By Ron Cowen
Astronomers have confirmed the existence of the nearest known planet beyond the solar system. The body orbits the young star Epsilon Eridani just 10.5 light-years from Earth, and it’s 1.5 times as massive as Jupiter.
The observations, which include measurements taken by the Hubble Space Telescope, also reveal that the planet’s orbit has the same tilt as a disk of gas and dust that surrounds the 800-million-year-old star.
The alignment between planet and disk gives fresh support for the long-held notion that debris disks spawn planets, say G. Fritz Benedict and Barbara McArthur of the University of Texas in Austin and their colleagues. They report their findings in the November Astronomical Journal.
Six years ago, McArthur observed a subtle back-and-forth motion of Epsilon Eridani. But that indirect evidence of a planet’s gravity indicated only what the minimum mass of the orbiting body would be. That evidence also left open the possibility that astronomers might have been fooled by motion of the youthful star’s turbulent atmosphere, which can mimic the effect of an unseen planet tugging on a star.
By using Hubble’s fine-guidance sensors to track tiny changes in the star’s location in the sky over a 3-year period, the researchers removed any doubts about the planet’s existence and established its mass and orbit. They combined the Hubble data with data of several ground-based telescopes.
Late in 2007, when the planet makes its closest approach to Epsilon Eridani, it may reflect enough starlight for Hubble and large ground-based telescopes to take its first picture.
