Extrasolar

An artist's impression of the densely packed Kepler 11 system shows three planets transiting in front of their host star simultaneously. Image: NASA/Ames/JPL-Caltech/T. Pyle

There's lots of planets out there:

Kepler is well on its way to vastly augmenting the roster of known exoplanets, of which there are now 500 or so, and may have already gotten a whiff of several potentially habitable worlds. "We have 54 planets in the habitable zone of their stars," Borucki says, referring to the temperate orbital zone around a star that would allow for the existence of liquid water on a planet. "One of them is 0.9 times the radius of the Earth, and four of them are less than two Earth radii." Any of those would be the most Earth-like world ever detected outside the solar system. What is more, some of the larger, more Jupiter-like planets Kepler is sniffing at in the habitable zone might have moons, and some of those satellites would themselves be potentially habitable. "It's sort of awesome," Borucki says of Kepler's haul. "The implications are that there are an awful lot of planets out there."