New rocky planet discovered in orbit around nearby star

June 14, 2005



A new Earth-like planet, called Gliese 876 d, has been discovered orbiting a star called Gliese 876 about 15 light years from Earth. It is the first rocky planet to be discovered orbiting a star, although three other rocky planets have in the past been discovered in orbit around a pulsar. There are two other gaseous, Jupiter-like planets in orbit around the same star.

"This is the smallest extrasolar planet yet detected and the first of a new class of rocky terrestrial planets," said Paul Butler of the Carnegie Institution, one of the teams that discovered the new planet. "It's like Earth's bigger cousin."

The newly discovered world has about 7½ times the mass of Earth. Its orbital period, or "year", is a mere 2 days in length and its path takes it 10 times closer to its star than the closest planet is to our Sun. The temperature on the surface is estimated between 400 to 750 degrees Fahrenheit (200 to 400 degrees Celsius), and is too hot for life forms that are similar to those found on Earth.

"A planet seven and a half times the mass of the Earth could easily hold onto an atmosphere," explained Gregory Laughlin, an assistant professor of astronomy at the University of California in Santa Cruz. "It would still be considered a rocky planet, probably with an iron core and a silicate mantle. It could even have a dense steamy water layer. I think what we are seeing here is something that's intermediate between a true terrestrial planet like the Earth and a hot version of the ice giants Uranus and Neptune."

Astronomers are continuing to advance the science of detecting extrasolar worlds. "We are pushing a whole new regime at Keck [Observatory in Hawaii] to achieve one meter per second precision, triple our old precision, that should also allow us to see Earth-mass planets around sun-like stars within the next few years," Butler said.