When it comes to exoplanet speculations, we're still in the era when data are few and dominated by selection effect, which is why we began by finding so many 'hot Jupiters' -- such planets seem made to order for relatively short-term radial velocity detections. It's a golden age for speculation, with the promise of new instrumentation and a boatload of information from missions like Kepler and CoRoT to be delivered within a few years. What an extraordinary time to be doing exoplanetary science. The big questions can't be answered yet, but it shouldn't be long before we have an inkling about what kind of stars are most likely to produce terrestrial planets. And maybe a qualification is in order. M-dwarfs are so common in our galaxy -- some estimates run to seventy percent of all stars and up -- that finding habitable worlds around them would hugely increase the possible venues for life. But is there any way we could call planets around M-dwarfs 'Earth-like?' Maybe in terms of...

An exotic planetary environment right here in the Solar System may be a useful test for answering the key question of how common life is in the universe. So argues Jonathan Lunine (University of Arizona) in an upcoming paper. Lunine believes there is a plausible case for life to form on Titan, and that if we were to find it there, its very dissimilarity from Earth would make it a test-case for life in other extreme environments of the sort that may be common in the cosmos. We'd like to answer this question locally because it may be some time before we can answer it around other stars. After all, the best spectral signatures we can hope to get from the atmospheres of Earth-analogues elsewhere are quite possibly going to be ambiguous. Molecular oxygen can be a sign of photosynthesis but also of the abiotic escape of water from the upper atmosphere. Methane in the same atmosphere makes biology more likely but may be, Lunine thinks, difficult to detect from Earth. Image: One way to...

Does complex life emerge at a gradual, uniform rate? If so, we can come up with one answer to the Fermi paradox: We have not detected signs of extraterrestrial life because the time needed for complex life to appear generally exceeds the life of a star on the main sequence. But the assumption that intelligence appears over time with a gradual inevitability -- a key tenet of work by Brandon Carter, Frank Tipler and others in the 1980s, may not in fact be true. Solar system-wide events connect life with its stellar environment, while galaxy-wide events provide yet another context. Punctuated Evolution Among the Stars Milan ?irkovi? (Astronomical Observatory, Belgrade) and colleagues have much to say about this in a new paper in Astrobiology. It's a rich treatment of our older assumptions and newer thinking about punctuated evolution, the idea that life actually evolves in spasms rather than smooth ascents. Species remain relatively stable for long periods but endure sudden changes that...

As we contemplate using long-range tools like spectroscopy to examine distant exoplanets for life, we're also developing the hands-on equipment we'll need for seeking it out in our own Solar System. Project SLIce (Signatures of Life in Ice) is a case in point, an attempt to study how organic material behaves in ice on other worlds by using Earth settings as an analogy. On that score, the archipelago of Svalbard has proven to be a helpful testbed. Located in the Arctic Ocean between Norway and the North Pole, Svalbard is icy and spectacular. The image below conjures up memories of a nautical journey I took around Iceland in the 1970s, with white-capped seas pushing up against snow-clad peaks. The SLIce team sees Svalbard as a laboratory for looking for extant or extinct life, and a place to develop the protocols for working with rovers in operating environments like Mars. Image: I love Iceland, but pushing as far north as Svalbard would really bring out the adventurer in me. Here we...

Somehow I never thought of the IceCube neutrino telescope as a SETI instrument. Deployed in a series of 1,450 to 2,450 meters-deep holes in Antarctica and taking up over a cubic kilometer of ice, IceCube is fine-tuned to detect neutrinos. That makes it a useful tool for studying violent events like galactic collisions and the formation of quasars, providing insights into the early universe. But SETI? Perhaps, says Zurab Silagadze (Novosibirsk State University), who notes that most SETI work in the past has focused on centimeter wavelength electromagnetic signals. Says Silagadze: Here we question this old wisdom and argue that the muon collider, certainly in reach of modern day technology... provides a far more unique marker of civilizations like our own [type I in Kardashev's classification... Muon colliders are accompanied by a very intense and collimated high-energy neutrino beam which can be readily detected even at astronomical distances. Image: The IceCube array in the deep ice,...

If we can find a way to double the lifespan of Earth's biosphere, we'll have changed the odds for finding extraterrestrial civilizations. After all, the amount of time an advanced culture can exist is one of the variables in the famous Drake equation, which estimates how many intelligent civilizations there are in the Milky Way. Lengthen potential habitability and you give any civilization that much more chance to spread into the cosmos. Thus recent work out of Caltech intrigues us in several directions. Joseph Kirschvink and colleagues look at effects that could add a billion years on to our planet's projected habitability. Consider: Earth took some four billion years to develop intelligent life, leaving us about a billion before our planet becomes uninhabitable. That result would be caused by a brighter and hotter Sun, the loss of carbon dioxide in the atmosphere through the weathering of rocks, and the eventual evaporation of water from the oceans, leaving nothing alive. Reducing...

Among the most interesting of the future missions now being weighed by NASA, TESS (the Transiting Exoplanet Survey Satellite) would help scientists using the James Webb Space Telescope know where to look for Earth-like planets around nearby stars. While the invaluable Kepler mission scans 100,000 distant stars, hoping to gain statistics on Earth-sized exoplanets, TESS would have a different aim, looking for transiting terrestrial worlds around only the brightest stars. A 2012 launch is possible if the mission is approved. Here's Greg Laughlin (UC-Santa Cruz) on TESS' possibilities: TESS... provides the cheapest, shortest, and most direct path to the actual characterization of a potentially habitable planet. Included in the 2.5 million brightest stars are a substantial number of M dwarfs. Detailed Monte-Carlo simulations indicate that there's a 98% probability that TESS will locate a potentially habitable transiting terrestrial planet orbiting a red dwarf lying closer than 50 parsecs....

Imagine an extraterrestrial civilization that manages to colonize the entire galaxy. Then imagine the colonizing civilization collapsing so definitively that no trace of its existence has yet been detected, at least from our planet. We can call it, as Jacob Haqq-Misra and Seth Baum (Pennsylvania State University) do in a recently released paper, a 'graveyard civilization,' one whose remains might still be accessible provided we know where and how to look. Pushing the Limits of Growth What could bring down such a civilization? The idea here is that we can explain the Fermi paradox ('Where are they?') by assuming that exponential growth is not a sustainable development pattern for intelligent civilizations. The authors draw on human experience in analyzing this possibility. Here's the gist of it: The consequences of unsustainable development are often dire. In many documented cases, resource depletion caused by human activities has led to the permanent collapse of human populations,...

You wouldn't think life on a planet being bombarded by debris in the early days of its solar system would have much chance for survival. Indeed, the prospect of being pummeled for millions of years in the Late Heavy Bombardment has led to scenarios in which life started, was extinguished, and re-started on this planet, the idea being that the massive cratering we see on objects like the moon was also being enacted here. But maybe we can make a virtue of necessity and consider what all those incoming objects might have done long-term to improve the atmospheres of the planets they landed on. So goes the thinking in a new study that examines the composition of ancient meteorites to see what they would do when heated to temperatures like those caused by a fiery descent to Earth. Using a method called pyrolysis-FTIR, in which the meteorite fragments were quickly heated (at a remarkable 20,000 degrees Celsius per second), the team measured the carbon dioxide and water vapor released. It...

I'm glad to see the phrasing of the key question used in the SETI Institute's 'Earth Speaks' project. Assuming we one day detect a signal from an extraterrestrial civilization, the Institute asks, 'Should we reply, and if so, what should we say?' Given the apparent ease with which broadcasts to the stars have been made in the last few years, advertising everything from snack foods to movies, this question might easily have been 'What should we say when we respond to an extraterrestrial signal?' When or if? I come down on the side of the 'if' formulation, because the question deserves a global response, one reflecting a broad range of disciplines and perspectives. Such a response takes time to build. Another thing I like about 'Earth Speaks' is that it will give us an interesting take on our own species. The plan here is to encourage people to submit messages, pictures and sounds online, using the Internet to solicit ideas. Fine-Tuning an Interstellar Greeting The site is here, where...

Twenty different amino acids go into making up the vast variety of proteins so essential to life. But why does life on Earth use only left-handed versions of amino acids to build them? After all, amino acids can be made in mirror images of each other. Jason Dworkin (NASA GSFC) notes the key issue. Mix left- and right-handed amino acids and "...life turns to something resembling scrambled eggs -- it's a mess. Since life doesn't work with a mixture of left-handed and right-handed amino acids, the mystery is: how did life decide -- what made life choose left-handed amino acids over right-handed ones?" Image: This artist's concept uses hands to illustrate the left and right-handed versions of the amino acid isovaline. Credit: NASA/Mary Pat Hrybyk-Keith. It's a question with ramifications for life elsewhere in the universe. Suppose the day comes when we finally get a robotic lander to Enceladus. The news flashes around the world: Life discovered on one of Saturn's moons! But is it truly...

The planets in our Solar System rotate around the Sun more or less in a plane (the ecliptic) that is tilted some sixty degrees with relation to the galactic disk. It's interesting to speculate that this could have ramifications in terms of the SETI hunt. Shmuel Nussinov (Tel Aviv University) considers the possibility that any extraterrestrial civilizations might try to contact us only after they had a fair idea we were here. And just as we are now trying, via Kepler and CoRoT, to track down small planets using the transit method, so too might extraterrestrials try to observe our transits, and having done so, to transmit a message. Targeting habitable planets should optimize chances for a successful reception. From our end, a prudent SETI strategy might then be to home in on the 'stripes' of the sky within which our system's planetary transits are detectable from other solar systems. As Nussinov writes: The thickness of the galactic disc in our neighborhood is ? 150 parsecs. With the...

George Dvorsky takes on the 'rare earth' hypothesis in his Sentient Developments blog, calling it a 'delusion' and noting all the reasons why life in the galaxy is unlikely to be unusual. The post reminds me why the book that spawned all this was so significant. Rare Earth: Why Complex Life is Uncommon in the Universe (Copernicus, 2000) is Peter Ward and Donald Brownlee's take on our place in the cosmos, concluding that complex life is rare because an incredibly fortuitous chain of circumstances must arise for it to occur. Indeed, the authors argue that large parts of our galaxy are composed of what they call 'dead zones.' The argument is complex and looks at factors ranging from a planet's place in the galactic habitable zone (itself a controversial subject), its orbit around its own star, its size, its satellites, its magnetosphere, its plate tectonics, and more. I'm surprised to realize, looking through our archives here, that I haven't managed to do a complete review of Rare...

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...

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...

A Europan Scenario Between living dirigibles on gas giants and potential organisms under the ice, we've had quite a week in terms of exotic life-forms. I didn't have space in yesterday's review of Unmasking Europa to talk about the book's chapter on biology, but here's an interesting glimpse of a not implausible biosphere on that moon, as presented by physicist Richard Greenberg: Brisk tidal water sweeps over creatures clawed into the ice, bearing a fleet of jellyfish and other floaters to the source of their nourishment. As the water reaches the limits of its flow, it picks oxygen up from the pores of the ice, oxygen formed by the breakdown of frozen H2O and by tiny plants that breath it out as they extract energy from the sun. The floating creatures absorb the ocygen and graze on the plants for a few hours. The water cools quickly, but before more than a thin layer can freeze, the ebbing tide drags the animals deep down through cracks in the ice to the warmer ocean below. Most of...

By Larry Klaes 'The Gasbags of Jupiter' sounds for all the world like the title of an early 1930s novel that would have run in a venue like Science Wonder Stories. In fact, as Larry Klaes tells us below, the idea grew out of Carl Sagan's speculations about free-floating life-forms that might populate the atmospheres of gas giant planets like Jupiter. Cornell physicist Edwin Salpeter had much to do with the evolution of that concept, helping Sagan produce a paper that was a classic of informed imagination (and one that led to numerous science fiction treatments as the idea gained currency). Larry's celebration of Salpeter's life gives a nod to that paper but also notes his deep involvement in the study of the most distant celestial objects. On March 14, the Department of Astronomy at Cornell University will commemorate the life of one of their most prestigious faculty members: Edwin E. Salpeter, the James Gilbert White Distinguished Professor of Physical Sciences Emeritus. Salpeter...