Paul Gilster's Blog, page 62

A SETI Search of 10 Million Star Systems

As it is considered a precursor installation, the Murchison Widefield Array (MWA) in Western Australia doesn’t get the press that its proposed successor, the Square Kilometer Array (SKA) regularly receives. That’s to be expected, given the scope of the SKA, which will involve telescopes in both Australia and South Africa. 14 member countries are developing a project that is to reach over a square kilometer of collecting area, containing thousands of dishes and up to a million low-frequency antennas. If it is built, SKA’s angular resolution and survey speed will allow surveys thousands of times faster than those now being conducted.

But the Murchison precursor is alive and well, working the 70–300 MHz range and mapping the radio sky. Established and maintained by CSIRO, Australia’s national science agency, the MWA may be 50 times less sensitive than the SKA, but it has been put to work in areas ranging from the heliosphere to neutral hydrogen emission from the early universe. Its remit also includes several SETI studies, the latest being a search in the area of the constellation Vela (originally part of the larger Argo Navis constellation). The International Centre for Radio Astronomy Research, which supports the Australian bid to host SKA, calls this latest survey “the deepest and broadest search at low frequencies for alien technologies.” The results are now in the books, as reported in Publications of the Astronomical Society of Australia.

CSIRO astronomers Chenoa Tremblay and Steven Tingay (Curtin University) used the telescope’s wide field of view to observe millions of stars simultaneously. No technosignatures were detected, leading Tingay to observe:

“As Douglas Adams noted in The Hitchhikers Guide to the Galaxy, ‘space is big, really big’. And even though this was a really big study, the amount of space we looked at was the equivalent of trying to find something in the Earth’s oceans but only searching a volume of water equivalent to a large backyard swimming pool. Since we can’t really assume how possible alien civilisations might utilise technology, we need to search in many different ways. Using radio telescopes, we can explore an eight-dimensional search space. Although there is a long way to go in the search for extraterrestrial intelligence, telescopes such as the MWA will continue to push the limits—we have to keep looking.”

The scientists observed the sky in Vela for 17 hours, and point to the capabilities of the coming SKA, which if completed could be available late in this decade. SKA would extend the SETI search into billions of star systems, and would be capable of detecting what Tingay calls “Earth-like radio signals” from relatively nearby planetary systems, meaning, I assume, leakage radiation as opposed to directed signals designed to be interstellar. The current work follows earlier MWA surveys, one toward galactic center, the other in the anti-center direction.

From the paper:

Overall, our MWA surveys show the rapid progress that can currently be made in SETI at radio frequencies, using wide field and sensitive facilities, but also show that SETI surveys have a long way to go. The continued use of the MWA, and the future similar use of the SKA at much higher sensitivities, offers a mechanism to make significant cuts into the haystack fraction of Wright et al. (2018), while maintaining a primary focus on astrophysical investigations, making excellent commensal use of these large-scale facilities.

Image: Dipole antennas of the Murchison Widefield Array (MWA) radio telescope in Western Australia. Credit: Dragonfly Media.

On the matter of ‘haystack fractions,’ the phrase comes from a 2018 paper from Jason Wright (Penn State) and co-authors (two students in a graduate SETI course taught by Wright), which attempts to calculate the total fraction of the ‘haystack’ that has been searched to date, producing a result not far off what Jill Tarter calculated back in 2010: “…our current search completeness is extremely low, akin to having searched something like a large hot tub or small swimming pool’s worth of water out of all of Earth’s oceans.“ Tarter’s comparison was to a drinking glass’s worth of seawater, so we’re in the same range.

Although I cited it in an earlier article (see Into the Cosmic Haystack) this quotation from the Wright et al. paper bears repeating:

We should be careful, however, not to let this result swing the pendulum of public perceptions of SETI too far the other way by suggesting that the SETI haystack is so large that we can never hope to find a needle. The whole haystack need only be searched if one needs to prove that there are zero needles—because technological life might spread through the Galaxy and/or technological species might arise independently in many places, we might expect there to be a great number of needles to be found. Also, our haystack definition included vast swaths of interstellar space where we have no particular reason to expect to find transmitters; humanity’s completeness to subsets of this haystack—for instance, for continuous, permanent transmissions from nearby stars—is many orders of magnitude higher.

Noting that “the dream of ‘all-sky, all the time” high bandwidth coverage is still worth pursuing, and singling out the Tingay et al surveys at the MWA in particular, Wright and colleagues say that surveys with large bandwidth, long exposures, repeat visits and good sensitivity allow for searches that are orders of magnitude faster than surveys without these qualities. Indeed, the three MWA low frequency surveys, because of their very wide field and sensitivity, dominate the haystack search volume, and as Wright notes, they did this in only a few hours of searching. The paper also notes how rapidly Breakthrough Listen is cutting into this search space, and that was before the most recent Breakthrough results were announced (see SETI: Going Deep with the Data Search).

Image: A 20-second exposure showing the Milky Way overhead the AAVS station. Credit: Michael Goh and ICRAR/Curtin.

The paper is Tremblay and Tingay, “A SETI Survey of the Vela Region using the Murchison Widefield Array: Orders of Magnitude Expansion in Search Space”, Publications of the Astronomical Society of Australia September 8th, 2020 (abstract). The Wright paper is “How Much SETI Has Been Done? Finding Needles in the n-Dimensional Cosmic Haystack,” Astronomical Journal Vol. 156, No. 6 (14 November 2018). Abstract / Preprint.

Solaris: To the Sun’s High Latitudes

I can think of more than one way to get a good look at the Sun’s polar regions. After all, we’ve done it before, through the Ulysses spacecraft, which passed over the Sun’s north and south poles in 1994-1995. A gravity assist at Jupiter was the key to the mission, allowing Ulysses to arc out of the ecliptic and inward to the Sun. But Ulysses lacked the kind of remote-sensing instruments we’d like to use to compile an extensive dataset on the polar magnetic field and, as Don Hassler (SwRI) adds, “the surface/sub-surface flows” we might find in the polar regions. It’s good to see a mission designed for that purpose.

For Hassler is principal investigator on a concept that has just been approved for further study by NASA, with the haunting name Solaris. I say ‘haunting’ because it’s hard for this Stanislaw Lem reader to forget the novel of the same name, published in 1961, that explores the implications of a vast intelligence on a planet far from Earth. I realize this has been done as a film more than once and I’ve seen the films, but I leave their analysis to Centauri Dreams film critic Larry Klaes, who would know how to do justice to them. For me, the written word is the medium of choice, and this is a novel I intend to read again.

Anyway, the proposed Solaris mission is one of five science investigations just approved by NASA as part of the agency’s Medium-Class Explorer (MIDEX) program, with $1.25 million allocated for a nine-month contract for what are known as Phase A concept design studies and analyses to develop the concept. If it flies, Solaris would launch in 2025, like Ulysses using a gravity assist at Jupiter to sling it out of the ecliptic plane, flying over the solar poles at 75 degrees latitude. You might think of the surprises Cassini found at Saturn’s poles, and that odd hexagon at the north pole is still the subject of various competing hypotheses. Will we find something just as odd at the Sun? Hassler notes that we’ll at least get a good look:

“Solaris will spend more than three months over each pole of the Sun, obtaining the first continuous, high-latitude, months-long studies of the Sun’s polar regions. With focused science and a simple, elegant mission design, Solaris will also provide enabling observations for space weather research, such as the first polar views of coronal mass ejections, energetic events that spew highly magnetized plasma from the solar corona into space, causing radio and magnetic disturbances on the Earth.”

And. he adds, “It’s sure to stimulate future research through new unanticipated discoveries.”

Unexpected findings have characterized our explorations of the Solar System from the beginning, with Io and Triton being two outstanding examples, so let’s see what those solar polar regions look like. We’ll keep an eye on the progress of Solaris as it makes its way through the process. The concept calls for a Doppler magnetograph to study the polar magnetic fields and subsurface flows, along with an extreme ultraviolet instrument for polar imaging and a white light coronagraph to examine the solar corona from this perspective.

Image; Southwest Research Institute is developing the concept for a mission to study the Sun’s poles, one of the last unseen places in the solar system. This proposed solar polar NASA mission is designed to revolutionize our understanding of the Sun by addressing fundamental questions that can only be answered from a polar vantage point. Credit: Courtesy of Southwest Research Institute.

And keep an eye on another mission funded for similar Phase A concept design study, the Auroral Reconstruction CubeSwarm (ARCS), in the hands of principal investigator Kristina Lynch (Dartmouth University), a mission that would, like Solaris, be managed by SwRI. For me, the chief interest of ARCS is in its plan for 32 CubeSats and 32 ground-based observatories to work together, in this case on a study of the mechanisms driving Earth’s auroras. CubeSat designs of growing complexity are low-cost ways to fly ever more interesting missions, and the emerging notion of ‘swarm’ missions should turn out to be productive in areas as diverse as planetary imaging and extrasolar planet detection.

Meanwhile, I’m always glad to see continuing interest in missions to the Sun, given our need to understand the issues involved in close solar approaches for potential ‘sundiver’ missions deep into the gravity well for maximum acceleration to targets in the outer system. I’ll also mention Solar Cruiser as a fascinating sail design that could enable study of the Sun’s high latitudes using non-Keplerian orbits enabled by the momentum of solar photons. Principal investigator Les Johnson (MSFC) sees this as an outstanding opportunity to demonstrate the capabilities of large sails as we explore the nearest star in the cosmos.

For more on Solar Cruiser, see Heliophysics with Interstellar Implications. See also Johnson’s analysis “The Solar Cruiser Mission Concept — Enabling New Vistas for Heliophysics,” Bulletin of the American Astronomical Society, Vol. 52, No. 3 (June, 2020). Abstract.

A Deformed Protoplanetary Disk in a Triple Star System

This morning we have two interesting and complementary studies of GW Orionis to look at, both analyzing what is apparently a planet-forming disk with multiple, misaligned rings around this triple star system some 1300 light years from the Sun. In the more recent of the two, Stefan Kraus (University of Exeter) and colleagues used data from both the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Observatory’s Very Large Telescope (VLT) in detecting warm gas at the inner edge of the misaligned ring, which has broken away from the larger disc, and scattered light from the warped disk surface.

So what could be going on at GW Orionis? What the images reveal is an evolving young system much different from our own. Consider: The inner stars GW Ori A and GW Ori B orbit each other at a separation of a scant 1 AU, while the third star, GW Ori C, orbits the inner stars at a distance of roughly 8 AU, the latter in an orbit that is not aligned with the plane of the inner duo. In our Solar System, we’re used to planets that move in roughly the same plane around the Sun. Here we see a deformed protoplanetary disk that may produce an utterly different result.

Image: Representation of the disc structure and stellar orbit of the GW Orionis triple system, as derived from the ALMA and VLT observations by Kraus et al. Orange rings are the (misaligned) rings seen by ALMA. The transparent surfaces correspond to the lower-density dust filaments that connect the rings and that dominate the emission in scattered light. Credit: Kraus et al., 2020; NRAO/AUI/NSF.

What an intriguing place to study planet formation, and to ponder scenarios as the system evolves. The ALMA data reveal three separate rings with different orientations, located at 46, 185 and 340 AU from the barycenter of the system. The inner ring is misaligned in relation not only to the outer two rings but also to the three stars. Says Kraus:

“In our images, we see the shadow of the inner ring on the outer disk. At the same time, ALMA allowed us to measure the precise shape of the ring that casts the shadow. Combining this information allows us to derive the 3-dimensional orientation of the misaligned ring and of the warped disk surface.”

Image: New observations of GW Orionis, a triple star system with a peculiar inner region, revealed that this object has a warped planet-forming disk with a misaligned ring. The image on the right is from the SPHERE instrument on the European Southern Observatory’s Very Large Telescope, which allowed astronomers to see, for the first time, the shadows this ring casts on the rest of the disk. This helped the researchers figure out the 3D shape of the ring and the overall disk. The left panel shows an artistic impression of the disk’s inner region, including the ring, which is based on the 3D shape reconstructed by the team. Credit: ESO/L. Calçada, Exeter/Kraus et al.

Planets could well emerge here, with the research indicating that the inner ring contains about 30 Earth masses of dust. What’s intriguing is that any planets forming within this inner ring will orbit in a highly oblique fashion at wide separation from the star. Bear in mind that it’s now believed that more than half of the stars in the galaxy are born with one or more companion stars, making for the prospect of a large population of planets on highly inclined, distant orbits.

Kraus and team have been examining GW Orionis for over 11 years, mapping the gravitational interactions at work among the three stars over a full orbital period. It is clear that the stellar orbits are misaligned from each other and from the disk. We’re getting confirmation here through both observations and computer simulations that a theoretical ‘disk tearing effect’ is in play, one that emerges out of the gravitational pull of the three stars and causes the disk to break into separate rings. Observation of the shadow that the inner ring casts upon the rest of the disk was useful in calculating the shape of the ring and the overall disk structure. Moreover, the shape of the inner ring matches predictions of precisely how gravitational interactions would tear the original disk.

Image; ALMA and the SPHERE instrument on ESO’s Very Large Telescope have imaged GW Orionis, a triple star system with a peculiar inner region. Unlike the flat planet-forming discs we see around many stars, GW Orionis features a warped disc, deformed by the movements of the three stars at its centre. The ALMA image (left) shows the disc’s ringed structure, with the innermost ring separated from the rest of the disc. The SPHERE observations (right), repeated here for comparison, allowed astronomers to see for the first time the shadow of this innermost ring on the rest of the disc, which made it possible for them to reconstruct its warped shape. Credit: ALMA (ESO/NAOJ/NRAO), ESO/Exeter/Kraus et al.

The second team, led by Jiaqing Bi (University of Victoria, Canada), likewise used data from ALMA to observe the same disk misalignment, publishing their paper in May. This work confirms that the inner ring is misaligned relative to the outer ring and the three stars, with the outer ring being the largest yet observed in disks of this kind. Both teams used computer simulations to examine causes for the misalignment, with the Bi team suggesting a possibility that does not arise in the Klaus paper. This is team member Nienke van der Marel (University of Victoria):

“Our simulations show that the gravitational pull from the triple stars alone cannot explain the observed large misalignment. We think that the presence of a planet between these rings is needed to explain why the disk was torn apart. This planet has likely carved a dust gap and broken the disk at the location of the current inner and outer rings.”

Such a planet would be the first ever observed to orbit three stars. Moreover, it’s clear from the example of GW Orionis that stellar groupings like this can play havoc with the shape of a protoplanetary disk, doubtless producing worlds in highly inclined orbits around multiple stars. “We predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging campaigns,” says Kraus co-author and Exeter colleague Alexander Kreplin.

The paper is Kraus et al., “A triple star system with a misaligned and warped circumstellar disk shaped by disk tearing” Science Vol. 369, Issue 6508 (4 September 2020), pp. 1233-1238 (abstract). The Bi paper is “GW Ori: Interactions Between a Triple Star System and Its Circumtriple Disk in Action,” Astrophysical Journal Letters Vol. 895, No. 1 (21 May 2020), Abstract.

SETI: Going Deep with the Data Search

What Breakthrough Listen is calling the most comprehensive SETI search to date is now in the books, or at least, the journals, with results accepted and in process at Monthly Notices of the Royal Astronomical Society. Here we are in the realm of data reanalysis, using previously acquired results to serve as a matrix for re-calculation, with the catalog produced by the European Space Agency’s Gaia spacecraft as the key that turns the lock.

No signatures of extraterrestrial technology were detected in the two analyses produced by Breakthrough Listen in 2017 and 2020. The data for these efforts come largely from the Green Bank Telescope (GBT) in West Virginia and the CSIRO Parkes Radio Telescope in Australia, with a focus on 1327 individual stars. Results were published by the Breakthrough Listen science team at UC-Berkeley, and the choice of targets was telling. The search homed in on relatively nearby stars within about 160 light years of the Sun, under the assumption that less powerful transmitters would be detectable the closer they are to the Earth.

The new analysis of these results has been produced by Bart Wlodarczyk-Sroka, a masters student at the University of Manchester (UK) and his advisor Michael Garrett, working with Berkeley SETI director Andrew Siemion. The Manchester duo realized that when one of the large telescopes was pointed at an individual target, the observation also took in a wide range of background stars. This fact meant that stars much further away could be considered if we could make a determination about their distance.

The Gaia catalog measures the distances to over a billion stars. Wlodarczyk-Sroka and Garrett realized that Gaia now gave them measured parallaxes and inferred distances to stars that were found in the full width half-maximum (FWHM) of the main beam of the telescopes used for the Breakthrough Listen observations. FWHM specifies the angular width of the main beam — think of it as the width of the frequency range where less than half the signal’s power is attenuated. Although not targets of the earlier campaign, these numerous stars were available in the data, previously ignored because their distances from Earth were at the time unknown.

Image: This is Figure 1 from the paper. Caption: . An optical colour image of the stellar field centred on HIP109427 from the Pan-STARRS DR1 z and g broadband filters, showing the extent of the FWHM for the GBT L-band and GBT S-band receivers, circled in red and white respectively. 46 sources with geometric distances calculated from Gaia parallax data are marked with green crosses. Credit: Wlodarczyk-Sroka. Garrett & Siemion.

The Gaia information allowed the researchers to select targets out to 33,000 light years, all found within the original observations, thus expanding the number of stars examined from 1327 to 288,315. Their distance would mean that as the range increased, only more powerful transmitters would be visible to the telescopes. The sample takes in not only many main-sequence stars but extends to giant stars and white dwarfs as well.

Andrew Siemion comments on the significance of the effort:

“This work shows the value of combining data from different telescopes. Expanding our observations to cover almost 220 times more stars would have required a significant investment of our telescope time, not to mention the computing resources to perform the analysis. By taking advantage of the fact that we already had radio scans of stars in the background of our primary targets, and by reading their positions and distances from the Gaia catalog, Bart’s analysis has extracted additional information from the existing dataset. Work like this gets us one step closer to the goal of knowing the answer to humanity’s most profound question: Are we alone?”

Given that the only qualifying criteria for the stars in the new study is that they were within the view of the original observations (i.e., within the FWHM of the telescope beam), the range of stellar types is broad, and this marks the first time scientists have been able to place limits on the prevalence of continuous extraterrestrial transmitters on the basis of spectral type.

In earlier studies, no evidence was found of continuous transmitters associated with stars systems within 50 parsecs of the Sun, given power constraints as explained in the paper:

Both Enriquez et al. (2017) and Price et al. (2020) find no evidence for continuous (100% duty cycle) transmitters associated with the nearby (d < pc) star systems observed. This includes directional transmitters (e.g. radio beacons) directed at the Earth with a power output equal to or greater than the brightest human-made transmitters (e.g. a canonical Arecibo planetary radar-like system with a gain of 70 dB and a transmitter power of ∼ 1 MW). To detect a non-directional isotropically radiating antenna, the transmitter power must be ∼ 1013 W (around the current energy consumption of our own civilisation).

We don’t know if any civilizations in this range are broadcasting at all, but the data are consistent with the statement that fewer than ∼ 0.1% of the stellar systems within 50 pc are using these types of transmitters to contact us. The new work now moves well past the nearby sampling of stars, while factoring in the decrease in sensitivity at larger distances. At 100 to 200 parsecs, for instance, fewer than 0.061 such transmitters can be present, given the same power constraint. We have no candidate signals, but we have hugely widened the scope of the search and tightened the numbers. Wlodarczyk-Sroka comments:

“Our results help to put meaningful limits on the prevalence of transmitters comparable to what we ourselves can build using 21st century technology. We now know that fewer than one in 1600 stars closer than about 330 light years host transmitters just a few times more powerful than the strongest radar we have here on Earth. Inhabited worlds with much more powerful transmitters than we can currently produce must be rarer still.”

Setting constraints is not glamorous work, but it’s how we go about building information. We’ve seen the same phenomenon in exoplanet studies. At Proxima Centauri, scientists progressively drilled down by radial velocity research, first eliminating large gas giants and then progressively smaller worlds as possibilities until finally uncovering Proxima Centauri b, at about Earth size. All the patient data analysis builds the structure needed to arrive at eventual conclusions. When it comes to SETI, we’re learning, bit by bit, what is not there, and also clarifying how much remains to be explored.

As just one case in point: What if the beam is not continuous? Should we expect it to be? See SETI: Figuring Out the Beacon Builders for more on ‘Benford Beacons,’ a topic of frequent discussion in these pages.

The paper is Wlodarczyk-Sroka et al., “Extending the Breakthrough Listen nearby star survey to other stellar objects in the field,” accepted at Monthly Notices of the Royal Astronomical Society (preprint).

Andromeda’s Vast Halo Offers Clues about Galactic Evolution

Wait long enough — something like 4.5 billion years — and we’ll have a huge elliptical galaxy resulting from the merger of our own Milky Way with Andromeda (M31). I’ve always been fascinated with Andromeda because being the nearest large galaxy, and a fine spiral at that, it gives us a look at how our own galaxy must appear from the outside. Its faintness to the naked eye belies its size, an object considerably larger than the Moon from our perspective, though best seen, of course, on a Moonless night. And now we learn it is even bigger than we thought.

The Absorption Map of Ionized Gas in Andromeda (Project AMIGA) is the source for this information. A new study coming out of this program uses Hubble data to map the vast gas envelope surrounding Andromeda, a diffuse halo of plasma extending 1.3 million light years from the galaxy and in some directions, as far as 2 million light years. To put this into perspective, Andromeda itself is 2.5 million light years away, meaning that our two galaxies may already be encountering each other as their two haloes nudge up against each other.

Now the reference to the Moon gives way to an even larger one. If we could see Andromeda along with its halo, we’d be dealing with an object the width of three Big Dippers. If the entire structure were visible, no other feature of the nighttime sky would be as large. The AMIGA study, led by Nicolas Lehner (University of Notre Dame) reveals the layered nature of this plasma halo, one that contains two nested and distinct shells of gas. Says Lehner:

“We find the inner shell that extends to about a half million light-years is far more complex and dynamic. The outer shell is smoother and hotter. This difference is a likely result from the impact of supernova activity in the galaxy’s disk more directly affecting the inner halo.”

Image: At a distance of 2.5 million light-years, the majestic spiral Andromeda galaxy is so close to us that it appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be seen with the naked eye, it would be about three times the width of the Big Dipper—easily the biggest feature on the nighttime sky. Credit: NASA, ESA, J. DePasquale and E. Wheatley (STScI) and Z. Levay.

Sometimes it’s necessary to step back from the minutiae of nearby exoplanet research to see the broader perspective afforded by these cities of stars. Lehner’s co-researcher Samantha Berek (Yale University) calls haloes like these “reservoir[s] of gas” that contain the stuff of future star formation, including the outflows from supernovae. That makes a galactic halo a laboratory for its future evolution, and given its size in our sky, there is no better place to study the phenomenon than Andromeda. Indeed, the team has already found the telltale signs of heavy elements in the halo here, the result of stellar explosions that will seed new worlds.

But despite its relative proximity, how do we go about studying something as diffuse as a galactic halo? AMIGA looks at the light of 43 quasars, those brilliant cores of active galaxies that can be seen in objects much further away than M31. The method: Work with background quasar light as filtered through the Andromeda halo and examine the patterns of absorption in different regions. The data come from Hubble’s Cosmic Origins Spectrograph (COS), working on quasar light in the ultraviolet, a wavelength absorbed by Earth’s atmosphere.

Image: This illustration shows the location of the 43 quasars scientists used to probe Andromeda’s gaseous halo. These quasars—the very distant, brilliant cores of active galaxies powered by black holes—are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars’ light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo’s material. Credit: NASA, ESA, and E. Wheatley (STScI).

Ionized gas from carbon, silicon and oxygen turn up in these data, the signature of radiation stripping electrons from atoms. The new maps tune up work Lehner and colleagues performed in 2015, when the Andromeda halo’s complexity was still unknown. Fellow Notre Dame scientist Christopher Howk comments on the scope of the new study:

“Previously, there was very little information—only six quasars—within 1 million light-years of the galaxy. This new program provides much more information on this inner region of Andromeda’s halo. Probing gas within this radius is important, as it represents something of a gravitational sphere of influence for Andromeda.”

Image: This diagram shows the light from a background quasar passing through the vast, gaseous halo around the neighboring Andromeda galaxy (M31), as spectroscopically measured by the Hubble Space Telescope. The colored regions show absorption from two components that make up the halo. For ionized silicon, a significant absorption is shown in both plots. The more highly ionized carbon is absorbed by only one component. Astronomers can tell the two components apart because their line-of-sight motions, known as radial velocity, cause a Doppler shift that changes the wavelength of light being absorbed. Credit: NASA, ESA, and E. Wheatley (STScI).

The size and nearness of Andromeda thus pay off for the study of galactic haloes. Astronomers have examined them in more distant galaxies, but their distance means that there are far fewer background quasars that line up to allow analysis of the haloes. Here we have the kind of extensive sampling from which we can draw meaningful conclusions, using not just one or perhaps two sightlines but over 40, according to Lehner. Future space telescopes working in the ultraviolet will begin to extend such studies beyond the 30 galaxies of the Local Group.

The paper is Lehner et al., “Project AMIGA: The Circumgalactic Medium of Andromeda,” Astrophysical Journal, Volume 900, Number 1 (27 August 2020). Abstract.

What If SETI Finds Something, Then What?

Beyond its immediate cultural and philosophical implications, the reception of a signal from another civilization will call for analysis across all academic disciplines as we try to make sense of it. Herewith a proposal for an Interstellar Communication Relay, both data repository and distribution system designed to apply worldwide resources to the problem. Author Brian McConnell is an American computer engineer who has written three technical books, two about SETI (the search for extraterrestrial intelligence), and one about electric propulsion systems for spacecraft. The latter, A Design for a Reusable Water-Based Spacecraft Known as the Spacecoach (Springer, 2015) has been the subject of extensive discussion on Centauri Dreams (see, for example, Brian’s A Stagecoach to the Stars, and Alex Tolley’s Spaceward Ho!). Brian has also published numerous peer reviewed scientific papers and book chapters related to SETI, and is an expert on interstellar communication systems and on translation technology. His new paper on the matter is just out.

by Brian McConnell

SETI organizations understandably focus most of their efforts on the initial step of detecting and vetting candidate signals. This work mostly involves astronomers and signal processing experts, and as such involves a fairly small group of subject matter experts.

But what if SETI succeeds in discovering an information bearing signal from another civilization? The process of analyzing and comprehending the information encoded in an extraterrestrial signal will involve a much broader community. Anyone with a computer and a hypothesis to test will be able to participate in this effort. I would wager that the most important insights will come from people who are not presently involved in SETI research. What will that process look like?

The first step following the detection of an extraterrestrial signal will be to determine if the signal is modulated to transmit information. Let’s consider the case of a pulsed laser signal that optical SETI (OSETI) instruments look for. This type of signal consists of a laser that emits very bright but very short pulses on nanosecond time scales. By transmitting very short pulses, the laser can outshine its background star while it is active, and without requiring excessive amounts of energy. OSETI detectors work by counting individual photons as they arrive. Photons from the background star will be randomly distributed over time, while the pulsed signal’s photos will arrive in tight clusters.

This type of signal can be modulated to transmit information in several ways. The duration of each pulse can be altered, as can the time interval between pulses. The transmitter can also transmit on several different wavelengths (colors) to further increase the data rate of the combined signal.

Image: Pulse interval modulation varies the delay between individual pulses.

This type of modulation will be easy to see with currently deployed OSETI detectors, so it is possible that in the case of an OSETI detection, we would also be able to extract data from the signal right away.

How much information can be encoded in an OSETI signal that is also designed to be easy to detect? We can calculate the transmission rate as follows.

Let’s work an example as follows. The signal has 20 distinct color channels and chirps on average about ten times per second. Each pulse can have a duration of 1, 2, 3 or 4 nanoseconds, and so it encodes two bits of information in the pulse width. The interval between pulses can have 256 unique values, and so it encodes 8 bits of information in the pulse interval. Plugging these numbers into the equation, we get 2,000 bits per second. While this is glacially slow compared to high speed internet connections, this works out to 172 megabits of data per day, or 21.6 megabytes per day. At this rate, the sender could transmit several thousand high resolution images per year.

The Interstellar Communication Relay, described in a recently published paper in the International Journal of Astrobiology, is a system that will be deployed in the event of a detection of an information bearing signal. It is modeled off the Deep Space Network, although it will be much less expensive to build and operate, as it will use virtualized / cloud based computing and data transfer services. The ICR will enable millions of amateur and professional researchers worldwide to obtain data extracted from an ET signal, and to participate in the analysis and comprehension effort that will follow the initial detection.

What type of information might we encounter in an alien transmission? This is anyone’s guess, and that is why it will be important to have a broad range of people and expertise represented in the message analysis and comprehension effort. Anything that can be represented in a digital format could potentially be included in a transmission.

Let’s consider images. A civilization that is capable of interstellar communication will, by definition, be proficient at astronomy and photography. Images are trivially easy to encode in a digital communication channel. Images are an interesting medium because they are easy to encode, and can represent objects and scenes on microscopic to cosmological scales. Certain types of images, such as planetary images, will be especially easy to recognize, and can be used to calibrate the decoding process on the receiver’s end.

The bitstream below is an example of what an undecoded image might look like in a raw binary stream. The receiver only needs to guess the number of pixels per row to see the image in its correct aspect ratio. This image is encoded with nine bits per pixel, with the nine bits arranged in 3×3 cells, so the undecoded image appears in its correct aspect ratio. Even before the image is decoded, it is obvious that it depicts a spheroid object against a black background, which is what a planetary image will look like,

The receiver only needs to work through a small number of parameters to decode the image successfully, and once they have learned the transmitter’s preferred encoding scheme(s), they will be able to decode arbitrarily complex images. Because planetary images have well understood properties, the receiver can also use these to calibrate the decoding algorithm, for example to implement non-linear brightness encodings.

Image: The bitstream above decoded as a grayscale (monochrome) image. Credit: NASA / Apollo 17.

What about color? Color is a physical property that will be well understood by any astronomically literate civilization. The sender can assist the receiver in decoding photographs with multiple color channels by sending photographs of mutually observable objects such as nebulae.

Image: The Cat’s Eye nebula, imaged in red, green and blue color channels.

Image: Combining these color channels yields the following image. A receiver can work out which color channels were used in an image by combining them and comparing the output against images they have taken of the same object.

Images are a good example of observables. Observables, such as images and audio, are straightforward to encode digitally. Communicating qualia, internal experiences, may be quite difficult or impossible due to the lack of shared senses and experiences, but it will be possible to communicate quite a bit through observables which, in and of themselves, may be quite interesting. Photographs from another inhabited world would surely captivate scientists and the general public.

Computer programs or algorithms are another type of information to be on the watch for. Computer programs will be useful in interstellar communication for a number of reasons. The sender can describe an interpreted programming language using a small collection of math and logic symbols. While this foundation can be quite simple, with about a dozen elemental symbols, the programs written in this language can be arbitrarily complex and possibly even intelligent.

An algorithmic communication system will have a number of advantages over static content. The programs can interact with their receivers in real-time, and thus eliminate the long delays associated with two-way communication across interstellar distances. Algorithms can also make the communication link itself more reliable, for example by implementing robust forward error correction and compression algorithms that both boost the information carrying capacity of the link, and allow transmission errors to be detected and corrected without requesting retransmission of data.

Take images as an example. Lossy compression algorithms, similar to the JPEG format, can reduce the amount of information needed to encode an image by a factor of 10:1 or more. Order of magnitude improvements like this will favor the use of algorithmic systems compared to static, uncompressed data.

These are just a couple of examples of the types of information we should be on the watch for, but the range of possible information types we may encounter is much greater than that. That’s why it will be important to draw in people representing many different areas of expertise to evaluate and understand the information conveyed by an ET signal.

The paper is McConnell, “The interstellar communication relay,” International Journal of Astrobiology 26 August 2020 (abstract).

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.”