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NASA says Kepler spacecraft proves it can find Earth-like planets

Readings on the planet HAT-P-7b indicate that the craft's instruments should be able to spot small Earths in the habitable zones around stars in our galaxy.

August 07, 2009|John Johnson Jr.

NASA's planet-hunting spacecraft, Kepler, has made radical new discoveries about a hellish planet a thousand light years away -- proof, scientists say, that the craft will be able to carry out its mission of finding other Earths in our galaxy, provided they exist.

NASA scientists released Kepler's analysis Thursday of an already known "hot Jupiter" planet called HAT-P-7b in the constellation Cygnus. The spacecraft mapped the planet's orbit and gave new details about its hazy, ozone-like atmosphere, where temperatures climb as high as 5,000 degrees Fahrenheit.

The analysis proves that Kepler's onboard telescope and light-detecting instruments are at least 100 times more precise than the ground-based detectors that originally found HAT-P-7b, the scientists said at a briefing at NASA headquarters in Washington. That should be good enough to spot any pint-sized planets -- about the size of Earth -- in a star's so-called habitable zone, where temperatures are warm enough for water to be liquid but not so hot as to torch the planet's surface.

"Kepler has the ability to detect Earth-sized planets," Alan Boss, an astrophysicist with the Carnegie Institution of Washington, said at the briefing. "The question that remains is: How many Earths are there?"

Kepler, which was launched in March, is the first spacecraft with a mission to find potentially habitable worlds. Over the next few years, as it circles the sun in an Earth-trailing orbit, it will scan 100,000 stars in the constellations of Cygnus and Lyra, looking for planets.

Of the previously discovered 350 or so extrasolar planets -- those that lie outside our solar system -- none is a candidate for the "Goldilocks" planet, where things are just right for life to gain a foothold. Teams in Europe and the United States have found several super-Earths, planets that are slightly larger than our home planet. But all are either too close to their star and thus baking hells like Venus, or too far away and therefore ice-cube worlds like Pluto.

Since the launch of Kepler, controllers have spent most of their time tuning its sophisticated instruments, which are designed to detect the tiniest variations in light from a star thousands of light-years away that might indicate a planet orbiting it. Only in the last few weeks has the science team begun putting Kepler through its paces, gathering data.

Most extrasolar planets are detected by measuring the dimming of the light from their parent stars, which is caused by the planets passing in front of them. This is known as a transit. By determining the degree of dimming and how far away the star is from Earth, scientists can find out how big the planet is, even if they can't see it directly.

The challenge of finding an Earth-sized planet at the right distance from its star is illustrated by the fact that a planet the size of Jupiter blocks out 1% of a typical star's light, whereas one the size of the Earth blocks 100 times less, or .01%.

HAT-P-7b was discovered last year by Earth-based instruments. It was classified as a Jupiter-sized planet orbiting only 4 million miles from its star -- so close that a year on HAT-P-7b is only two Earth days long. At that distance, the planet glows from the heat as it circles its star.

Kepler's instruments detected the same dip in starlight as Earth-based observers did as HAT-P-7b crossed in front of its parent star. But Kepler was able to do more. It also detected a second small dip when the planet went behind the star, which is known as an occultation.

Because that dimming is a hundred times smaller than the dimming caused by the transit, the scientific team became convinced that Earth-sized planets are within reach of Kepler.

Kepler's instruments showed that the planet HAT-P-7b is absorbing a "huge amount of energy" from its star, according to Sara Seager, a planetary scientist at Massachusetts Institute of Technology. This could be caused by particles high in the planet's atmosphere, or some sort of ozone-like haze.

She emphasized that all of these findings came from only 10 days of observing.

"These exquisite data are just the tip of the iceberg," she said.

Kepler will ultimately be judged, however, on whether it will help answer one of humankind's grandest questions: Are we alone?

Answering that question is going to take time. Because it will take three orbits to confirm a planet's existence, it might be 2012 before any major discovery is announced, said Bill Borucki, a space scientist at the NASA Ames Research Center in Mountain View, Calif.

Already, Borucki said, "we are finding signals that could be planets." But he cautioned patience. He said that he wanted to avoid what happened in the early days of research on extrasolar planets, when scientists prematurely announced discoveries they later had to retract.

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john.johnson@latimes.com

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