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The search for Earth II continues

This month marks the first anniversary of NASA's Kepler robot spacecraft mission. Kepler was launched from Cape Canaveral, Fla., atop a Delta II rocket in March 2009.

Kepler is a bold mission that is hunting for exoplanets, perhaps even another Earth. There are certainly no guarantees of finding "Earth II", but the way Kepler has been performing so far, an exciting discovery may be just around the corner.

Kepler has already earned its keep: the spacecraft recently detected an atmosphere around exoplanet HAT-P-7b, a known gas giant 1,000 light years away. Kepler's chance discovery was made even before NASA researchers officially started the science phase of the mission. Now that's a hardworking spacecraft!

In January, NASA officials announced the discovery of five exoplanets. Great news, but no "Earth II"-at least not yet.

"As an astronomer, I'm particularly proud of the Kepler science team who have all worked very hard to make this exciting discovery possible," said NASA Ames Research Center Director S. Pete Worden at a recent news conference. "This is a really cool mission and truly is what NASA is all about."

Worden said researchers expect to find several terrestrial-size planets between 2010 and 2012 with the aid of Kepler's complex telescope.

According to Worden, "the Kepler mission is designed to observe more than 150,000 stars continuously and simultaneously for signs of Earth-size planets until at least November 2012. Some of the planets are expected to orbit in a star's habitable zone, a warm region where liquid water could pool on the surface."

Kepler's main instrument is the sophisticated 0.95-meter diameter telescope-camera; technically it's called a photometer-a giant light meter-and is the largest camera ever launched.

Kepler's photometer measures so-called dips in the brightness of distant stars.

Here's how it works: Because planets cross in front of parent stars (called transiting), starlight will "blink" as seen by Kepler's big eye. Using this blinking effect, a far distant exoplanet's size can be determined-and all with just a tiny alteration in the parent sun's brightness as seen by Kepler. With this basic information, scientists can then figure out the planet's uppermost atmospheric or surface temperature, even figure out the world's orbital period and the luminosity of the star.

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