NASA’s Kepler Mission Primed to Hunt Earth-like Worlds

NASA's planet-hunting Kepler space telescope is set for a planned March 5 launch to begin searching for alien worlds the size of Earth and bigger, mission leaders said Thursday.

"We're only two weeks from launch and there's a lot of activities going on down at the Kennedy Space Center right now," said Jon Morse, director of the Astrophysics Division at NASA Headquarters in Washington, D.C.

The probe, which is slated to blast off from the Cape Canaveral Air Force Station in Florida aboard a Delta 2 booster, will be searching for Earth-sized planets orbiting other stars in the region where liquid water - essential to life as we know it - might exist. The spacecraft is expected to move to its launch pad today, mission managers said.

Over the last two decades, scientists have spotted more than 300 extrasolar planets circling other stars in our Milky Way galaxy. Most of these planets have been about the size of Jupiter or larger, making it unlikely they would harbor life.

"Most of these planets do not have Earth-like sizes or orbits," Morse said.

Over the course of its planned 3 1/2-year mission, Kepler will search the skies for planets 30 to 600 times smaller than Jupiter - closer to an Earthly girth. After launch, Kepler will enter a 372.5-day orbit around the sun, trailing in Earth's wake. It is expected to be the first to find truly Earth-sized planets orbiting stars like our own sun.

"I call it our planetary census-taker," Morse said.

Astrophysicist Alan Boss, of the Carnegie Institution in Washington, D.C., recently estimated that there are about ten thousand billion billion habitable planets in the observable universe, with some of those being Earth-like worlds.

Kepler will also be looking for Earth-like planets, rocky bodies that orbit what is called a star's "habitable zone," the region where liquid water, and perhaps life, could exist.

"Kepler's designed to find hundreds of Earth-like planets if they're common around stars," said Kepler principal investigator William Borucki of NASA's Ames Research Center in Moffett Field, Calif.

While Kepler will be looking for planets that could support life, it won't actually find any little green men.

"Kepler is not hoping to find E.T., it's hoping to find E.T.'s home," Borucki said.

Kepler won't yield any spectacular Hubble-esque images, but its 0.95-meter diameter telescope and array of 42 charge-coupled devices (light-sensitive microchips also found in standard digital cameras) will search for planets by measuring the change in brightness that occurs when a planets moves in front of its star (from the perspective of Earth).

By measuring the amount of fluctuation in light and how long it lasts, scientists can estimate the size of the planet, the size of its orbit and potentially even the planet's temperature.

This same transit technique is responsible for finding most of the known exoplanets to date.

The potential planets Kepler spots will later be further examined by Earth-based telescopes, to rule out false-positives and gather more observations.

Kepler, a Discovery-class mission, was selected by NASA in 2001. Its original price tag has risen over the last eight years, now reaching nearly $600 million.

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