Donald Savage

Headquarters, Washington, DC

(Phone: 202/358-1547)

Amber Jones

National Science Foundation, Arlington, VA

(Phone: 703/306-1070)

Tim Stephens

University of California, Santa Cruz, CA

(Phone: 831/459-4352)

RELEASE: 99-140

ASTRONOMERS DISCOVER SIX NEW PLANETS ORBITING NEARBY STARS

A team of astronomers searching the galaxy with powerful
telescopic instruments has found six new planets orbiting
nearby stars, increasing the number of planets astronomers
have discovered outside our solar system by more than 25
percent. This brings the total number of known planets
outside the solar system to 28, all of which have been found
within the last five years.

“These scientists have added significantly to our knowledge
of planetary systems,” said Morris Aizenman of the National
Science Foundation’s Astronomical Sciences Division. “We’re
rapidly gaining information about Jupiter-sized planets,
their orbits and orbital distances.

We hope to have enough information soon to tell us what
fraction of nearby stars have Jupiter-sized planets, and
ultimately, how many stars throughout the galaxy have planets
of any size,” he added.

The astronomers made the discoveries as part of a long-term
project supported by the National Science Foundation and NASA
to survey 500 nearby stars for orbiting planets. Steven
Vogt, University of California, Santa Cruz; Geoffrey Marcy,
University of California, Berkeley; and Paul Butler, Carnegie
Institution, along with Kevin Apps, a student at the
University of Sussex, England, used the Keck I telescope in
Hawaii, outfitted with the “HIRES” spectrometer. They will
report their findings in the Astrophysical Journal.

The six planets orbit stars that are similar in size, age,
and brightness to the sun and are at distances ranging from
65 to 192 light years from earth. The planets themselves
range in mass from slightly smaller to several times larger
than the planet Jupiter. They are probably also similar to
Jupiter in their compositions — basically giant balls of
hydrogen and helium gas, according to researcher Steven Vogt.
Their orbits tend to be quite eccentric, tracing oval rather
than circular paths.

“It is beginning to look like neatly stacked, circular orbits
such as we see in our own solar system are relatively rare,”
said Vogt.

The presence of a planet around a star is revealed by the
variation in the star’s velocity through space as a result of
the gravitational force exerted on it by the orbiting planet.
Vogt and his coworkers independently confirmed this method
for detecting planets recently when they were able to measure
the dimming of a star as a planet passed in front of it.

In addition to the discovery of six new planets, the
researchers gathered new data on four known planets, whose
orbits they had previously studied. Two of them showed long-
term trends in their orbits indicating the presence of a
companion, which could be an additional planet. These
findings are significant because previously only one other
system of multiple planets, around the star Upsilon
Andromedae, had been identified outside our solar system.

Further information about the planet search is available on
the Web at:

http://cannon.sfsu.edu/~gmarcy/planetsearch/planetsearch.html

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