New Planet in Earthlike Orbit

Astronomers announced today the discovery of a planet outside our solar system that orbits its star in just under one of our years, the most Earth-like extrasolar planet found to date. Although the planet is probably barren, its moons--if they exist--may harbor life.

Over the past 4 years, scientists have found some 20 extrasolar planets, but most have very tight or extremely elliptic orbits. Using the European Southern Observatory's 3.6-meter telescope at Cerro La Silla in Chile, an international team led by Martin Kürster of the European Space Agency found velocity changes in light streaming from the southern star Iota Horologium (Iota Hor), 56 light-years from Earth, that could only be caused by a planet circling the star once every 320 days. Iota Hor b, as the planet has been dubbed, moves in a slightly elongated orbit, swinging between 117 million and 162 million kilometers from the star. (Earth's average distance to the sun is 150 million kilometers.) Because Iota Hor is much like our sun, the planet's surface temperature should be comparable to Earth's.

The planet is not hospitable to life, however, as its mass is more than twice that of Jupiter, or 720 times the heft of Earth. Therefore, it's probably a gas giant without a solid surface, like Jupiter. But if the planet also has Jupiter-like moons, says team member Artie Hatzes of the University of Texas, Austin, some of them may be more friendly to life. Four of Jupiter's satellites are comparable in size to our moon and the planet Mercury, and at least three of them contain lots of ice. Had they been closer to the sun, that would have been water, a prerequisite to life as we know it. Unfortunately, astronomers have not yet invented a telescope that can detect, from this distance, whether similar moons may be orbiting Iota Hor b.