POSTED: Thursday, December 17, 2009

At least six low-mass planets around two nearby sun-like stars, including two “;super-Earths”; with masses five and 7.5 times the mass of Earth, have been identified by planet hunters using the W.M. Keck Observatory on Mauna Kea.

The “;super-Earths”; are the first found around sun-like stars, said the researchers, led by Steven Vogt of the University of California, Santa Cruz, and Paul Butler of the Carnegie Institution of Washington.

“;These detections indicate that low-mass planets are quite common around nearby stars,”; said Vogt, a professor of astronomy and astrophysics. “;The discovery of potentially habitable nearby worlds may be just a few years away.”;

The international team described the new planetary systems in two papers appearing in the Astrophysical Journal and the results were reported in news releases by Keck Observatory and UC-Santa Cruz.

The new planet systems were identified with combined data gathered with the 10-meter Keck I telescope and the Anglo-Australian Telescope in New South Wales, Australia.

Three of the new planets orbit the bright star 61 Virginis, which can be seen with the naked eye in dark skies in the spring constellation Virgo.

This star, which is 28 light-years from Earth, stands out as one of the best twins of the sun in terms of age, mass and other properties, the scientists said.

The second new system identified features a planet 7.5 times the mass of Earth orbiting HD 1461, “;another near-perfect solar twin located 76 light years away.”;

HD 1461, lying in the constellation Cetus, also can be seen with the naked eye in the early evening under dark sky conditions.

“;At least one planet orbits the star and two others are strong candidates,”; the astronomers said.

They said they can't tell yet whether HD 1461b, the 7.5-Earth-mass planet, is a scaled-up version of the Earth, composed largely of rock and iron, or whether it's composed mostly of water similar to Uranus and Neptune.

Butler said there is “;a tremendous advantage”; to combining data from the Keck and AAT telescopes. “;'It's clear that we'll have an excellent shot at identifying potentially habitable planets around the very nearest stars within just a few years.”;

Eugenio Rivera, lead author of one of the papers and a postdoctoral UCSC researcher, said a habitable Earth-like world could exist in the unexplored region between the newly discovered planets and the outer dust disk of 61 Vir, based on extensive numerical simulations.

Gregory Laughlin, a research collaborator at UCSC, said, “;It's come down to a neck-and-neck race as to whether the first potentially habitable planets will be detected from the ground or from space.

“;A few years ago, I'd have put my money on space-based detection methods, but now it really appears to be a toss-up. What is truly exciting about the current ground-based radial velocity detection method is that it is capable of locating the very closest, potentially habitable planets.”;