Number of planets in our solar system: 9 (questionably). Number of planets outside our solar system but within 652 light years of it: 162, and counting. At the 4th annual Astrobiology Science Conference this morning, Chris McCarthy of the California & Carnegie Planet Search gave a state-of-the-universe address. So far we may be alone in it, but the hunk of rock we sit on is certainly not.
Because these planets are a billion times fainter than the stars they orbit, nearly all of them have been identified using the Doppler Method, which essentially measures the wobble of stars created by an orbiting planet's gravitational pull. Scientists can up their odds of locating planets, McCarthy says, by searching stars rich in heavy metals like iron.
But finding planets suitable to life will be a bit trickier. In a scientific twist the Grimm Brothers would appreciate, there are two classes of planets that are definitely not quite right. "Hot Jupiters" have orbital periods of just a few days, and pass so close to their stars that their temperatures reach thousands of degrees. "Eccentric Giants" swoop through the habitable zone, throwing everything off-kilter and ruining the chance for life anywhere in their solar systems.
The number of planets will no doubt keep rising, and with it the potential for habitable candidates. The Automated Planet Finder Telescope will begin collecting data at California's Lick Observatory later this year, detecting changes in star velocity as small as one meter a second. It will also map stars for the Space Interferometer Mission (SIM), scheduled for launch in 2012. —J.Bogo