Paul Gilster's Blog, page 246

Space Exploration: A Closing Window?

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.

Jupiter Icy Moons Explorer

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.

Planetary Annihilation around White Dwarfs

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.

Rogue Stars Leaving the Galaxy

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.

The Asteroid and the Telescope

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.

Bringing an Asteroid to Lunar Orbit

Long before Planetary Resources was a gleam in the eye of its founders, John Lewis (University of Arizona) wrote a book that put asteroid mining into the public consciousness. Mining the Sky: Untold Riches from the Asteroids, Comets and Planets (Perseus Books, 1996) contains no shortage of wonders, as in the well publicized idea that a single one-kilometer asteroid could produce enough gold and silver to equal world production for a century. David Brin writes about this on George Dvorsky’s Sentient Developments site, noting that while that would produce a collapse in gold and silver prices, it would also produce incalculable benefits in terms of raw materials production that could change the economic paradigm entirely.

Lewis is a natural fit with Planetary Resources, the highly buzzed-about startup that plans to make asteroid mining a reality, and it’s no surprise to see that he serves as one of its advisors. But remembering Mining the Sky, I was startled to discover that the idea of using asteroid resources goes all the way back to Konstantin Tsiolkovskii, who wrote about it in The Exploration of Cosmic Space by Means of Reaction Motors in 1903 — it was in this same work that the Russian rocket scientist and visionary first proposed multistage rockets using liquid hydrogen and liquid oxygen for space exploration. It seems fitting that there is an asteroid with a Tsiolkovskii connection, the object 1590 Tsiolkovskaja being named for his wife.

Image: An artist’s concept of a fragmented asteroid laden with resources. Image: NASA/JPL-Caltech/Handout , Reuters files.

A New Study on Asteroid Retrieval

Caltech’s Keck Institute for Space Studies has examined asteroid possibilities in the just released Asteroid Retrieval Feasibility Study, whose April 12 appearance was timed to perfection by the powers behind Planetary Resources. What the Keck study is interested in is returning an object not to low-Earth orbit but a high lunar orbit, allowing the project to be conducted with far more relaxed propulsion constraints than would be applied deep in Earth’s gravity well. A corollary to this is the fact that larger asteroids can be captured. The study authors settled on an asteroid 7 meters in diameter with a mass on the order of 500,000 kg. This was a 6-month study enlisting a wide range of space-minded talent (see the contributor list on p. 6 of the report).

The Keck report meshes with NASA’s current goals of sending a manned expedition to a near-Earth asteroid halfway into the next decade, though given the mutable nature of NASA’s funding, that’s the least of the reasons to make this happen. Even so, an asteroid retrieval has definite consequences for manned flight. What Keck has in mind is robotic, unmanned missions that culminate in a scout mission, also robotic, to enable detailed mission planning. The full retrieval mission is seen as a precursor to subsequent human missions to this and other NEAs. An NEA in high-lunar orbit then becomes an obvious and accessible target for astronaut visitation.

Again, no astronauts on the retrieval mission, which is robotic. But:

Taken together, these attributes of an ACR [Asteroid Capture and Return] mission would endow NASA (and its partners) with a new demonstrated capability in deep space that hasn’t been seen since Apollo. Once astronaut visits to the captured object begin, NASA would be putting human explorers in contact with an ancient, scientifically intriguing, and economically valuable body beyond the Moon, an achievement that would compare very favorably to any attempts to repeat the Apollo lunar landings.

Reasons for Snatching an Asteroid

Why retrieve an asteroid in the first place? Here’s a distilled rational from the executive summary, one that begins with a focus on the effect of spurring manned spaceflight:

It would provide a high-value target in cislunar space that would require a human presence to take full advantage of this new resource. It would offer an affordable path to providing operational experience with astronauts working around and with a NEA that could feed forward to much longer duration human missions to larger NEAs in deep space. It would provide an affordable path to meeting the nation’s goal of sending astronauts to a near-Earth object by 2025. It represents a new synergy between robotic and human missions in which robotic spacecraft retrieve significant quantities of valuable resources for exploitation by astronaut crews to enable human exploration farther out into the solar system.

All true, of course, but it’s only after this spadework has been done that the report turns to what has electrified the space community about Planetary Resources and its own asteroid plans, and it’s nothing like an Apollo-style effort to get people to particular destinations. The goal is broader and much longer-lasting. Once we have an asteroid, either by traveling to it or by inducing it into a lunar orbit for further exploitation, we have the ability to extract materials from it. All this gets into the real infrastructure-building components of asteroid mining:

…water or other material extracted from a returned, volatile-rich NEA could be used to provide affordable shielding against galactic cosmic rays. The extracted water could also be used for propellant to transport the shielded habitat. These activities could jump-start an entire in situ resource utilization (ISRU) industry. The availability of a multi-hundred-ton asteroid in lunar orbit could also stimulate the expansion of international cooperation in space as agencies work together to determine how to sample and process this raw material. The capture, transportation, examination, and dissection of an entire NEA would provide valuable information for planetary defense activities that may someday have to deflect a much larger near-Earth object. Finally, placing a NEA in lunar orbit would provide a new capability for human exploration not seen since Apollo.

Aspects of the Retrieval Mission

Two aspects of the asteroid retrieval campaign are immediately obvious. Before retrieving anything, we need an extended effort to identify objects that fit the bill physically and offer up orbital parameters that would make them good candidates for the return mission. We also need a transportation method, and here what the Keck study advocates is a ~40-kW solar electric propulsion system with a specific impulse of 3,000 seconds. It’s interesting to see by the report’s figures that, given a single launch to low-Earth orbit aboard an Atlas V-class vehicle, the ultimate plan would be to retrieve 28 times the mass launched to LEO and bring it into high lunar orbit.

The mission plan is fascinating and fodder for science fiction writers. The solar electric propulsion system would be used to spiral the vehicle into high-Earth orbit and a lunar gravity assist would then put the vehicle on a trajectory to the NEA. The report allocates 90 days for studying the NEA and capturing and ‘de-tumbling’ the asteroid, transporting it back to the Earth-Moon system for a second lunar gravity assist that would be used to capture it. Transfer to a stable high lunar orbit would take place about 4.5 months after the first gravity assist.

All of this presupposes mechanisms for stabilizing and moving the asteroid, which the report says could be done with a high-strength bag assembly, deployable and inflatable arms and cinching cables, the bag being 10 meters by 15-meters in diameter looking like this:

Image: The capture mechanism deployed and in operation. Credit: Rick Sternbach/KISS.

But before any such mission can be flown, we also need improved ways of studying potential targets. Planetary Resources has the idea of launching inexpensive telescopes that could sample a wide variety of NEAs, while the Keck report notes the value of the solar electric propulsion system for sending multiple-target robotic precursors that would precede any human missions. As opposed to the upcoming (2016) OSIRIS REx mission, which will return 60 grams of surface material, a robotic precursor like this would be used to bring back large boulders and regolith samples from any human targets prior to sending manned crews there.

The report’s focus on resource acquisition in space is heartening. Check this:

The asteroidal material delivered to cislunar space could be used to provide radiation shielding for future deep space missions and also validate in-situ resource utilization (ISRU) processes (water extraction, propellant production, etc.) that could significantly reduce the mass and propulsion requirements for a human mission. The introduction of ISRU into human mission designs could be extremely beneficial, but until the processing and storage techniques have been sufficiently tested in a relevant environment it is difficult to baseline the use of ISRU into the human mission architecture. Bringing back large quantities of asteroid materials to an advantageous location would make validation of an ISRU system significantly easier.

Well said — the whole notion of in situ acquisition and utilization is critical as we look toward building a true human future in space. Part of the Planetary Resources plan is to extract water from asteroids not only for human needs (much better than launching from deep within the gravity well) but also for the creation of rocket fuel. The report’s emphasis on the need to bring back asteroid materials to study the prospects in detail is wise, because we need to learn how effectively we can go about extracting these materials and turning them around for space use.

But there are other areas where moving into the asteroids, first with robots and then human crews, makes abundant sense. Tomorrow I want to examine asteroid deflection as one major area that will benefit from these activities, and we’ll also look at the ramifications of all those telescopes Planetary Resources plans to put into space. We may only be scratching the surface of how useful our future ability to move tools and crews to asteroids — or to move asteroids themselves — may turn out to be in building the next phase of human civilization.

Advent of the ‘Belters’

On the Trail of the Space Pirates was a 1953 adventure written by Carey Rockwell, a house pseudonym used by a Grosset & Dunlop writer who may or may not have been one Joseph Greene, an editor for the firm in that era. We don’t know for sure who ‘Carey Rockwell’ was and no one has come forward to claim the title, but see the Tom Corbett Space Cadet website for another possible clue to authorship. In any case, On the Trail of the Space Pirates took readers such as my grade school self out into the asteroid belt, where all manner of adventures occur and uranium prospectors ply their trade harassed by evil doers. The asteroids became a lively analogue to the American wild west.

Asteroid mining and the culture it spawns has a robust history in science fiction, but I couldn’t help recalling this particular book when I read about Planetary Resources and its ambitious plan to mine asteroids. The company’s intentions don’t extend all the way to the main belt, but focus on asteroids much closer to home, of which there are plenty, and out of which some 1500 may prove to be of high interest if mining is the intention. What caught me up in the spirit of the science fictional ‘belters’ was this pitch on the Planetary Resources website encouraging people to work for the company. It’s titled ‘We’re looking for a few good asteroid miners’:

1. We are finding a new way to explore space beyond Earth orbit.

2. We are a growing business with incredible people who are dedicated to Planetary Resources’ long-term objectives.

3. Like all small businesses, we are a family. We love our team and what we do.

4. You will get your hands dirty. If you prefer your hands clean, go somewhere else.

5. We have a grill. We are not afraid to use it.

6. Seattle, Washington. Ok, so it rains. It’s gorgeous, and anyone who says otherwise is from California.

7. Bottom line – we build spaceships and explore asteroids. If you need any other motivation to apply, don’t bother.

The brash spirit of those comments is a nice tonic in an era when government space programs seem rudderless and strapped for cash. Whether Planetary Resources can deliver on its promise to study and then mine iron, nickel, gold, platinum and water resources on nearby chunks of rock remains to be seen, though the list of backers — Ross Perot Jr., son of the former presidential candidate, Eric Schmidt and Larry Page of Google, movie mogul James Cameron, X Prize founder Peter Diamandis — offers hope and plenty of cash. And let’s not forget Eric Anderson (Space Adventures) and the well-traveled Charles Simonyi, who is unusual among space tourists in having made not one but two flights to the International Space Station.

This is a genuinely exciting startup that is going to teach us a lot about how fast and how soon we can develop resources in nearby space that can help us go much further afield. In Centauri Dreams terms, I always think about building the needed infrastructure in the Solar System that can one day support an interstellar effort. Extracting water that does not need to be boosted into Earth orbit and creating rocket fuel from space resources to supply future missions fits that bill, as does the hope that enough money can be turned from the extraction of precious metals to make the venture self-sustaining and prosperous. Good fortune to Planetary Resources!

The context in which this new company moves is suggested by a recent report from Caltech’s Keck Institute for Space Studies which was released in early April, and which was invariably mentioned in news reports in tandem with the Space Resources news conference on the 24th. I want to start digging into this report in the next day or two because although it focuses specifically on retrieving an asteroid, it has obvious implications not only in terms of how we might exploit its resources but learn to manipulate its trajectory. All that, of course, takes us into the realm of asteroid threat mitigation. If we one day find an asteroid that is moving on a dangerous trajectory, will we have the time and the know-how to actually do something about it?

Here it’s worth noting that the Apollo missions were able to return 382 kilograms of lunar materials over the course of their six lander missions, while NASA’s OSIRIS-REx mission is slated to retrieve about 60 grams from the asteroid known as 1999 RQ36, which orbits the Sun every 1.2 years and crosses the Earth’s orbit every September. 60 grams isn’t much, but neither is the Apollo sample return when compared to the ~500,000 kilograms of asteroid material the Keck Institute study talks about, an entire asteroid delivered to high lunar orbit by around 2025.

Can it be done? Even more significantly, can it be done without endangering the home planet? I’ll be looking further into the report tomorrow. Meanwhile, have a look at Alan Boyle’s excellent discussion of Planetary Resources’ prospects and the problems they’ll encounter along the way. And check NextBigFuture’s challenging look at a different way to use those small, inexpensive telescopes Planetary Resources intends to put into space as part of the infrastructure for studying asteroid targets. They could conceivably be used as the basis for a ‘hypertelescope,’ an interferometer with a 16,000 kilometer baseline. The possibilities for a close-up look at an exoplanet are intriguing, to say the least, and we’ll discuss them further in coming days.

I’ve believed for a long time that planetary defense demanded we develop the technologies that would get us into the outer Solar System, and we may be seeing the first steps in that process now. The painstaking study of nearby asteroids that the Planetary Resources concept will demand should pay dividends if we ever have to move one not just for resources but for safety.

Lasers: Protecting the Starship

Interesting new ideas about asteroid deflection are coming out of the University of Strathclyde (Glasgow), involving the use of lasers in coordinated satellite swarms to change an asteroid's trajectory. This is useful work in its own right, but I also want to mention it in terms of a broader topic we often return to: How to deal with the harmful effects of dust and interstellar gas on a fast-moving starship. That's a discussion that has played out many a time over the past eight years in these pages, but it's as lively a topic as ever, and one on which we're going to need a lot more information before true interstellar missions can take place.

Lasers and the Asteroid

But let's set the stage at Strathclyde for a moment. The idea here is to send small satellites capable of formation flying with the asteroid, all of them firing their lasers at close range. The university's Massimiliano Vasile, who is leading this work, says that the challenge of lasers in space is to combine high power, high efficiency and high beam quality simultaneously. He adds:

"The additional problem with asteroid deflection is that when the laser begins to break down the surface of the object, the plume of gas and debris impinges the spacecraft and contaminates the laser. However, our laboratory tests have proven that the level of contamination is less than expected and the laser could continue to function for longer than anticipated."

Vasile believes using a flotilla of small but agile spacecraft, each with a highly efficient laser, is more feasible than trying to deflect an asteroid with a single, large spacecraft carrying a much larger laser. One benefit is that the system is scalable — add as many spacecraft as needed for the job at hand. The other is that you have the redundancy afforded by multiple laser platforms. The Strathclyde work is also investigating whether a similar system could be used to remove space debris by de-orbiting problematic objects to avoid potential collisions.

Erosion Shields on the Starship?

If lasers can be used to alter an asteroid's trajectory, we need to consider their uses in clearing out the space ahead of futuristic space probes. That the interstellar medium itself was going to be a problem became apparent as researchers began to study starship deceleration concepts in the early 1970s. Get your vehicle moving in the range of 0.3 c and any grain of carbonaceous dust a tenth of a micron in diameter it encounters carries a relative kinetic energy of 37,500,000 GeV, according to Dana Andrews (Andrews Space) in a 2004 paper. How that kinetic energy is dealt with is clearly a major issue.

By the late 1970s, aluminum and then graphite had been considered as possible erosion shields, with the preference going to graphite, but in 1978 Anthony Martin reviewed the literature and suggested a beryllium payload shield be deployed on the Project Daedalus probe, which would be moving at .12 c. It would be quite a large object, some 9 millimeters thick and 32 meters in radius, and even it didn't completely solve the problem, for Daedalus would, upon arrival, be moving into a still denser gas and dust environment around Barnard's Star. Daedalus designer Alan Bond suggested additional shielding in the form of a cloud of dust deployed from the probe, which would vaporize larger particles before they could damage the vehicle.

Image: Diagram of the Project Daedalus probe, developed by the British Interplanetary Society in the 1970s. Note the beryllium shield at upper left. Credit: Adrian Mann.

Clearing Out the Path

We're still not through, though. What about particles larger than dust grains, up to hailstones in size? We are now talking about collisions that would be catastrophic, and must turn from passive to active measures to tackle the problem. Gregory Matloff and Eugene Mallove have suggested using a light or X-ray laser or a neutral particle beam firing ahead of the ship to deflect any objects detected in its forward-pointing radar. The Project Icarus team has looked at creating a bumper out of graphene, as discussed in this blog entry, and coupling it with a laser defense:

What I'm interested in for shielding is making a large, low-mass "bumper" which cosmic sand-grains run into before hitting the craft. After passing through several layers of graphene the offending mass is totally ionized and forms a high-energy spray of particles, but particles that can now be deflected by the vehicle's cosmic-ray defences (akin to the mag-sail, but smaller with a higher current) and safely diverted away from sensitive parts.

The notion seems an adaptation of Conley Powell's 1975 work on shields that move ahead of the ship, trapping ionized material on impact within a magnetic field. The earlier Daedalus researchers found that Powell's ideas resulted in less erosion than other methods then being studied. This is an interesting shield, one placed perhaps 100 kilometers ahead of the spacecraft. Moreover, it is not passive but can signal the vehicle when grains have passed through it without being ionized:

This causes a signal to be sent back to the vehicle which then activates its final layer of defence, high-powered lasers. In microseconds the lasers either utterly ionize the target or give it a sideways nudge via ablation – blowing it violently to the side via a blast of plasma. Such an active tracking bumper would need to be further away than 100 km to give the laser defence time to react, though 1/600th of a second can be a lot of computer cycles for a fast artificial intelligence. The lasers might use advanced metamaterials to focus the beam onto a speck at ~100 km, without needing to physically turn the laser itself in such a split-second. Highly directional, high-powered microwave phased arrays exist which already do so purely electronically and an optical phased-array isn't a stretch beyond current technology.

All of which takes me back to the University of Strathclyde work on laser deflection, and makes me wonder whether laser technologies first deployed against asteroids in our Solar System may one day be used to protect our interstellar voyagers.

Anthony Martin's paper is "Bombardment by Interstellar Material and Its Effects on the Vehicle," Project Daedalus Final Report (Journal of the British Interplanetary Society, 1978): S116–S121. Alan Bond discusses in-system shielding in "Project Daedalus: Target System Encounter Protection," S123–S125 in the same publication. The Dana Andrews paper is "Things to Do While Coasting Through Interstellar Space," AIAA-2004-3706, 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit, Fort Lauderdale, Florida, July 11-14, 2004.

The Largest Solar System Yet

The Kepler mission's exoplanet discoveries have been so numerous that an extension of the mission seemed all but inevitable. At the same time, bureaucracies can be unpredictable, which is why it was such a relief to have the Senior Review of Operating Missions weighing in with an extension recommendation, one followed up by NASA with extensions not just for Kepler but also for the Spitzer telescope and the US portion of ESA's Planck mission. Kepler's extension runs through fiscal 2016 (subject to review in 2014), allowing for plenty of time to home in on Earth-sized planets in the habitable zone around stars like our Sun.

While Kepler's scheduled mission duration was 3.5 years, the mission was intended to be extendible to 6 years or more and this news is more than satisfying. But of course while we continue to monitor the Kepler work, we're following numerous other exoplanet stories including the European Southern Observatory's observations of the prolific star HD 10180, a Sun-like star about 127 light years away in the constellation of Hydrus. The ESO work, performed with the HARPS spectrograph attached to the 3.6 meter telescope at La Silla in the Chilean Andes back in 2010, revealed the presence of at least five and possibly seven planets. Now astronomer Mikko Tuomi (University of Hertfordshire) has performed further data analysis on the HARPS radial velocity data, concluding that the system may contain as many as nine planets.

Image: The circle shows the location of the class G near-solar star HD 10180, which may be orbited by as many as nine planets. Credit: Jim Kaler/UIUC.

The two new worlds Tuomi's work reveals range from 1.9 to 5.1 Earth masses respectively, allowing them to be classified as probable super-Earths with orbits of 10 and 68 days. If the findings are confirmed, this would make the HD 10180 system more fecund than our own, at least in terms of number of planets. Tuomi also reports he has verified the inner planet signature first announced in 2011, indicating a planet on a 1.18 day orbit with a minimum mass as low as 1.3 Earth masses. He has also revised the orbital parameters of the other six planet candidates around the star. Add it all up and you get nine planets. From the paper:

As noted by Lovis et al. (2011), the star is a very quiet one without clear activity-induced periodicities, which makes it unlikely that one or some of the periodic signals in the data were caused by stellar phenomena. Also, the periodicities we report, namely 9.66 and 67.6 days, do not coincide with any periodicities arising from the movement of the bodies in the Solar system. Therefore, we consider the interpretation of these two new signals of being of planetary origin to be the most credible explanation.

If this is borne out, then we have exceeded our Solar System's planet count for the first time in exoplanet studies. The paper notes the need for additional high-precision radial velocity studies to confirm these findings. And we may not be through. There appear to be stable orbits for a low-mass companion in or near the habitable zone of HD 10180, one whose mass would be unlikely to exceed 12.1 Earth masses based on Tuomi's samplings. All that should keep this star among our targets for some time to come as the data are mined for confirmation of these worlds.

The paper is Tuomi, "Evidence for 9 planets in the HD 10180 system," accepted for publication in Astronomy and Astrophysics (preprint).

Splashdown on Titan?

Getting to the stars may involve a sudden breakthrough — we can't rule out disruptive technologies, nor can we predict them — but my guess is that interstellar flight is going to be a longer, more gradual process. I can see a sort of tidal expansion into the outer system, forays to Mars, for example, followed by reassessment, retrenchment, then one day deeper study of Jupiter's moons with advanced robotics that can get under Europa's ice. The search for life may become so provocative that we have to explore Titan and Enceladus with human crews, and the imperative for planetary protection may help us further tune up our deep space technologies.

The thing is, one wave of exploration inevitably begets another. Let's put no timeframe on that kind of expansion because, like the tides, it may surge at times and then fall back, hostage to budgetary problems and waves of public interest that can as easily ebb. But I could see an eventual civilization that extends throughout the Solar System and, in shaping its essential infrastructure, pushes its propulsion and life support systems to begin exploring out into the Kuiper Belt and beyond. This assumes that we keep doing what we can right now, with resources that are stretched thin but may still give us something like the AVIATR airplane on Titan, or perhaps an instrument package that can splash down in one of Titan's seas.

We build the Solar System infrastructure one step at a time, and our robotic missions have given us a glimpse of what is waiting for us. Imagine the scientific return when we can begin sending human crews to some of the places so far glimpsed only by our probes! But the probes come first and the Titan Mare Explorer (TiME), which Johns Hopkins Applied Physics Laboratory (JHU/APL) champions, is a cost-capped $425 million mission concept that would parachute a robotic boat right into Ligeia Mare, the second largest of Titan's northern seas. Active mission time on Titan would be 96 days, with a launch between 2016 and 2018 if TiME is chosen over two competing proposals as a NASA Discovery-class mission. We'll know the answer to that later this year.

Image: Ligeia Mare, in Titan's northern polar region, could reveal its secrets to the TiME probe following a 2023 splashdown. Credit: NASA/JPL.

Every time we get a closer look at a distant world (think Cassini), we find compelling reasons to revisit the destination with ever more sophisticated technologies. Voyager and Galileo ramped up interest in Europa's hidden ocean, and it's likely that a Neptune orbiter would tell us things about Triton that might compel a future mission there. A major player in all this, of course, is the search for life, which makes Enceladus well nigh irresistible along with more likely targets.

As for Titan, it is already the site of the farthest landfall in human history, and it could now become the first place in which a probe lands in an alien sea. The interaction between liquid methane and ethane with Titan's climate and weather patterns would be a prime area for study, but TiME would also look at the kind of complex organic chemistry that may be similar to what led to life's formation on Earth billions of years ago. Says TiME project scientist Ralph Lorenz:

"These are disciplines that, to this point, have been strictly Earth science. How are heat and moisture exchanged between the ocean surface and atmosphere? How are waves generated? We have an opportunity to explore these processes in a completely different, alien environment."

A 2009 presentation to the Decadal Survey by principal investigator Ellen Stofan (Proxemy Research) notes that the lakes and seas of Titan are probably at least tens of meters deep and may extend down beyond 100 meters, and they clearly play a major role in the overall methane cycle on the moon. Ethane has been detected in Ontario Lacus near the south pole, and the same lake shows changes to its shoreline over time that suggest seasonal effects. A key goal of TiME will be to examine the methane cycle and show its similarities and differences from the hydrologic cycle on Earth from the probe's unique vantage point awash in Ligeia Mare.

Like AVIATR, the TiME mission would also offer a useful technology shakeout of the Advanced Stirling Radioisotope Generators (ASRGs) that would provide power for the probe, both in the deep space environment and in a non-terrestrial atmosphere. This first nautical exploration of an extraterrestrial sea could be providing science from Titan by 2023, including imagery from Ligeia Mare's surface showing us clouds and rain moving across the moon's orange skies. As I speculated last week, the choice of TiME would probably make the AVIATR airplane mission less likely to fly, given the inexorable logic of budgeting. We may be looking, then, at a choice between two compelling concepts to deepen our exploration of Saturn's most intriguing moon.

Related: Planetary Lake Lander is an attempt to study these technologies right here on Earth, with implications for what could fly aboard the TiME mission. From Five Steps Toward Future Exploration, in Astrobiology Magazine:

The Planetary Lake Lander project is led by Principal Investigator Nathalie Cabrol of NASA Ames Research Center and the SETI Institute, and involves a three-year field campaign at Laguna Negra (Black Lagoon) in the Central Andes of Chile. Here the team will test mission scenarios and technologies for deploying a floating, robotic platform that can perform scientific studies remotely while swimming the waters of Laguna Negra. Ultimately, this work will pave the way for a lake lander mission to Saturn's moon Titan. NASA has never attempted a lake landing before, so this field campaign is an essential first step in identifying the challenges that mission developers must contend with when they turn their sights toward the methane lakes of Titan.

You can follow the ongoing work of the Planetary Lake Lander project here. From the most recent blog entry (December 15, 2011), as the team prepared to return to the US, leaving the robotic device behind to monitor Laguna Negra:

Our plane takes off at 9:15 pm the following evening, and we are back in the US and home by 11:00 am on December 17. The morning air is clean and brisk, not unlike that of the lake, where for now, PLL is a reminder that we were there. It is logging data every hour and calling "home" (at NASA Ames) every evening, sharing more knowledge about melting glaciers and climate change. In a few months, it will be proactively monitoring the environment at Echaurren, as a precursor to what, maybe some day, another Lake Lander will do on Titan.