Monday, February 20, 2006

It's life, Jim, but not as we know it...

So CNN reports that a group of astronomers have developed a short list for more focused study of existence of extraterrestrial life forms. The lead astronomer in the groups indicates that they should looks for life "not as we know it". I find that interesting, but amusing. I and others I have dealt with have always wondered why we're looking for life forms that somewhat resemble those here on Earth. It always seemed to be a mild annoyance to me personally that we'd think aliens would have appendages, eyes, nose etc etc.

In any case, here is the list of star systems they want to target:

Five top candidate stars for those listening for radio signals from intelligent civilizations: 1. beta CVn: A sun-like star about 26 light-years away in the constellation Canes Venatici (the Hound Dogs). 2. HD 10307: A star about 42 light-years away.3. HD 211415: About half the metal content of sun and a bit cooler, this star is in just a little farther away than HD 10307. 4. 18 Sco: The star, in the constellation Scorpio, is almost an identical twin to our sun. 5. 51 Pegasus: In 1995, Swiss astronomers reported they had detected the first planet beyond our solar system in orbit around 51 Pegasus. Five candidates for those trying to detect Earth-like planets in orbit around nearby stars: 1. epsilon Indi A: A star only about one-tenth as bright as the sun. It is about 11.8 light-years away in the constellation Indus. 2. epsilon Eridani: A star somewhat smaller and cooler than our sun, located about 10.5 light-years away in the constellation Eridanus (the River). 3. omicron2 Eridani: A yellow-orange star about 16 light-years away, roughly the same age as our sun. 4. alpha Centauri B: Long considered one of the places in the Milky Way that might offer terrestrial conditions. This star is part of a triple star system. 5. tau Ceti: A G-class star with the same brightness category as our sun.


Observer said...

51 Peg doesn't make much sense. There's no habitable planetary orbit there that would be stable. I wonder what their reasoning is? I mean, sure, life can find a foothold anywhere (probably), but intelligent life probably needs some stable time to develop, and it's not going to happen in that system.

And Epsilon Indi A doesn't make much sense. We don't generally look around cool stars because the planet would have to be so close for liquid water that it would have to be tidally locked to the parent star. I think, too, that those cool red stars have something else screwy I can't recall at the moment. Maybe the spectral line blanketing that blocks out a lot of the visible light. Or maybe it's that they flare a lot or something.

My favorite book on SETI right now is "Rare Earth" by one of my old profs, Don Brownlee, and paleontologist Peter Ward. I'm not as pessimistic as they are, but it's a very thought-provoking read. As for candidate lists, I'm looking forward to the Kepler mission, which has the chance (via transit searches) to ferret out a whole bunch of systems.

That's the best planet finder we're going to have until the pie-in-the-sky Terrestrial Planet Finder gets going. Space-based infrared interferometry. Whoo. That's a lot of moving parts.

Phil said...

Downright fascinating, all this. It seems to me we have made some major strides in this area. I'm not as knowledgable as you are in this field, but the fact that we can just about select which stars we feel are capable of possesing planets that could support life, based on what we now know, is very exciting.

One thing I have always been curious about is: What happens when we do find something? How does it get announced? Will it? Is there protocol for such a thing? What implications would have it on the religious world?

I shall keep an eye out for that book you mention. Does it discuss any of the above points, or is more of a scientific approach that doesn't consider social factors?

Observer said...

"Rare Earth" is strictly about the science. I also enjoyed the tangentially related "What If the Moon Didn't Exist?" The best simulation I've seen of what would happen in the event of an actual signal detection was done by Sagan in the movie "Contact" (book is excellent and somewhat different, by the way, if you haven't read it ... surely you've seen the movie).

When trying to select a candidate star for an extrasolar planet search, we almost always select stars mostly like the Sun. Stars much hotter/more massive are either unstable (A stars) or, worse, have very short lifetimes so that life couldn't get started on an orbiting planet in time (plus the radiation is too "hard").

Stars much cooler, you have to be super close in for water to exist in liquid form. So odds are good for some kind of tidal locking situation, which is bad for life. Plus there are other problems with cool, red stars as I mentioned.

As for further SETI reading, I haven't read any recent SETI-related books, but I'm sure there are some good new ones searchable on Amazon. In 1994 or 1996, Scientific American did a special edition on SETI with about 7-8 articles dealing some with the questions you asked. Not much has changed on the philosophical side since that time, though we have made enormous technical leaps in finding planets.

I bet you could find some good stuff at the public library.