Why would you want to take pictures of Earth from a spacecraft in orbit around Venus? Aside from the wish to see a familiar place from a distant location, our planet can also become an interesting testbed for exoplanetary studies. We've run into this idea before in the EPOXI mission, which is the combined extended mission of the Deep Impact spacecraft. Here the cometary component of Deep Impact was recently augmented with observations of Earth that can suggest how to study the glint of light off distant oceans, or the signature of land masses. The extrasolar component of EPOXI is called EPOCh, for Extrasolar Planet Observation and Characterization, and it primarily involves an examination of stars with known transiting planets, looking for other planets in the system (EPOXI can detect transits of objects down to about half the diameter of the Earth) or possibly moons around the known ones. Meanwhile, the spacecraft continues its journey to comet Hartley 2 for observations there, its...

The idea of a galactic habitable zone (GHZ) has a certain inevitability. After all, we talk about habitable zones around stars, so why not galaxies? A stellar habitable zone is usually considered to refer to those areas around the star where liquid water can exist on a planetary surface. Those who believe that confining habitable zones to regions like these carries an implicit bias -- limiting them to life much like our own -- miss the point. The habitable zone concept simply tells us where it makes the most sense to search for the kind of life we can most readily recognize, and as such, it hardly rules out other, more exotic forms of life. But while liquid water takes precedence in a stellar habitable zone, a galactic HZ is still being defined. Charles Lineweaver and team have examined it, among other things, in terms of stellar metallicity (the elements heavier than hydrogen and helium found in the body of a star), concluding that there is a ring several kiloparsecs wide...

The idea that life on Earth might have originated elsewhere, on Mars, for example, has gained currency in recent times as we've learned more about the transfer of materials between planets. Mars cooled before the Earth and may well have become habitable at a time when our planet was not. There seems nothing particularly outrageous in the idea that dormant bacteria inside chunks of the Martian surface, blasted into space by comet or asteroid impacts, might have crossed the interplanetary gulf and given rise to life here. But what of an interstellar origin for life on Earth? The odds on meteoroids from a system around the average galactic field star not only striking the early Earth but delivering viable microbes are long indeed. But if we consider the Sun's probable origin in a cluster of young stars, all emerging from the same collapsing cloud, the picture changes significantly. Now we're dealing with much smaller distances between stars and slow relative motion as well, conditions...

Making contact with an extraterrestrial civilization, whether by microwave, laser or neutrino, highlights the problem of time. Suppose you are looking for a newly emerging technological culture around another star. When do you transmit? After all, even the most powerful signal sent to Earth a million years ago would have no listeners, which is why some have suggested putting actual artifacts in promising solar systems. Rather than transmitting over time-scales measured in eons, you leave an object that can be decoded and activated for communications. All kinds of interesting science and science fictional scenarios flow from that idea. But what if you want to contact not just a few highly targeted systems, but instead send a signal intended for everyone in the galaxy with the means to receive it? As John Learned (University of Hawaii) and team speculate in a new paper, one way to do that would be to select highly visible and important stars to carry your message. Cepheid variables are...

'Hanny's Voorwerp' may soon enter the astronomical lexicon as a reference to anomalous objects in deep space. 'Hanny' is Hanny van Arkel, a 25-year old Dutch school teacher and participant in the Galaxy Zoo project, where she and 150,000 other volunteers worldwide help to scan galaxy images online. 'Voorwerp' is the Dutch word for 'object,' in this case a conglomeration of gas heated to about 10,000 degrees Celsius and marked by a hole in its center. The suspicion grows that van Arkel has stumbled upon an entirely new class of astronomical object. Out of such finds does the work of a computer-armed volunteer become fodder for the Hubble Space Telescope, which will soon have 'Hanny's Voorwerp' under observation. The object is apparently being illuminated by a source we cannot see, leading the Galaxy Zoo team to look at the nearby galaxy IC 2497. The quasar at the heart of this galaxy seems to have shut down some time in the past 100,000 years -- at least, that's the theory -- while...

Imagine a form of life so unusual that we cannot figure out how it dies. That's exactly what researchers are finding beneath the floor of the sea off Peru. The microbes being studied there -- single-celled organisms called Archaea -- live in time frames that can perhaps best be described as geological. Consider: A bacterium like Escherichia Coli divides and reproduces every twenty minutes or so. But the microbes in the so-called Peruvian Margin take hundreds or thousands of years to divide. "In essence, these microbes are almost, practically dead by our normal standards," says Christopher H. House (Penn State). "They metabolize a little, but not much." House goes on to discuss what a slow metabolism may imply about environments outside our own planet. Imagine hydrothermal vents on Europa, where the energy ration may be slim. For that matter, with Phoenix still working its magic at the Martian pole, imagine subsurface aquifers on that planet whose energy resources may be just enough...

Without the explosions of supernovae, the heavy elements so essential to life itself would be unavailable, and stars would lack the raw materials to form planets. Thus Carl Sagan's famous "We are star-stuff" quotation, an idea validated by our extrasolar studies, which allow us to correlate the presence of planets with the existence of heavy elements in their stars. Much remains to be done here, but stars with higher metallicity and more heavy elements do appear more likely to have planets. Volker Bromm (now at the University of Texas) puts it this way: "We're now just beginning to investigate the metallicity threshold for planet formation, so it's hard to say when exactly the window for life opened. But clearly, we're fortunate that the metallicity of the matter that birthed our solar system was high enough for the Earth to form. We owe our existence in a very direct way to all the stars whose life and death preceded the formation of our Sun. And this process began right after the...

We know that organic compounds have been found in meteorite fragments. But are they truly extraterrestrial, or the result of contamination here on Earth? The subject, always controversial, has been given new impetus by a paper that points to the former, with interesting ramifications. Did life begin on Earth or was the Earth seeded by life from the cosmos? Or perhaps a third alternative exists, with pre-existing life influenced by infall from outer space. If we can build a viable case for the latter two possibilities, we can build one just as viable for planets around a wide variety of stars, giving the idea that granted enough time, life of some kind may become ubiquitous a most interesting boost. The scientists involved have been working with fragments of the Murchison meteorite, which fell in 1969 about 100 km north of Melbourne, Australia. Quite a bit of material -- over 100 kg -- could be recovered, enough for batteries of subsequent tests and the discovery of various amino...

When it comes to SETI investigations, the Low Frequency Array (LOFAR) being built in Europe offers intriguing possibilities. With a plan to encompass roughly 25,000 small antennae, arranged in clusters spread out over an area 350 kilometers in diameter, LOFAR may prove sensitive enough to detect the radiation leakage of transmitters in the radio and television bands from extraterrestrial civilizations. The array will operate between 10 and 240 MHz. When completed, it will offer not only myriad astronomical possibilities but SETI opportunities with a difference. Michael Garrett (Leiden University) is general director of ASTRON, the Netherlands Institute for Radio Astronomy, now involved in building the new array. Garrett makes note of what's possible if LOFAR's formidable resources are turned to SETI: "LOFAR can extend the search for extra-terrestrial intelligence to an entirely unexplored part of the low-frequency radio spectrum, an area that is heavily used for civil and military...

Imagine a team of astronomers from a distant extraterrestrial civilization. Anxious to find blue and green living planets like their own, they study various methods of planetary detection and put them to work on small, relatively nearby stars. Detecting planetary transits, they refine their techniques until they trace the signature of a planet much like home. Now assume that, despite the presence of their own version of skeptics like myself (some of us think that sending deliberate signals to the stars is premature without further, wider discussion), they decide to encode information about themselves into a message to be sent by a repeating beacon. Naturally, they turn to those stars around which they've found planets that look to be not only the right size, but in the right position, within the habitable zone where water could exist on the surface. Fanciful? You bet, especially in the idea that a nearby extraterrestrial civilization would be more or less at the same state of...

It's not my usual practice to begin a post with a quotation, but Lee Billings, writing in a recent essay for SEED Magazine, so precisely captures an essential truth about our future in space that I want to give it pride of place. Looking at the ways we search for life on planets around other stars, Billings says this: Throughout history, our knowledge has grown through human ambition and curiosity, only to regress beneath human apathy and caprice. The greatest obstacle to efforts to find another Earth, to discover life elsewhere in the universe, isn't some flaw in our methodology or our technology, but in our will. Most of us alive today are unlikely to see these efforts bear their fullest fruit. Even optimistic young astronomers are uncertain that they will see the light from other living worlds in their careers, or even their lifetimes. But they work as though they will. Whether they see it personally doesn't matter; what matters is that these other planets be seen someday. In...

SETI quite naturally started with the assumption that we should look in the realm of photons for signals from other stars. After all, radio or optical wavelengths were things we understood, and the interest in radio and attendant theorizing about 'waterhole' frequencies and interstellar beacons continues to be worth examining. But a truly advanced civilization might be using methods we haven't yet managed to exploit. Of these, a singularly interesting choice is communication by neutrino. John Learned (University of Hawaii) and colleagues take on this issue in a new paper just posted to the arXiv site, looking at the advantages of the notoriously elusive neutrino. A major plus is that the signal to noise problem is tricky for radio and optical methods, especially in the galactic plane, whereas neutrinos, depending on their energy levels, can offer an essentially noise-free band. We also run into severe problems with photons as we look at line of sight communications anywhere near the...

How much would an extraterrestrial civilization resemble our own? The question resonates because on the one hand, the signature of our activities is what we tend to translate into the SETI search. We look, for example, for the signs of civilizations that are like us but more advanced technologically, which means we apply human thinking and motivations to cultures that are by definition not human. This is natural enough, because we're the only technological civilization we know about, but it leads to results that may mislead us and obscure the actual situation. Fermi's Great Silence bothers us because we assume that what Milan ?irkovi? calls advanced technological civilizations (ATCs) will necessarily move out into the galaxy to colonize it. Yet we see no signs of this, no presence of an expansive power, no characteristic emissions telling us of any intelligence operating around nearby stars. This observation becomes a paradox only if we think in specifically human terms, relating...

Our recent look at panspermia concepts was largely devoted to the transmission of life via microbes or spores here in our own Solar System. The even richer question of how life might pass from star to star is far more problematic, but as a follow-up to that earlier story, I want to look at work that graduate student Jess Johnson did with Jonathan Langton and advisor Greg Laughlin at the University of California, Santa Cruz. Their work suggests that while life might readily survive an interstellar journey, it is unlikely to wander close enough to seed another system. Ponder the era here on Earth known as the Late Heavy Bombardment (LHB). After the period of planetary accretion ended some 4.4 billion years ago, life apparently began. But 3.8 to 4 billion years ago, the LHB saw the planet again pummeled, causing debris to be ejected into space. Looking specifically at the mass that is ejected at 16.7 kilometers per second in the direction of the Earth's motion (this is Solar System...

Olaf Stapledon's Last and First Men (1930), amongst other wonders, pictures our descendants millions of years hence moving from world to world as they attempt to save the species. The Moon approaches the Earth, an imminent peril the 'Fifth Men' escape by terraforming Venus, unfortunately destroying indigenous life forms there. Later, the Fifth Men move on to Neptune, and when their existence there is endangered, they make an attempt to save themselves as a species by seeding their cells among the stars. Interestingly enough, Francis Crick (famed as a co-discoverer of the structure of DNA) suggested in 1973 that life could have been intentionally sent from elsewhere in the universe with the express purpose of finding a new home, an idea that made the later work of Fred Hoyle and Chandra Wickramasinghe seem positively tame. We're talking panspermia, the idea that life can survive long journeys through space to seed other planets (a notion Hoyle addressed in 1982's Evolution from...

Suppose for a moment that life really is rare in the universe. That when we are able to investigate the nearby stars in detail, we not only discover no civilizations but few living things of any kind. If all the elements for producing life are there, is there some kind of filter that prevents it from proceeding into advanced and intelligent stages that use artifacts, write poetry and build von Neumann probes to explore the stars? Nick Bostrom discusses the question in an article in Technology Review, with implications for our understanding of the past and future of civilization. Choke Points in the Past Maybe intelligent beings bring about their own downfall, a premise that takes in more than the collapse of a single society. Alaric's Goths took Rome in 410, hastening the decline of a once great empire, but the devastated period that followed saw Europe gradually re-build into the Renaissance. And as Bostrom notes, while a thousand years may seem like a long time to an individual,...

Alexander Zaitsev's latest contribution to the debate over sending messages to the stars is a short paper that looks at how visible our planet might be thanks to transmissions from planetary radars like Arecibo, Goldstone or the Evpatoria site from which directed transmissions have already been sent. METI (Messaging to Extra-Terrestrial Intelligence) is broadly dedicated to transmitting messages to stars likely to have habitable planets, but so far the number of transmissions is relatively sparse. The debate over METI discusses the wisdom of continuing them without broader discussion. But tucked within that debate is the specific question of our civilization's visibility. For in addition to the messages that have already been sent, beginning with the Arecibo message in 1974 and continuing in the far more targeted transmissions from Evpatoria between 1999 and 2003, we are using our planetary radars to perform crucial astronomical studies. The work these dishes do in refining our...

Larry Klaes tackles the METI question -- do we intentionally broadcast to the stars? -- in Athena Andreadis' Astrogator's Logs today, looking at the pros and cons of an issue that continues to bedevil the scientific community. Of METI advocate Alexander Zaitsev (Russian Academy of Science), for example, Klaes writes this: In a paper Zaitsev published in 2006, the scientist notes that "SETI is meaningless if no one feels the need to transmit." Zaitsev also feels that if there are advanced cultures bent on harming humanity, they will find us eventually, so it is in our best interests to seek them out first. Zaitsev sees the great distances between stars and the physical limits imposed by attempting to attain light speed serve as a natural protective barrier for our species and any other potentially vulnerable beings in the galaxy. David Brin among others takes the other side of the debate in an article tuned for newcomers to these issues. And that's an important audience. Most...

Although I suspect that intelligent life is rare in the cosmos, I'm playing little more than a hunch. So it's interesting to see that Andrew Watson (University of East Anglia) has analyzed the chances for intelligence elsewhere in the universe by looking at the challenges life faced as it evolved. Watson believes that it took specific major steps for an intelligent civilization to develop on Earth, one of which, interestingly enough, is language. Identifying which steps are critical is tricky, but in the aggregate they reduce the chance of intelligence elsewhere. A linguist at heart, I wasn't surprised with the notion that the introduction of language marks a crucial transition as intelligence develops. But what are the other steps, and how do they feed into the possibility of life elsewhere? These interesting questions relate to how long the biosphere will be tenable for life as we know it. If, as was thought until relatively recently, Earth might support life for another five...

"Were the chemicals here on Earth at the time when life began unique to us? We used to think so. But the most recent evidence is different. Within the last few years there have been found in the interstellar spaces the spectral traces of molecules which we never thought could be formed out in those frigid regions: hydrogen cyanide, cyano acetylene, formaldehyde. These are molecules which we had not supposed to exist elsewhere than on Earth. It may turn out that life had more varied beginnings and has more varied forms. And it does not at all follow that the evolutionary path which life (if we discover it) took elsewhere must resemble ours. It does not even follow that we shall recognise it as life -- or that it will recognise us." -- Jacob Bronowski, from The Ascent of Man How accurate do you think we are in projecting what extraterrestrial civilizations might do? The question is prompted by recent speculation on Dyson spheres and the supposition that advanced cultures will...