Astronomers using the NASA/ESA Hubble Space Telescope have confirmed the existence of a Saturn-mass exoplanet in the binary system OGLE-2007-BLG-349L, located 8,000 light-years away towards the center of our Milky Way Galaxy. The newly confirmed exoplanet’s official name is OGLE-2007-BLG-349L(AB)b. The planet is somewhat less massive than Saturn. It orbits roughly 300 million miles from the pair of red dwarf stars, about the distance from the asteroid belt to our Sun. It takes about 7 years to circle its parent stars. The two stars, OGLE-2007-BLG-349LA and OGLE-2007-BLG-349LB, are a mere 7 million miles apart, or 14 times the diameter of the Moon’s orbit around Earth. “This exoplanet was observed as a microlensing event in 2007,” said Dr. David Bennett of the NASA Goddard Space Flight Center. The event, dubbed OGLE-2007-BLG-349, was detected by the Optical Gravitational Lensing Experiment (OGLE) Collaboration Early Warning System and announced on July 2, 2007. OGLE searches for and observes effects from small distortions of spacetime, caused by stars and exoplanets, which were predicted by Albert Einstein in his theory of General Relativity. These small distortions are known asmicrolensing. The OGLE observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify. “The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star,” Dr. Bennett explained. The sharpness of images from Hubble’s Wide Field Planetary Camera 2 allowed the astronomers to separate the background source star and the lensing star from their neighbors in the very crowded star field.
The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our Sun. “So, the model with two stars and one planet is the only one consistent with the Hubble data,” Dr. Bennett said. “OGLE has detected over 17,000 microlensing events, but this is the first time such an event has been caused by a circumbinary planetary system,” said Dr. Andrzej Udalski from the University of Warsaw, Poland. Now that the team has shown that microlensing can successfully detect events caused by circumbinary planets, Hubble could provide an essential role in this new realm in the continued search for exoplanets. The research paper reporting this discovery has been accepted for publication in the Astronomical Journal. |
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January 2017
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