilemma is that we are achieving global impact without any sense of global control. The analysis is filled with Grinspoon’s experience as an astrobiologist and it draws together themes that are at the heart of how we consider our own future and how we look at other civilizations. For make no mistake, when we examine SETI, we’re forced to address questions like the lifespan of a technological civilization. If such societies persist, how do they do it, and equally of interest, what sort of signature would they leave? Stanislaw Lem comes to mind, and Grinspoon quotes him from his Summa Technologiae:

We need to overcome the habit of considering outcomes of human activity as more imperfect than those of nature’s activity — understandable as such a habit may be at the current stage of development — if we are to talk about what is going to happen in a faraway future.

Are we not ourselves a part of the nature we study, and rather than deploring the fact, should we not be considering how to make our own contribution to the mindfulness that intelligent life brings to the universe? You may pick up a bit of Sagan in these themes, particularly the Sagan (and Shklovskii) of the 1966 masterwork Intelligent Life in the Universe. The connection is borne out by Grinspoon’s relationship with Sagan, who worked with the author’s father at Harvard and shaped his boyhood and early career. No wonder Sagan and Shklovskii’s influence on SETI play such a vital and entertaining role in his book.

A Third Route for SETI

A confluence of events marks the beginning of SETI, with Frank Drake’s early efforts at Project Ozma following swiftly after the famous “Searching for Interstellar Communications” paper by Giuseppe Cocconi and Philip Morrison. But I think you could say that the discipline put down its formative roots at two conferences, the first being the one Drake hosted at Green Bank in 1961, the second the First All-Union Conference on Extraterrestrial Civilizations and Interstellar Communication, which was held in 1964 at the Byurakan Astrophysical Observatory in Soviet Armenia. Between the two we see a foundational SETI defined.

Frank Drake’s famous equation emerged from Green Bank, a conference with only 11 attendees that took SETI out of the realm of theory and into observational science. At Byurakan, Iosif Shklovskii criticized the Cocconi and Morrison paper for being too restrictive — the authors, Shklovskii argued, assumed that extraterrestrial civilizations would be on approximately the same level as ourselves. Shklovskii believed that any civilizations we detected would be far more advanced technologically than ourselves, for “We are only infants as far as science and technology are concerned,” and technology’s growth is rapid.


Grinspoon’s treatment of SETI is relaxed and knowledgeable, but it is the weaving of the anthropocene theme into SETI’s subsequent development that gives these chapters punch. For Nikolai Kardashev, then a young student of Shklovskii’s, was also at Byurakan to make the case for his three types of technological civilization, based on what he saw as a predictable and steady increase in the use of energy. Thus the categories most Centauri Dreams readers have come to be familiar with:

Type I: A civilization that can use all the energy resources of its own planet.

Type II: A civilization using all the energy resources available from its star. This is a civilization that has mastered its own stellar system and travels readily in space.

Type III: A civilization that can harness the energy of its entire galaxy. This is obviously an interstellar culture that moves freely between stars.

Image: Astrobiologist and author David Grinspoon, now a senior scientist at the Planetary Science Institute in Tucson.

We have often considered in these pages how advanced civilizations might present themselves to a distant observer; i.e., what kind of signature their engineering might leave in star systems and, indeed, in entire galaxies. Searches for Dyson spheres and odd stellar phenomena like the light curves of KIC 8462852 (Boyajian’s Star) continue to push the boundaries of radio and optical SETI. At a second conference in Byurakan, put together by Sagan and Shklovskii following the success of their book, the discussions of advanced technologies clustered around the Kardashev scale and its potential observables.

Radio and optical SETI, the first level of SETI, are complemented by a Dysonian SETI (level 2) that looks through our astronomical data for the signs of technological activity. But Grinspoon points out the key assumption of the Kardashev scale: That civilizations will inevitably increase their energy use in order to fuel a continuing expansion into the cosmos.

This is an idea of progress that is generally accepted — Grinspoon calls it the ‘inevitable expansion fallacy’ — but it is one that doesn’t take into account that key term (L in Drake’s equation) about the lifetime of a technological civilization. What if, in short, expanding in the Kardashev manner is the most likely way to end the growth of a culture?

A third level of SETI now emerges. You can see how Grinspoon is tying this back into the idea of an Anthropocene epoch on Earth. Let me quote him on this:

…it is reasonable to suppose that truly successful, long-lived species have all discarded the expansion imperative, and replaced it with an ethic of sustainability, of valuing longevity of expansion. If technological intelligence has a true and lasting form, one of its basic properties must be that it moves beyond the exponential expansion phase (characteristic of simple life in a petri dish or on a finite planet) before it hits the top of the S-curve and crashes. For us, achieving this kind of planetary intelligence will require critically examining our inherited biological habits and shedding those that have become liabilities.

And what exactly does a planetary intelligence involve? Grinspoon explains it as:

…thoughtful control over one’s self, escape from the mindless drives to multiply, to expand, to lay waste, kill, and drown in your own waste. Perhaps this is why we will not find what Shklovskii called ‘miracles,’ the highly visible works of vastly expanded super-advanced civilizations. Because advanced intelligences are not stupid.

At this point, we’ve stood Kardashev’s ideas on their head, for what Grinspoon is saying is that the kind of technological intelligence that lasts is one that has the ability to overcome its biological need for exponential growth. If this is the case, then we are confronted with the possibility that the more advanced a technological civilization becomes, the less likely we will be to distinguish it from natural phenomena. We may confront a cosmos rife with advanced civilizations whose work is so harmonized with their surroundings as to be invisible.

In earthly terms, the ‘mature Anthropocene’ is where we begin to move out of the era when the changes we make to our planet are beyond our comprehension, and into the era when we begin to consciously shape the Earth’s future, a time when, as Grinspoon writes:

…we fully incorporate our uniquely human powers of imagination, abstraction, and foresight into our role as an integral part of the planetary system. The mature Anthropocene differentiates conscious, purposeful global change from the inadvertent, random changes that have largely brought us to this point.

In SETI terms, consider the Anthropocene a metaphor for what can happen on other worlds. As we first confront the danger of technological over-reach in our environment and then learn to heal the wounds that limit sustainable growth, we may turn toward a balance that sustains our planetary ecology while ensuring the survival of our civilization. What Grinspoon calls the ‘Sapiezoic’ eon would be the long-lived stage of technological civilization that leads conceivably to immortality. Exponential expansion may simply be an evolutionary dead end, and the likelihood of finding civilizations that are learning this lesson the hard way is vanishingly small. They are simply not in existence long enough for us to see them.

Do we have a chance at detecting a civilization that operates according to the long-term model? Let’s talk about that tomorrow as we continue to look at this third route for SETI. We’ll also see that in Grinspoon’s view, expansion into space has a major role to play in the survival of long-haul civilizations. Developing a stable relationship with world-changing technologies is the key.



Nearby Super-Earth at GJ 536

by Paul Gilster on November 18, 2016

The discovery of a super-Earth of about 5 Earth masses orbiting the star GJ 536 is a helpful addition to our catalog of nearby red dwarf planets. About 33 light years out, GJ 536b orbits its primary at a distance of 0.06661 AU, an 8.7 day orbit that is too close to be in the habitable zone. But its very proximity to the star implies the possibility of a transit, which could pay big dividends in spectroscopic studies of its atmosphere. Follow-ups as soon as next year should tell us whether it does in fact transit.

The work comes out of the Geneva Observatory, working with researchers in France and Portugal, and involves data from the HARPS (High Accuracy Radial velocity Planet Searcher) spectrograph on the European Southern Observatory’s 3.6 meter telescope at La Silla (Chile). And it has me thinking about the problems and benefits of red dwarf studies. For one thing, astronomers can use nearby M-dwarfs for exoplanet detection because the low mass of the star offers up a robust radial velocity signal — RV was the method used in this detection.

But as the paper on this work notes, M-dwarfs also produce plentiful activity on the surface, which can not only introduce noise into the signal but can actually mimic a planetary signature. Tread carefully in this region, in other words, and be wary of false positives. Thus the research team, headed up by Alejandro Suárez Mascareño (Instituto de Astrofísica de Canarias), also reports a second significant radial velocity signal at 43.8 days which can be readily ruled out:

The second radial-velocity signal of period 43.8 d and semi amplitude of 1.6 ms−1 is a magnetic activity induced signal related to the rotation of the star. We also found a magnetic cycle shorter than 3 yr which would place this star among those with the shortest reported magnetic cycles.

As with our own Sun, whose magnetic cycle runs to 11 years, we’re looking at stellar activity that can alter the star’s radiation, produce starspots and perhaps produce flares.


Image: Radial velocity signal of a planet. This is Fig. 10 from the GJ 536b paper, captioned “Phase folded curve of the radial velocity using the 8.7 d period. Grey dots are the raw radial-velocity measurements after subtracting the mean value and the 43.9 d signal. Credit: Mascareño et al. (citation below).

Let’s back out to a broader picture for a moment. Although the Kepler instrument as well as numerous radial velocity and transit studies by ground-based telescopes have given us a priceless catalog of planets, we’re still talking about no more than about a hundred confirmed planets around M-dwarfs. Of these, only a subset consists of rocky planets. We do see systems with Neptune-mass planets and super-Earths, not to mention a few planets near Earth mass, the most spectacular being the world around Proxima Centauri.

We don’t have nearly as much hard data about the frequency of rocky planets around M-dwarfs as we would like, which is why I pay so much attention to such discoveries. We’d like to learn more about the probabilities, particularly in light of work like that of Ravi Kopparapu, who reported in these pages back in 2014 about his own estimate. The Penn State scientist recalculated work by Harvard’s Courtney Dressing and David Charbonneau and came up with what he calls a ‘conservative’ estimate that 48 percent of M-dwarfs should have Earth-size planets in the habitable zone. In other words, an impressive 1 out of every 2.

Given that 75 to 80 percent of the stars in the galaxy are M-dwarfs, this opens up vast numbers of possibly habitable worlds. You can refresh your memory on Kopparapu’s work in How Common Are Potential Habitable Worlds in Our Galaxy, which also discusses the probabilities of habitable planets around G-class stars like our Sun (Kopparapu discusses estimates of about 1 in 5 but believes they are too low). In any case, we need to do with small rocky worlds around nearby stars what we did with the Kepler field stars; i.e. we need to pull in enough data to build up a significant statistical sample. Upcoming missions like TESS (Transiting Exoplanet Survey Satellite) are vital, while the James Webb Space Telescope should be able to analyze the kinds of gases present in the atmospheres of planets around M-dwarfs.

Back to GJ 536b: The authors calculate that for a planet to be in the habitable zone of GJ 536, it would have to orbit in no less than 20 days. At 8.7 days, GJ 536b is too close to the star for habitable conditions to exist. But note this:

The stability of its rotation signals and the low amplitude of the radial-velocity signals with a magnetic origin makes this star a good candidate to search for longer period planets of moderate mass. A rough estimate of the detection limits tells us there is still room for Earth-like planets (∼ 1 M) at orbits smaller than 10, super-Earths (< 10 M) at orbits going from 10 to 400 days, and even for a Neptune mass planet (< 20 M) at periods longer than ∼3 yr.

So the hunt for planets around GJ 536 is clearly not over. We can expect the action to heat up for red dwarf planets in the solar neighborhood as we get new assets into space and continue developing the next generation of ground-based telescopes. If planets in the habitable zones around these stars are as plentiful as some scientists think, we’ll count on spectroscopic analysis of many an atmosphere to give us clues about the possibility of life.

The paper is Mascareño et al., “A super-Earth orbiting the nearby M-dwarf GJ 536,” accepted at Astronomy & Astrophysics (preprint).


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Fast Radio Bursts as Cosmological Probes

by Paul Gilster on November 17, 2016

One of the brightest Fast Radio Bursts seen since the phenomena were first detected in 2001 has been observed by the Parkes radio telescope in New South Wales. Maybe it should come as no surprise that Parkes was involved, given that most of the 18 FRBs that have so far been detected have been found there, including the so-called ‘Lorimer’ burst of 2001, which launched researchers’ interest in these mysterious processes. This one is thought to be particularly helpful in constraining magnetic fields and gases in intergalactic space, for observed distortions produced by an FRB’s travel yield data about the medium.

Ryan Shannon (ICRAR-Curtin University), a co-author of the paper, refers to the region between the galaxies as the ‘cosmic web,’ a region of all but invisible gases and plasma particles that is extremely hard to map. FRBs are short but intense pulses of radio waves — each lasts about a millisecond — that are usually discovered by accident, and no two look the same. Radio pulse FRB 150807, however, may be uniquely useful because its travel path can be traced back to an area in space that contains only a small number of stars and galaxies.

“This FRB, like others detected, is thought to originate from outside of Earth’s own Milky Way galaxy,” says Shannon, “which means their signal has travelled over many hundreds of millions of light years, through a medium that – while invisible to our eyes – can be turbulent and affected by magnetic fields. It is amazing how these very few milliseconds of data can tell how weak the magnetic field is along the travelled path and how the medium is as turbulent as predicted.”


Image: The radio pulse FRB 150807. The colour shows the frequency of the waves, which is like the colour of light. The brightness varies with frequency due to a process termed “scintillation”, which is caused by the twinkling of the burst in the cosmic web. This scintillation is the fingerprint of turbulence in the cosmic web and tells us that web is very placid. Credit: Dr Vikram Ravi/Caltech and Dr Ryan Shannon/ICRAR-Curtin/CSIRO.

So we have a probe of sorts of the intergalactic medium, one that was detected in 2015 and has now made its way into the literature. But just how deeply can we probe this region with FRBs? The paper argues that the bursts thus far studied may revolutionize cosmology, a bold claim, but one based on the information within FRBs that may be obtained in no other way.

From the paper:

Besides probing a heretofore-unknown astrophysical phenomenon, the bursts potentially carry imprints of propagation through inhomogeneous, magnetized plasma in the ionized interstellar media of other galaxies, and the diffuse intergalactic medium (IGM). Simultaneous measurements of redshifts and line-of-sight free electron column densities for FRBs can constrain the cosmological mass-density and ionization history of baryons.

Using FRBs as cosmological probes has been made difficult by the uncertainty about their origins, which is why FRB 150807 is so helpful — we can reconstruct its path. The archival images the team is using show three stars and six galaxies that are possible sites (see image below). The brightest galaxy is between 1 and 2 gigaparsecs away — roughly between 3.3 and 6.6 billion light years. The other galaxies are fainter than this object by factors of 6 and more, and all are thought to be more than 500 Mpc (1.6 billion light years) distant. This assumes, of course, that we can associate the burst with a star or a galaxy.


Image: The location of the FRB 150807. The yellow circle shows the typical location of an FRB. There are thousands of stars and galaxies in this direction. Because the burst was very bright researchers were able to locate it to a small region near the edge of that circle, shown as the pink banana-shaped region in the inset. In this region there are only 6 detected galaxies. The position of the most likely host galaxy, VHS7, is highlighted on the plot. Credit: Dr Vikram Ravi/Caltech and Dr Ryan Shannon/ICRAR-Curtin/CSIRO.

A supercomputing group led by Matthew Bailes (Swinburne University of Technology) produced the software that has been used in the analysis of the burst. The hope among the researchers is that technologies like Parkes’ multibeam receiver, the Murchison Widefield Array (MWA) in Western Australia, and the upgraded Molonglo Observatory Synthesis Telescope near Canberra can be used to detect and study future FRBs.

“Ultimately, FRBs that can be traced to their cosmic host galaxies offer a unique way to probe intergalactic space that allow us to count the bulk of the electrons that inhabit our Universe,” said Bailes. “To decode and further understand the information contained in this FRB is an exceptional opportunity to explore the physical forces and the extreme environment out in space.”

And get this: Lead author Vikram Ravi (Caltech) believes that there are between 2,000 and 10,000 FRBs occurring in the sky every day, with one in 10 being as bright as FRB 150807. We’ll take a step forward in finding the locations of these bursts when the Deep Synoptic Array also comes online. This array of 10 dishes at the Owens Valley Radio Observatory in California will pinpoint individual galaxies, allowing astronomers to use distance measurements and FRB analysis to further probe this deepest of all deep space.

The paper is Ravi et al., “The magnetic field and turbulence of the cosmic web measured using a brilliant fast radio burst,” published online in Science 17 November 2016 (abstract).



Pluto: Sputnik Planitia Gives Credence to Possible Ocean

by Paul Gilster on November 16, 2016

We’ve been looking at the idea of an ocean beneath Pluto’s icy surface for some time, including interesting work on the thermal evolution of the dwarf planet’s ice shell from Guillaume Robuchon and Francis Nimmo (University of California at Santa Cruz). Back in 2011, The Case for Pluto’s Ocean looked at their view that the stretching of Pluto’s surface would have clear implications for an ocean kept warm by radioactive decay in the interior. Now Nimmo is back with a post-New Horizons analysis that also points to an ocean.

The key here is Sputnik Planitia, forming part of the heart-shaped feature that was so distinctive during the flyby — think of Sputnik Planitia as the heart’s ‘left ventricle.’ The impact basin here is aligned almost exactly opposite from Charon. We learn in Nimmo’s paper in Nature that there is only a 5 percent chance that the feature’s alignment with Pluto’s tidal axis is by coincidence. To Nimmo and colleagues, the alignment is a dead giveaway that extra mass in the location is indicated. This would cause tidal interactions between Pluto and Charon that oriented Sputnik Planitia opposite the Charon side.


Image: In this image of Pluto taken by NASA’s New Horizons spacecraft, different colors represent different compositions of surface ices, revealing a surprisingly active body. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.

Thus we’re looking at forces that led to a re-alignment of the two small worlds, and enough mass to make that kind of shift possible. A deep basin doesn’t provide the heft, but an ocean could explain the result. In this way of thinking, Sputnik Planitia is the result of a major impact, which would have been followed by an infusion of water pushing up from below. The ice shell at the top hardens, leaving a deep basin gradually filling with nitrogen ice. Both the nitrogen ice and the water from below are necessary to explain the mass needed.

“It’s a big, elliptical hole in the ground,” says Nimmo, “so the extra weight must be hiding somewhere beneath the surface. And an ocean is a natural way to get that.”


Image: These schematic diagrams show how the gravity anomaly at Sputnik Planitia is affected by an uplifted ocean and the thickness of the nitrogen layer. Either a nitrogen layer more than 40 km thick (panel b) or an uplifted ocean (panel c) could result in a present-day positive gravity anomaly at Sputnik Planitia; otherwise, the gravity anomaly will be strongly negative (panel a). Credit: Nimmo et al., Nature, 2016).

Researchers also believe that the frozen nitrogen ice in the Sputnik Planitia basin may be convecting thanks to a weak spot at the bottom which would let heat rise from the interior. That would be an indication of a thin crust in this area, which would have allowed material from below to push upward to create, along with the nitrogen ice, the extra mass observed.

“Pluto is small enough that it’s just about almost cooled off but still has a little heat, and it’s about 2 percent the heat budget of the Earth, in terms of how much energy is coming out,” says New Horizons co-investigator Richard Binzel (MIT), a co-author of the Nimmo paper. “So we calculated Pluto’s size with its interior heat flow, and found that underneath Sputnik Planitia, at those temperatures and pressures, you could have a zone of water-ice that could be at least viscous. It’s not a liquid, flowing ocean, but maybe slushy. And we found this explanation was the only way to put the puzzle together that seems to make any sense.”

Nimmo believes the subsurface ocean is mostly water mixing with ammonia. This natural ‘anti-freeze’ slows the refreezing of the ocean, but as it continues to freeze, the ocean stresses the icy shell enough to cause the fractures we see in New Horizons imagery. We have images from the flyby that appear to be nitrogen glaciers flowing out of mountainous terrain around Sputnik Planitia, adding credence to the idea that the impact basin filled with nitrogen that froze out in the higher elevations and gradually migrated downward.

Looking into nitrogen flows on Pluto for this post, I came across a separate study, submitted to Icarus and led by Orkan Umurhan (NASA Ames), that supports the movement of this material near Sputnik Planitia. Note this:

We find that the wavy transverse dark features found along the northern shoreline of Sputnik Planum may be a transitory imprint of shallow topography just beneath the ice surface suggesting the possibility that a major shoreward flow event happened relatively recently within the last few hundred years. Model results also support the interpretation that the prominent darkened features resembling flow lobes observed along the eastern shoreline of the Sputnik Planum basin may be a result of wet nitrogen glacial ice flowing into the basin from the pitted highlands of eastern Tombaugh Regio.


Image: Tip o’ the heart: This animation shows how Pluto reoriented in response to volatile ices filling Sputnik Planitia (the left lobe of Pluto’s “heart”). Sputnik Planitia started northwest of its present position, and as it filled with ices, the tides from Charon (Pluto’s largest moon) caused the entire dwarf planet to reorient. If Sputnik Planitia is still accumulating ice, then Pluto may still be reorienting. Credit: James Keane/NASA/JHUAPL/SWRI).

The same issue of Nature that features the Nimmo work also includes a paper by James Keane and Isamu Matsuyama (University of Arizona), who back the re-orientation idea. In their view, a pileup of frozen nitrogen is what caused Pluto’s ‘polar wander,’ re-orienting it to place extra mass close to the equator. Keane believes Sputnik Planitia continues to accumulate nitrogen as frozen gases sublimate and re-condense on the other side of the dwarf planet, causing seasonal ‘snowfall’ there.

To understand this pattern, remember that Pluto spins on its side, so that the planet’s poles get the most sunlight during the course of a year, while the equatorial region stays permanently cold. Frozen polar gases that sublimate as they warm up during the Plutonian year can play a major role not just in the world’s weather but also in its orientation:

“Each time Pluto goes around the Sun, a bit of nitrogen accumulates in the heart,” Keane said. “And once enough ice has piled up, maybe a hundred meters thick, it starts to overwhelm the planet’s shape, which dictates the planet’s orientation. And if you have an excess of mass in one spot on the planet, it wants to go to the equator. Eventually, over millions of years, it will drag the whole planet over.”

The duo’s computer models, moving Sputnik Planitia and observing the effect on Pluto’s spin axis, bear this out. Thus while Nimmo and team see a subsurface ocean as necessary to explain the position of Sputnik Planitia, Keane and Matsuyama argue for re-orientation keyed to the cycling of volatiles, an adjustment of Pluto’s position that grows out of its weather. Even so, both teams agree that tectonic faults on Pluto are clues to the existence of an ocean.

The Umurhan paper is “Modeling glacial flow on and onto Pluto’s Sputnik Planum,” accepted at Icarus (preprint). The Keane paper is “Reorientation and faulting of Pluto due to volatile loading within Sputnik Planitia,” published online by Nature 16 November 2016 (abstract). The Nimmo paper is “Reorientation of Sputnik Planitia implies a subsurface ocean on Pluto,” published online by Nature 16 November 2016 (abstract).



Project Blue: Imaging Alpha Centauri Planets

by Paul Gilster on November 15, 2016

We know about an extremely interesting planet around Proxima Centauri, and there are even plans afoot (Breakthrough Starshot) to get probes into the Alpha Centauri system later in this century. But last April, when Breakthrough Initiatives held a conference at Stanford to talk about this and numerous other matters, the question of what we could see came up. For in Alpha Centauri, we’re dealing with three stars that are closer to us than any other. If there are planets around Centauri A and/or Centauri B, are there ways we could image them?

This gets interesting in the context of Project Blue, a consortium of space organizations looking into exoplanetary imaging technologies. This morning Project Blue drew on the work of some of those present at Stanford, launching a campaign to fund a telescope that could obtain the first image of an Earth-like planet outside our Solar System, perhaps by as early as the end of the decade. The idea here is to ignite a Kickstarter effort aimed at raising $1 million to support needed telescope design studies. A $4 million ‘stretch goal’ would allow testing of the coronagraph, completion of telescope design and the beginning of manufacturing.


Project Blue thinks it can bring this mission home — i.e., launch the telescope and carry out its mission — at a final cost of $50 million (the original ACEsat was a $175 million design). The figure is modest enough when you consider that Kepler, which has transformed our view of exoplanets, cost $600 million, while the James Webb Space Telescope weighs in at $8 billion. About a quarter of the total cost, according to the project, goes into getting the telescope into orbit, which will involve partnering with various providers to lower costs.

But Project Blue also hopes to build a public community around the mission to support design and research activities. Jon Morse is mission executive for the project:

“We’re at an incredible moment in history, where for the first time, we have the technology to actually find another Earth,” said Morse. “Just as exciting — thanks to the power of crowdfunding — we can open this mission to everyone. With the Project Blue consortium, we are bringing together the technical experts who can build and launch this telescope. Now we want to bring along everyone else as well. This is a new kind of space initiative — to achieve cutting-edge science for low cost in just a few years, and it empowers us all to participate in this moment of human discovery.”

I go back to last April because it was at Stanford that I saw Eduardo Bendek’s model of a small space telescope called ACEsat, which was conceived at NASA Ames by Ruslan Belikov and Eduardo Bendek and submitted (unsuccessfully) for NASA Small Explorer funding. Belikov had gone on to present the work at the American Astronomical Society meeting in 2015 (see “How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope,” available here). You’ll recall that Ashley Baldwin wrote up the concept in superb detail on this site in December of that year as ACEsat: Alpha Centauri and Direct Imaging.

Now we have Project Blue, which has connections to the BoldlyGo Institute, its offshoot Mission Centaur, the SETI Institute and the University of Massachusetts Lowell. The aim is to launch a space telescope with a 45-50 centimeter aperture, looking for potentially habitable planets from 0.5 to 1.5 AU within the habitable zones of both Centauri A and B. The ultimate hope, then, is to ‘see blue’ — meaning oceans and atmosphere, a world on which life could emerge. This is Sagan’s ‘pale blue dot,’ only now it’s not our own planet but an Earth 2.0.

The Project Blue space telescope would spend two years in low Earth orbit accumulating image after image — hundreds, thousands, tens of thousands — as a way of teasing out its faint targets. When it comes to ‘another Earth,’ Centauri A and B up the ante on Proxima Centauri. The Proxima planet may well be habitable, but a true Earth analog is not going to be tidally locked to its star, as Proxima b probably is, and it’s not going to orbit a red dwarf.

Neither Belikov or deputy principal investigator Eduardo Bendek are formally connected to Project Blue, but their work in the form of papers and conference presentations feeds directly into the concept driving the project. The original mission now cedes the floor to the private sector, whose job it will be to raise enough cash to support the development of the needed coronagraph to filter out the light of two very close stars, along with other key flight hardware elements. The next step, though, long before building flight hardware, is to finalize the telescope design.

The new Kickstarter campaign will pay for analysis, design, and simulations, but Project Blue has an eye on other partnerships as well as wealthy donors and foundations. Usefully, the project should be able to test coronagraph technologies similar to those being considered on much larger space instruments currently under study by the major space agencies, thus providing a useful testbed for such designs. To make this work, everything must fall into place — the coronagraph for starlight suppression, a deformable mirror to feed the coronagraph and rock-solid stability. No aspect can be allowed to fail if the mission is to achieve its goal.

If the Project Blue planners are correct, we can solve the attendant problems and get this mission into space is as little as 4 to 6 years. The goal is hugely ambitious but it also opens the door to citizen-science, with private donors contributing to an instrument that will not be the result of a government program or a for-profit commercial space effort. The initial Kickstarter campaign is designed to bolster the technical groundwork needed for the telescope, but stretch goals could see publicly funded flight component manufacturing.

Looking for Earth-like planets around other stars is like looking for bioluminescent algae next to a lighthouse. But I keep coming back to that Breakthrough Discuss meeting in Stanford, because I remember Ruslan Belikov telling his audience that the key advantage of Alpha Centauri is how large the habitable zones around its component stars appear in terms of angular size. We would need a significantly larger instrument to attempt something similar around other nearby stars. The Alpha Centauri stars are nature’s gift, and it’s one we would do well to exploit. Check the Kickstarter page for more on this low cost, high impact idea.

For more on the technical background of the ACEsat concept, see Belikov et al., “How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope” (preprint) and Bendek et al., “Space telescope design to directly image the habitable zone of Alpha Centauri” (preprint).



Your Choice of Starships

by Paul Gilster on November 14, 2016

Think fast. You’ve only got a day or so to work on this. You’ve been asked to come up with a plausible way of getting a fictional crew from one star to another, but laser sails and fusion rockets won’t do. The target might be thousands of light years away, so you have to be thinking faster-than-light. Maybe Miguel Alcubierre comes to mind, or perhaps a wormhole, but a nod in either direction isn’t enough. You’re being asked for a high level of detail, and you’d better have some serious equations available to show you’re not just blowing smoke.

As you might guess, the question relates to the Denis Villeneuve film Arrival, which Paramount released in the U.S. last Friday following its premiere at the Venice Film Festival. No spoilers here, just an entertaining tale. For the person who was asked to dream up fast interstellar transport was Stephen Wolfram, whose public relations people had received a request from the filmmakers to upgrade the science in the film, which was based on a 1998 short story by the brilliant Ted Chiang, a Nebula Award winning short story writer.


As to Wolfram, he heads up Wolfram Research and is the chief designer of both technical computing engine Mathematica and the Wolfram Alpha online presence. In what I might jokingly refer to as his ‘spare time’ he is the author of the recent A New Kind of Science, written during breaks from his work on knowledge-based programming, the latter being an expansion of Mathematica into what is now called the Wolfram Language.

Wolfram, in other words, is a formidable source when it comes to ideas pushing out to the edges of what we know. Intrigued by the challenge of Arrival, Wolfram and son Christopher traveled to Montreal to meet with the film crew. Soon both men were involved with analysis and computations as they turned questions from the director into Wolfram Language code and visualizations. But time was short, and the biggest challenge was coming up with a theory of interstellar space flight in the course of a single evening.

I don’t know if Wolfram is a movie buff or not, but I’d imagine that working this closely with actors and writers and everyone else on the site is enough to make him one. In any case, he’s keen to avoid giving away anything about the film — for that you have to see it — so you can go to his essay Quick, How Might the Alien Spacecraft Work? without concern that it will deflect your enjoyment of a film that is beginning to get a pretty solid buzz (I suspect our resident movie critic Larry Klaes is going to turn up with an essay about this movie, too).

What we get here is only an introduction into the material Wolfram supplied the filmmakers, but it’s intriguing in its own right. It draws from his own speculations about fundamental physics and the lowest level structure of space itself, the idea being that it is, in his words, ‘a network of nodes, where all that’s defined is connectivity.’ Thus space as we perceive it emerges as a large-scale feature even though it’s made up of discrete nodes. He likens this to water, which is made up of discrete molecules but ‘emerges’ as oceans and rivers.

The three-dimensional network underlying the universe, Wolfram supposes for the sake of his model, is made up mostly of local connections, while a few are long-range connections, which correspond to quantum entanglement. The trick is somehow to exploit these long-range connections, which involves disconnecting the outside of the ship from the rest of the network.

This calls for a form of matter that is not made from standard elementary particles, but as Wolfram says, “might be like a giant crystal formed directly from connections that make up space.” Thus the skin of the imagined ship is a dynamic metamaterial, and it is this boundary layer material that creates the needed interaction with the outside universe. And yes, it’s unobtainium, but remember, we’re in a fictional universe studying alien technologies.

We can’t go any further without going into the movie itself, but what comes across in Wolfram’s lively essay is the author’s sheer enjoyment at creating a self-consistent theory that could be referenced in the script. Numerous ideas for science fiction dialogue ensued, most of them not necessary in the actual film, but enlivening in their own right:

Here are a few of the ones that (probably for the better) didn’t make it into the final script. “The whole ship goes through space like one giant quantum particle.” “The aliens must directly manipulate the spacetime network at the Planck scale.” “There’s spacetime turbulence around the skin of the ship.” “It’s like the skin of the ship has an infinite number of types of atoms, not just the 115 elements we know” (that was going to be related to shining a monochromatic laser at the ship and seeing it come back looking like a rainbow). It’s fun for an “actual scientist” like me to come up with stuff like this. It’s kind of liberating. Especially since every one of these science fiction-y pieces of dialogue can lead one into a long, serious, physics discussion.

Wolfram says he got involved in Arrival because Hollywood films all too often don’t get the science input they need, a fact he attributes to directors being more attuned to human conflict and character development than the ‘science texture’ of their movies. But of course we have seen some films with an active science advisor, like Kip Thorne in the recent Interstellar, who conjured up its black hole effects with Mathematica. And (I hadn’t known this), Marvin Minsky worked on artificial intelligence issues for 2001: A Space Odyssey, while mathematician Manjul Bhargava spent years helping to bring The Man Who Knew Infinity to the screen, with careful attention to the math. Agreed, that one isn’t exactly science fiction, being a study of Indian mathematician Srinivasa Ramanujan.

Even so, science fiction in Hollywood hasn’t been known for its history of verisimilitude. Wolfram again:

When I watch science fiction movies I have to say I quite often cringe, thinking, “someone’s spent $100 million on this movie — and yet they’ve made some gratuitous science mistake that could have been fixed in an instant if they’d just asked the right person.” So I decided that even though it was a very busy time for me, I should get involved in what’s now called Arrival and personally try to give it the best science I could.

There’s a lot more than starship talk in Wolfram’s essay, especially on establishing communications with an alien intelligence (Wolfram starts with cellular automata), the similarities between software design and movie production, and the possible uses of gravitational waves (massive, spinning non-spherical objects produce them). I keep thinking that with people like Stephen Wolfram involved, the science standards in our films are bound to be on the uptrend presaged by Kip Thorne’s presence in Interstellar.

That could lead to some interesting choices of scripts as we tap the vast store of written science fiction, all too little exploited, for film plots with a genuinely scientific underpinning. Countless short stories and novels form a rich tradition growing out of the science fiction magazines and emerging in the late 20th Century as a vibrant literature in its own right. It’s time Hollywood embarked upon a much deeper acquaintance with this material.



Into the ‘Brown Dwarf Desert’

by Paul Gilster on November 11, 2016

A newly discovered brown dwarf dubbed OGLE-2015-BLG-1319 is significant on several fronts, not the least of which is how it was found. Not only are we dealing here with another instance of gravitational microlensing, where the light of a background star is affected by a foreground object in ways that give us information about the closer star, but this instance of microlensing saw two space telescopes working together to make sense of the event, the first time a microlensing event has been observed by two space telescopes and from the ground.

The space-based instruments in question are the Spitzer and Swift telescopes, whose combined observations give us different magnification patterns rising from the same event. Spitzer observed the binary system containing the brown dwarf in July of 2015 from its perch about 1 AU away from the Earth. Swift, in low Earth orbit, also saw the system in late June of that year, marking its first microlensing observation. The first notification of the event came from the Optical Gravitational Lens Experiment (OGLE) in Chile, and it was also observed by the Microlensing Observations in Astrophysics (MOA) collaboration in New Zealand.


Image: This illustration depicts a newly discovered brown dwarf, an object that weighs in somewhere between our solar system’s most massive planet (Jupiter) and the least-massive-known star. This brown dwarf was discovered when it and its star passed between Earth and a much more distant star in our galaxy. This created a microlensing event, where the gravity of the system amplified the light of the background star over the course of several weeks. Credit: NASA/JPL-Caltech.

Combining the data and including observations from ground-based instruments allows scientists to make a call on the mass of the brown dwarf, between 30 and 65 Jupiter masses. The brown dwarf orbits a K-class star with about half the mass of the Sun. But focus on this: One of two possible distances between brown dwarf and star is 0.25 AU, which would put the object in what is known as the brown dwarf desert. The latter is a reference to the fact that stars of about the Sun’s mass rarely have a brown dwarf orbiting within 3-5 AU.

We don’t know for sure because there are two solutions to the distance question, the second being 40-52 AU. The paper notes that the Swift satellite is not distant enough from the Earth to allow for a separate measurement of the microlensing parallax, which would have made it possible to refine the distance measurement further. We get two solutions for the projected separation of brown dwarf and star, a well-known problem called close-wide degeneracy in which the perturbation patterns of close and wide objects can appear similar.

But if the 0.25 AU distance is correct, it would add to mounting evidence that the so-called ‘desert’ may be a mirage. For it turns out that OGLE-2015-BLG-1319 is hardly the first brown dwarf found through microlensing. In fact, there have been 15 published microlensing events involving brown dwarfs before this one, including one that hosted a planet, ten brown dwarfs around main sequence stars (with nine around M-dwarfs and one around a G-K class star), two binary brown dwarfs and two isolated brown dwarfs. In about half of these we also have questions about the distance between brown dwarf and star, but note this from the paper:

…the accumulation of detections suggests that BDs around main-sequence stars are not rare at separations of 0.5–20 AU, where microlensing is sensitive (this range is larger than for exoplanets due to higher detection sensitivity). This is in contrast to estimates through other techniques, such as radial velocity and transit, who find that BDs are rare (< 1%, Grether & Lineweaver 2006) at closer separations.

What to make of this? The paper continues:

One possible explanation for this difference, as suggested by Shvartzvald et al. (2016), is the different host stars that are mostly probed by each technique — FGK stars by radial velocity and transits versus M stars by microlensing.

Or as lead author Yossi Shvartzvald (JPL) puts it in this JPL news release:

“We want to understand how brown dwarfs form around stars, and why there is a gap in where they are found relative to their host stars. It’s possible that the ‘desert’ is not as dry as we think.”

The paper is Shvartzvald et al., “First simultaneous microlensing observations by two space telescopes: Spitzer & Swift reveal a brown dwarf in event OGLE-2015-BLG-1319,” Astrophysical Journal Vol. 831, No. 2 (7 November 2016). Abstract / preprint.



New Imaging of Protoplanetary Disks

by Paul Gilster on November 10, 2016

Our knowledge of protoplanetary disks around young stars is deepening. This morning we have news of three recently examined disks, each with features of interest because we know so little about how such disks evolve. What we do know is that planets are spawned from the gas and dust we find within them, as we see in the disk below discovered using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope in Chile.


Image: A team of astronomers observed the planetary disc surrounding the star RX J1615, which lies in the constellation of Scorpius, 600 light-years from Earth. The observations show a complex system of concentric rings surrounding the young star, forming a shape resembling a titanic version of the rings that encircle Saturn. Such an intricate sculpting of rings in a protoplanetary disc has only been imaged a handful of times before. Credit: ESO, J. de Boer et al.

The comparison with Saturn is not amiss, for this is a complex system of concentric rings that is uncommon among protoplanetary disks we’ve found so far. While dating such systems is difficult, astronomers believe this disk is a bit less than 2 million years old. Bear in mind that we’re still trying to work out the mechanisms that cause these sculpted effects. They’re surely the result of planets in formation, but it’s worth noting that while the disk around RX J1615 is strikingly regular, we’re just as likely to encounter gaps, voids and spiral arms in such disks.

The work here is from Jos de Boer (Leiden Observatory), who has put the SPHERE instrument to good use. SPHERE (Spectro-Polarimetric High-contrast Exoplanet REsearch) was built as a planet imager, one that would take direct images of exoplanets rather than detecting them through their star’s Doppler shifts or through transits of the planet. An advanced coronagraph, SPHERE blocks out the central star, using a polarimetric differential imaging mode that draws on the fact that the light of the star is unpolarized, while the light scattered by the disk is polarized, allowing sharp images of the disk to be extracted.

Another researcher from Leiden University, Christian Ginski, is behind work on a different young system. The star is HD 97048, about 500 light years from Earth. Here again we see a striking symmetry in the ring system. Four gaps and rings can be found here. But finding any planets that are sculpting this system is not going to be easy, as the paper on this work notes:

We find that nascent planets are one possible explanation for the structures that we are observing. However, given the low planet masses needed to carve out the gaps that we detected, it is unlikely that the planet’s thermal radiation is directly detectable by current generation planet search instruments such as SPHERE or GPI [Gemini Planet Imager]. This conclusion is strengthened by the fact that the gaps are most likely not completely devoid of material and thus any thermal radiation from a planet inside the gap would be attenuated by the remaining dust.


Image: The planetary disc surrounding the star HD 97048 in the constellation of Chameleon, about 500 light-years from Earth. The juvenile disc is formed into concentric rings. This symmetry is in contrast to most protoplanetary systems which contain asymmetrical spiral arms, voids and vortexes. The displayed image is a composite derived from two independent observations that targeted the inner and outer regions of this disc. The central part of the image appears dark because SPHERE blocks out the light from the brilliant central star to reveal the much fainter structures surrounding it. Credit: ESO, C. Ginski et al.

Contrast the two disks above with what Tomas Stolker and colleagues (Anton Pannekoek Institute for Astronomy, the Netherlands) have found. In the image below, we’re looking at HD 135344B, some 450 light years from Earth. Here the disk is obviously asymmetrical, consisting of a central cavity and two spiral arms thought to be the result of planet formation.

And in this system we have a feature that changed noticeably in the months between observing periods. The feature in question is one of the dark streaks that are evidently shadows created by material in motion within the protoplanetary disk. Planetary evolution in real time? That’s what this ESO news release calls it, an indication of the level of detail we can pick out in the inner disk regions of some stars with the SPHERE instrument.

The paper puts the matter this way:

The variable or transient nature of this shadow could be explained by several scenarios, including a local perturbation of the inner disk or an accretion funnel flow from the inner disk onto the star.


Image: The planetary disc surrounding the star HD 135344B, about 450 light-years away. The disc shows prominent spiral arm-like structures. Credit: ESO, T. Stolker et al.

In any case, we’re seeing change within months in this evolving system. And as to the spiral arms themselves:

An explanation for the spiral arms could not be uniquely determined. In the context of linear perturbation theory, the spiral arms are best explained by two protoplanets orbiting exterior of the spiral arms. Protoplanet solutions inside the scattered light cavity seem unlikely because the spiral arm pitch angles would require unphysical disk temperatures.

Understanding how planets shape the disks from which they form is a step forward in planet formation theory, and it’s clear that the environment of young systems like these is complex and varied enough to produce a wide range of outcomes in the evolving disk.

The papers are de Boer et al., “Multiple rings in the transition disk and companion candidates
around RX J1615.3-3255. High contrast imaging with VLT/SPHERE,” Astronomy & Astrophysics 595 (2016), A114 (preprint). On HD 97048, the paper is Ginski et al., “Direct detection of scattered light gaps in the transitional disk around HD 97048 with VLT/SPHERE,” accepted for publication at Astronomy & Astrophysics (preprint). The paper on HD 135344B is Stolker et al., “Shadows cast on the transition disk of HD 135344B,” accepted at Astronomy & Astrophysics (preprint).



Proxima Centauri Observations Launch Parkes Effort

by Paul Gilster on November 9, 2016

In the last two days we’ve looked at a discussion of a possible SETI observable, a ‘shielding swarm’ that an advanced civilization might deploy in the event of a nearby supernova. As with Richard Carrigan’s pioneering searches for Dyson swarms in the infrared, this kind of SETI makes fundamentally different assumptions than the SETI we’ve grown familiar with, where the hope is to snag a beacon-like signal at radio or optical wavelengths. So-called ‘Dysonian SETI’ assumes no intent to communicate. It is about observing a civilization’s artifacts.

Both radio/optical SETI and this Dysonian effort are worth pursuing, because we have no idea what the terms of any discovery of an extraterrestrial culture will be. The hope of receiving a deliberate signal carries the enthralling possibility that somewhere there is an Encyclopedia Galactica that we may one day gain access to, or at the least that there is a civilization that wants to talk to us. A Dysonian detection would tell us that civilizations can survive their youth to become builders on a colossal scale, pushing up toward Kardashev levels II and III.

Keeping both SETI tracks engaged is good science. It’s encouraging on the radio front to see that the Parkes radio telescope in Australia has now joined the Green Bank Telescope (West Virginia) and the Automated Planet Finder (Lick Observatory) in SETI observations funded by Breakthrough Listen. A key component of the Breakthrough Initiatives effort (which includes Breakthrough Starshot), Breakthrough Listen has just announced the activation of its SETI project at Parkes with observations of the newly discovered planet around Proxima Centauri.

About this study, several points. First, Parkes marks a welcome expansion of the northern hemisphere efforts. Situated about 20 kilometers north of the town of Parkes in New South Wales, the telescope can observe those parts of the sky that are not visible to its northern counterparts, making it a major component in any comprehensive SETI effort.


Image: The Parkes radio telescope in New South Wales. Credit: CSIRO.

As to Proxima Centauri, we now have an Earth-sized planet orbiting in what appears to be its habitable zone, meaning that temperatures could allow liquid water to exist on its surface. The discovery of Proxima b has enlivened the interstellar community as we examine ways to learn more about it, including the Breakthrough Starshot flyby probe studies. But I think we can agree that the chances of finding a civilization on any particular planet are low.

So says Andrew Siemion, director of the Berkeley SETI Research Center and leader of the Breakthrough Listen science program. And he adds:

“…once we knew there was a planet right next door, we had to ask the question, and it was a fitting first observation for Parkes. To find a civilisation just 4.2 light years away would change everything.”

It was in the same spirit that a number of SETI instruments have been turned to Boyajian’s Star (KIC 8462852), whose unusual light curves have drawn a great deal of attention because we have so far been unable to explain them. In both cases, we have a high-interest target, in the Proxima system because of its sheer proximity to Earth and in the Boyajian’s Star system because one explanation for those light curves is intelligent engineering.

So I am all for examining Proxima Centauri even though I think the real action there will be in one day analyzing its atmosphere for signs of biosignatures. 14 days of commissioning and test observations at Parkes led up to the first observation of Proxima on November 8 (local time). The broader strategy is to continue the SETI effort at radio wavelengths across a wide range of targets, as listed in this Breakthrough Initiatives news release.

  • All 43 stars (at south declinations) within 5 parsecs, at 1-15 GHz. Sensitive to the levels of radio transmission at which signals ‘leak’ from Earth-based radar transmitters (with available receivers).
  • 1000 stars (south) of all spectral-types (OBAFGKM) within 50 parsecs (1-4 GHz).
  • One Million Nearby Stars (south). In 2016-2017, first 5,000 stars; 1 minute exposure (1-4 GHz).
  • Galactic plane and Center (1-4 GHz).
  • Centers of 100 nearby galaxies (south declinations): spirals, ellipticals, dwarfs, irregulars (1-4 GHz).
  • Exotic sources will include white dwarfs, neutron stars, black holes, and other anomalous natural sources (1-4 GHz).

Bear in mind as these efforts proceed that Breakthrough Listen will also be coordinating searches with the FAST (Five hundred meter Aperture Spherical Telescope) in southwest China, exchanging observing plans, search methods and data. Thus we move toward a global SETI effort that can quickly share promising signals for analysis. Data from Parkes and the other Breakthrough Listen telescopes will be made available to the public online.