Space

04 July 2003

Scientists Discover Planetary System Similar to Ours

(Starlight "wobble" indicates planet similar to Jupiter) (1270)
An international team of scientists has discovered a planetary system
consisting of a star similar to the Sun that is orbited by a gas-giant
planet larger but very similar to the planet Jupiter, the National
Science Foundation (NSF) announced on July 3.
Scientists, using the Anglo-Australian Telescope in Siding Spring,
Australia, made precise calculations of light spectra from a star
identified as HD 70642, revealing a barely detectable "wobble" that
indicates the presence of a planet about twice the size of Jupiter.
"The planet, a gas giant, is right where it should be if the solar
system evolved like ours, suggesting that other planets may be found
nearby and that the system could potentially harbor life," according
to the NSF press release.
"The NSF-sponsored Anglo-Australian Planet Search is the only southern
hemisphere planet search capable of detecting solar system analogs
with large planets similar to our own Jupiter and Saturn," said team
member Chris McCarthy of the Carnegie Institution of Washington. "The
discovery of planets orbiting other stars allows us to put our own
Earth and solar system in a bigger context, a galactic context, for
the first time."
Following is the text of a July 3 press release from the National
Science Foundation:
(begin text)
Press Release 
National Science Foundation 
July 3, 2003 
Scientists Discover Planetary System Similar to Our Own
Arlington, Virginia -- An international team of scientists has
discovered a planet and star that may share the same relationship as
Jupiter and our Sun, the closest comparison that researchers have
found since they began their search for extra-solar planets nearly a
decade ago.
By analyzing light spectra collected with the 3.9-meter
Anglo-Australian Telescope in Siding Spring, Australia, scientists
from the United States, Australia, and Britain made precision
measurements of the star HD 70642.
The telescope data reveal a wobble in the star's position, an artifact
from the gravitational tug of a planet roughly twice the size of
Jupiter. The star is similar in size and structure to our Sun. From
the wobble of HD 70642, the team has learned that the orbit of its
planet is similar to the orbit of Jupiter in both shape and distance.
The planet, a gas giant, is right where it should be if the solar
system evolved like ours, suggesting that other planets may be found
nearby and that the system could potentially harbor life.
The researchers, supported by the National Science Foundation (NSF),
conduct the Anglo-Australian Planet Search (AAPS), one of the leading
extra-solar planet searches in the world.
"There's hardly anything more exciting than finding other planets,"
said Philip Ianna, the program director who oversees NSF support for
extra-solar planet searches. For 50 years, NSF has provided U.S. and
international astronomers with access to facilities for ground-based
exploration of the universe, including the world's largest fully
steerable radio telescope in Green Bank, West Virginia; the world's
largest single-dish radio telescope at Arecibo, Puerto Rico; and the
twin Gemini telescopes on Mauna Kea in Hawaii and on Cerro Pachón in
Chile that together can see the entire night sky.
AAPS team member Hugh Jones of Liverpool John Moores University in the
United Kingdom announced their latest findings at the conference
"Extra-solar Planets: Today and Tomorrow," in Paris, France, on July
3, 2003. The team will publish their findings in an upcoming issue of
Astrophysical Journal Letters under lead author Brad Carter of the
University of Southern Queensland, Australia.
NSF has supported the hunt for extra-solar planets since the beginning
of search efforts, including the research of AAPS team members Paul
Butler of the Carnegie Institution of Washington and Geoffrey Marcy of
the University of California at Berkeley. In 1995, Marcy and Butler
confirmed the discovery of the first known extra-solar planet, and in
1996 the researchers became the first Americans to discover a new
planetary system.
Marcy and Butler spent eight years developing a technique sensitive
enough to detect the tiny gravitational tug that a planet imposes on
its host star. By inserting a glass cell filled with iodine between
the incoming starlight and their measuring tools, the researchers
establish a reference set of spectral lines against which the team can
track a wobbling star's changing light waves.
"During the long struggle to develop the iodine technique, it was not
clear that we were going to succeed," said Marcy. "It was NSF's
steady, visionary support that made our success possible."
Before the first extra-solar planets were discovered, researchers
assumed that other solar systems would be like ours. However, while
researchers have discovered more than 70 gas giants orbiting distant
stars, only a handful of the gaseous planets follow nearly circular
orbits like in our solar system -- most have elliptical orbits. In
addition, many of the extra-solar planets orbit either too close or
too far from their host star for the planetary system to be similar to
our own. Of the few planetary systems that appear to look like ours,
this latest discovery is the closest match.
"The NSF-sponsored Anglo-Australian Planet Search is the only southern
hemisphere planet search capable of detecting solar system analogs
with large planets similar to our own Jupiter and Saturn," said team
member Chris McCarthy of the Carnegie Institution of Washington. "The
discovery of planets orbiting other stars allows us to put our own
Earth and solar system in a bigger context, a galactic context, for
the first time."
The researchers continue their hunt for stars by studying the changes
in an object's spectrum, its light wave "fingerprint," as the
celestial body wobbles.
The technique that Marcy and Butler have perfected, called Doppler
velocity measurement, is based on the motion of the star and planet
around a center of gravity. The star and any orbiting bodies are
latched to each other by their mutual gravitational pull, with the
center of gravity lying closer to, but not within, the star. "You can
think of the star and the large planet as dance partners, spinning
around while clasping their outstretched hands," said Ianna.
"The smaller partner on the outside is moving greater distances in a
larger circle," he added, "while the larger inside partner only moves
his or her feet in a very small circle-the movement around the very
small inner circle is the 'wobble' that we see in these stars."
As the star moves toward us in its wobble, the light waves coming off
of it are compressed and appear more blue, while the opposite occurs
as the star swings around and moves away from us, stretching the light
and shifting the light color towards the redder regions of the
spectrum.
The research team has refined the technique to a fine point, measuring
changes in the star's velocity equivalent to a brisk human walk-3
meters per second-in stars tens and hundreds of light-years distant.
"We are working to place all 2,000 of the nearest Sun-like stars under
survey, all the Sun-like stars out to 150 light-years," said Butler.
"Our goal is two-fold," he added, "to provide a first Reconnaissance
-- a first census -- of our nearest neighbors in space, and to provide
the first data to address the fundamental question, how common or how
rare is our own Solar System?"
In addition to the National Science Foundation, the research is
supported by the U.K. Particle Physics and Astronomy Research Council
and the Australian government.
(end text)
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Department of State. Web site: http://usinfo.state.gov)