The Kepler countdown proceeds and, naturally, will preoccupy many of us during the day. I won’t try to keep up with the minutiae, as we’re not set up to be a news site at that level of granularity. Go instead to the Kennedy Space Center’s countdown page, where you’ll find live video feeds, or the Kepler portal. You can track the Kepler feed on Twitter here, although it’s been quiet all morning. The launch is scheduled for 10:49 EST (03:49 UTC) and the clock, as they say, is running. NASA TV should kick in about two hours before launch.
If you want a Kepler diversion, try Astrobiology Magazine‘s story on Ceres as a possible source for life on Earth. What’s not to like about yet another candidate for life in the outer Solar System? Even so, this one seems to be quite a stretch.
The story focuses on a theory from Joop Houtkooper (University of Giessen), who sees the ‘dwarf planet’ (I think that’s the right IAU terminology these days) as a potentially living world, a place a bit like Europa, although lacking the immense tidal force exposure that makes the latter so interesting. You may remember Houtkooper as the man who claimed that the Viking landers found life on Mars. In that controversial 2006 work, he re-examined old data from the Viking gas exchange experiment (GEx) and speculated on life-forms using hydrogen peroxide.
Image: A Hubble image of Ceres. Could the tiny object once have held life? Could it still? Credit: NASA, ESA, J. Parker/SWRI, P. Thomas/Cornell, L. McFadden/Univ. of Maryland.
As to Ceres, the scientist notes that the total volume of water on the tiny object is much greater than can be found in all the oceans of the Earth. “[I]f life is not unique to the Earth and could exist elsewhere, then these icy bodies are the places where life may have originated,” says Houtkooper, who points to the survival of Ceres’ water during the Late Heavy Bombardment, when asteroid impacts wreaked havoc on our own planet. From the story:
If there was life on Earth before this dangerous era, it was most likely eradicated and had to begin again after much of this cosmic debris had cleared out of the inner solar system. Interestingly, evidence indicates that Ceres avoided being pummeled by devastating impacts during this time. If it had been bombarded, it would have completely and forever lost its water mantle, as its gravitational force is too weak to recapture it. This is probably what happened to the asteroid Vesta, which has a very large impact crater and no water.
So we may be looking at an ocean of liquid water under the ice, a small place with a rocky core that could have the kind of hydrothermal vents that produce primitive organisms. In that case, an ancient survivor of catastrophe could have, through rocks blown off its surface that drifted to Earth, become the source of renewed life here. Let’s hope the DAWN mission can tell us more. It reaches Ceres in 2015, at which point we’ll learn whether, like Enceladus, Ceres may suddenly swim into focus as a potential home for living organisms.
We’ve already speculated here that if the Kepler mission finds few Earth-like planets in the course of its investigations, the belief that life is rare will grow. But let’s be optimists and speculate on the reverse: What if Kepler pulls in dozens, even hundreds, of Earth-sized planets in the habitable zones of their respective stars? In that case, the effort to push on to study the atmospheres of such planets would receive a major boost, aiding the drive to launch a terrestrial planet hunter with serious spectroscopic capabilities some time in the next decade.
Budget problems? Let’s fold Darwin and whatever Terrestrial Planet Finder design wins approval into the same package, and make this a joint NASA/ESA mission. Finding numerous Earth-like planets will be a driver, as will gradual economic recovery.
Finding Many Earths
The discovery of numerous ‘Earths’ would also galvanize public interest in interstellar flight, which offers a useful educational opportunity. Even the short-lived boomlet for Gliese 581 c inspired talking television heads to ask how we might get to the place, prompting the media to look into the distances involved and the challenges of propulsion. In my conversations, the initial response is usually dismay at the magnitude of the challenge, but it’s often followed by interest. Isn’t there anything we can do?
Image: Kepler at work in the search for Earth-like planets. Credit: NASA.
As we wait for the start of the Kepler mission, still scheduled for Friday night, the question of Kepler’s impact upon our SETI views also arises. It’s one thing to be trying to detect signals from an extraterrestrial civilization in a galaxy crowded with Solar Systems like our own, but fewer terrestrial worlds would correspondingly lower the chance for contact. Yet even a single civilization that attained star-faring status at some point in our galaxy’s evolution may have been able to construct self-replicating probes to explore the galaxy robotically. If star travel is possible, Fermi’s ‘Where are they?’ still resonates even in an uncrowded universe.
Kepler and Deep Time
Let me direct you to Charles Magee, Jr.’s Fermi paradox meets the timescale, where this field geologist sees the question through the lens of deep time. “As a geochronologist, I don’t wonder where and why, I wonder when,” writes Magee, who goes on to generate fifty random alien arrival times within the approximately 4.5 billion year window since the Solar System emerged from its accretion disk. He lists them in order, the most recent of them being 125 million years ago in the era of the dinosaurs.
That appearance in the Cretaceous is preceded by an alien visit at 270 million years ago at a time of Gondwanan glaciers, and a 352 million year old visit in the Carboniferous era of swamps and giant insects. Clearly, Magee’s aliens aren’t finding much to communicate with, but these eras would at least have been filled with enormous biological diversity. Keep going back in time and you realize what a tiny veneer our own species’ existence represents over the deep time that encrusts planet Earth.
Image: What an alien visitor might have seen in the Cretaceous. No technological cultures here! Source: Canadian Museum of Nature.
Suppose, for example, that our aliens showed up in the Late Heavy Bombardment some 3.875 billion years ago. Their take on life’s chances would be correspondingly gloomy — what could survive this — or at least tempered by the knowledge that what did develop in the aftermath would not be a technological factor for aeons to come. And so it goes, from Mesoproterozoic to Neoarchean to the colossal whack of a Mars-sized object into the Earth that would create the Moon, back in the Hadean era.
Magee’s point is clearly made:
As you can see, for aliens looking for ‘Earthlike’ planets, the actual Earth was easy to overlook for most of its history. In this simulation, there was only macroscopic life for 3 of 50 visits. From another POV, three visits were either during the Late Heavy Bombardment, or during the moon forming impact- both of which would appear (to the casual alien visitor) to make long-term viability of life on Earth pretty unlikely.
So as we start to find ‘earth-like’ planets in our sky surveys, it is important to remember that Earth has only been Earthlike for a relatively short period of time.
The Rise of Ancient Probes
I’ve often noted the frequent public misconception of interstellar distances and their true scale, but I think we’re all sometimes guilty of forgetting our own context within deep time, a context Magee brings into high visibility in this post. And, of course, no matter what Kepler finds, we’ll still be a long way from knowing whether life of any kind, much less complex life, exists on the worlds it finds. The question will still be not so much whether any other technological civilizations could arise in the same galaxy, but whether they’re numerous enough to arise at the same time.
Have a quick look at this video, produced by Claire Evans at SEED Magazine. It condenses 4.6 billion years of history into a single minute, offering a unique perspective:
So much depends upon the question of civilization lifetimes. But again, let’s assume that at least a few civilizations have found a way to get past their technological infancy, past the period when they were likely to destroy themselves with their own tools, and have expanded into nearby space. If Frank Tipler’s view is reasonably correct, then a million years is a sufficient time for self-replicating probes to work their way through the entire galactic disk. Indeed, Tipler went on in his famous 1980 paper to say that the Local Group of galaxies could be colonized within ten million years, and the entire Virgo cluster within a hundred million years.
Knowing When to Wake Up
You can think of places within the Solar System where an ancient probe, self-repairing and dormant, might wait for whatever it is that would trigger its awakening. We commonly assume that it is the emergence of creatures like us that would do the trick, but why? We have no galactic context in which to place ourselves. We may be numbingly rare as an intelligent species, or merely a transitional phase between biology and other forms of consciousness, a stopgap along the way to true maturity.
Image: The spiral galaxy M81 in Ursa Major. Could self-replicating probes reach every solar system in such a galaxy within a million years? Credit: Giovanni Benintende.
Why assume, in other words, that a von Neumann probe of this kind, perhaps lurking in one of the Lagrangian points, or out in the asteroid belt, or perhaps in the Kuiper Belt, would be activated by our current level of development? In the absence of such knowledge, we might well conclude no such probes exist, but it is conceivable that infrared studies of the outer system, of the sort advocated by Gregory Matloff and Anthony R. Martin, may one day turn up just the kind of anomalous signature that an artificial body would throw. It’s certainly worth the look, and a reminder that there are potential SETI venues that are closer to home than the nearest stars.
Further Reading
Two interesting places to start are twin papers by Matloff and Martin. The first is “A Proposed Infrared Search for Artificial Kuiper Belt Objects,” Journal of the British Astronomical Society 57 (November/December 2004, pp. 283-287, while “Suggested Targets for an Infrared Search for Artificial Kuiper Belt Objects,” JBIS 58 (January/February 2005), pp. 51-61 follows up on that work. Also useful is Allen Tough, “Small Smart Interstellar Probes,” JBIS 51, no. 5 (May 1998), p. 167 ff. The British Interplanetary Society needs to get some of this good material online.
And I almost forgot the Tipler paper, which is “Extraterrestrial Beings Do Not Exist,” in Quarterly Journal of the Royal Astronomical Society 21 (1980), pp. 267-81. Carl Sagan and William Newman’s rebuttal is “The Solipsist Approach to Extraterrestrial Intelligence,” Quarterly Journal of the Royal Astronomical Society 24 (1983), p. 113, which sees self-reproducing probes as too virus-like to win the approval of extraterrestrial planners.
If we’re looking for pristine environments for life, Antarctica offers much. More than 150 subglacial lakes have been discovered beneath the ice sheet, isolated from the surface for long periods and possibly home to species that have never before been observed. From November 2007 to February 2008, a subglacial lake named Lake Ellsworth was studied by a four-person team that used seismic and radar surveys to map the lake’s depth and take other measurements that made clear its potential for exploration. Their blog is archived here, and it makes for good reading.
Image: A DeHavilland Dash-7 flying near the British Antarctic Survey research station at Rothera. The station is 1630 kilometers southeast of Punta Arenas, Chile, and served as a staging area for the Lake Ellsworth studies of 2007-2008. Credit: Natural Environment Research Council.
Europa, anyone? Well, there are certain resemblances. If the thickness of the ice on Europa is still controversial, we know for a fact that Lake Ellsworth’s ice is three kilometers thick, covering a lake that is 150 meters deep. Lake-floor sediments here could offer clues to Earth’s past climate. The water remains liquid not only because of the insulating effect of the ice above, but because of heat from below coming up through the bedrock. Of course, Lake Ellsworth will require drilling to get into its uncontaminated water in the hunt for life. Europa, as we’ve seen recently, may not — a lander exploring near older cracks in Europan ice may turn up evidence for life-forms exposed to the surface by periodic melting.
Lake Vostok, in east Antarctica, is probably the best known subglacial lake, but they’re all interesting because the water within them may be as old as the ice sheet above. In Lake Ellsworth’s case, that means on the order of 150,000 years and perhaps more. The success of the recent studies have now led to a new effort involving researchers from a host of British institutions and funded by the UK’s Natural Environment Research Council. In the 2012-2013 Antarctic winter season, they’ll try to reach pristine lake water to sample it for life and extract sediments from the lake bed.
David Blake is head of technology and engineering at the British Antarctic Survey:
“This project is a great scientific challenge and the technology required to drill 3 km through the ice without contaminating the lake is equally ambitious. Over the next few years we will build a hot water drill and probe, and make preparations to transport a sophisticated operation deep into the interior of West Antarctica. We really are at the frontiers of scientific exploration.”
That bit about not contaminating the lake says it all. This is tricky business — recall that we eventually dispatched the Galileo Jupiter orbiter to a crushing end within the depths of Jupiter’s atmosphere, all because we wanted to be sure that it would never impact Europa. If a spacecraft that had been exposed to space for almost fourteen years was still thought a potential contamination hazard, how do we get a probe through Lake Ellsworth’s ice without introducing surface life? Clearly, the progress of the Lake Ellsworth effort will be worth watching. You can track developments at the Exploration of Subglacial Lake Ellsworth site.
With an atmospheric pressure one hundred thousand times less than that on Earth, Pluto becomes an even more intriguing object than usual when it moves closer to the Sun in its 248-year orbit. This period, occurring now, causes the temperature of the surface to increase, and that causes what had been frozen nitrogen (with trace amounts of methane and, probably, carbon dioxide) to sublimate into gas. Studying these matters with ESO’s Very Large Telescope, astronomers have now found unexpectedly large amounts of methane in that atmosphere.
Image: Artist’s impression of how the surface of Pluto might look, according to one of the two models that a team of astronomers has developed to account for the observed properties of Pluto’s atmosphere. The image shows patches of pure methane on the surface. At the distance of Pluto, the Sun appears about 1000 times fainter than on Earth. Credit: ESO/L Calçada.
A second discovery: The atmosphere of the distant ice world is some forty degrees Celsius hotter than the surface, so that the global weather on Pluto seems to be characterized by a thermal inversion, with warm air sitting above cold (this is the kind of pesky weather situation on Earth that can trap smog and sharply reduce visibility). Sublimation seems to be the cause of this inversion. Think of winter snow evaporating even when it never moves through a liquid state, or comets approaching the Sun, their coma and tails forming through the effects of sublimating ice.
Warming the atmosphere, sublimation in turn cools the surface. The model for all this draws on spectrographic observations that show methane represents about half of one percent of the atmosphere. The team, led by Emmanuel Lellouch, believes that two different models can explain these findings at Pluto, one involving a thin layer of methane at the surface, the other invoking distinct areas of pure methane. From the paper:
Two scenarios… have been described to explain this elevated methane abundance (i) the formation, through surface-atmosphere exchanges, of a thin methane-rich surface layer (the so-called “detailed balancing” layer), which inhibits the sublimation of the underlying, dominantly N2, frost, and leads to an atmosphere with the same composition as this frost (ii) the existence of geographically separated patches of pure methane, warmer than nitrogen-rich regions, and which under sublimation boost the atmospheric methane content.
New Horizons should be able to tell us more when it reaches Pluto/Charon in 2015. Until then, I’m inclined to agree with Hans-Ulrich Käufl, a co-author of the paper on this work, as he describes the team’s use of the CRIRES spectrograph on the VLT: “It is fascinating to think that with CRIRES we are able to precisely measure traces of a gas in an atmosphere 100,000 times more tenuous than the Earth’s, on an object five times smaller than our planet and located at the edge of the Solar System.” Indeed.
The paper is “Pluto’s lower atmosphere structure and methane abundance from high-resolution spectroscopy and stellar occultations,” in press at Astronomy & Astrophysics (abstract).
With the Kepler launch scheduled for no earlier than Friday, I’m keeping one eye on the mission site while I develop today’s material. Kepler launches aboard a Delta II, but engineers are now having to check common hardware between that rocket and the Taurus XL launch vehicle that failed to get NASA’s Orbiting Carbon Observatory into orbit last week. Thus the March 5 launch date slips to March 6, which itself is still tentative.
Meanwhile, an unusually interesting story in Nature also has my attention, dealing not with exoplanets but with the early Solar System and what may have been a period of planet migration that caused heavy asteroidal bombardment of the inner planets. This one comes out of the University of Arizona, where scientists have been looking at the distribution of asteroids with diameters greater than fifty kilometers. UA’s David Minton and Renu Malhotra ran simulations beginning with a uniform asteroid belt to see how the present-day gaps in the belt may have arisen over time.
At issue are the so-called Kirkwood gaps, which occur in areas where gravitational effects from both Jupiter and Saturn perturb the belt and eject asteroids. The result of the simulations: Areas exist where asteroid orbits are stable but no asteroids exist. But if the effects of giant planet migration in the early system are added to the mix, the simulated belt matches up well to what we see today. Those extra areas of asteroid depletion, then, may be the signature of planetary migration. Says Malhotra:
“Our interpretation is that as Jupiter and Saturn migrated, their orbital resonances swept through the asteroid belt, ejecting many more asteroids than is possible with the planets in their current orbits. And the particular pattern of missing asteroids is characteristic of the pattern of Jupiter’s and Saturn’s migration.”
Thus we have evidence that the giant planets formed with closer spacing than in today’s Solar System, with Jupiter then moving slightly closer to the Sun, while Saturn, Uranus and Neptune moved farther from the Sun and from each other. These events would have been destabilizing enough for the asteroid belt that the possibility of linking them to early, heavy bombardment of the inner planets is worthy of further study.
Graduate student Minton and planetary sciences professor Malhotra seem to make a good team — you may also want to have a look at their recent study of the extrasolar system OGLE-2006-BLG-109L, which examines a possible system architecture that includes the two detected massive planets and has the potential for two terrestrial-class worlds which, if they exist, could create an environment that mimics our Solar System. That paper is “Prospects for the Habitability of OGLE?2006?BLG?109L,” Astrophysical Journal Letters 683 (August 10, 2008), pp. L-67-70 (abstract). The asteroid paper is “A record of planet migration in the main asteroid belt,” Nature 457 (February 26, 2009), pp. 1109-1111 (abstract).
In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For many years this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image courtesy of Marco Lorenzi).
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