Centauri Dreams
Imagining and Planning Interstellar Exploration
Far Ultraviolet Flares an Issue for M-dwarf Planets
SPARCS is the name of a CubeSat-based space mission out of Arizona State University, the acronym standing for Star-Planet Activity Research CubeSat, with astronomer Evgenya Shkolnik as principal investigator. The idea here is to look at ultraviolet flare activity on M-dwarf stars, a wavelength about which we could do with a great deal more information. The plan is to target specific stars that will be observed continuously over at least one complete stellar rotation, which could be anything from five to forty-five days.
That this is a good idea is borne out by what we are learning about GJ 887, also known as Lacaille 9352 and known to be orbited by at least two planets. Located in the southern constellation of Piscis Austrinus, the star has the fourth highest known proper motion, with parallax measurements indicating it is a bit less than 11 light years from the Sun. It is one of the brightest M-dwarfs in our sky. When TESS (Transiting Exoplanet Survey Satellite) fixed its gaze on GJ 887, it found no detectable flares over 27 days of continuous observation.
Which goes to show how much older data can help us. Fellow ASU astronomer Parke Loyd worked with Shkolnik and co-authors from the University of Colorado, Boulder and the Naval Research Laboratory (Washington DC) to demonstrate on the basis of Hubble Space Telescope data that GJ 887 is anything but a quiescent star. In fact, its flares occur on an hourly basis, the spikes in brightness showing up only at ultraviolet wavelengths. The paper on their findings has been published as a Research Note of the American Astronomical Society. Says Shkolnik:
“It is fascinating to know that observing stars in normal optical light (as the TESS mission does) doesn’t come close to telling the whole story. The damaging radiation environment of these planets can only fully be understood with ultraviolet observations, like those from the Hubble Space Telescope.”
Image: Violent outbursts of seething gas from young red dwarf stars may make conditions uninhabitable on fledgling planets. In this artist’s rendering, an active, young red dwarf (right) is stripping the atmosphere from an orbiting planet (left). Credits: NASA, ESA and D. Player (STScI).
At an estimated age of 3 billion years, GJ 887’s lack of detectable flares and scarce rotational variability is belied by the Hubble findings, an indication that atmospheric erosion is a serious concern for the two and possibly three planets we thus far know about. We’re now learning that flare activity in the far ultraviolet (FUV) may be a feature of numerous M-dwarfs. Here is part of the paper’s Figure 1, illustrating how GJ 887 looks at these wavelengths.
Image: Archival far-ultraviolet (FUV) data of GJ 887. Top panel: The FUV spectrum of GJ 887. Credit; Loyd et al.
The authors note that X-class solar flares, major events that can trigger long-duration radiation storms, are almost always accompanied by coronal mass ejections, and add that far ultraviolet flares with equivalent durations occur every few hours on other M-dwarfs across a wide range of emission levels and ages. The paper continues:
GJ 887’s similar rate of FUV flares strengthens the possibility that all early to mid M stars share the same FUV flare frequency distribution (FFD) when cast in equivalent duration. This universal M-star FFD implies that most of the molecule-splitting FUV photons M-star planets receive could be delivered in short, intense bursts that are not captured by sparse and brief FUV observations (Loyd et al. 2018a).
The paper speaks of the need to account for the “hidden UV lives” of M-dwarfs, whose radiation may have a great deal to say about photochemistry, heating and evaporation in the atmosphere of orbiting planets. At GJ 887, we may be looking at a system whose planets lost their atmospheres through erosion from such flares long ago. The goal of the SPARCS mission is to provide the extended observing time needed to extend our knowledge of flare activity on the most common type of star in the galaxy.
The paper is Loyd, “When ‘Boring’ Stars Flare: The Ultraviolet Activity of GJ 887, a Bright M Star Hosting Newly Discovered Planets,” Research Notes of the AAS Vol. 4, No. 7 (20 July 2020) (full text).
Evidence for a Shift of Europa’s Icy Crust
A hypothesis about an astronomical object snaps into sharper detail when it can be tested. Thus the new findings on Europa and the movements of the ice shell that covers its ocean, which are the subject of a paper in Geophysical Research Letters. The work of Paul Schenk (Lunar and Planetary Institute, Houston) and colleagues, the paper argues that the shell has rotated by about 70 degrees during the last several million years. Clearly, such movement can only happen with a shell floating freely over a liquid ocean beneath, and Europa Clipper should be able to tell us more.
Remember, we are talking about a geologically young surface on this Jovian moon, as indicated by, among other things, the relative smoothness of the terrain and the paucity of impact craters. All that is consistent with ice in motion in one way or another. Schenk’s team homes in on large global-scale circular patterns that can be made out by reference to Galileo and Voyager data, previously identified features that could only have been formed during a reorientation of the shell. The process moves the outer shell with respect to the moon’s spin axis, and is known as true polar wander (TPW). The implications are striking, according to Schenk:
“Our key finding is that the fractures associated with true polar wander on Europa cross-cut all terrains. This means that the true polar wander event is very young and that the ice shell and all features formed on it have moved more than 70° of latitude from where they first formed. If true, then the entire recorded history of tectonics on Europa should be reevaluated.”
Image: Perspective views of fractures on the surface of Europa formed during true polar wander. The large cracks crossing the scene from left to upper right are ~3 kilometers (1.9 miles) wide and 200 meters deep. The double ridges crossing the scene are similar in width. Credit: P. Schenk/USRA-LPI.
The reorientation of an ice shell has been proposed for a variety of icy worlds, with the best cases, according to the paper, being made for Pluto and possibly Ganymede, the latter a world we’ll be able to analyze up close with the arrival of the JUICE mission in the 2030s. There is speculation about true polar wander as well on Miranda and Enceladus, among others.
Maps produced from Galileo and Voyager data are at the heart of this paper, as Schenk worked with Isamu Matsuyama (University of Arizona) and Francis Nimmo (UC-Santa Cruz) to correlate large fractures on the Europan surface with concentric circular depressions that had already been identified. The team analyzed the global map largely at 200-meter resolution, with highest-resolution in some areas reaching 40 meters per pixel.
The fracture systems are related to the circular true polar wander tectonic patterns previously found, according to the paper, and we can get a sense of their age because the fractures cut across all known terrains. The team concludes that the global orientation of the ice shell had to have been one of the last major events to occur on Europa. Moreover, the thickness of the ice shell, a key factor in any attempt to reach the ocean below, may have increased with time.
The work makes predictions that we can test when the Europa Clipper mission reaches Europa. “In addition to generating global-scale tectonic features, true polar wander also produces global-scale gravity and shape perturbations, which affects gravity and shape constraints on the interior structure,” says co-author Matsuyama.
The spacecraft is to complete our map of Europa, including high resolution images of critical surface features, allowing scientists to determine more precisely the age of Europan fractures and depressions. From the preprint:
A return to Europa will be necessary to map out the full distribution of all known and candidate TPW-related features on Europa (including troughs, fissures, plateaus, folds, etc.) to determine their extent, stratigraphic ages, structural strain and other characteristics. These will constrain TPW processes and timing, as well as properties of the ice shell during the epoch in which they formed and will be key objectives of NASA’s Europa Clipper mission. Any putative previous TPW episodes may also be resolved in global high-resolution mapping in the form of cryptic troughs or fractures.
The paper is Schenk et al., “A Very Young Age for True Polar Wander on Europa from Related Fracturing,” in process at Geophysical Research Letters (abstract).
Aspects of Interstellar Transhumanism
In Shakespeare’s famous lines from The Tempest, the spirit Ariel addresses Ferdinand, prince of Naples, now grieving over the death of his father in the shipwreck that has brought them to a remote island in an earlier era of exploration. The lines have an eerie punch given our discussion of the changes humanity may bring upon itself as we adapt to deep space:
Full fathom five thy father lies;
Of his bones are coral made;
Those are pearls that were his eyes;
Nothing of him that doth fade,
But doth suffer a sea-change
Into something rich and strange…
From this has emerged the modern shadings on ‘sea-change,’ yet another Shakespearean coinage that has enriched the language. I thought about The Tempest while reading through the Working Track Report from TVIW 2016, a symposium in which these adaptations took center stage. The new edition of Stellaris: People of the Stars (Baen, 2020), discussed last Friday, contains the short report, prompting this examination of its conclusions along with a look at some of the fiction and non-fiction that takes up the bulk of the volume, all on the topic of human transformation.
Species Bifurcation at the Oort
In what sense will interstellar travelers be humans like us, and in what sense will they become a new species? One point that emerged in the discussions in Chattanooga was that adaptations to our species will be mission-specific. Exploratory expeditions have the need to adapt to issues like isolation and long confinement as well as, depending on spacecraft configuration, low gravity or other controllable environmental factors. Actual colonies have far different needs: Long-term adaptation to an environment possibly much unlike Earth and the need to support and sustain a growing population. The kinds of human engineering we’ve been discussing come into play, though through a natural process of development, destination by destination.
Imposing genetic and/or physical changes will be slow and adaptive, and doubtless the process will only be possible if begun and examined thoroughly in a space-based infrastructure right here in the Solar System. A multi-generational human presence in space also allows the social structures to develop that can support life off-planet, though these will doubtless evolve within specific mission parameters.
The generation that leaves the Solar System for the first time may face sharp distinctions in its mode of travel. Shorter exploratory missions to nearby stars make their own demands, different from those experienced by worldships that move at much slower pace, producing generations that are born and live out their lives on the vessel. In a sense, worldships can be seen as antithetical to interstellar colonization, if as the working track participants did, we make the assumption that spacecraft on this scale develop their own kind of inhabitants:
Worldships are an end in and of themselves. Moving such a large biosphere to another star system would likely take centuries. If a worldship would be viable for the projected duration of the mission, then it would most likely be viable well in excess of that timeline. Thus, a worldship is a colony; once established, attaching engines or even an interstellar drive to a worldship may provide mobility, but to what end? Furthermore, if it is used merely as a vessel to transport colony and crew, then what is the guarantee that they will want to leave the habitat once the destination is reached?
I’ve written before about the prospect of an important bifurcation in our species on this issue. Those who inhabit massive space structures — perhaps hollowed-out asteroids, or arcologies ‘grown’ in space by future forms of nanotech — and those who live on planetary surfaces and choose to travel through faster technologies to planets around other stars. I can imagine ‘slow boat’ travel between the stars as humans move gradually out into the Oort Cloud exploiting cometary resources and eventually moving into a presumably similar cloud around the Centauri stars, for example. Here we’re talking about missions in the thousands of years, and ‘crews’ — inhabitants — who may well choose to move on to another system after studying the first.
By contrast, those shorter exploratory missions, given the problems of propulsion, may themselves be, at minimum, decades long and likely centuries. Here the Working Track saw the need for deep sleep:
…interstellar exploration will most likely require some form of metabolic suspension. While such medical technology is still science fiction, it has its roots in present-day advances in surgical techniques, in the as-yet-unexplored functions resident in what has been called junk DNA, and in lessons learned from vertebrate animals which can successfully survive freezing temperatures without damage to cells caused by the formation of ice crystals.
Alternating crew shifts into and out of hibernation could sharply reduce the subjective passage of time, with ramifications for both social engineering and life support systems.
Image: The vast interior of an O’Neill cylinder presents a more spacious view of what a worldship might become. Credit: Rick Guidice/NASA.
The Biomedical Transition: Shifting the Curves
You would think that technologies like CRISPR already take us a long way toward the modification of the human genome, but the way ahead is challenging indeed as we go from treating single diseases like cystic fibrosis to modifying complex traits of intelligence or longevity. It’s the difference between single-gene engineering and dealing with hundreds of genes and their interactions over time and changing environments. Thus Nikhil Rao (University of Florida), whose contribution to Stellaris explores the outcomes we want to achieve as we go transhuman.
No easy matter, this, for as Rao puts it:
Ultimately, most positive traits in humans are emergent functions of genes, environment, our interactions, and time. While gene manipulation and nanotechnology may modify these processes, potentially eliminating negative traits, they will likely not change the fact that human traits are ultimately distributed along a series of bell curves, even as science shifts the shape of those curves.
Shifting those curves will involve adjustments to the human immune function, mild immunodeficiency being surprisingly common. We might see accelerated evolution in Earth-based pathogens that have been unwittingly carried with us onto a worldship, for example. A seasonal allergy is an example of something that triggers inflammation and destruction of the body’s own tissues as a response to pollen, bacteria or viruses. Genetic engineering may eventually produce altered immune systems to cope with deadly reactions.
If you watch shows like The Expanse, you’ll see one visualization of changes to the human form resulting from lower levels of gravity, as in the example of the ‘Belters’ who live far from a planetary surface. Candidate planets for future settlement beyond Sol will demand body adjustments to cope with blood circulation and connective tissue issues, perhaps ruling out higher-gravity worlds. To the extent we can engineer for it, we may keep the example of Earth cultures in mind, says Rao. The short-stature, thick-torso Inuit are an adaptation to issues of heat dissipation and retention. Contrast them with “the long and lanky Masai of the hot, dry savannah.” Over time, we can expect adaptive evolution, or engineer for it in advance.
Meanwhile, life extension continues to be explored, with cellular repair mechanisms running headlong into the threats of toxins or radiation on a space voyage. Direct intervention to prevent gene mutation through gene editing may strengthen our protective systems, as could tinkering with the monoclonal antibodies that can be used to rid the body of mutation. Perhaps nanomedicine will emerge to intervene against everything from cancer to dementia.
Rao also talks about forms of cryonic storage, which has been in the interstellar voyage conversation for decades. Here we have the kind of suspended animation science fiction has long advocated as a solution to long voyages (and the plot problems they introduce into a story). He sees few advances in true cryonics but leans toward hibernation as a solution. After all, we know that animals can manage it, so it is biologically feasible and perhaps enhanceable through gene editing. Hibernation also has “clear endogenous (hormone and blood protein) triggers for induction and exit,” and offers the advantage of dramatically slowing metabolic processes to delay waste accumulation and cell damage (lower rates of cellular turnover).
Image: A Bussard ramjet in flight, as imagined for ESA’s Innovative Technologies from Science Fiction project. Credit: ESA/Manchu.
Here Rao echoes the working group in the idea of crew shifts:
Hibernation could reduce caloric needs by up to ninety percent based on animal models and produce up to a ninety-percent lengthening of lifespan at the theoretical high end. Simply stated, a month of lifespan is earned for every year of hibernation. Ten individuals in hibernation would strain life-support systems about as much as one individual active and awake. If every individual spent one year as crew and nine in hibernation during the journey to Alpha Centauri, that 150-year journey suddenly becomes a fifteen-year journey, which is far more doable within a single crew’s lifespan.
Rao is a psychiatrist specializing in critically and chronically ill children, a perspective that reminds us that shipboard and colony life in a strange new environment will stress the human personality over perhaps multigenerational timescales. He offers no easy solutions, but rather falls back on the persistence of older traits amidst whatever bioengineering we are able to pull off. He sees humans as capable of long-lasting cooperative networks and the kind of reciprocal altruism that took our species out of Africa, creating dreams of destinations as distant as the stars. Along the way, we’ll use our technological tools to adjust the human genome as needed.
Imagining the Mission
Although generally unmodified, I now wear glasses, so it could be argued, as editor and contributor Les Johnson does in Stellaris, that I am partly cybernetic.
I doubt many Centauri Dreams readers have trouble envisioning or accepting some physical changes to the human form — some noticeable, some not — or even machine/human interfaces that internalize digital technologies and offer access to information. But I think many in the general public would need to think twice about the fact that an insulin pump for diabetics, or an artificial heart, takes us into cyborg territory even today. We’re well on our way, in other words, to the kind of implants that may one day be common among deep space crews.
Transhumanism has been explored by many a science fiction writer, and I think immediately of David Brin’s ‘uplifted’ dolphins and chimpanzees as an example of what future technologies might allow. Johnson mentions bioengineered super-abilities in Timothy Zahn’s novels, or Nancy Kress’ explorations of humans that tech allows to ‘turn off’ sleep. I also think back to the four stories that went into James Blish’s The Seedling Stars (1957), where humans alter themselves to fit alien environments, already a well established trope in science fiction.
Blish referred to adapting the human form to an alien environment as ‘pantropy.’ Such adaptations can become extreme indeed: In the wonderful “Surface Tension,” an original human crew seeds a water world with new humans that are virtually microscopic and released into fresh water ponds. I also think back to Frederick Pohl’s Man Plus, which copped the Nebula for best novel in 1976. Here a cyborg is vividly adapted to handle the rigors of the Martian surface as a way of setting up a future colony on the planet. The transformation is grim as the protagonist loses his links with humanity on Earth but explores his new identity on Mars.
Johnson’s entry in Stellaris posits an extension of the issue. If our propulsion technologies still demand centuries to get to the stars, can we overcome the problem by sending human embryos that can be activated upon arrival to form a colony? The issues are vexing: Who raises the infants? In “Nanny,” Johnson writes of a starship that contains a crew that alternates in and out of cryostorage to maintain the ship and is intended to raise the first human generation born on the new world, but a catastrophe aboard the ship alters the plan.
Image: Les Johnson, shown here with a sample of solar sail material that may one day be used to send a spacecraft deep into the outer system using only the pressure of sunlight for propulsion.
Are there other kinds of nannies that can raise children? The child whose voice introduces the tale seems to have few problems with hers:
Yesterday was Birthday One and we had a big party. Nanny said the day the first group of us were born was the happiest in memory. Thirteen Earth-years ago, the first fifty of us were removed from the artificial wombs and put in Nanny’s care. Fifty. I cannot even begin to imagine what it was like shepherding fifty babies, and then toddlers, around the house. But then I remembered that eight of the first group died, leaving just forty-two. Nanny doesn’t like to talk about that and has never told us exactly what happened to them.
I won’t either — no spoilers here — but how humans fit into the loop of automated systems is very much on Johnson’s mind in this cunning tale. An expert in deep space propulsion with extensive experience in solar sails (he is principal investigator for a mission we’ve discussed here, Near-Earth Asteroid Scout, as well as the much more ambitious Solar Cruiser), Johnson is an author and editor who sees abundant scope for humans as we populate first the Solar System and then nearby stars, beings who, “no matter their form, will be much like us.”
Homo Stellaris: Space and Human Transformation
In the sixteen years I’ve been writing Centauri Dreams, I’ve often used written science fiction to illustrate points about our ongoing science discussions. This also gives me a chance to poke around in my collection of old SF magazines, always a pleasure, as I’ve been collecting them since i was a boy and they go back to the glory days of newsstand fiction, which extended well beyond SF to mysteries, westerns and the various other genres defined by the pulp magazines of the early 20th Century.
What a kick, then, to read a short story by Robert E. Hampson and find a starship named Centauri Dreams! Not only that, but Robert, a professor of physiology and pharmacology at Wake Forest School of Medicine, gives me a nod by naming the orbital hub through which travelers pass in the story ‘Gilster Station.’ Thank you, Robert!
The story is “Those Left Behind,” which appears in the collection Stellaris: People of the Stars, a volume Hampson edited with Les Johnson. First published in 2019, the book now emerges in a new paperback edition from Baen Books. Hampson’s story is provocative, dealing with issues of human/machine augmentation that long-haul spaceflight may require. When humans reach the nearest stars, will they be human as we know the term, or an emerging branch of the species in charge of its own evolution?
Image: Wake Forest’s Robert Hampson, author and physiologist, who continues to explore the human response to space exploration. Credit: Wake Forest University.
The great question hanging over all this is whether there are human traits that would endure despite not just mental but physical transformation. We can imagine, as Hampson does, the reaction among those who will find augmented humanity a step too far. Here the question disrupts a family even as they look toward a colony at Proxima Centauri and ponder what it will take to get people there, all the while dealing with an emerging movement of those committed to ending human modification:
“You thought because I didn’t meet your expectation of a human — that I was bioengineered for low gravity — that I would be weak?” Sandy stood over the intruder, body language signaling anger and rage. “You argue about biological purity, about ‘unaltered’ humans, yet you live with modern medicine, vaccines, gene therapies and corrective surgeries.”…
“…simple spectrography,” Mace said, dismissively. “Diaminotoluene in the hair means hair color. Probably to cover the gray and change his appearance. Fine scars around the nose and eyes from plastic surgery — either vanity or to fool facial recognition. There’s a scleral scar and artificial lens in his right eye.”
Sandy practically snarled. “So, correcting your vision and changing your appearance with surgery is okay for you — just not for the people who are trying to give mankind a future?”
Some of us started reading science fiction in the first place because a good writer can pick up an idea like this and rotate it in and out of our present and into the future, forcing the big questions that technology enables, or perhaps demands. I know Robert Hampson from our encounters at conferences, the last one being the Tennessee Valley Interstellar Workshop’s 2017 symposium in Huntsville, where he moderated a panel on human life off-planet and a working track on the role of security and intel in space. “Those Left Behind” reminds me why he has become a go-to guy for science fiction writers pondering just what homo stellaris will be.
Where Intelligent Life Goes
Stellaris: People of the Stars collects fiction as well as non-fiction essays on just the matters addressed above, the changes that expansion in the universe may force upon our species. Although not limited to authors at the event, the book draws on many discussions at the Tennessee Valley Interstellar Workshop’s 2016 symposium, which was held in Chattanooga, TN, and included a working track on the transition of the human body and mind to the interstellar environment. I should note that the organization now does business as the Interstellar Research Group at irg.space.
Over the years I’ve gotten to know many of the authors within the volume, but I’ve only had one chance to meet Sir Martin Rees, Britain’s Astronomer Royal, though to be honest that was just a brief introduction at one of the Breakthrough Starshot meetings. But revisiting Robert Hampson’s story gives me a chance to talk about Rees’ essay “The Future of Intelligent Life in the Cosmos,” from the same volume. Rees is intrigued, to say the least, by exobiology, and is the author of On the Future: Prospects for Humanity (Princeton 2018), among numerous other books and essays.
Image: Martin Rees, astrophysicist, cosmologist and Britain’s Astronomer Royal.
One of the changes that have become apparent about public perception of these matters in the past two decades has been the commonplace discovery of exoplanets, which have gone from being a curiosity to an almost daily news item, their wide range a matter for comment and speculation. Rees speaks of this as being ‘morale-boosting,’ which it is to those anxious to identify other life in the universe, but a biosignature, perhaps detectable in a few decades, is a different thing entirely from a technosignature, and it’s an open question how humanity would react to the latter.
The challenge of estimating human reaction is that, as the Hampson story explores, humanity itself may be on the cusp of change, which may include not only genetic modification but augmentation through artificial intelligence. Thus biotech looms large as we make decisions about the relationship we choose to have with technology. In space, we continue to mine data from Cassini, New Horizons and Rosetta, even as we look forward to exploring the Jovian satellites through missions like the European Space Agency’s JUICE, with its intention of orbiting Ganymede, and NASA’s Europa Clipper. A key fact: We’re getting better and better at robotic exploration. The question this forces is inevitable. Says Rees:
The next step will be the deployment of robotic fabricators in space that can build large structures. For example, giant successors to the James Webb Space Telescope (JWST) will have immense gossamer-think mirrors assembled under zero gravity. These structures will further enhance our imaging of exoplanets as well as the cosmos. Will there be a role for humans?
Good question. Rees readily admits the powers of human observation (“It cannot be denied that NASA’s Curiosity, trundling across a giant Martian crater, may have missed startling discoveries that no human geologist could overlook”). Even so, he makes the case that the startling advance of machine learning coupled with sensor technology, not to mention the cost differential between manned and unmanned missions, means that the case for manned spaceflight is less clear-cut than it was a few decades ago.
While we explore the question, the near-term future for humans in space hinges on what Rees calls “inspirationally led private companies” who will engage in manned launches in terms of competition. This is a high-risk environment that reminds me of the early days of aviation, when records fell almost daily as pilots pushed their equipment higher and faster than ever before. Such adventurers may well wind up reaching other nearby worlds, where the changeable nature of humanity comes into play:
The pioneering explorers will be unsuited to their new habitat, sustaining a more compelling incentive to adjust themselves compared to those of us still on Earth. They will harness the powerful genetic and cybernetic technologies that will be developed in future decades. These techniques will be heavily regulated on Earth as well as on prudential and ethical grounds; however, settlers on Mars will exceed the clutches of regulators. Therefore, we should wish them luck in modifying their progeny to adapt to alien environments, as this might be the first step toward divergence into a new species. Ultimately, it will be these brave space voyagers who lead the post-human era.
I think about this often in terms of longer-range missions into the interstellar medium. Assume for a moment not one but many habitats in space, O’Neill-type arcologies housing larger and larger numbers of people in coming centuries who find the prospect of an engineered vs. a natural world enticing. If this happens, surely one day the idea of simply untethering from the Sun’s gravitational influence will strike some as irresistible. Imagine such a worldship nudging out into the Oort Cloud, to exploit the abundant cometary resources available there, and perhaps eyeing passage to another star. How many centuries will it take for such beings to diverge from our species?
So that maybe we don’t reach another stellar system and meet the aliens. Maybe the explorers who, after centuries or millennia, arrive at Wolf 1061c or Proxima Centauri b, are the aliens, at least in terms of their differentiation from ourselves.
Staying Human Closer to Home
We may have to make changes to our physiology if we plan to create a long-term human presence in space, by which I mean actual people living full-time off-world, either on planets or in the kind of structures I’ve mentioned above. And we can’t rule out the possibility that the advantages of electronic intelligence will simply be too great, causing our descendants to largely continue interstellar exploration with robotics of a kind so advanced over what we have today that they do indeed seem magical. I imagine Arthur C. Clarke would be right at home with a prospect like that.
It’s striking, then, to see how swiftly we dismiss some of the major issues regarding humanity in space when we look at what does seem feasible soon, a trip to Mars. In particular, I can remember a presentation that Robert Hampson makes about gravity and its lack. Mark Shelhamer, in the same Stellaris volume, goes into the question, a good thing because we’ve only begun to examine it seriously. It’s simply not enough to put astronauts in an environment like the ISS and take notes. We also have to ask what happens to humans longer-term, colonists on Mars, say, who plan to live out their lives in 0.38 Earth gravity. Does the body ultimately adapt or not?
Some of these issues have already come up in manned spaceflight close to home. We’ve learned about problems in visual acuity from extended ISS stay, evidently due to fluid pressure changes that move toward the back of the eye over time, distorting the shape of the eye and distorting its optical properties. Shelhamer (Johns Hopkins) is well suited to examine the questions this raises. He has worked with NASA on sensorimotor adaptation to spaceflight; he also is an advisor to the commercial spaceflight industry, and has served as chief scientist for the NASA Human Research program at JSC.
Image: Mark Shelhamer examining zero-g aboard NASA’s ‘vomit comet,’ a modified Boeing jet that simulates the weightlessness of the ISS. Creedit: Johns Hopkins Medicine.
Gravity is, of course, only one of the factors he discusses in his essay, but I focus on it because research on the matter seems so crucial and yet relatively unexplored. We do know to provide exercise venues for orbiting astronauts to maintain bone integrity and cardiovascular function as well as keeping muscles tuned for eventual return to Earth. But we still have much to learn, including the vital question of bone mineral density as it applies to bone strength and the interrelation between the two in internal structure.
ISS astronauts get about two hours of exercise per day per person (which also offers a mental break from the various demands of the job). So you could say that the ISS is a laboratory in gravitational studies impacting physiology, but we need a better one. Delivering a debilitated crew to the Martian surface serves no one well, so we need to find out whether the spacecraft that carry our astronauts there will need artificial gravity. We can induce the effect by rotating the craft in a variety of configurations, but it clearly has a huge impact upon design. How much artificial gravity do we need?
What we need in the short term is an orbiting laboratory that can explore these questions, a structure designed specifically to treat human issues in space and in particular questions of human performance under varying levels of g. In an ideal universe we would manage artificial gravity by using constant acceleration to target, with a turnaround at the halfway point. Lacking that capability, our best bet is rotation inducing a centripetal force proportional to the distance from the rotation axis. We’ll want to vary artificial gravity through spinning.
That, of course, raises a slew of other questions. Just how much artificial gravity do we need, and at what level? It’s possible that parts of a long-haul spacecraft might rotate while others do not, so that the crew might sleep, for example, in zero g and work much of the time in an artificial gravity environment. We know that many of the problems of bone and muscle mass loss could be avoided through artificial gravity, but we don’t have much experience with the vestibular system involving the balance organs in the inner ear, which is used to orient a person within inertial reference frames.
We don’t, in other words, know enough about rotating environments, and we need to explore how to mitigate their effects. We also need to consider, as Shelhamer goes on to point out, that weightlessness may have beneficial effects of its own. Here the psychological effects of space upon the crew may come into play. The famous ‘overview effect,’ explored by Frank White in his book of the same name in 1998, may partially be the result of the zero gee environment. It would be useful to explore possibilities that involve rotating only part of the spacecraft, providing living quarters that include artificial gravity for at least part of the astronaut working day.
The prospect of physiological transformation is something we also need to learn a great deal more about. Let me quote Shelhamer on this intriguing point:
Faced with a dramatically different environment — altered gravity level, unfamiliar atmospheric pressure and composition, different magnetic field, to name a few — evolutionary processes in the human organism might be accelerated. Under such circumstances, epigenetic alterations might take on a larger role in the heritability of acquired traits. Whatever the mechanism, settlers will likely be faced with the problems inherent in rapid change — only this will involve changes to the humans themselves. The possibility that some of these changes will be undesired — and could interact with other changes to the overall detriment of the person — should not be ignored.
Do we acknowledge such adaptive alterations if they begin, or do we try to slow them down? In other words, do we willfully let our species branch into new physiological directions, or do we try to mitigate the possibility? Here we also need to look at the role of genetic modification, about which we need to be cautious. As Shelhamer says, “in a space-settler setting where there is precious little backup capability (you can’t go home again) even subtle second-order effects can take on outsized significance.”
Ganymede: Largest Impact Crater in the Solar System?
Have a look at what two of our older spacecraft saw on Jupiter’s giant moon Ganymede, a world that will snap into much greater focus once the JUICE mission arrives in 2029. The JUpiter ICy moons Explorer is slated for launch in 2022, with the intention of studying Ganymede, Callisto and Europa. But it’s Ganymede that will get the lion’s share of the attention from this European Space Agency effort as JUICE slides into orbit around the moon in 2032, marking the first time a spacecraft has orbited a moon circling a planet other than our own.
Image: Images of Ganymede’s surface taken by Voyager 2 (left) and Galileo (right). The Dark Terrain and Bright Terrain areas can be recognized, with concurrent furrows present in the Dark Terrains. Credit: NASA.
We looked at more recent Juno views of Ganymede just last month (see Glimpses of Ganymede), along with interesting results from its most recent flyby on disruptions in the crystalline structure of the moon’s north polar ice due to incoming plasma. Now we return to Jupiter space because of a new paper from Naoyuki Hirata (Kobe University) and colleagues that examines the orientation and distribution of tectonic troughs on Ganymede’s surface. Their concentric arrangement implies what may be the largest impact structure identified in the Solar System. The data used in the work come from both Voyagers and the Galileo spacecraft.
Image: Azimuthal equidistant map centered at 20° south 180° west showing Ganymede’s Dark Terrain and furrows (indicated by yellow lines). (Bottom) Azimuthal equidistant map of Ganymede’s surface centered at 20° north and 0° west. This shows the opposite hemisphere of Ganymede from the top image. The white areas indicate Bright Terrain. Credit: NASA.
Hirata’s team used computer simulations at the National Astronomical Observatory of Japan (NAOJ), speculating that what we are looking at is the result of an asteroid impact, a mighty blow struck by an object significantly greater than 50 kilometers in radius, and perhaps as much as 150 kilometers in radius, moving at 20 kilometers per second.
Almost all the furrows found in the spacecraft imagery are concentric rings aligned around a single point centered at 20°S 180°W, with the radial extent of the structures measuring 7800 kilometers. Bear in mind that the mean circumference of Ganymede is only 16,530 kilometers. If we really are seeing a crater here, it dwarfs Callisto’s 1900 kilometer crater, previously thought the largest in our system.
A 150 kilometer impactor would produce a melt pool with a radius of 1000 kilometers, a possible explanation for the central region of Ganymede’s Marius Regio, which is free of furrows. Usefully, the Hirata simulations lead to a prediction that we will soon be able to test. From the paper:
Our numerical impact simulation for the case of Rimp = 150 km (Rimp
=50 km) demonstrates the generation of a large melt region with a radius of ~1000 km (~500 km). This large melt region would allow the dense material to gravitationally segregate, which generate positive gravity anomaly such as mass concentrations seen on the lunar impact basins. Therefore, we predict that, if our view is correct, positive gravity anomaly with a radius of ~1000 km when Rimp = 150 km (or a radius of ~500 km when Rimp = 50 km) should exist around 20°S 180°W. This can be tested by future geodetic observations of Ganymede such as the JUICE (Jupiter Icy moon Explorer) or Europa Clipper mission.
Image: Jupiter (background, left) and its moon Ganymede (foreground, right) visualized using the Four-Dimensional Digital Universe viewer “Mitaka.” The furrows found on the older, Dark Terrain, areas of Ganymede’s surface could actually be parts of a single, giant, multiring impact crater. Credit: Tsunehiko Kato, 4D2U Project, NAOJ.
The paper is Hirata et al.,”A global system of furrows on Ganymede indicative of their creation in a single impact event,” Icarus Vol. 352 (July 15, 2020), 113941 (abstract).
95 Nearby Cool Brown Dwarfs Identified
The boundary between planet and star is hard enough to pin down without thinking of some recently discovered brown dwarfs that are cool enough to approach Earth temperatures. Yet worlds/stars like these are among the haul assembled by volunteers working data for Backyard Worlds: Planet 9, a citizen science project whose latest findings include 95 cool brown dwarfs in the Sun’s neighborhood, as reported in the Astrophysical Journal.
Despite a determined search, we’ve yet to find such an object closer than the nearest stars at Alpha Centauri. But 23 light years out — the distance of the closest of these brown dwarfs — is definitely close in galactic terms, and most of the brown dwarfs tracked in the new work are between 30 and 60 light years from Earth. That makes sense, for objects like these are faint enough that identifying them at greater range is all but impossible.
The data used in the brown dwarf collection come from a range of observatories including W. M. Keck, Mont Mégantic, Las Campanas, Kitt Peak and Cerro Tololo. Space-based data from WISE (Wide-field Infrared Survey Explorer) were also valuable, as were follow-up observations from the Spitzer Space Telescope providing photometric confirmation. Low temperature brown dwarfs like these build our catalog while also clarifying gaps in the low-temperature population.
Jackie Faherty (American Museum of Natural History) is a co-author of the paper, whose lead author is Aaron Meisner (NSF NOIRLab). Faherty places the work in context, while giving a nod to the Backyard Worlds participants:
“This paper is evidence that the solar neighborhood is still uncharted territory and citizen scientists are excellent astronomical cartographers. Mapping the coldest brown dwarfs down to the lowest masses gives us key insights into the low-mass star formation process while providing a target list for detailed studies of the atmospheres of Jupiter analogs.”
Image: Artist’s impression of one of this study’s superlative discoveries, the oldest known wide-separation white dwarf plus cold brown dwarf pair. The small white orb represents the white dwarf (the remnant of a long-dead Sun-like star), while the brown/orange foreground object is the newly discovered brown dwarf companion. This faint brown dwarf was previously overlooked until it was spotted by citizen scientists, because it lies right within the plane of the Milky Way. Credit: NOIRLab/NSF/AURA/P. Marenfeld. Acknowledgement: William Pendrill.
We can also thank NOIRlab’s Community Science and Data Center (CSDC), which made the large survey sets available through its Astro Data Lab science platform. The web portal makes matching data sets from a variety of observatories available to citizen scientists. Meisner adds:
“The technical burden of downloading billion-object astronomical catalogs is typically insurmountable for individual investigators—including most professional astronomers. Thankfully, the Astro Data Lab’s open and accessible web portal allowed Backyard Worlds citizen scientists to easily query massive catalogs for brown dwarf candidates.”
The authors make the point that some of the objects in this study will be potential targets for follow-up spectroscopy by the James Webb Space Telescope:
Among our most exciting discoveries are new candidate members of the 10 pc sample, two objects moving faster than 200″/yr, three T type subdwarf candidates, five Y dwarf candidates, and a new T8 plus white dwarf co-moving system. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf, making them potential targets for JWST spectroscopy. Backyard Worlds is actively pursuing additional ground-based follow-up of the discoveries presented in this study, especially spectroscopy where feasible. While this work’s new brown dwarf candidates already demonstrate the power of citizen science for mapping the solar neighborhood, these objects make up only a small fraction of Backyard Worlds moving object discoveries to date. As NEOWISE continues scanning the sky, Backyard Worlds will endeavor to search all of its newly delivered data for yet more cold and close neighbors to the Sun.
Backyard Worlds volunteers have discovered more than 1,500 stars and brown dwarfs near the Sun. The current batch represents some of the coldest brown dwarfs in that collection. More than 100,000 citizen scientists are involved in the project, a network that examines telescope images to identify the movements of nearby dwarfs and planets. Putting human eyes on large data sets is integral to the search for rare objects, an approach astronomers will exploit with data gathered by the Vera C. Rubin Observatory (VRO). Now under construction in the Chilean Andes, the instrument will survey the southern hemisphere sky every three nights over a ten year period.
The paper is Meisner et al., “Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project,” accepted at the Astrophysical Journal (preprint).
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