Rocky Earthlike planet discovered

DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 21 April, 2009

Researchers today confirmed the existence of a rocky Earthlike planet with a mass of 1.9 Earth masses, orbiting in the Gliese 581 system.

Artist's impression of the newly discovered planetary system Gliese 581. Image: ESO.

Another planet in the four planet system was also found to be lying in the star's habitable zone, the region where liquid water oceans could exist. The findings are the result of over four years of observations using the world's leading low-mass exoplanet hunter, the HARPS spectrograph attached to the 3.6 metre telescope at La Silla in Chile.

The system was already known to harbour a Neptune-sized planet and two super-Earths of 16, seven and five Earth-masses respectively. As Michel Mayor said in this morning's press conference: "this is a step in the right direction of finding an Earth twin."

The new planet is orbiting far too close to its host star for it to be habitable, however, the seven Earth mass planet lies towards the far edge of the star's habitable zone, orbiting with a period of nearly 67 days. "Gliese 581 d is probably too massive to be a rocky planet, it's probably an icy planet that has migrated closer to the star," says Mayor. "It could even be covered with a large and deep ocean."

Gliese 581 is roughly one-third the mass of the Sun, and with a much lower luminosity. Therefore a planet would need to be situated much closer to this star than our own Sun in order to receive a comparable amount of energy as the Earth. The holy grail of planet hunting will be to find a true Earth twin.

"I'm absolutely quite confident that in the next one or two years we'll arrive at the level of Earth mass planets," says Mayor, who was the first person to discover an extrasolar planet fifteen years ago.

And with the Kepler spacecraft currently being prepped for its three year search for Earth mass planets in the Cygnus-Lyra region of the sky, the race is well and truly on.

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