HANOVER, N.H. – Two Dartmouth researchers are part of the team that has discovered a planetary system where the two largest planets are very 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.

“This is the first discovery of a multi-planet system that could be analogous to our solar system,” says Alison Crocker, an author on the paper, a member of the Dartmouth Class of 2006, and a Rhodes Scholar currently studying at Oxford University, U.K. “The other 28 multi-planet systems detected thus far consist of much more massive planets usually orbiting very close to their stars.” Crocker collected some of the data used in the Science paper while an undergraduate student at Dartmouth.

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 at Dartmouth. “The 2.4-meter telescope we used is worth about $4 million; it is not often that one leaves an undergrad 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.”

As part of coursework in March 2006, Crocker and Chaboyer happened to be using the telescope at Kitt Peak in Arizona 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 which 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.