For alien life-seekers, new hope

In the new report, Michel Mayor of the Geneva Observatory and his colleagues said they had found 45 planets that were only a few times as massive as our beloved blue base, which means that they, like Earth, are probably built of rock.

The tally is proportionally impressive as well: roughly one in three stars surveyed showed signs of harbouring stony planets, and other researchers performing similar studies said the figure might be more like one in two. And though the 45 planets on the Geneva list are all “star-huggers,” as one astronomer put it, with orbital periods of 2 to 50 days—even Mercury needs nearly three months to circumnavigate the Sun—researchers are confident that other rocky planets remain to be found at Earthier distances from their suns.

Sara Seager, a planetary theorist at the Massachusetts Institute of Technology, said astronomers hunt for planets by detecting telltale wobbles they induce in their host stars, a method that selectively nets the too big or too near. Nevertheless, she said, “the fact is, as soon as astronomers started looking for low-mass planets, they found a whole bunch, and that’s a real breakthrough.” Just imagine the orgy of moderation that a more inclusive scan would reveal.

To some theorists, the new results virtually guarantee the existence of other Earthlike worlds.

“Suppose you have a tribe, and the most noticeable members are the warriors, because they’re adventuresome, they roam around, they’re the first to be spotted,” said Douglas N. C. Lin, a professor of astronomy and astrophysics at the University of California, Santa Cruz. “But you know that for every warrior, there’s a family behind the warrior.”

Dr. Lin continued, “Just as you can extrapolate from the warriors you see what the size of the larger population deep in the woods may be, so the presence of these short-period, super Earths implies that there are clusters of other planets farther out.” Potentially pleasant planets at that. “I would imagine that a significant fraction of ordinary Sunlike stars, maybe more than 10 percent, have habitable planets around them,” Dr. Lin said.

If planets abound, scientists suspect that life abounds, too, at least of the microbial kind. After all, they said, life arose here relatively quickly, maybe 800 million years after Earth’s condensational birt-h-and then stayed unicellular for the next three billion-plus years.

Eager to identify other candidate Gaias, astronomers have high hopes for the Kepler spacecraft to be launched in February. Kepler will take a different approach in its planetary scan, Dr. Seager said, searching not for stellar wobbles but for “tiny drops in brightness,” possible signs of a planet transiting across the distant Sun’s face. Kepler will track 100,000 stars for four years, enough to detect the occasional crossing of any planets with leisurely orbits like ours. “It will be akin to the great age of exploration, the explorers of the 16th century,” Dr. Shostak said. “We will nail down what fraction of stars have planets,” and more important, “what fraction of those planets are small, terrestrial planets.”
-NATALIE ANGIER(NYT)