Distant solar system’s two planets familiar

Researchers have discovered two planets in a solar system 5,000 light-years away that appears to be structured in some important ways like our own.

The planets are gas giants similar to but smaller than Jupiter and Saturn, and their relative sizes are also similar. In addition, they circle their star at a distance proportional to the distances of Jupiter and Saturn from the sun.

“This is the first time we’ve found a Jupiter-like planet in the same system as a Saturn planet,” said Scott Gaudi of Ohio State University, lead investigator on the project. “There’s reason now to believe there are probably many more solar systems like it.”

The discovery, published today in the online edition of the journal Science, lends support to the long-held belief of many astronomers that there are many planets orbiting their stars in ways similar to our solar system. Most of the more than 260 planets discovered so far have orbited their suns far more closely than theorized, and the planets have been larger than expected.

Gaudi said that was most likely a result of the techniques used to search for the planets, techniques that work best at finding large planets that orbit close in. His group used a different method, called gravitational micro-lensing, that required collaboration with professional and amateur astronomers from around the world.

The star and its planets were observed when they passed in front of a more distant star in 2006. A lensing effect magnified the light of the distant star 500 times, the researchers said.

Gaudi analyzed the data and discovered 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.

It took two months to confirm the two-planet find. David Bennett, a research associate professor of astrophysics and cosmology at the University of Notre Dame, refined the preliminary model revealing additional details about the system.

“This is a landmark discovery because it implies that solar system analogs may be very common, at least scaled-down versions,” said Sara Seager, an extra-solar planet expert from the Massachusetts Institute of Technology. “We are on an inexorable path to finding other Earths.”

Seager said, “We are seeing the emergence of a new planet-finding technique, one that opens up an entirely new capability for planet finding. It is more powerful than we ever thought possible.”

This is the third time a Jupiter-mass planet has been found by micro-lensing, Gaudi explained. In the previous two cases, the presence of any additional planets would have been very difficult to detect.

“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.”