by Paul Gilster | May 9, 2012 | Culture and Society |
Our expectations determine so much of what we see, which is one of the great lessons of Michael Michaud’s sweeping study of our attitudes toward extraterrestrial intelligence in Contact with Alien Civilizations (Springer, 2006). But extraterrestrials aside, I’ve also been musing over how our attitudes affect our perceptions in relation to something closer to home, the human space program. Recently I was reminded of Richard Gott’s views on the space program and the Copernican Principle, which suggest that just as our location in the universe is not likely to be special, neither is our location in time.
My expectation, for example, is that whether it takes one or many centuries, we will eventually have expanded far enough into the Solar System to make the technological transition to interstellar missions. But Gott (Princeton University) has been arguing since 2007 that there is simply no assurance of continued growth. In fact, his work indicates we are as likely to be experiencing the latter stages of the space program as its beginnings. The view is controversial and I like to return to it now and again because it so shrewdly questions all our assumptions.
Image: Apollo 17 Saturn V rocket on Pad 39-A at dusk. Will manned space exploration ever achieve the levels of funding that made Apollo possible again? Credit: NASA.
So ponder a different, much more Earth-bound future, one in which funding for human spaceflight may end permanently. Examples abound, from the pyramid-building phase of Egypt’s civilization to the return of Cheng Ho’s fleet to China — not every wave of technology is followed up. Thus Gott, in a short but intriguing discussion called A Goal for the Human Spaceflight Program:
Once lost, opportunities may not come again. The human spaceflight program is only 48 years old. The Copernican Principle tells us that our location is not likely to be special. If our location within the history of human space travel is not special, there is a 50% chance that we are in the last half now and that its future duration is less than 48 years (cf. Gott, 2007). If the human spaceflight program has a much longer future duration than this, then we would be lucky to be living in the first tiny bit of it. Bayesian statistics warn us against accepting hypotheses that imply our observations are lucky. It would be prudent to take the above Copernican estimate seriously since it assumes that we are not particularly lucky or unlucky in our location in time, and a wise policy should aim to protect us even against some bad luck. With such a short past track record of funding, it would be a mistake to count on much longer and better funding in the future.
This application of the Copernican Principle goes against my deepest presumptions, which is why I appreciate the intellectual gauntlet it hurls down. Because what Gott is sketching is a by no means impossible future, one in which the real question becomes how we can best use the technologies we have today and will have in the very near future to ensure species survival. Gott’s answer is that within the first half of this century or so, we will have the capability of planting a self-sustaining colony on Mars, making us a two-planet species and thus better protected against global disaster of whatever sort. We will have created an insurance policy for all humanity.
Let’s act, in other words, as if we don’t have the luxury of an unbroken line of gradual development, because an end to the space program some time in the 21st Century might mark the end of any chance we have to get into the Solar System, much less to the stars. Skip the return to the Moon, a hostile environment not conducive to colonization, and go for the one best chance for extending the species, a planet with water, reasonable gravity and the resources needed to get an underground base off to a survivable start. The real space race? The race to get a colony planted in the most likely spot before all funding for human spaceflight ends.
Gott is reminded of the library of Alexandria, a laudable effort to collect human knowledge but one that eventually burned, taking most (but thankfully not all) of Sophocles’ plays with it. Here he’s thinking of the surviving seven Sophoclean plays and weighing them against the 120 that the dramatist wrote, by way of making the case for off-world colonies as soon as possible:
We should be planting colonies off the Earth now as a life insurance policy against whatever unexpected catastrophes may await us on the Earth. Of course, we should still be doing everything possible to protect our environment and safeguard our prospects on the Earth. But chaos theory tells us that we may well be unable to predict the specific cause of our demise as a species. By definition, whatever causes us to go extinct will be something the likes of which we have not experienced so far. We simply may not be smart enough to know how best to spend our money on Earth to insure the greatest chance of survival here. Spending money planting colonies in space simply gives us more chances–like storing some of Sophocles’ plays away from the Alexandrian library.
As I said, this is bracing stuff (and thanks to Larry Klaes for the pointer). Gott is not the only one wondering whether there is a brief window that will allow us to move into the Solar System and then close, but he is becoming one of the more visible proponents of this view. The motto of the Tau Zero Foundation — ad astra incrementis — assumes a step-by-step process over what may be centuries to develop the technologies for travel to other stars. But Gott’s point is emphatic and much more urgent: For incremental development in space to occur, we should multiply the civilizations that can achieve it, spinning off colonies that back up what we have learned against future catastrophe.
That’s a job not for the distant future but for the next 4-5 decades. Gott reckons that if we put up into low Earth orbit as much tonnage in the next 48 years as we have in the last 48 years (in Saturn V and Shuttle launches alone) we could deliver 2,304 tons to the surface of Mars. And while he talks about heavy lift vehicles like the Ares V, we also have commercial companies like SpaceX with its Falcon Heavy concept and the continuing efforts of Robert Zubrin’s Mars Society to make something like this happen even absent massive government intervention.
Will the first interstellar mission be assembled not by an Earth team but by the scientists and engineers of a colony world we have yet to populate? There is no way to tell, but a Mars colony of the kind Gott advocates would give us at least one alternative to a future Earth with no viable space program and no prospects for energizing the species through an expansive wave of exploration. One colony can plant another, multiplying the hope not only of survival but renaissance. But all of it depends upon getting through a narrow temporal window that even now may be closing.
by Paul Gilster | May 8, 2012 | Outer Solar System |
Mars has always been a tempting destination because of the possibility of life. Thus the fascination of Schiaparelli’s ‘canals,’ and Percival Lowell’s fixation on chimerical lines in the sand. But look what’s happened to the question of life elsewhere in the Solar System. We’ve gone from invaders from Mars and a possibly tropical Venus — wonderful venues for early science fiction — to a vastly expanded arena where, if we don’t expect to find creatures even vaguely like ourselves, we still might encounter bacterial life in the most extreme environments.
Astrobiology will push exploration. This is not to say that objects in deep space aren’t worth studying in their own right, possible life or not, but merely to acknowledge that if we find life on another world, it deepens our view of the cosmos and fuels the exploratory imperative. A ‘second genesis’ off the Earth, once confirmed, would heighten interest in other targets where microbial life might take hold, from the cloud tops of Venus out to the icy moons of Jupiter and Saturn. We can’t completely discount even the remote Kuiper Belt in terms of dwarf planets and their possible internal oceans.
Jupiter’s Intriguing Moons
The latest mission news from the European Space Agency makes the point as well as anything. The Jupiter Icy Moons Explorer (JUICE) mission, recently approved as part of the agency’s Cosmic Vision 2015-2025 program, takes us from French Guiana aboard an Ariane 5 to Europa, Ganymede and Callisto, all three candidates for internal oceans. It’s no surprise that the major themes of Cosmic Vision at play here are the conditions for planet formation and the emergence of life.
2022 is the scheduled launch date, with arrival in Jupiter space in 2030, after which the spacecraft will spend three years studying these interesting worlds and reporting back to Earth. The Guardian quotes Leigh Fletcher (Oxford University) in this recent article:
“Scientists have had a lot of success detecting the giant planets orbiting distant stars, but the really exciting prospect may be the existence of potentially habitable ‘waterworlds’ that could be a lot like Ganymede or Europa.
“One of the main aims of the mission is to try to understand whether a ‘waterworld’ such as Ganymede might be the sort of environment that could harbour life.”
The notion of a habitable zone — habitable for human beings — gives way to the much broader ‘life zone’ where some form of life might emerge, and Jupiter offers an extremely useful environment in which to probe it. How does Ganymede’s magnetic field, for example, protect it from the hostile radiation belts spawned by the solar wind interacting with Jupiter’s huge magnetosphere and Io’s plasma? How do Europa and Callisto compare to what we’ll find on Ganymede, and which of the three is most likely to offer conditions in which life might prosper?
Assessing the Radiation Risk
The JUICE mission will make flybys of Callisto and Europa in search of answers, making the first measurements of the thickness of Europa’s crust. It will then enter into orbit around Ganymede in 2032 to study both the surface and internal structure of the moon, the only one in the Solar System known to generate its own magnetic field. You can find ESA’s matrix of science objectives here. Following its selection, the mission now enters a definition phase lasting 24 months. As you might guess, radiation is a major concern, with a late 2011 technical report noting that a shielding analysis should be carried out as soon as possible and a major effort put into shielding simulations to clarify the impact radiation protection will have on payload:
Since 2008 a development was conducted which re-analysed all available in situ measurement data from all missions that visited the Jupiter system (gravity assist and the mission that orbited Jupiter, Galileo), but using primarily Galileo data. The locations of these measurements were first mapped into the Jupiter magnetic field and then parameterised This so called JOREM model was just concluded and validated… at the beginning of the Reformulation Study and was therefore taken as the new baseline. The mean level prediction of the environment by JOREM is higher than the previously used model by about a factor of 2. Furthermore Europa flybys were added to the mission profile, increasing the total dose by about 25%. In comparison, the Callisto phase is only contributing about 9% to the total dose.
Image: Electrodynamic interactions play a variety of roles in the Jupiter system: generation of plasma at the Io torus, magnetosphere/satellite interactions, dynamics of a giant plasma disc coupled to Jupiter’s rotation by the auroral current system, generation of Jupiter’s intense radiation belts. Credit: ESA.
The effects of intense radiation on glasses, fibre optics and other optical and electro-optical components all come into play here, just as they do in the astrobiological questions that go beyond the issue of building the spacecraft. The interaction between the Galilean moons and Jupiter itself through gravitational and electromagnetic forces will be illuminating as we look at the question of possible life in these ‘water worlds.’ From the ‘Yellow Book’ report on JUICE, which contains the results of ESA’s assessment study of the mission:
…organic matter and other surface compounds will experience a different radiation environment at Europa than at Ganymede (due to the difference in radial distance from Jupiter) and thus may suffer different alteration processes, influencing their detection on the surface. Deep aqueous environments are protected by the icy crusts from the strong radiation that dominates the surfaces of the icy satellites. Since radiation is more intense closer to Jupiter, at Europa’s surface, radiation is a handicap for habitability, and it produces alteration of the materials once they are exposed…
That difference will be useful as we compare and contrast the three moons for potential astrobiology. And the differences affect the instruments needed to do the job:
The effect of radiation on the stability of surface organics and minerals at Europa is poorly understood. Therefore, JUICE instrumentation will target the environmental properties of the younger terrains in the active regions where materials could have preserved their original characteristics. Measurements from terrains on both Europa and Ganymede will allow a comparison of different radiation doses and terrain ages from similar materials. The positive side of radiation is the generation of oxidants that may raise the potential for habitability and astrobiology. Surface oxidants could be diffused into the interior, and provide another type of chemical energy…
I’ve focused on radiation here as simply one of the major issues that makes Jupiter such an interesting target when we’re looking at astrobiological possibilities. The Yellow Book report says the Galilean satellites “…provide a conceptual basis within which new theories for understanding habitability can be constructed.” Voyager and Galileo have given us enough of a look at these worlds to know how much we will benefit from an orbiter around Ganymede, even if a far more radiation-hardened Europa orbiter isn’t yet in the cards. But we do get the Callisto and Europa flybys with JUICE, and the path ahead is clearly defined as we try to set needed constraints on the emergence of life on icy satellites in our own Solar System and around other stars.
by Paul Gilster | May 7, 2012 | Deep Sky Astronomy & Telescopes |
Can we tell something about the planets around another star by examining that star’s atmosphere? A new study out of the University of Warwick makes a strong case for the method in the study of white dwarfs, following up on a landmark 2007 paper by Benjamin Zuckerman (UCLA) that looked at pollution in white dwarf photospheres. ‘Pollution’ as in metals that shouldn’t be there, which suggests an accretion disk of material feeding the star, which itself would have collapsed from a red giant stage and is perhaps now absorbing planetary material around it.
What we would expect to find in the atmosphere of a white dwarf is little more than hydrogen and helium — heavy elements should quickly sink to the core and not be observable. But white dwarfs with metal-contamination in their atmospheres have been observed for almost a century now. Let me Boris Gänsicke and colleagues on this, from the paper on the University of Warwick work (internal references deleted for brevity):
…the rapidly growing number of white dwarfs that are accreting from circumstellar discs… unambiguously demonstrates that debris from the tidal disruption of main-belt analogue asteroids or minor planets… or Kuiper-belt like objects…, likely perturbed by unseen planets…, is the most likely origin of photospheric metals in many, if not most polluted white dwarfs.
In a study of more than 80 white dwarfs using the Cosmic Origin Spectrograph on the Hubble Space Telescope, the researchers found four that showed not only oxygen, magnesium, iron and silicon, but a small amount of carbon in their photospheres, closely matching the composition of rocky planets, including the Earth, that orbit close to our Sun. The evidence is that all four stars once had at least one rocky planet orbiting them which has now been destroyed. And because heavy elements like these would be pulled into the core in short order, the researchers believe they are observing the final phase of the destruction of these worlds, an inflow of material falling into the stars at a rate of up to 1 million kilograms every second.
Image: A white dwarf sits in the centre of the remnant of a planetary system. Asteroid sized debris is scattered inwards by interaction with the remaining planets and is tidally disrupted as it approaches the white dwarf forming a disc of dust some of which is raining down onto the star. The researchers have found that the composition of the debris that has just fallen onto the four white dwarfs matches the composition of Earth-like rocky worlds. Credit: Mark A. Garlick.
The white dwarf PG0843+516 turns out to be particularly interesting because of the amount of iron, nickel and sulphur in its atmosphere — the study refers to it as ‘extremely polluted’ — strongly suggesting the star is swallowing the core of a rocky planet that had undergone the same kind of differentiation that occurred in the Earth. Gänsicke sees this as a glimpse of the processes that will one day play out long after our Sun has left its red giant phase:
“What we are seeing today in these white dwarfs several hundred light years away could well be a snapshot of the very distant future of the Earth. As stars like our Sun reach the end of their life, they expand to become red giants when the nuclear fuel in their cores is depleted. When this happens in our own solar system, billions of years from now, the Sun will engulf the inner planets Mercury and Venus. It’s unclear whether the Earth will also be swallowed up by the Sun in its red giant phase – but even if it survives, its surface will be roasted.”
Not a pretty picture, but the rest of the Solar System will be likewise disrupted:
“During the transformation of the Sun into a white dwarf, it will lose a large amount of mass, and all the planets will move further out. This may destabilise the orbits and lead to collisions between planetary bodies as happened in the unstable early days of our solar system. This may even shatter entire terrestrial planets, forming large amounts of asteroids, some of which will have chemical compositions similar to those of the planetary core. In our solar system, Jupiter will survive the late evolution of the Sun unscathed, and scatter asteroids, new or old, towards the white dwarf. It is entirely feasible that in PG0843+516 we see the accretion of such fragments made from the core material of what was once a terrestrial exoplanet.”
All of the more than 80 white dwarfs in the study are within several hundred light years of Earth, offering us a glimpse into deep time, a reminder that our own system formed long after many nearby stars were fully mature and doubtless orbited by planets of their own. The paper is Gänsicke et al., “The chemical diversity of exo-terrestrial planetary debris around white dwarfs,” accepted for publication in the Monthly Notices of the Royal Astronomical Society (preprint). The Zuckerman paper cited above is “Externally Polluted White Dwarfs with Dust Disks,” Astrophysical Journal 663 (2007), p. 1285 (preprint). A University of Warwick news release is also available.
by Paul Gilster | May 4, 2012 | Deep Sky Astronomy & Telescopes |
Having just re-read Arthur C. Clarke’s The City and the Stars for the first time in a couple of decades, I’ve been preoccupied by the idea of ‘deep time,’ and astronomical events that play out over billions of years. The fictional trick, of course, is to pair human observation with events that take aeons to unfold. In Clarke’s novel, the city of Diaspar is a place that is almost outside of time, a self-contained and beautiful place whose very inwardness ultimately becomes stultifying. But the vision of this glowing jewel of a city surviving amidst the dunes of an ancient Earth is one of those science fiction images that stick with you over a lifetime of reading.
New work out of Vanderbilt University now suggests other deep time images, but they’re likely to be more fantasy than science fiction. Imagine a star moving fast enough to escape the galaxy, living out its life on a long trajectory that will take it into intergalactic space. Kelly Holley-Bockelmann and Lauren Palladino think they can identify more than 675 stars moving out of the Milky Way that have been ejected from the galactic core, red giants with high metallicity — a large proportion of chemical elements other than hydrogen and helium — that are presumably the result of close encounters with the supermassive black hole at the center of the galaxy.
Moving at something like 900 kilometers per second, a hypervelocity star of the kind catalogued by Holley-Bockelmann and Palladino takes roughly 10 million years to travel from the galactic hub to the outer edge of the spiral. Pushing out into the intergalactic dark, it would go through normal stellar evolution that takes it to the red giant stage, having begun as a small star relatively like our Sun. So could planets exist around such a star? If so, any civilization that might emerge on them would play out its lifetime well beyond the vast city of stars that is the Milky Way.
Image: A supermassive black hole at galactic center may be responsible for hypervelocity stars that are leaving the galaxy at high speeds. Credit: NASA/JPL.
That would make for some interesting tales, and science fiction stories like Poul Anderson’s World Without Stars (1966) explore the experience of extraterrestrials living in a system outside the galaxy. But planets would be seriously problematic among hypervelocity stars, given that the scenario under investigation involves a young binary system that wanders too close to the four-million solar mass black hole at the hub. While one star spirals in toward the black hole, the other would be flung outward, presumably disrupting any nascent planetary system around it.
Another mechanism involves a single star making too close a pass when the central black hole is ingesting a smaller black hole. Both situations produce the hypervelocity kick that propels a star out of its galaxy. That’s quite a lot to ask for the stability of any planetary system.
Working with Sloan Digital Sky Survey data, the Vanderbilt work probes these mechanisms, beginning with what has been called a ‘field of streams’ that extends out to about 100 kiloparsecs from the Milky Way. A similar stream extends outward from M31, the Andromeda Galaxy. Given that our two galaxies are not (yet) interacting, the black hole scenarios make a better explanation for these streams of stars than interactions between galaxies. To become intergalactic wanderers, stars must exceed the Milky Way’s escape velocity, now pegged at somewhere between 500 and 600 kilometers per second. So we have a mixture of bound stars on highly eccentric orbits and hypervelocity stars that are escaping from the galaxy altogether.
Stars on their way out of the Milky Way should show a definite signature. From the paper:
It is useful to compare this to theoretical predictions of stellar ejections from the Milky Way (Kollmeier et al. 2009). Stars ejected from the galaxy center through three-body interactions with a SMBH [supermassive black hole] will typically have much higher metallicity than stars that were stripped from satellite galaxies originating in the outskirts of a galaxy halo…
Or as Holley-Bockelmann puts it in this Vanderbilt news release:
“These stars really stand out. They are red giant stars with high metallicity which gives them an unusual color.”
Usefully, stars between galaxies may offer up insights into the history and evolution of galaxy clusters, but followup observations are needed to weed out any candidates that are actually much closer brown dwarfs rather than hypervelocity red giants. As to my musings about planetary systems around hypervelocity stars, they’re likely to be little more than that, because how a planetary system could stay gravitationally bound to a star that has had a violent encounter with a black hole remains a mystery — most likely any previously existing planets would be torn away to become lone wanderers themselves. But if anyone has seen any work on planetary survival in these scenarios, please let me know. It seems a wild stretch.
The paper is Palladino et al., “Identifying High Metallicity M Giants at Intragroup Distances with SDSS,” accepted for publication in The Astronomical Journal Vol. 143, No. 6 (May, 2012), p. 128 (abstract / preprint). Another science fictional treatment of stars outside galaxies is Iain Banks’ Against a Dark Background (1993), which is finally nearing the top of my reading stack.
by Paul Gilster | May 3, 2012 | Asteroid and Comet Deflection |
One of the topics receiving fairly little coverage in the excitement of the Planetary Resources announcement is asteroid deflection. It seems clear that learning how to reach an asteroid and extract everything from water to platinum-group metals from it will also teach us strategies for changing an asteroid’s trajectory, in the event we find one likely to hit the Earth. The recent report from the Keck Institute of Space Studies makes this point clearly in the context of its own mission study, a plan to retrieve a small (7 m) asteroid and park it in lunar orbit.
What Asteroid Operations Can Teach Us
Although Planetary Resources estimates there are more than 1500 asteroids that are as easy to get to as the Moon, we still have a long way to go in understanding basic facts about these objects and their composition. Take dust, which will probably vary from object to object, but which could cause problems for ‘gravity tractor’ concepts where a spacecraft is used to deflect an asteroid without physically contacting it. If the rendezvous with the asteroid can be managed far enough from Earth, the gravitational field of a nearby orbiting body as tiny as a spacecraft can, over a period of years or even decades, bring about the needed course change.
But assuming your vehicle works with the kind of solar electric propulsion envisioned by the Keck study, dust could be a factor if the engine exhaust reaches the asteroid as part of needed station-keeping (this is perhaps an argument for solar sail technologies in these scenarios). What seems to be a small issue becomes a big unknown when you think about the multi-year presence of a gravity tractor spacecraft around such an asteroid. Direct study, as via Planetary Resources robotic technologies or manned crews examining a captured asteroid in lunar orbit, should help us learn more about how dust is moved and settles on an asteroid surface.
Other factors listed by the Keck report:
Anchoring: We need to acquire the ability to land a robotic spacecraft on an asteroid and anchor it there, a challenge any mining venture will have to resolve.
Structural characterization: This is a big one. We need to understand an asteroid from the inside out, since a prime deflection method is to hit the asteroid with enough of a blow to change its course. But we know little about what happens to an asteroid when this occurs because ejecta from the impact could multiply the momentum given to the NEA by the impactor.
Proximity operations: How do we dock with the asteroid and navigate near it? We’ll learn many of these things through actual robotic asteroid operations, and as we saw last time, having a small asteroid available for examination in lunar orbit would far surpass the 60 grams of surface material we’re going to have returned from the upcoming OSIRIS-REx mission.
These are all technical matters, but it goes without saying that a successful asteroid retrieval of the kind Keck envisions would also draw public attention to the asteroid defense element of all our studies of near-Earth objects. And in addition to its uses in providing unique, space-based resources for radiation shielding and propellant extraction, an asteroid retrieval would offer up some of the options we may someday want to use in space elevators. Says the report:
One day, in the more distant future, it is possible that a small NEA (~10 m) returned to E-M L2/L1 could act as an orbiting platform/counter weight for a lunar space elevator to allow routine access to and from the lunar surface and also function as a space resource processing facility for mining significant quantities of materials for future human space exploration and settlement and possible return and inclusion in terrestrial markets.
Eye on an Exoplanet
The asteroid mining and retrieval idea seems so loaded with possibilities that the Keck Institute’s 51 page report can barely contain them all, but I want to close with the idea NextBigFuture has been discussing recently. Planetary Resources makes a point about the Arkyd Series 100 space telescopes it intends to begin launching as soon as 24 months from now. These are intended to begin with studies in low Earth orbit but the Arkyd Series 200 that follows would contain a propulsion system so that missions directly to new asteroid targets will become possible.
We get the same kind of look at an asteroid, says Planetary Resources, as we got when exploring the Moon with the Ranger missions (1961-65) or the Deep Impact mission at Comet 9P/Tempel in 2005. The name of the game is data acquisition as we try to decide which near-Earth asteroids are the best candidates for future operations. NextBigFuture took a look at all those telescopes — Planetary Resources describes them as “the first private space telescope… simple enough to be designed, manufactured, tested and integrated by a small team, yet robust enough to get the job done.” Could they be massed for deep space studies?
The principle is interferometry, which would allow the creation of huge telescopes, mixing signals from a cluster of small instruments to achieve high-resolutions unavailable from a single, monolithic lens. The idea has been thoroughly vetted, and with great success, with Earth-bound instruments, but French astronomer Antoine Émile Henry Labeyrie (Collège de France) has been studying what he calls a ‘hypertelescope,’ which would involve huge numbers of free-flying spacecraft combining their data to produce images that could show surface detail on exoplanets.
Labeyrie’s presentation on the topic at a European Space Agency meeting in 2009 describes a “laser-driven hypertelescope flotilla at L2” that could image continents and oceans on a world 10 light years away. These would be telescopes whose mirrors were placed kilometers apart, each of them small instruments but forming what he has called a ‘sparse giant mirror.’ Here’s the image from Labeyrie’s talk that NextBigFuture also ran. Note the resolution shown for Earth at the 10 light year distance, and the swarm of spacecraft that have been used to produce it.
In a 1996 paper, Labeyrie had this to say about interferometry and exoplanets:
As the technical difficulties will become mastered, a continuous evolution towards larger sizes is to be expected. Jupiter-like planets at 5 pc can be imaged from Earth with 10 km arrays, while Earth-like planets at 5 pc require 100 km arrays, preferably installed in space. Because such images can also yield spectra for each of their resolved elements, they should provide a better diagnostic for the presence of life, and possibly civilisation, than would spectra of unresolved planets. Other objects such as pulsars, galactic nuclei and QSOs [quasi-stellar objects] are also candidates for high resolution imaging.
Labeyrie went on to develop the concept he calls Exo-Earth Imager, one that made an appearance in New Scientist in 2006 in an article by Govert Schilling:
Labeyrie’s design for a hypertelescope takes dilute optics to the extreme. Ultimately his Exo-Earth Imager will consist of at least 150 mirror elements, each measuring 3 metres across, and spread out over an area of about 8000 square kilometres. Together, they would fly in formation around the sun to make a hypertelescope with a diameter of 100 kilometres – large enough to pick out clouds and continents on a distant relative of our home planet.
Whether or not Planetary Resources would eventually wind up creating a hypertelescope flotilla anything like this as an offshoot of its asteroid mining effort remains to be seen, but what is exciting here is the prospect of lower-cost space telescopes whose very presence may spur refinements in interferometric techniques. The same network could boost the effort to exploit sunshade concepts, in which the light of the central star is effectively nulled and the faint light of exoplanets made visible. All in all, an effort to reach and take advantage of asteroid resources could have large ramifications indeed, not all of them confined to our own Solar System.
Two papers by Antoine Labeyrie are relevant here. They are “Resolved imaging of extra-solar planets with future 10-100km optical interferometric arrays,” Astronomy and Astrophysics Supplement, v.118 (1996) p.517-524 (abstract) and “Snapshots of Alien Worlds: The Future of Interferometry,” Science 285 (1999), pp. 1864-65 (abstract). The Schilling article is “The hypertelescope: a zoom with a view,” New Scientist 23 February 2006.
