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Two Dartmouth researchers are part of a team that has discovered a planetary
system where the two largest planets are similar to Jupiter and Saturn, in
terms of mass and distance from their host star. The study appears in the Feb.
15 issue of the journal Science.
An illustration of the analogous planetary system (Image by: Cheongho Han,
Chungbuk National University, Korea)
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“This is the first discovery of a multiplanet system that could be analogous
to our solar system,” says Alison
Crocker ’06, an author on the paper and a Rhodes Scholar currently studying
at Oxford University, UK. As an undergraduate, she worked with Associate
Professor of Physics and
Astronomy Brian
Chaboyer on the collaborative effort. “The other 28 multiplanet systems
detected thus far consist of much more massive planets usually orbiting very
close to their stars.”
The researchers used a new technique called gravitational microlensing to
detect the Jupiter- and Saturn-like planets. Most extra-solar planet
discoveries rely on detecting the planet’s indirect influence on its host star:
either a wobble in the star’s movement from the planet’s gravitational pull, or
a dip in the star’s brightness as the planet passes directly in front. Instead,
microlensing detects the gravitational fields of the planets directly. In
microlensing, as a star passes in front of a background object, its
gravitational field temporarily bends the light from the background object
causing the light from the background star to be focused on Earth. If the star
has planets, the gravitational field of the planets causes an amplification
that deviates from what is expected with a single star. By carefully modeling
this deviation, the presence and masses of planets can be determined.
“Alison was a very quick learner, and I was confident in her abilities,”
says her professor, Brian Chaboyer, associate professor of physics and
astronomy. “The 2.4-meter telescope we used is worth about $4 million; it is
not often that one leaves an undergraduate in charge of a complex, expensive
piece of equipment. Alison was one of the best students I have taught at
Dartmouth, and I was not surprised when she was awarded a Rhodes
scholarship.”
Associate Professor of Physics and Astronomy Brian Chaboyer is part of a team
of scientists that discovered a new planetary system. (Photo by Joseph Mehling
´69)
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Crocker and Chaboyer happened to be using the telescope at Kitt Peak
National Observatory in Arizona in March 2006 when the global microlensing
event occurred, and they joined the collaborative effort to gather data.
“When I was on the mountain, the weather was not very good, but after I
left, Alison was able to get some nice data that was used in the
Science paper,” says Chaboyer.
Crocker adds, “It was amazing to have the opportunity to go observing with
Professor Chaboyer as an undergraduate. There are so many things that are hard
to really understand about astronomical observing until you actually get out
there and observe yourself. I remember taking detailed notes from Professor
Chaboyer on what we would be doing, but things only really made sense after
seeing and operating the telescope myself.”
The researchers say that there have been six confirmed microlensing planet
detections, and the fact that two of the six are very similar to those in our
own solar system suggests that planetary systems like our own may be common in
the Milky Way galaxy.
By SUSAN KNAPP
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