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Nearest exoplanet orbits in a disk.

A TEAM OF ASTRONOMERS has determined that Epsilon Eridani b, at 10.5 light-years the nearest known extrasolar planet, orbits its parent star in the same plane as the star's dust disk, which was imaged by submillimeter telescopes in 1998. This finding supports the long-standing idea that planets are born in circumstellar disks of gas and dust.

The giant planet follows an eccentric 6.85-year orbit. Several teams detected it in the late 1990s by measuring small variations in the star's line-of-sight velocity caused by the planet's gravitational tug (S&T: June 2001, page 34). But this radial-velocity technique doesn't yield information on the orbital tilt.

Now a team led by Fritz Benedict (University of Texas, Austin) has measured Epsilon Eridani's tiny 2-milliaresecond wobble on the sky, using one of the Hubble Space Telescope's fine-guidance sensors and reams of ground-based data. As reported in the November 2006 Astronomical Journal, these observations confirm that the orbit lies in the same plane as the disk. Moreover, the team could pin down the planet's mass at 1.5 Jupiters.

"I'm not surprised by the result," says Michael Jura (University of California, Los Angeles). "But it's very important to demonstrate with real data what we think we would have expected."

What's even more important, says Jane Greaves (University of St. Andrews, Scotland), the first to image Epsilon Eridani's dust disk, is that astronomers "now know exactly where the planet is, and where it will be at any future time when we could try to observe it."

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Title Annotation:Epsilon Eridani b
Author:Schilling, Govert
Publication:Sky & Telescope
Article Type:Brief article
Geographic Code:1USA
Date:Jan 1, 2007
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