INTERNATIONAL ASTRONOMICAL UNION

XXIVth GENERAL ASSEMBLY, MANCHESTER, UK

7 – 18 August 2000

Media release

From Jacqueline Mitton (Meeting Press Officer)

jmitton@dial.pipex.com

phone: +44 (0)1223 564914

Phone contact 7 – 16 August

[Meeting Press Room]

+44 (0)161 275 7832

+44 (0)161 275 9458

+44 (0)161 275 9499

Mobile phone 07770 386133

CONTACT FOR THIS RELEASE:

Dr. William Cochran

University of Texas Austin Dept. of Astronomy

wdc@astro.as.utexas.edu

Phone (+1) (512) 471-6474

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AUSTIN, Texas — Astronomers from The University of Texas at Austin’s
McDonald Observatory and other members of an international planetary
research team have discovered a new planet in a solar system only 10.5
light-years away from Earth. The planet, which is composed of gas, is
orbiting a star called Epsilon Eridani. Epsilon Eridani is the fifth
brightest star in the constellation Eridanus.

Dr. William D. Cochran, a research scientist with McDonald and UT Austin’s
Department of Astronomy, will present the planetary search team’s findings
at a symposium on “Planetary Systems in the Universe,” as part of the 24th
General Assembly of the International Astronomical Union in Manchester,
England, Aug. 7-18. The planetary symposium is scheduled for Aug. 7-10.
About 40 new planets have been discovered in recent years, including three
discoveries by the UT Austin program.

“Detecting a planet orbiting Epsilon Eridani — a star very similar to our
own Sun and only 3.22 parsecs from Earth — is like finding a planet in our
own backyard, relatively speaking,” said Cochran. “Not only is this planet
nearby, it lies 478 million kilometers (or 297 million miles) from its
central star — roughly the distance from the Sun to the asteroid belt in
our own solar system.” McDonald research scientists on the team included
Cochran, Dr. Artie P. Hatzes and Barbara McArthur. They worked with Dr.
Gordon Walker and Bruce Campbell, University of British Columbia; Dr. Alan
Irwin, University of Victoria; Dr. Sallie Baliunas, Harvard-Smithsonian
Center for Astrophysics; Dr. Martin Kuerster and Dr. Michel Endl, European
Southern Observatory; Dr. Geoffrey Marcy, University of California,
Berkeley; Dr. Paul Butler, Carnegie Institution of Washington: Stephenson
Yang, University of Victoria; and Sebastian Els, European Southern
Observatory Group.

The team’s 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.

Cochran and Hatzes drew from data collected by three other planet search
groups, including the Canada-France-Hawaii Observatory on Mauna Kea, Hawaii;
the Lick Observatory in Santa Cruz, California; and the European Southern
Observatory in La Serena, Chile.

The new-found planet’s mass is estimated somewhere between 0.8 times the
mass of Jupiter and 1.6 times the mass of Jupiter, Cochran said. Its orbit
lasts just under seven years — about 60 percent the orbital period of
Jupiter but longer than that of most other recently discovered planets.
Astronomers are excited about the new planet’s rough similarity to Jupiter,
because astrobiologists believe Jupiter played an important role in the
development of life on Earth. The largest planet in the solar system and the
fifth planet from the Sun, Jupiter is a massive ball of gas. It exerts such
a strong gravitational pull that it is believed to serve as a protective
barrier, generally preventing asteroids and meteorites from crashing down on
Earth.

“The exciting thing about this discovery is that having a large planet
orbiting fairly far out from Epsilon Eridani means there could be room for
Earth-like planets in a reasonably stable orbit closer into the star,”
Cochran said. “All the planets found so far that are the size of Jupiter are
much closer to the parent star. It means there could be room for an
Earth-like planet closer to Epsilon Eridani and — perhaps — in a habitable
zone.”

In contrast to Jupiter, however, Cochran said this particular planet’s orbit
is highly eccentric and elliptical. The orbits of Earth and its eight
immediate neighbors are more circular. Stable orbits also are considered of
crucial importance in the development of life. Still, Cochran said, the
discovery of the new planet circling Epsilon Eridani raises the tantalizing
possibility of detecting planets with longer orbital periods and of
detecting multiplanet systems like the solar system. Epsilon Eridani is
located in one of the 10 nearest star systems and is bright enough to be
seen with the naked eye. “You can go outside at night, even in Austin, and
point at it and say that star there has a planet around it,” Cochran said.

The planet has not been named because at present there is no accepted
agreement on naming planets. Cochran said this is one of the issues that
will be decided at the convention.