<img alt=“phot-33a-09-fullres.jpg” src=“https://blogs.nature.com/news/thegreatbeyond/phot-33a-09-fullres.jpg” width=“340” height=“227” hspace=10 align=right border=0 />
Astronomers from a major European planet-hunting team announced improved measurements of the density of a small exoplanet at the European Planetary Science Congress in Potsdam, Germany, confirming earlier guesses that CoRoT-7b is more Earth-like than Jupiter-like.
The zippy little planet, previously estimated at 5-10 times the Earth’s mass with a radius less than twice the Earth’s, was first announced in February 2009 (Tiniest exoplanet found, Nature News, 3 February 2009). Today’s more complete analysis appears in Astronomy and Astrophysics, in which the authors report that CoRoT7-7b’s mass is likely just about five times that of the Earth. The study relies on 70 hours of spectroscopic observations over several months to more firmly establish the relative masses of the host star CoRoT-7 and its planetary companions, and also reveals the presence of a second rocky planet.
“This is a day we’ve been waiting for for a long time,” exoplanet researcher Sara Seager told Wired.com, which also ran a quote in which she called an Earth-like planet the “holy grail” of exoplanet research, “and maybe in all of science.”
Most of the 300+ exoplanets found to date are gas giants more akin to Jupiter or Neptune than Earth, but thanks to improved technology and detection techniques, recent inductees in the club include exoplanets with masses potentially as low as 1.9 times the Earth’s (Exoplanets lighten up, Nature News, 21 April 2009). Because they were detected indirectly by the wobbles they induced on their host stars, astronomers did not know the planets’ radii, and without knowing the geometry of the planetary system, they cannot rule out that the planet might have a larger mass. The present analysis, which combines two independent means of detecting CoRoT-7b, yields a new density estimate indistinguishable from that of the Earth, though because the planet is larger, astronomers think its composition could be mostly silicates with an iron core or could contain up to 40% water.
Team member Artie Hartzes told the Associated Press that astronomers are calling it “the lava planet.” Its surface temperature may range from 200 degrees below 0 at night to a balmier 2000 degrees Celsius by day.
Physics World got a critical quote from an outside astronomer, noting that sunspots on the host star may have interfered with the spectroscopic measurements on which the mass and density estimates are based.
For more background on exoplanets, see Nature’s Q & A with exoplanet expert Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics.
Photo: ESO