San Jose Mercury News
POSTED: 12:48 p.m. HST, Jan 12, 2011
SAN JOSE, Calif. — It resembles a glowing briquette, with scorching temperatures, no water and possibly clouds of toxic melted silicon. An inviting place to live? No. But the discovery of this small and rocky world by astronomers, using the Keck Telescope on Mauna Kea and a NASA satellite, offers an important addition to the growing list of planets beyond our solar system — and a missing link between hot gaseous giants and Earth-like homes.
The team, led by San Jose State University scientist Natalie Batalha of NASA's Kepler satellite team, says the new orb is the most definitive evidence yet of a rocky planet outside our solar system. Dubbed Kepler-10b, it is closest in size to Earth of the more than 500 extra-solar planets discovered so far. About 1.5 times the Earth's diameter and almost five times as massive, it speeds 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 Batalha, who directed the study of the planet and reported her findings Monday at a meeting of the American Astronomical Society.
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," Batalha said. Its size and composition are significant because astronomers are seeking places with a rocky core, like Earth.
Kepler-10b is too hot to sustain life as we know it, because it doesn't spin and is 20 times closer to its star than Mercury is to the sun. But it still has astronomers excited.
"This planet will go into astronomy textbooks worldwide," said astronomer Geoff Marcy of the University of California-Berkeley.
Two years ago, a French team found another planet that might be rocky.
And in September, astronomers led by University of California-Santa Cruz professor Steve Vogt announced they had found a place, called Gliese 581g, that could be Earth-like because of its location, orbiting in the potentially habitable "goldilocks zone." But some other scientists quibble over data analysis, and have discounted those discoveries.
Of this latest discovery, Vogt dismissed it as "the equivalent of a well-lit charcoal briquette, several thousands of degrees, with no chance of liquid water or life. This may be an 'Earth-sized' planet, but it is definitely not 'Earth-like,' nor habitable by anyone's stretch of imagination."
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 is one of the first major dividends 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."