Jupiter-sized Planet Discovered Orbiting Epsilon Eridani

Keith Cowing Thursday, August 03, 2000

Editor's note: A total of ten new extrasolar planets were announced this morning at a meeting of the International Astronomical Union (IAU) in Manchester, UK. The total number of extrasolar planets now known is 50. Details on all of these discoveries can be found in an article on SpaceRef.

A Jupiter-sized planet has been discovered orbiting the nearby star Epsilon Eridani. The announcement was made by Dr. William Cochran of the McDonald Observatory in conjunction with a presentation at the IAU Symposium on "Planetary Systems in the Universe" being held in Manchester, England.

Epsilon Eridani is a sun-like (K2V orange-red dwarf) star located in the constellation Eridanus 10.5 light years from Earth. Epsilon Eridani is much younger than our sun (a G2 star) with an age estimated at less than one billion years. It is also smaller and cooler with 79% the mass, 80% the diameter, and 34% luminosity of our sun. The metallicity of Epsilon Eridani is also lower than our sun (i.e it is less enriched in elements heavier than hydrogen) with only 58% of our sun's iron. A variety of names and catalog nomenclature have been assigned to this star: 18 Eridani, HR 1084, Gl 144, SAO 130564, BD-09 697, FK5 127, Hip 16537, HD 22049, and LHS 1557.

The newly-discovered planet is in an elliptical and somewhat eccentric orbit with a semi-major axis of 297 million miles - a distance roughly equivalent to the distance that the asteroid belt is from our own sun. The planet is suspected of being a gas giant ranging from 80% to 160% the size of Jupiter and takes approximately 7 years to complete one orbit.

The world wide team

The discovery was made by Dr. William Cochran and Dr. Artie Hatzes of the McDonald Observatory at the University of Texas at Austin. According to an IAU press release "the research was based on a combination of six independent data sets taken with four different telescopes and with three different measurement techniques. Observations were made with the 2.7-meter (107-inch) Harlan Smith Telescope at McDonald Observatory, a UT Austin research facility located 16 miles north of Fort Davis."

This was truly a global, community-wide collaboration with collaborators spread out around the world:

According to a University of Texas press release, "to arrive at its discovery, the team studied nearly 20 years of high-precision radial velocity (RV) measurements of Epsilon Eridani. The team noted that the star's high level of chromospheric activity is consistent with its relatively young age, less than a billion years old. "We looked very hard at several years worth of spectrophotometric data for Epsilon Eridani, to make sure that the star's low RV -- 19 meters per second -- was not due to periodic stellar cycles," stated Dr. Artie Hatzes of the McDonald Observatory. "Especially helpful were the Ca II H and K S-index measurements that Dr. Sallie Baliunas, our collaborator at the Harvard-Smithsonian Center for Astrophysics, had made and analyzed of 100 lower main sequence stars, Epsilon Eridani among them."