55 Cancri Takes Record For Number Of Extrasolar Planets
Astronomers at NASA's Jet Propulsion Laboratory recently
announced the discovery of a fifth planet circling 55 Cancri, a
star beyond our solar system. The star now holds the record for
number of confirmed extrasolar planets orbiting in a planetary
system.
55 Cancri is located 41 light-years away in the constellation
Cancer and has nearly the same mass and age as our sun. It is
easily visible with binoculars. Researchers discovered the fifth
planet using the Doppler technique, in which a planet's
gravitational tug is detected by the wobble it produces in the
parent star. NASA and the National Science Foundation funded the
research.
"It is amazing to see our ability to detect extrasolar planets
growing," said Alan Stern, associate administrator for the Science
Mission Directorate at NASA Headquarters, Washington. "We are
finding solar systems with a richness of planets and a variety of
planetary types comparable to our own."
The newly discovered planet weighs about 45 times the mass of
Earth and may be similar to Saturn in its composition and
appearance. The planet is the fourth from 55 Cancri and completes
one orbit every 260 days. Its location places the planet in the
"habitable zone," a band around the star where the temperature
would permit liquid water to pool on solid surfaces. The distance
from its star is approximately 116.7 million kilometers (72.5
million miles), slightly closer than Earth to our sun, but it
orbits a star that is slightly fainter.
"The gas-giant planets in our solar
system all have large moons," said Debra Fischer, an astronomer at
San Francisco State University and lead author of a paper that will
appear in a future issue of the Astrophysical Journal. "If there is
a moon orbiting this new, massive planet, it might have pools of
liquid water on a rocky surface."
Fischer and University of California, Berkeley, astronomer Geoff
Marcy, plus a team of collaborators discovered this planet after
careful observation of 2,000 nearby stars with the Shane telescope
at Lick Observatory located on Mt. Hamilton, east of San Jose, CA,
and the W.M. Keck Observatory in Mauna Kea, Hawaii. More than 320
velocity measurements were required to disentangle signals from
each of the planets.
"This is the first quintuple-planet system," said Fischer. "This
system has a dominant gas giant planet in an orbit similar to our
Jupiter. Like the planets orbiting our sun, most of these planets
reside in nearly circular orbits."
"Discovering these five planets took us 18 years of continuous
observations at Lick Observatory, starting before any extrasolar
planets were known anywhere in the universe," said Marcy, who
contributed to the paper. "But finding five extrasolar planets
orbiting a star is only one small step. Earth-like planets are the
next destination."
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