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Department of Astronomy

MicroFUN - MicroLensing Follow-Up Network

Discovery of a Jupiter/Saturn Analog in OGLE-2006-BLG-109

The MicroFUN Collaboration, in conjunction with the OGLE, MOA, and PLANET/RoboNet Collaborations, have discovered a planetary system that looks a lot like our own solar system. Our data reveal planets orbiting a star ~5000 light years away that resemble smaller versions of Jupiter and Saturn. The star is smaller, cooler, and dimmer than our Sun, but the planets are also smaller than Jupiter and Saturn, and are closer to their parent star. Even so, the entire system looks like a scaled-down version of our solar system.

OB06109 Portrait
Artist's conception of the OGLE-2006-BLG-109 planetary system.
[Full Resolution (2Mb JPEG)]

We also know that there are no other gas giant planets in this system, but there may well be planets closer to the star similar to own own Mercury, Venus, Earth, and Mars. There may also be more lower mass ice giants, reminiscent of Uranus and Neptune.

These are the fourth and fifth planets discovered using the microlensing technique, and the third and fourth found by the MicroFUN collaboration, the others being OGLE-2005-BLG-071, a Jupiter-mass planet announced in May 2005, and OGLE-2005-BLG-169, a Neptune-Mass "Super-Earth" Planet.

Interestingly, this is the first time that we've detected a giant planet with microlensing where we had high sensitivity to a Saturn-like planet. The fact that we did detect a second gas giant, may mean solar systems like our own are common throughout the Galaxy.

Technical Details

The microlensing method works by using the gravity of the star and its orbiting planets as a lens, bending and magnifying the light from a background star.

By measuring and studying how the complex patterns of the magnified background light change as the planetary system passes in front of the background star, we can determine the properties of the planets and their star. The 'light curve' of the brightness variations of OGLE-2006-BLG-109 is shown below, and is composed of data from 11 different observing sites located around the world from the OGLE, MicroFUN, MOA, and PLANET/RoboNet collaborations.

OB05169 Light Curve
Light Curve of OGLE-2006-BLG-109 composed of data from the OGLE, MicroFUN, and PLANET/RoboNet sites. [Full Resolution (453k JPEG)]
For this system, we were able to use subtleties in the microlensing brightness variations to infer a surprisingly large amount of information about the star and its planets. The star is half a solar mass and the planets are 70% of Jupiter's mass and 90% of Saturn's mass, respectively.

Implications for the Frequency of Solar System Analogs

Before the initial discovery of extra-solar planets orbiting normal stars in 1995, it was thought that most solar systems should resemble our own. However, very few of the planetary systems found so far look anything like our solar system.

"The known multi-planet systems are shown below; these systems tend to have gas giant planets that are much closer to their parent stars than the giant planets in our solar system, and so have much higher temperatures.

Gallery of Multi-Planet Systems Gallery of Multi-Planet Systems
Gallery of known multiple-planet systems, including our own system (bottom row) and the planetary system orbiting OGLE-2006-BLG-109L (2nd row from the bottom).
Left: Planetary systems arranged by distance from their parent star (orbital semi-major axis) in AU.
Right: Same systems as at right, but now plotting the equilibrium temperatures of the planets for their parent stars. Blue indicates the zone of liquid water, dark blue indicates the "snow line" beyond which ices can form.
We are now developing the sensitivity to find planetary systems like our own, and our discovery suggests that perhaps the initial predictions actually got it mostly right: while some planetary systems look nothing like ours, those that do may actually be quite common.
Discovery Paper in Science
Gaudi et al. 2008, Science, 319, 927-930 (Abstract only).

Preprint on arXiv.org:
arXiv:0802.1920 (full text)

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