Astronomers are First to Successfully Predict Extra-Solar Planet(Forwarded)

Office of University Communications
University of Arizona
Tucson,Arizona

Contact Info:
Rory Barnes, 520-626-3154 (after Jan. 11)

Media Contact:
Lori Stiles, 520-626-4402

January 9, 2008

Astronomers are First to Successfully Predict Extra-Solar Planet

A researcher who attended the UA as an undergraduate led the team.

By University Communications

Astronomers, including one at The University of Arizona, have successfully
predicted the existence of an unknown planet, the first since Neptune was
predicted in the 1840s. This planet, however, is outside our own solar
system, circling a star a little more than 200 light years from Earth.

The UA's Rory Barnes and his associates predicted the unknown planet from
their theoretical study of the orbits of two planets known to orbit star
HD 74156. Barnes announced the discovery today at the American
Astronomical Society meeting in Austin, Texas.

Barnes, who was an astronomy and physics undergraduate at UA, is now a
post-doctoral associate at the UA's Lunar and Planetary Laboratory. He and
his colleagues studied the orbits of several planetary systems and found
that planets' orbits tend to be packed as closely together as possible
without gravity destabilizing their orbits. They reasoned that this tight
packing resulted from universal processes of planetary formation.

But the two planets, named "B" and "C", orbiting the star HD 74156 had a
big gap between them. They concluded that if their "Packed Planetary
Systems" hypothesis was correct, then there must be another planet between
planets B and C, and it must be in a particular orbit.

"When I realized that six out of seven multiplanet systems appeared
'packed,' " Barnes said, "I naturally expected there must be another
planet in the HD 74156 system so that it, too, would be packed."

Jacob Bean and his colleagues from the University of Texas observed the
planetary system carefully and confirmed that a new planet was located
where Barnes had predicted (see diagram). The new planet is named, by
convention, HD 74156 D.

Those who collaborated with Barnes in making the successful prediction are
Sean Raymond, now a post-doctoral associate at the University of Colorado,
and professor Thomas Quinn of the University of Washington. The discovery
team, from the University of Texas at Austin, includes Jacob Bean's
adviser, professor Barbara McArthur, and professor Fritz Benedict.

Steven Soter, astronomer with the American Museum of Natural History in
New York, has been following the discoveries of "extra-solar" planets, or
planets orbiting other stars beyond our solar system. Soter noted that
Barnes, Raymond and Quinn are the first to successfully predict the
existence of an unknown planet since Neptune was predicted more than 160
years ago. Mid-19th century astronomers John Couch Adams in England and
Urbain-Jean-Joseph Le Verrier in France independently calculated the
position of Neptune based on irregularities in the motion of Uranus.

"As well as providing a way to predict planet discoveries, the Packed
Planetary Systems hypothesis reveals something fundamental about the
formation of planets," Barnes said. "The process by which planets grow
from the clouds of dust and gas around young stars must be very efficient.
Wherever there is room for a planet to form, it does."

The Packed Planetary Systems hypothesis also predicts that gaps between
known planets in other systems are probably occupied by other, still
undiscovered planets. Barnes noted that shortly after the discovery of HD
74156 d, a different team of astronomers found a planet orbiting the star
55 Cancri, again in an orbit that Barnes and Raymond predicted.

Barnes and colleagues also have predicted a specific planet orbiting a
third system, HD 38529. So far, no planet has been discovered there.
However, the scientists say they expect future observations may confirm
another successful prediction by the Packed Planetary Systems hypothesis.

Extra Info: http://www.lpl.arizona.edu/~rory/prediction

[NOTE: Images supporting this release are available at
http://uanews.org/node/17491 ]