International team discovers new solar system with scaled-down versions of Jupiter and Saturn

Feb. 14, 2008

International team discovers new solar system with scaled-down versions of Jupiter and Saturn

LIVERMORE, Calif. – Harnessing Lawrence Livermore’s pioneering work in gravitational microlensing, supercomputer modeling and adaptive optics, scientists have found two planets in a solar system much like our very own.

A team of international scientists have discovered a solar system nearly 5,000 light years away that contains two scaled-down gas giant planets. They are about half the distance from their source star as Jupiter and Saturn are from our sun, but the two new planets are the same distance apart as Jupiter and Saturn are to each other.

Because this is just the fifth exoplanetary system found via microlensing, the finding suggests that our galaxy hosts many solar systems like our own.

“This is the first time something analogous to our solar system has been found,” said Kem Cook, one of three LLNL researchers on the team and a pioneer in gravitational microlensing. “This indicates that our kind of planetary system is relatively common and that in and of itself is exciting.”

The research appears in the Feb. 15 issue of the journal, Science .

The two planets were seen when the star they orbit crossed in front of a more distant star as seen from Earth (gravitational microlensing). For a two-week period from late March through early April 2006, the nearer star’s gravity magnified the light shining from the farther star. The planets altered this magnification in a distinctive manner.

The gravitational microlensing planet search method is sensitive to multiple-planet systems containing analogs of all of our solar system planets except Mercury.

The new planets resemble a scaled-down version of our solar system, because the mass ratio, separation ratio and equilibrium temperatures are similar to those of Jupiter and Saturn. The planets’ masses are about 71 percent and 90 percent, respectively, of Jupiter and Saturn; their sun is about 50 percent the mass of our sun.

“It looks more like our solar system than any other system we’ve seen so far,” said Bruce Macintosh, another of the Livermore authors. “This system resembles our own and it has room in it for a planet like Earth.”

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.  Analyzing the data in real time, Ohio State Professor Scott Gaudi (the lead author) realized that this observation was likely to be a two-planet event, instead of the hoped for single-planet event, making the discovery even more exciting.

To confirm the existence of the two planets, Livermore researchers went a step further. LLNL’s Sergei Nikolaev used the Lab’s supercomputer Zeus to run codes that would constrain the parameters of the microlensing model and would allow the planetary motions to be included in the solution in a reasonable amount of calendar time. The result: The code confirmed the existence of the two scaled-down Jupiter and Saturn-like planets. Notre Dame University’s David Bennett (another author of the paper) developed the code and helped in the analysis.

Macintosh used the adaptive optics (AO) system at the Keck Observatory in Hawaii to isolate the lens star (the star of the new planetary system) from other stars in the extremely crowded region toward the center of our galaxy. Adaptive optics allow astronomers to minimize the blurring effects of the Earth’s atmosphere, producing images with unprecedented detail and resolution. The Keck adaptive optics image allowed a direct measurement of the source system’s brightness and color, helping constrain the source system’s mass. Cook, in addition to belonging to one of the follow-up teams (Probing Lensing Anomalies NETwork or PLANET), analyzed the Keck AO data.

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.

The planetary system represents a scaled down version of our own solar system, with a less-massive sun. However, the scaling down is consistent with the core-accretion paradigm in which giant planets form near the snow line– thepoint in the protoplanetary disk beyond which ices are stable. Planet mass decreases as the distance beyond the snow lineincreases.

Other coauthors include scientists from Ohio State University, Notre Dame University, Warsaw University Observatory, Auckland Observatory, Tel-Aviv University, Farm Cove Observatory, Mt. John Observatory, Princeton University Observatory, Universidad de Concepción, 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, Universit Pierre et Marie Curie, Liverpool John Moores University, University of St. Andrews, University of Tasmania, Université Paul Sabatier-Toulouse, Dartmouth College and the University of Oxford.