Epsilon Eridani

Epsilon Eridani is a fourth magnitude, class K2 main sequence dwarf. It is an ordinary, though relatively young, hydrogen-fusing star. Merely 10.5 light years away, it is the 10th closest star system to the Earth. Its temperature of 5080 K and low luminosity (34% solar) indicate a lower mass, 83% that of the Sun. Though its rotation speed appears similar to the Sun's, Epsilon Eridani is much younger - about 800 million years, as opposed to the Sun's 4.6 billion. It displays considerable solar-like activity.

Dust Disk

In 1998, a dust disk was discovered around the star, at a similar distance as the Kuiper belt is from our Sun. The dust disc contains approximately 1000 times more dust than is present in the inner system around our Sun, which may mean it has about 1000 times as much cometary material as our solar system. Within 35 AU of the star, the dust is depleted, which may mean that the system has formed planets which have cleared out the dust in this region.

Planets

Epsilon Eridani is the closest star known to have a planet, and maybe two of them. Unlike many stars so far found to have planets, Epsilon Eridani is not metal-rich; its metal content actually a bit less than the Sun's (about 80% solar). With an average orbital radius of 3.39 AU, the planet takes 6.85 years to orbit Epsilon Eridani. Combination of stellar velocity and positional measures of the star show the planet to have a mass 1.55 times that of Jupiter, with an uncertainty of only 15%. Its orbital inclination, 30 degrees to the plane of the sky, agrees well with the inclination of the circumstellar dust disk. Unlike Jupiter, the planet is in a highly eccentric orbit that takes it from as far as 5.8 AU from the star to as close as 1.1 AU. The planet will be farthest from Epsilon Eridani - 1.7" - late in the year 2010, when we have the best hope of imaging it directly, even though it will be 20 million times fainter than the star. Slow changes in the apparent orbit suggest another "Jupiter" with a period greater than 50 years (which would place it at least 13 AU from the star).

SETI and Science Fiction

Epsilon Eridani achieved lasting fame as one of the first to be examined for radio signals produced by intelligent life, when Frank Drake turned an 85-foot radio telescope to it and to Tau Ceti in 1960. No signals were found. Epsilon Eridani appears regularly in science fiction, however; most notably in the television series Babylon-5, where the space station of the same name orbits the third planet in the system (Epsilon 3).

[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]