Researchers speaking today at the National Science Foundation announced the discovery of the smallest extrasolar planet yet found - one that resembles our own planet much more than any other yet discovered.
The planet is between 6 to 9 times the mass of Earth and orbits its host star once every 1.9 days at a distance of 2 million miles. The surface of the planet is hot and has been estimated from observations and calculations to be between 400-700F.
The host star which this planet circles is Gliesse 876, a small red dwarf one third the mass of our sun and is located 15 light years from our solar system
According to Jack Lissauer "this is the most Earth like planet discovered since the dawn of history -- but it is not likely to hold that title for long."
According to astronomer Geoff Marcy, "155 extrasolar planets have been discovered over the past decade. To date all of these planets are gas giants - similar to Jupiter and Saturn with masses 100 to 1000 times that of Earth. Last year we reported two Neptune-class planets. Today we report a new type of planet - much lower than any reported around a sunlike star. It is more similar to Earth than any previously discovered planet. We have no analog like this in our solar system. We do not know its composition - whether it is all rock or some chimera of rock, ice, and a thick atmosphere - perhaps a hybrid of Earth and Uranus."
The discovery of this planet was serendipitous. According to Marcy there were two previously discovered Jupiter-sized planets orbiting this star further out. "These two planets pull on each other and change their orbits notably every year. We were using the Keck telescope to study these two planets and discovered this small planet fortuitously using the Doppler effect." Paul Butler noted: "we would have announced this 3 years ago except for the signal of a third planet."
Marcy went on to note that numerous improvements have been made in use of the Doppler effect. "This technology allows us to measure the speed of a star to an accuracy +/- 1 meter per second -- that's human walking speed."
Geoff Marcy put the discovery in context saying: "for the first time we are able to find our planetary kin among the stars".