The Kepler spacecraft keeps its eye on more than 156,000 stars. So far, NASA's famed space telescope has succeeded in its exoplanet hunt. See more space exploration pictures.
Image courtesy NASA
Long before there were telescopes, astronomers or written history, people gazed up at "wandering stars" that later observers would call planets. As we applied our myths of faraway realms to these heavenly bodies, we began to wonder about the possibility of life on other worlds, an idea that has enthralled us ever since.
One of the earliest musings about conditions on another "planet" was a 1634 novel called "Somnium" (Latin for "The Dream"). The tale, perhaps the earliest work of science fiction, describes a journey to the moon, which, like the sun, had sometimes been categorized as a planet.
Johannes Kepler, father of the laws of planetary motion and one of the people chiefly responsible for the ultimate success of the Copernican revolution of heliocentrism, wrote that book. Appropriately, he's also the namesake of one of the most important instruments yet devised for finding planets outside our solar system, called exoplanets or extrasolar planets, that could support life.
According to William Borucki and his Kepler mission colleagues, our galaxy alone boasts a minimum of 50 billion exoplanets, 500 million of which likely orbit within habitable zones (areas around stars with temperature ranges conducive to the existence of liquid water) [source: Borenstein].
In its first four months of operation, Kepler located 1,235 possible planets orbiting other stars, 15 of which have been confirmed by subsequent observations [source: Ames Research Center, NASA Finds Earth-size Planet Candidates]. Here's the February 2011 breakdown of these candidates, according to Ames Research Center:
- 68 are approximately Earth-sized.
- 288 are super-Earths (almost twice the Earth's diameter).
- 662 are Neptune-sized (about four times Earth's diameter, or 57 times its volume).
- 165 are the size of Jupiter (about 11 times Earth's diameter, or 1,300 times its volume).
- Finally, 19 are even larger than Jupiter.
"The fact that we've found so many planet candidates in such a tiny fraction of the sky suggests there are countless planets orbiting sun-like stars in our galaxy," said Borucki in a press release. "We went from zero to 68 Earth-sized planet candidates and zero to 54 candidates in the habitable zone, some of which could have moons with liquid water."
Of the 54 new planet candidates found by Kepler in habitable zones, five are near-Earth-sized and the other 49 range from up to twice the size of Earth to larger than Jupiter [source: Ames Research Center, NASA Finds Earth-size Planet Candidates].
Johannes Kepler used science fiction to argue subtly for a revolutionary view of the cosmos that fits the observational data. Now his namesake spacecraft is providing data that is transforming our understanding of that universe.
In this article, we'll take a closer look at the instruments and techniques scientists use to locate exoplanets, how they work and the exciting discoveries they've already made.
