Scientists discover rocky, Earth-sized planet outside our solar system

SAN JOSE ---- The place is inhospitable, with molten temperatures and possibly clouds of melted silicon. But a discovery across the galaxy is giving hope to searchers of intelligent life.

A team led by NASA Ames researchers has confirmed the existence of the first rocky planet outside our solar system. Kepler-10b is closest in size to Earth of 519 extra-solar planets discovered so far. It is about 1 1/2 times the Earth's diameter and speeding around a star similar to our sun in the constellation Cygnus, about 560 light-years away.

"It's unquestionably a rocky world orbiting a star outside our solar system," said Natalie Batalha, deputy science team leader for the Kepler Mission at NASA Ames. She and about 50 other scientists published their discovery last week in Astrophysical Journal.

Unlike the majority of the so-called exoplanets detected so far, Kepler-10b is solid and not gaseous. "It's something you can stand on," she said.

Its size and composition are significant because an Earth-sized, solid planet is more likely to harbor water, essential for life. Kepler-10b, which is 20 times closer to its star than Mercury is to the sun, can't sustain life. But it still has astronomers excited.

In September, astronomers led by a UC Santa Cruz professor announced they had found what was probably a rocky planet, called Gliese 581g. But other scientists discounted the discovery, pointing to an error in data analysis. So its existence is unconfirmed.

One reason controversies arise over planets outside the solar system is that even astronomers' most powerful tools can't see them. Instead, scientists prove the existence of exoplanets by scanning the galaxy and searching for regular but slight dimming of light from stars. That dimming can be caused by a "planet transit," when an orbiting planet periodically blocks the star's light, like an eclipse. A planet's size can be calculated from how much light it blocks when passing in front of its star.

Kepler-10b's discovery, announced Monday at a meeting of the American Astronomical Society in Seattle, is a major dividend paid by NASA Ames' Kepler spacecraft, launched in March 2009.

From its lonely orbit around the sun and with its view undistorted by the Earth's atmosphere, Kepler fixes its meter-wide lens on 150,000 stars, measuring light every 30 minutes. Scientists pore over the data, searching for signs of planet transit.

In July 2009, Batalha's team members noticed those signs and stepped up observations. They ordered the spacecraft to gather data once a minute, to better assess the star Kepler-10 because they needed more information.

"Other astrophysical signals in nature can masquerade as a planet transit," said Batalha, who also teaches physics and astronomy at San Jose State University.

They gathered evidence of star turmoil, such as earthquakes, revealing the star's structure and properties. "Stars kind of vibrate and ring like a bell," said Edna DeVore, co-investigator for the Kepler mission.

The team reserved precious time on the Keck telescope on Hawaii's Mauna Kea to help disentangle the signals.

By September, they knew that their planet was rocky.

Was it exciting?

"Do you want me to tell you how high I was jumping?" Batalha said. In months of combing through data to watching signs steadily emerging, she said, "It was a joy to watch."

While Kepler-10b is "in our solar neighborhood," Batalha said, it would be premature to make travel plans. First, its distance from the Earth means that even whizzing there at the speed of light would take 560 years.

The planet's day side is significantly hotter than molten lava, Batalha said. Its night side is cooler, but probably still has hostile temperatures and perhaps toxic dust. The planet circles with the same side facing its star, similar to the way our moon orbits Earth, but in less time than one Earth day.

While scientists mine the trove of data, the essential question remains. "We want to know if we're alone in our galaxy," Batalha said. "This is one step in that direction."