A Scientist’s Guide to Finding Alien Life: Where, When, and in What Universe

A variety of new findings point to the “habitable zones” where we’re likely to find extraterrestrials.

by Adam Frank

From the May 2009 issue, published online May 11, 2009

Massive stars give, but they also take away—and that puts the inner limit on the galactic habitable zone. The supernova explosions that create and spread heavy elements also unleash a torrent of high-energy radiation: gamma rays, X-rays, and ultraviolet light. Those stellar explosions can have lethal effects on planets orbiting stars even tens of light-years away. In the crowded central regions of the galaxy, home to large numbers of massive stars, supernovas are so common that the evolution of complex life-forms might be difficult if not impossible.

The big question is how bad the supernova effect is. Lineweaver and his colleagues calculate that radiation poisoning could exclude the inner 20 percent of the Milky Way, which encompasses about half of all the stars in the galaxy.

“You are looking for that sweet spot,” says Fred Adams of the University of Michigan, “where you are not so close to the center that conditions are hostile and not so far out that the metal abundance is too low.” But the Milky Way is huge, so Adams suggests putting things in perspective. “At worst the amount of galactic real estate favorable to life is reduced by a factor of two or three,” he says.

Full article here:

http://discovermagazine.com/2009/may/11-a-scientists-guide-to-finding-alien-life/article_view?b_start:int=1&-C=