It is a sad reflection on science education that many people believe in space aliens. Science is not helped at all by wacko former astronauts who claim to have heard mysterious music in space [though none of the other crew members did!].
The brutal fact is that we have no evidence whatsoever of life outside Earth. Now absence of evidence doesn't mean it's not there, but we have to suppose as a working hypothesis that what we see is what we have: NO LIFE OUT THERE.
On January 8, 2005, Jeffrey Bada reviewed a book on astrobiology. This book review is Bada, J. L. 2005. A field with a life of its own. Science 307, p. 46. There's no Web site, but this will be freely available on the Web later in 2005. I can't resist quoting one sentence. Bada writes,
"scientific curiosity alone likely cannot explain the explosive growth of astrobiology. After reading The Living Universe, I came to the conclusion that one of the field's attractions was money: and lots of it."
I fully recognize that LOTS of good science has come from "astrobiologists", even if they haven't discovered any astrobiology yet.
Many planetary systems may be very vulnerable to catastrophic disturbance over geological time scales. These systems occur where stars are densest, so include perhaps most of the stars in the Universe (and most of the planetary systems).
Small planets like Earth may not normally last long. The star that ate a planet, from PhysicsWeb, May 9, 2001.
The chances of inhabitable Earth-like planets out there drop again: BBC News OnLine, January 28, 2003.
Our Sun may be a much more friendly star than most, with extraordinary stability over geological time scales. Other stars have "superflares" that would have disastrous effects on any life on their planets. See this page too.
Our solar system may be very unusual (with all that implies for the origin of life). Press release, August 18, 2004. For previous stories coming to a similar conclusion by another route, see Earth-like planets may be rare and other Earths are rare. Obviously, otherwise aliens would be here already. But it's refreshing to see it stated clearly.
Even more catastrophic are gamma-ray bursts, astoundingly powerful explosions that could sterilize a large section of an entire galaxy. From Scientific American, 2002.
At the same time, gamma-ray bursts might be involved along with supernovae in the formation of starts and planets. If this affects planetary formation, then the chances of alien life out there is dramatically lessened.
So even on astronomical evidence, the numbers that should be plugged into the Drake Equation (see below) may give a relatively slim chance for intelligent, star-faring life out there in the cosmos.
Finally, as a geologist, I suspect that another factor that should be included in the Drake Equation, but isn't: the chances of a planet having plate tectonics. Without plate tectonics, there's no recycling of crust, no recycling of volcanic material, therefore no recycling of water (vapor) to the surface. See Mars, for example. So what are the chances of a planet having plate tectonics? Small. So cut the Drake result by another factor of 10.
Overall, perhaps the most futile of human "scientific" endeavors is the attempt to send messages to space aliens. See this news article. However, this latest effort does not seem to involve my (tax) money, so as long as it is financed by the individuals who want to send the messages, that is just fine by me. I wish they would spend their money on improving our own planet, but that's a judgment call.
Recent research seems (to me) to increase the chances that we are either alone in the Universe, or alone in this galaxy. And we are likely to remain alone for a long time. A 2000 book by Ward and Brownlee argues that life may be abundant in the cosmos, but complex or intelligent life is not. The New York Times liked it.
Here are two must-read essays. Bruce Moomaw attended NASA's "First Annual" Astrobiology Conference, and these two essays were written as reports on the conference talks and posters. Overall, I get the impression that not even "astrobiologists" are very hopeful about complex life on other planets:
Mini-essay first written in January 1999; last updated March 5, 2006.
Links last checked September 29, 2005.
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