What Stephen Hawking thinks about aliens made news this weekend, and Centauri Dreams readers will know from our past discussions more or less what Hawking has to say. Assuming we come into contact with an extraterrestrial civilization, it is widely assumed that one of two things will happen. Either an alien visit will be devastating, as has all too often happened when cultures with widely different technologies met, or a benign transfer of information will occur, in which case we benefit by our exposure to new science and revolutionary ideas. A Threat to Humanity? Hawking, who has been working on an upcoming program for the Discovery Channel, opts for the former, as this story in TimesOnline notes. Most life elsewhere in the universe, the physicist believes, will be relatively simple, microbial or primitive animals. But there will be exceptions: ...a few life forms could be intelligent and pose a threat. Hawking believes that contact with such a species could be devastating for...

Just as SETI is redefining its parameters, astrobiology has been going through a shift that widens our notion of habitable zones. Not so long ago, the concept seemed simple. Take a Sun-like star and figure out at what distance a planet could maintain liquid water on its surface. Assume, in other words, that the life you're looking for is more or less like what's found on Earth, and therefore needs the same conditions to persist. Now we're finding remote venues like Enceladus that remind us liquid water can turn up in unusual places, and we've parachuted a probe onto a world, Titan, where it's not inconceivable that exotic forms of life can develop. Throw in the possibility that objects as distant as the Kuiper Belt may contain subsurface liquids and what used to be a constrained habitable zone seems to be vast indeed. And perhaps we've already found another living planet, as astrobiologist Dirk Schulze-Makuch tells Lee Billings in a recent interview. Along with David Darling,...

Changing approaches to SETI are getting public attention these days, as witness a new article in The Economist that makes reference to the probable cause of the interest, the publication of Paul Davies' The Eerie Silence (Houghton Mifflin Harcourt, 2010). Sub-titled 'Renewing Our Search for Alien Intelligence,' Davies' book is making accessible to the general public the kind of discussion we've often had in these pages, looking at the question of whether our SETI strategies at radio and optical wavelengths aren't too limited for any chance of success. The Economist is just one sign of the new interest. After all, technologies like spread spectrum encoding are already masking straightforward radio communications, while conventional broadcasting is giving way to such heavy use of fiber-optics that a planet like ours may go dark at radio wavelengths within a relatively short time as civilizations go, and no more than an infinitesimal flicker in cosmological terms. Thus the interest in...

There is enough going on at the Royal Astronomical Society's 2010 meeting to keep us occupied for some time, but I don't want to go any farther without circling back to UGPS 0722-05, an unusually cool brown dwarf now thought to be the seventh closest star to the Sun. The parallax measurements of its distance are still being refined, but the dwarf is currently thought to be some 9.6 light years from Earth, roughly twice the distance of Proxima Centauri. With a temperature between 130 and 230 degrees Celsius, this is the coolest brown dwarf ever observed, its mass ranging somewhere between five and thirty times that of Jupiter. A number of readers sent links to this discovery, for which many thanks, and I note how interest seems to be growing in the idea that a brown dwarf may exist closer to us than the Alpha Centauri stars. Brown dwarfs are now thought to be relatively common in the galaxy, perhaps as common as normal stars, which suggests that missions like WISE may well discover...

by James and Gregory Benford Interstellar beacons continue to draw discussion, and the Benford brothers now return with further thoughts on the matter in response to reader comments here. How to distinguish a beacon from a natural source, and why consider it in terms of cost? The answer is below, as is an interesting twist on the Fermi paradox. We proposed making cost a useful, perhaps universal, standard because it is a quantitative constraint. Our aim is to help observers look for plausible beacons that may exist. Using transient events seen by observers is an economic way to ask these next, exploratory questions. Speculations always yield to data, and at its 50th anniversary SETI needs a vital data point: first detection. In our latest work, we point out that researchers should be aware of the likely properties of beacons. In particular, beacons may mimic pulsars in repetition rate. But they would distinguish themselves in some way, such as amplitude modulation, varying pulse...

Recently we looked at James and Gregory Benford's thoughts on interstellar beacons, noting that using cost as a likely constraint allowed the authors to discuss how cost would affect design, and therefore the parameters of any beacon we would be likely to observe. But what is it about interstellar beacons that sets them apart from transient phenomena? After all, it was no longer ago than 1963 that Nikolai Kardashev proposed that the radio source CTA 102 could be evidence of a Type II or III extraterrestrial civilization (i.e., one that is able to use the entire energy output of its star, or in the most extreme case, of its entire galaxy). When Gennady Sholomitskii announced his observation that CTA 102's radio emission was varying, something of a sensation ensued. Those of us of a certain age can recall Roger McGuinn's song 'CTA 102,' written and performed by McGuinn's group The Byrds. It was on their Younger Than Yesterday LP, released in 1967. A sample: CTA 102 Year over year...

by James & Gregory Benford Talk of interstellar beacons invariably heats up the discussion, and I was fascinated to read not only Bob Krekorian's take on the concept, but the follow-up comments of James and Gregory Benford, whose work on beacons has been examined previously in these pages. See A Beacon-Oriented Strategy for SETI, as well as Jim Benford's Regarding METI and SETI Motives and Jon Lomberg's Interstellar Beacons: A Silence in Heaven? for our treatment of this topic. Meanwhile, what about putting some constraints on how an interstellar beacon would operate? Here are the Benford brothers with a look at one way to proceed. Bob Krekorian's ideas invite comments. He takes a simple model which has the virtues of minimizing Doppler shifts in SETI beacons: an outward-facing array in an AU scale orbit around a star, fed by solar panels and radiating outward. The concept isn't fleshed out quantatively, so can't be compared to approaches such as ours. And of course he couldn't say...