A Thousand Planets

The scientists operating NASA's Kepler spacecraft made a major announcement yesterday:

In a long-awaited announcement, scientists operating NASA’s Kepler planet-hunting satellite reported on Wednesday that they had identified 1,235 possible planets orbiting other stars, potentially tripling the number of known planets.

Of the new candidates, 68 are one and a quarter times the size of the Earth or smaller — smaller, that is, than any previously discovered planets outside the solar system, which are known as exoplanets. Fifty-four of the possible exoplanets are in the so-called habitable zones of stars dimmer and cooler than the Sun, where temperatures should be moderate enough for liquid water.

I think this answers one of the questions we have long had about our universe: planets are very common, including rocky planets of the same general size as the earth.