Artist's rendering of exoplanets around a star. (Credit: NASA)

The Earth may not be as unique as we think it is. That's according to findings announced today by UC Berkeley. Astronomers there believe that Earth-sized planets may be more abundant in the universe than previously thought.

For five years, a team of scientists lead by UC Berkeley watched 166 stars, similar in size to our Sun and all within 80 light years of Earth. In all, they discovered extra-solar planets or "exoplanets" orbiting 22 of the stars. Some are as large as Jupiter while others are about three times the size of Earth, the smallest planet they can detect. Smaller planets were found more frequently than the larger planets.

"We found smaller planets in spades," said astronomer Andrew Howard of UC Berkeley. Using the data, Howard and his team created a statistical model to predict what other planets might be present. "We extrapolated that trend down to Earth-sized planets."

Howard says the data shows that nearly one in four stars like our Sun could have Earth-sized planets. "This is really the first quantitative estimate of the fraction of sun-like stars that have Earth-like planets. Before, the guesses were all over the map. Some people thought it was 100%. Some people thought it was one in a million."

The 33 planets found in the study orbit very close to their stars, meaning temperatures there are most likely too high to support life. The discoveries were made with the Keck Observatory in Hawaii using 10-meter ground telescopes. The planets were found using the "wobble" of the stars – the subtle movement that occurs when a star is pulled by the gravity of its orbiting planets.

The announcement joins a number of exoplanet discoveries in recent months, including NASA's finding of two exoplanets in August. Today's findings were published in the journal Science.

Howard says while the ultimate goal is to find Earth-like planets that could have liquid water, this finding is an important first step. "People have wondered for millennia: is the Earth common or is it rare? And we're starting to learn that the Earth is not a one-off in the universe. It may have cousins out there."

For more on how scientists find exoplanets, check out this QUEST story.

QUEST on KQED Public Media.

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Image: NASA, ESA, P. Kalas, J. Graham, E. Chiang, E. Kite
(University of California, Berkeley), M. Clampin (NASA Goddard
Space Flight Center), M. Fitzgerald (Lawrence Livermore National
Laboratory), and K. Stapelfeldt and J. Krist (NASA Jet Propulsion
Laboratory)

Exoplanets are planets in other solar systems. Though astronomers have detected over 300 exoplanets since 1995, we only have visible-light images of one of them. These photos of the planet Fomalhaut b, taken by the Hubble Space Telescope, have just been published in Science magazine by UC Berkeley astronomer Paul Kalas. The exoplanet Fomalhaut b orbits the star Fomalhaut (pronounced "foam-a-lot"), and at 25 light years away is the closest exoplanet that we know of.

Up until now, astronomers could only detect exoplanets using indirect methods. To learn more about the star wobbles and dips in starlight that indicate other planets are out there, check out QUEST's radio story, Exoplanets, and QUEST's television story, Planet Hunters. These exoplanets are trillions of miles away, but the research happens close to home at the Lick Observatory near San Jose, and at the Chabot Space and Science Center in Oakland.

Over the next few years, astronomers will likely detect additional exoplanets, and will learn much more about them. In 2009, NASA will launch the satellite telescope Kepler, which will be able to detect smallish Earth-sized planets. And in 2013, the James Webb Space Telescope will go into orbit. As stated in this press release, astronomer Paul Kalas hopes the James Webb Space Telescope will tell us whether there are other planets orbiting Fomalhaut – and whether those planets might be able to sustain life. Who knows – maybe on one of those planets, aliens are collecting snapshots of Earth.

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