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an image of a satellite launch and an arist rendering of the kepler craft The Kepler mission was launched from Cape Canaveral, Florida, on Friday, March 6 (left), placing the Kepler telescope (artist rendering, right) into space. (Photos: NASA, NASA/AMES Research Center/W.Stenzel (OSC))

In Search of Other Earths

NASA launches telescope to see if Earthlike planets exist beyond our solar system

By Dante A. Ciampaglia | March 9 , 2009

For thousands of years, humans have looked at the stars in the night sky and wondered: Are we alone?

The answer to that question might never be answered. But scientists at the National Aeronautics and Space Administration (NASA) are giving it their best shot.

On Friday, March 6, NASA launched a first-of-its-kind telescope called Kepler that will search for Earthlike planets in other parts of our galaxy, known as the Milky Way.

The spacecraft will orbit the sun for three-and-a-half-years. It will observe a patch of sky about 20 full moons wide between the Cygnus and Lyra constellations. There are more than 4 million stars in that part of the Milky Way, and Kepler will only watch about 140,000 of them.

Once it's in orbit and has its gaze fixed, Kepler will use a 55-inch telescope and a 95-million-pixel digital camera to detect little blips in the light coming off those stars. Those tiny disruptions in the light might mean that a planet the size of Earth is passing in front of the star.

/images of the sun with shadows of planets crossing it
The top image is what Jupiter would like like against the sun if observed from outside our solar system. The bottom image is what the Earth would like against the sun if observed from outside our solar system. (Photos courtesy NASA)

Scientists usually discover planets that exist outside our solar system—called exoplanets—using what they call the wobble method. They will watch a star, and if there is a wobble in its light that might mean that a planet's gravity is influencing the star's gravitational pull. More than 340 planets have been discovered that way since 1995. Most have been about the size of Jupiter.

But Earthlike planets are too small and have a gravitational pull that's too weak to be found using the wobble method. Scientists will instead use interruptions in starlight to try to discover planets similar to Earth.

It's a much more difficult task.

"Trying to detect Jupiter-size planets crossing in front of their stars is like trying to measure the effect of a mosquito flying by a car's headlight," Dr. Jim Fanson, Kepler project manager, said. "Finding Earth-sized planets is like trying to detect a very tiny flea."

It will take about a year for an Earthlike planet to orbit a star, so scientists will have to wait a little while before making any discoveries.

Scientists hope that the information Kepler sends back to them will give them a better idea of how many Earthlike planets are out there. They say there's a possibility that there aren't any and that Earth is unique. But they expect to discover that there are many Earth-size planets in our galaxy.

If scientists do find Earthlike planets, the Kepler mission would be the first step in finding out if life exists in other parts of the universe.

NASA wants to launch a new generation of telescopes after Kepler that would be able to capture images of what those Earth-size planets look like. These new telescopes would also analyze the atmospheres of those planets for gases that might indicate the presence of lifeforms.

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