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, DC, 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

“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, Universite 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.


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An artist’s concept and animation will be available June 13 at: