New Telescope To Hunt For Earth-Like Planets

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March 6, 2009 · NASA is getting ready to launch a new space-based telescope that will search for Earth-like planets around other stars.

The $600 million Kepler mission should reveal how common it is for other solar systems to contain small, rocky planets that might support life.

"The expectation is that such Earth-like planets will be quite common," says Alan Boss, a planetary scientist at the Carnegie Institution of Washington who is part of Kepler's science team. "But Kepler will actually prove that, one way or the other."

Back in 1995, scientists announced the first definitive discovery of a planet orbiting another sunlike star. Since then, more than 300 other planets have been detected outside of our solar system.

"These planets are generally gas giant planets, very much like Jupiter and Saturn, enormous gas balls," says William Borucki of NASA's Ames Research Center, the principal science investigator for the Kepler mission.

These previously discovered planets are also generally in orbits that make them too hot to support life.

In contrast, the Kepler telescope could potentially find hundreds of small, rocky planets orbiting in or near the so-called Goldilocks zone — a region around a star that is not too hot and not too cold.

"If we find that many, it certainly will mean that life may well be common throughout our galaxy," Borucki says.

But if Kepler doesn't find any planets like that, it would mean that Earth — and life — might be very rare. "It will mean," says Borucki, "there will be no Star Trek."

The Kepler telescope will orbit the sun, spending more than three years just staring at a patch of space in the constellations Cygnus and Lyra. The region contains more than 100,000 stars.

Every half-hour, the telescope will measure the brightness of these stars, watching for the slight, tell-tale dimming that will occur when an orbiting planet passes between its star and Kepler.

"The bigger the planet, the more light it blocks," explains Borucki, "so we get the size of the planet from the size of the dimming."

A small, Earth-like planet will produce a miniscule amount of dimming. A good comparison is what a person might see while watching a flea crawl across a car headlight that's several miles away.

Once a planet has been detected, scientists can tell at what distance it orbits from its star — and whether temperatures on the planet might allow liquid water and life — by watching to see how long it takes before the planet crosses Kepler's view of the star again.

It will be several years before scientists have enough information to know for sure whether Kepler has found any Earth twins.

And even if they find some, they still won't know if these planets harbor any life. "Kepler will not find E.T.," says Borukci. "It's hoping to find E.T.'s home."

Once Kepler has found some potential homes, however, space agencies will have a better sense of how to design another space telescope, says Boss, one that could "actually take a picture of a nearby Earth-like planet and tell us something about its atmosphere."

If that kind of future telescope detected things like oxygen, carbon dioxide, water and methane, Boss explains, "that would tell us that the planet is probably not only habitable but even inhabited."