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There’s finally proof that Earth-like planets can exist outside our solar system: Scientists have managed to measure the mass of exoplanet COROT-7b, revealing that it’s the first exoplanet with a confirmed density similar to our own.
“This is a day we’ve been waiting for for a long time,” said exoplanet researcher Sara Seager of the Massachusettes Institute of Technology, who was not involved in the research. “It’s the first definitive rocky world beyond our solar system, and it’s opening a new gate for our research. We’re really, really excited about it.”
When astronomers discovered COROT-7b in February, they couldn’t determine its mass because they didn’t have precise enough measurements of the velocity of its star. Now, using 70 hours of observation data from the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, scientists from the European Southern Observatory have calculated that the exoplanet is only about five times more massive than Earth.
Combined with the planet’s known radius, which is almost twice that of Earth, the new mass measurement makes COROT-7b the first exoplanet with a known density similar to Earth’s.
Most exoplanets are gaseous giants that resemble Jupiter or Neptune. But if extraterrestrial life exists in the universe, Seager said we’re most likely to find it on a small, rocky exoplanet with a density similar to Earth. “The holy grail in exoplanets, and maybe in all of science, is to find another planet like Earth, a planet that has signs of life on it,” she said.
Unfortunately, with daytime temperatures above 2,000 degrees Fahrenheit and nighttime temps of minus 200, the environment on COROT-7b is probably too extreme to support life. “But it’s helping to tell us that these things must be pretty common,” Seager said.
Indeed, scientists have found about a dozen small exoplanets that might be Earth-like, including a sister planet called COROT-7c that they discovered while studying COROT-7b. “But COROT-7b is the only one with a measurement of the mass,” astrophysicist Claire Moutou of the Laboratory of Astrophysics of Marseilles in France wrote in an e-mail. Moutou and her colleagues presented their results Wednesday at the European Planetary Science Congress in Germany.
Although scientists guessed COROT-7b might have an Earth-like density as soon as they detected the small planet, the variable activity of the planet’s star made it hard to know for sure. The COROT satellite detects exoplanets by measuring tiny changes in a star’s brightness as a planet passes in front of it, but the COROT-7 star is almost constantly twinkling.
“The stellar activity (presence of changing starspots on its surface) generates a strong scattering of the measurements,” Moutou said. “It was pretty hard to disentangle the effect of stellar activity from the planet signal.”
In addition to being the first rocky exoplanet, COROT-7b also orbits closer to its host star than any other known exoplanet. Whipping around at a record-breaking speed of 750,000 kilometers per hour, the planet’s extreme environment may include lava or boiling oceans on its surface. Because this is the first exoplanet of its kind, researchers don’t know quite what to expect.
Just last week, before the announcement of COROT-7b’s mass, astronomer Greg Loughlin of the University of California, Santa Cruz, told Wired how exciting it would be to find such a planet. “We have no idea what a five-Earth-mass planet is like,” Loughlin said. “It could be an oversized version of Earth, it could be a super-Earth. Or alternately, it could be a sub-Neptune or a sub-Uranus. It really is the last basic fundamental kind of planet that we have not had any kind of a look at.” -Alexis Madrigal, Wired.com