Astronomers announced today the first discovery of a new class of
planets beyond our solar system about 10 to 20 times the size of Earth
– far smaller than any previously detected. The planets make up a new
class of Neptune-sized extrasolar planets.
In addition, one of the new planets joins three others around the
nearby star 55 Cancri to form the first known four-planet system.
31 August 2004: Detection of a Neptune-mass planet in the rho Cancri system using the Hobby-Eberly Telescope
The discoveries consist of two new planets. They were discovered by
the world renowned planet-hunting team of Drs. Paul Butler and
Geoffrey Marcy of the Carnegie Institute of Washington and University
of California, Berkeley, respectively; and Barbara McArthur of the
University of Texas, Austin. Both findings were peer-reviewed and
accepted for future publication in the Astrophysical Journal. NASA and
the National Science Foundation funded the research.
“NASA, along with our partner NSF, is extremely proud of this
significant planetary discovery,” said Al Diaz, Associate
Administrator of NASA’s Science Mission Directorate. “The outcome of
the tremendous work of the project scientists is a shining example of
the value of space exploration.”
“These Neptune-sized planets prove that Jupiter-sized, gas giants
aren’t the only planets out there,” Marcy said. Butler added,
“We are beginning to see smaller and smaller planets. Earth-like
planets are the next destination.”
Future NASA planet-hunting missions, including Kepler, the Space
Interferometry Mission and the Terrestrial Planet Finder, will seek
such Earth-like planets. Nearly 140 extrasolar planets have been
discovered.
Both of the new planets stick very close to their parent stars,
whipping around them in a matter of days. The first planet, discovered
by Marcy and Butler, circles a small star called Gliese 436 about
every two-and-one-half days at just a small fraction of the distance
between Earth and the Sun, or 4.1 million kilometers (2.6 million
miles). This planet is only the second known to orbit an M dwarf, a
type of low-mass star four-tenths the size of our own sun. Gliese 436
is located in our galactic backyard, 30 light-years away in the
constellation Leo.
The second planet, found by McArthur, speeds around 55 Cancri in just
under three days, also at a fraction of the distance between Earth and
the sun, at approximately 5.6 million kilometers (3.5 million miles).
Three larger planets also revolve around the star every 15, 44 and
4,520 days, respectively. Marcy and Butler discovered the outermost of
these in 2002. It is still the only known Jupiter-like gas giant to
reside as far away from its star as our own Jupiter. The 55 Cancri is
about 5 billion years old, a bit lighter than the sun, and is located
41 light-years away in the constellation Cancer. “55 Cancri is a
premier laboratory for the study of planetary system formation and
evolution,” McArthur said.
Because the new planets are smaller than Jupiter, it is possible they
are made of rock, or rock and ice, rather than gas. According to the
scientists, the planets may have, like Earth, formed through gradual
accumulation of rocky bodies. “A planet of Neptune’s size may not have
enough mass to hold onto gas, but at this point we don’t know,” Butler
said.
Both discoveries were made using the “radial velocity” technique, in
which a planet’s gravitational tug is detected by the wobble it
produces in the parent star. Butler, Marcy and collaborators,
including Dr. Deborah Fischer of San Francisco State University and
Dr. Steven Vogt of the University of California, Santa Cruz,
discovered their “Neptune” after careful observation of 950 nearby
stars with the W.M. Keck Observatory in Mauna Kea, Hawaii. They were
able to spot such a relatively small planet, because the star it tugs
on is small and more susceptible to wobbling.
McArthur and collaborators Drs. Michael Endl, William Cochran and
Fritz Benedict of the University of Texas discovered their “Neptune”
after obtaining over 100 observations of 55 Cancri from the
Hobby-Eberly Telescope at McDonald Observatory in West Texas.
Combining this data with past data from Marcy, Fischer and Butler from
the Lick Observatory in California, and archival data from NASA’s
Hubble Space Telescope, the team was able to model the orbit of 55
Cancri’s outer planet. This, in turn, allowed them to clearly see the
orbits of the other three inner planets, including the new
Neptune-sized one.
For visuals depicting the new planets and information about NASA’s
planet-hunting missions on the Internet, visit:
