Embargoed until 1 p.m. EDT
NSF PR 02-54 - June 13, 2002
Newfound Planetary System Has "Hometown" Look
After 15 years of observation and a lot of patience,
the world's premier planet-hunting team has found
a planetary system that reminds them of our home solar
system.
Geoffrey Marcy, astronomy professor at the University
of California, Berkeley, and astronomer Paul Butler
of the Carnegie Institution of Washington, D.C., today
announced the discovery of a Jupiter-like planet orbiting
a Sun-like star at nearly the same distance as the
Jovian system orbits our sun.
"All other extrasolar planets discovered up to now
orbit closer to the parent star, and most of them
have had elongated, eccentric orbits. This new planet
orbits as far from its star as our own Jupiter orbits
the sun,'' said Marcy. The National Science Foundation
(NSF) and NASA fund the planet-hunting team.
The star, 55 Cancri in the constellation Cancer, was
already known to have one planet, announced by Butler
and Marcy in 1996. That planet is a gas giant slightly
smaller than the mass of Jupiter and whips around
the star in 14.6 days at a distance only one-tenth
that from Earth to the sun.
Using as a yardstick the 93-million mile Earth-sun
distance, called an astronomical unit or AU, the newfound
planet orbits at 5.5 AU, comparable to Jupiter's distance
from our sun of 5.2 AU (about 512 million miles).
Its slightly elongated orbit takes it around the star
in about 13 years, comparable to Jupiter's orbital
period of 11.86 years. It is 3.5 to 5 times the mass
of Jupiter.
"We haven't yet found an exact solar system analog,
which would have a circular orbit and a mass closer
to that of Jupiter. But this shows we are getting
close, we are at the point of finding planets at distances
greater than 4 AU from the host star," said Butler.
"I think we will be finding more of them among the
1,200 stars we are now monitoring," he added.
The team shared its data with Greg Laughlin, assistant
professor of astronomy and astrophysics at the University
of California, Santa Cruz. His dynamical calculations
show that an Earth-sized planet could survive in a
stable orbit between the two gas giants. For the foreseeable
future, existence of any such planet around 55 Cancri
will remain speculative.
Marcy, Butler and their team also announced a total
of 15 new planets today, including the smallest ever
detected: a planet circling the star HD49674 in the
constellation Auriga at a distance of .05 AU, one-twentieth
the distance from Earth to the sun. Its mass is about
15 percent that of Jupiter and 40 times that of Earth.
This brings the total number of known planets outside
our solar system to 91.
Discovery of a second planet orbiting 55 Cancri culminates
15 years of observations with the 3-meter (118-inch)
telescope at Lick Observatory, owned and operated
by the University of California. The team also includes
Debra Fischer, UC Berkeley; Steve Vogt, UC Santa Cruz;
Greg Henry, Tennessee State University, Nashville;
and Dimitri Pourbaix, the Institut d'Astronomie et
d'Astrophysique, Université Libre de Bruxelles.
Marcy and Butler used a technique that measures the
slight Doppler shift in starlight caused by a wobble
in the star's position, due to the gravitational tug
of an orbiting planet. By observing over a period
of years, they can infer a planet's approximate mass
and orbital size and period.
The star 55 Cancri is 41 light years from Earth and
is about 5 billion years old. Further data are needed
to determine whether yet another planet is orbiting
it, because the two known planets do not explain all
the observed Doppler wobbling. One possible explanation
is a Saturn-mass planet orbiting about .24 AU from
the star.
For more information, see: http://exoplanets.org
An artist's concept and animation will be available
June 13 at:
http://www.jpl.nasa.gov/images/newplanets
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