Astronomers discover scaled-down Jupiter and Saturn in a faraway solar system like our own (Forwarded)

Research Communications
Ohio State University

Contact:
Scott Gaudi, (614) 292-1914

Written by:
Pam Frost Gorder, (614) 292-9475

Embargoed until Thursday, February 14, 2008 at 2:00 p.m. ET, to coincide
with publication in the journal Science.

ASTRONOMERS DISCOVER SCALED-DOWN JUPITER AND SATURN IN A FARAWAY SOLAR
SYSTEM LIKE OUR OWN

COLUMBUS, Ohio -- An international team of astronomers has discovered two
planets that resemble smaller versions of Jupiter and Saturn in a solar
system nearly 5,000 light years away.

The find suggests that our galaxy hosts many planetary systems like our own,
said Scott Gaudi, assistant professor of astronomy at Ohio State University.

He and his colleagues reported their results in the February 15 issue of the
journal Science.

The two planets were revealed when the star they orbit crossed in front of a
more distant star as seen from Earth. For a two-week period from late March
through early April of 2006, the nearer star magnified the light shining
from the farther star.

The phenomenon is called gravitational microlensing, and this was a
particularly dramatic example: the light from the more distant star was
magnified 500 times.

The Optical Gravitational Lensing Experiment (OGLE) first detected the
event, dubbed OGLE-2006-BLG-109, on March 28, 2006. The Microlensing Follow
Up Network (MicroFUN), led by Andrew Gould, professor of astronomy at Ohio
State, then joined with OGLE to organize astronomers worldwide to gather
observations of it. Andrzej Udalski, professor of astronomy at Warsaw
University Observatory, is the leader of OGLE.

Gaudi took the lead in analyzing the data as they came in. As he studied the
light signal, he saw a distortion that he thought was caused by a
Saturn-mass planet. Then, less than a day later, came an additional
distortion he wasn't expecting: a "blip" in the signal that appeared to be
caused by a second, larger planet orbiting the same star.

Over the next few months, Gaudi demonstrated that this two-planet
interpretation was correct. Then David Bennett, a research associate
professor of astrophysics and cosmology at the University of Notre Dame,
refined Gaudi's preliminary model using sophisticated software, and revealed
additional details about the system.

This is the third time a Jupiter-mass planet was found by microlensing,
Gaudi explained. In the previous two cases, additional planets would have
been very difficult to detect, had they been there.

"This is the first time we had a high-enough magnification event where we
had significant sensitivity to a second planet -- and we found one." Gaudi
said. "You could call it luck, but I think it might just mean that these
systems are common throughout our galaxy."

Astronomers have found two planets at once before, "but using other
techniques that don't pick up on solar systems like ours," he said.

The newly-discovered planets appear to be gaseous planets like Jupiter and
Saturn -- only about 80 percent as big -- and they orbit a star about half
the size of the sun. The star is dim and cold compared to ours, issuing only
five percent as much light.

Still, the new solar system appears to be a smaller analog of our own. The
larger planet is about as massive compared to its star as Jupiter is to
ours. The smaller planet shares a similar mass ratio with Saturn.

Also, the smaller planet is roughly twice as far from its star as the larger
one, just as Saturn is roughly twice as far away from the sun as Jupiter.
Although the star is much dimmer than our sun, temperatures at both planets
are likely to be similar to that of Jupiter and Saturn, because they are
closer to their star.

"The temperatures are important because these dictate the amount of material
that is available for planet formation," Gaudi said. "Most theorists think
that the biggest planet in our solar system formed at Jupiter's location
because that is the closest to the sun that ice can form. Saturn is the next
biggest because it is in the next location further away, where there is less
primordial material available to form planets."

"Theorists have wondered whether gas giants in other solar systems would
form in the same way as ours did. This system seems to answer in the
affirmative."

The fact that astronomers found the planets during the first event that
allowed such a detection suggests that these scaled-down versions of our
solar system are very common, he added.

Previously, astronomers had found four planets using microlensing; two of
those were found by the Ohio State University-based MicroFUN group. The
latest two planets make six, and he expects that number to double over the
next year as other teams publish new findings.

"We're just getting better at what we do," Gaudi said. "We've hit our stride
with this technique."

He has also calculated that the next generation of microlensing experiments
-- using telescopes on the ground and in space -- will likely be able to
detect analogs to all of our solar system's planets, except for the tiniest
one, Mercury.

The current discovery relied on 11 different ground-based telescopes in
countries around the world, including New Zealand, Tasmania, Israel, Chile,
the Canary Islands, and the United States.

Both professional and amateur skywatchers joined in. People from three other
microlensing collaborations -- the Microlensing Observations in Astrophysics
(MOA) Collaboration, the Probing Lensing Anomalies NETwork (PLANET), and the
RoboNet Collaboration -- all contributed observations and are co-authors of
the study with MicroFUN and OGLE.

Gaudi described this microlensing event as the most complicated one ever
studied. The astronomers carefully modeled their data on computers, and
explored all possible explanations for the light signal. A year and a half
later, they were confident that they'd found two planets. In part, their
confidence came from additional observations from the W.M. Keck Observatory
in Hawaii, which they used to calculate the mass of the star.

Ohio State coauthors on the Science paper included Darren DePoy and Richard
Pogge, both professors of astronomy; and Subo Dong and Stephan Frank, both
graduate students.

Other coauthors hailed from the University of Notre Dame, Warsaw University
Observatory, Auckland Observatory, Tel-Aviv University, Farm Cove
Observatory, Mt. John Observatory, Lawrence Livermore National Laboratory,
Princeton University Observatory, Universidad de Concepci, University of
Cambridge, Chungbuk National University, Korea Astronomy and Space Science
Institute, Campo Catino Astronomical Observatory, Nagoya University, Massey
University, University of Auckland, University of Canterbury, Victoria
University, Konan University, Nagano National College of Technology,
University of Manchester, Tokyo Metropolitan College of Aeronautics,
University of Exeter, UniversitPierre et Marie Curie, Liverpool John Moores
University, University of St. Andrews, University of Tasmania, UniversitPaul
Sabatier-Toulouse, Dartmouth College, and the University of Oxford.

This work was sponsored by the National Science Foundation; NASA; the Polish
Ministry of Scientific Research and Information Technology; the SRC Korea
Science & Engineering Foundation; the Korea Astronomy & Space Science
Institute; Deutsche Forschungsgemeinschaft; the Particle Physics and
Astronomy Research Council; The European Union's Framework Programme for
Research and Technological Development; The Israel Science Foundation; the
Marsden Fund of New Zealand; the Japan Ministry of Education, Culture,
Sports, Science and Technology; and the Japan Society for the Promotion of
Science.

IMAGES:
High-resolution jpeg images of these illustrations and of Scott Gaudi and
Andrew Gould are available to accompany this story at
http://researchnews.osu.edu/archive/analogpix.htm

VIDEO:
An animation showing an artist's conception of what the new planets might
look like is available at
http://researchnews.osu.edu/archive/analogvideo.htm