spacetoday.net: "Super-Earth" exoplanets discovered

Posted: Tue, Jun 17, 2008, 6:31 AM ET (1031 GMT)
Three super-Earth exoplants around HD40307 (ESO)

Astronomers have discovered three low-mass extrasolar planets dubbed "super-Earths" because they are only slightly larger than the Earth. The three exoplanets, whose discovery was announced Monday, have estimated masses of between four and ten times that of the Earth, making them smaller than the smallest gas giants in our own solar system, Uranus and Neptune, which are each about 15 times the mass of the Earth. All three orbit the same star, HD 40307, a Sun-like star 42 light-years away. The planets were discovered with the same radial velocity technique used to find most exoplanets to date, where periodic Doppler shifts in the spectra of stars indicate the presence of orbiting planets, but these are among the smallest planets found to date with that method.