The idea that rocks may travel between planets is now widely accepted. But can rocks or other planetary ejecta wander between solar systems? A new paper examines this hypothesis, concluding that rocky materials and even life-bearing meteorites may make their way from one planetary system to the next. But here's the catch: this transfer is only likely between stars in young stellar groups and clusters, where the distances and relative velocities between stars are low. The authors -- the University of Michigan's Fred C. Adams and Princeton's David N. Spergel -- note that most stars occur in binary systems, making the chance of such transfer that much higher. The operative term is 'lithopanspermia,' the notion that life travels between worlds aboard meteorites. It is a variation on the older panspermia theory, which argued that life arrived directly from space. The concept dates back as far as Anaxagoras (5th Century B.C.) and was championed by Lord Kelvin, who declared in 1871, "...we...

Is biology as much a driver for interstellar travel as technology? Hungarian engineer Csaba Kecskes argues that it may be so; indeed, biology may hold the answer to Enrico Fermi's famous 'where are they?' question about extraterrestrials. While most scenarios for the growth of technological civilizations assume a 'galactic empire' model -- colonization modeled after 16th Century explorers, or the spread of Polynesian cultures through the islands of the Pacific -- Kecskes uses a different analogy: the migration of life from water to land. As he writes in a 2002 paper in Acta Astronautica: Using this analogy, the [Fermi] paradox simply disappears; fishes never meet lizards or rats. (In the Earth's biosphere there are large groups of animals which live in a mixed water/land environment, but every analogy has its limits. Man's adaptation to the space environment, especially to weightlessness, probably will create a very effective and final barrier). In other words, technical...

"The prospect of distributing realistic simulations of alien environments throughout the galaxy sheds light on 'Fermi's question,' named after the physicist Enrico Fermi, who is said to have inquired of intelligent extraterrestrials, 'Where are they?' The point of Fermi's question, much elaborated by later thinkers, is that a technically advanced civilization could set up colonies on the planets of nearby stars, which in turn could colonize other star systems, until their race had populated the entire galaxy. Since they are not here, the argument concludes, perforce they are not anywhere, and we are alone in the galaxy. "Interstellar colonization, however, is arduous and expensive by just about any imaginable standard. It can hardly be justified in terms of population pressure or a need for raw materials: Our Sun, for instance, has enough energy, and the solar system enough space, to accomodate the most vigorous forseeable expansion of our species for many millions of years into the...

"A recent book by the mathematician Amir Aczel makes the case for the probability of extraterrestrial life being 1. The physicist Lee Smolin wrote that 'the argument for the non-existence of intelligent life is one of the most curious I have ever encountered; it seems a bit like a ten-year-old child deciding that sex is a myth because he has yet to encounter it.' The late Stephen Jay Gould, referring to Tipler's contention that ETCs would deploy probe technology to colonize the Galaxy, wrote that 'I must confess that I simply don't know how to react to such arguments. I have enough trouble predicting the plans and reactions of people closest to me. I am usually baffled by the thoughts and accomplishments of humans in different cultures. I'll be damned if I can state with certainty what some extraterrestrial source of intelligence might do.' "It is easy to sympathize with this outlook. When considering the type of reasoning employed with the Fermi paradox, I cannot help but think of...

Every study using transit methods to detect objects around other stars is looking for planets. But a paper by Luc Arnold (Observatoire de Haute-Provence, France), soon to be published in The Astrophysical Journal, suggests that the same methods could be employed to find artificial planet-sized objects in orbit around stars. Arnold sees this as a possible SETI ploy, for transits of multiple objects could be used to emit signals that might be detected by other civilizations. What would such objects be? Giant solar sails, perhaps, or huge low-density structures of other configuration built purposely as a means of interstellar communication. Arnold's work inevitably recalls Freeman Dyson's 1960 Science article "Search for Artificial Stellar Sources of Infrared Radiation," which developed the idea that would later be known as a Dyson Sphere, an artificial cluster of rotating objects the size of a planetary orbit that would collect almost all the solar energy available and create a vast...

When is a planet habitable? The assumption, in studies of the 'circumstellar habitable zone' (CHZ) ranging back as far as 150 years, is that a planet is habitable if liquid water can be maintained on its surface. That this is a 'life as we know it' scenario is obvious: it works best if you assume a planetary system not so different from our own, one with roughly the same configuration of planets (gas giants in outer orbits, rocky worlds in close). Venus and Mars have served as test cases of the boundaries of habitable zones. But our view of habitable zones is evolving. I relied on Stephen Dole's groundbreaking study Habitable Planets for Man (New York: Blaisdell Publishing Company 1964) in Centauri Dreams. Dole's work was prepared for the RAND Corporation, and was released in popularized form as Planets for Man, in collaboration with Isaac Asimov (New York: Random House, 1964). Dole defined a stellar ecosphere as ". . . a region in space, in the vicinity of a star, in which suitable...

The search for extraterrestrial intelligence is, some would say, too passive -- it's pure listening, monitoring radio and, in some cases, optical wavelengths in hopes of intercepting either a message from another civilization or, perhaps, catching a snippet of its internal communications. But is there a place for an active SETI, one that is just as anxious to send a human message to the stars as to listen for the broadcasts of others? Not that there haven't been previous attempts to send signals, the most famous of which was the 1974 Arecibo message beamed in the direction of M13, a globular cluster in the constellation Hercules. The Hercules message, containing binary representations of the human form, the solar system, and other mathematical and chemical information, pushes us into the domain of long-term thinking, for it will take 25,000 years to reach its target (and, obviously, another 25,000 years for any reply). But M13 is also an interesting place to send a signal, for it is...

Here's an image of the possible Martian pack ice, taken by Mars Express' High Resolution Stereo Camera (HRSC), which is imaging the entire planet in full colour, 3-D and with a resolution of about 10 metres. The 3-D capability allows us to see Martian topography in unprecedented detail. Look here for other extraordinarily detailed images. This image, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, during orbit 32, shows what appears to be a dust-covered frozen sea near the Martian equator. It shows a flat plain, part of the Elysium Planitia. The scene is a few tens of kilometres across, centred on latitude 5º North and longitude 150º East. Credits: ESA/DLR/FU Berlin (G. Neukum) Meanwhile, findings from Mars Express were discussed in a news conference on the 25th. To say the session was packed with news is an understatement: we have not only the possible pack ice but discussions of Martian methane and formaledhyde and their significance for...

Storing and preserving living cells at low temperatures is a staple of science fiction. Who knows how many fictional interstellar journeys have taken place with the crew in cryogenic suspension (my favorite, Van Vogt's "Far Centaurus," springs quickly to mind, but there are many possible references). And with the possibility of Martian ice -- even an ancient Martian sea -- under observation by Mars Express, the question of life surviving in extreme conditions is drawing increased attention. Which is why the discovery of of a new bacterium called Carnobacterium pleistocenium is so interesting. NASA astrobiologist Richard Hoover and his team found the anaerobic bacteria, which grow on sugars and proteins in the absence of oxygen, at the U.S. Army's Cold Regions Research and Engineering Laboratory tunnel north of Fairbanks, Alaska. The tunnel was created in the 1960s to allow scientists to study permafrost as part of the preparation for building the Trans-Alaska Oil Pipeline. Hoover's...

Oliver Morton's excellent MainlyMartian weblog has a cautionary analysis of Vittorio Formisano's work on Martian formaldehyde, which we looked at on the 18th. From the weblog: I've posted on the formaldehyde story before. And, even more now than then, I think Formisano is making a mistake...[S]o do a number (quite possibly, from what I hear, all) of his colleagues on the PFS, including those who have more experience modelling atmospheric chemistry and interpreting spectrometer data than Formisano has. I don't want to rehash everything in the earlier post on the subject, but the gist is that a) formaldehyde is expected to have a very short lifetime in the atmosphere, and thus it is very hard to explain how there could be so much of it and b) earth-based telescopes have looked for the stuff and found no evidence for it even at levels far lower than those that Formisano appears to see. You can read Morton's comments here. He has also written thoughtfully on the 'Elysium Sea' (the...

The recent finding of a possible ancient sea on Mars has been one of the hotter topics at the ESA Mars Science Conference. The research team, led by John Murray of the UK's Open University, presented its findings at the conference on the 21st, with a paper coming up in Nature next month. One team member, Jan-Peter Muller of University College London had this to say about the significance of the find: "The fact that there have been warm and wet places beneath the surface of Mars since before life began on Earth, and that some are probably still there, means that there is a possibility that primitive micro-organisms survive on Mars today. This mission has changed many of my long-held opinions about Mars - we now have to go there and check it out." Amen to that, since even with instruments like Mars Express' High Resolution Stereo Camera, which offered up the 3D images used in this work, we need hard evidence from the surface before we can claim that life is anything more than a...

The Mars Express conference being held at the European Space Research and Technology Centre in the Netherlands runs through the 25th, and as we saw yesterday is already generating its share of high quality data. The program for the meeting can be found here. Of particular interest will be the special session on exobiology and the hunt for life on Mars that will be held on Thursday the 24th. We should get more information about that conjectural Martian ocean (discussed yesterday) at that gathering. Meanwhile, six papers published online by the journal Science have brought forth new findings about the early history of Mars. "If you want to resolve the big question about life on Mars, you want to go to the right places and get samples," said Brown University's John Mustard. "The new research tells us where some of those places may be." Mustard is part of an international team using data from the Mars Express OMEGA spectrometer that is mapping the surface of the planet in both visible...