Artist concept of an Earthlike Exoplanet. Credit: ESO
It's been a little over a year since NASA's Kepler telescope was launched into space. Its mission: to stare unblinkingly at 156,000 stars in a patch of sky in the constellations Lyra and Cygnus on a quest to spot extrasolar planets. Results so far? As anticipated…astounding.
It's been 15 years since the first extrasolar planet (exoplanet: planet orbiting a star other than our Sun) was confirmed to exist. Since that time and until the launch of Kepler, subsequent detections have racked up the number by about one a month to well over 400. Planets, see? Worlds! What would we name them if we knew them more intimately, as we do Jupiter and Neptune?
What are they like, and how are we seeing them? Well—we don't exactly see them; we detect their presence by their affect on their parent stars: small wiggles and wobbles that their gravity and motion cause in their star, or tiny dips in star brightness when they pass in front of it ("transit").
As for what they're like, so far we've detected mostly very large planets—gas giants, like Jupiter, Saturn, Uranus, and Neptune—that are relatively close to their stars. "Hot Jupiters" they've been called, for obvious reasons. The bigger the planet, the greater its gravitational or eclipsing effects; the closer the planet to its star, the shorter its orbital period and so the more frequently we can detect their influences.
NASA's Kepler mission has a slightly different goal than finding Hot Jupiters. Using the "transit method" of looking for small drops in star brightness, Kepler is looking for Earth-sized planets orbiting their stars at Earth-like distances—in a nutshell, we're looking for environments similar to those of Earth, since Earth's environment is the one that we know supports life.