Earth-like planet could harbour life
Tim Radford, science editor
Tuesday August 31, 2004
European scientists have found a planet circling a distant star that could be home to life.
The planet, the first detected so far that is enough like Earth for life to develop, orbits a star called mu Arae in the southern constellation Altar. The planet - astronomers call such things exoplanets - is only 14 times the mass of Earth and, like Earth, could be composed of rock and support an atmosphere.
No planet beyond the solar system has been seen by optical telescopes. But astronomers can infer the presence of a dark orbiting companion. Almost all the 120 exoplanets discovered so far have been Jupiter-sized or bigger: gas giants far too big to support life.
But the planet that orbits mu Arae every 9.5 days lies at the threshold of the largest possible rocky planets. The discovery, across a distance of 50 light years, was possible only because of the accuracy of an instrument called Harps, a spectrograph on the European Southern Observatory's 3.6m telescope at La Silla in Chile.
With this tool, researchers can measure changes in the radial velocity of a star to an accuracy of a metre a second. Any such cyclical changes are evidence of the gravitational tug of an invisible companion.
Researchers had already detected one Jupiter-sized companion to mu Arae, and a closer look with their new instrument showed an additional planet.
Francois Bouchy, one of the observing team, said: "This new planet appears to be the smallest yet discovered around a star other than the sun. This makes mu Arae a very exciting planetary system."