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Distant Uranus-sized exoplanet discovered through microlensing

THIS DIAGRAM SHOWS HOW ASTRONOMERS OBSERVED A DISTANT GAS GIANT PLANET AROUND OGLE-2005-BLG-169 USING MICROLENSING. view more   CREDIT: CREDITS: HUBBLE/STSCI

THIS DIAGRAM SHOWS HOW ASTRONOMERS OBSERVED A DISTANT GAS GIANT PLANET AROUND OGLE-2005-BLG-169 USING MICROLENSING. view more
CREDIT: CREDITS: HUBBLE/STSCI

NASA’s Hubble Space Telescope and the W.M. Keck Observatory in Hawaii have made independent confirmations of an exoplanet orbiting far from its central star, using a technique called gravitational microlensing.

The technique helps find exoplanets far from their central stars as Jupiter and Saturn are from our sun, revealed two papers published in the July 30 edition of the Astrophysical Journal.

The large majority of exoplanets cataloged so far are very close to their host stars but this is not the case with the microlensing technique, which can find more distant and colder planets in long-period orbits that other methods cannot detect.

Microlensing occurs when a foreground star amplifies the light of a background star that momentarily aligns with it. If the foreground star has planets, then the planets may also amplify the light of the background star, but for a much shorter period of time than their host star. The exact timing and amount of light amplification can reveal clues to the nature of the foreground star and its accompanying planets.

The system, cataloged as OGLE-2005-BLG-169, was discovered in 2005 by the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-Up Network (MicroFUN), and members of the Microlensing Observations in Astrophysics (MOA) collaborations–groups that search for extrasolar planets through gravitational microlensing.

Using Hubble and the Keck Observatory, two teams of astronomers have now found that the system consists of a Uranus-sized planet orbiting about 370 million miles from its parent star, slightly less than the distance between Jupiter and the Sun. The host star, however, is about 70 percent as massive as our Sun.

“These chance alignments are rare, occurring only about once every 1 million years for a given planet, so it was thought that a very long wait would be required before the planetary microlensing signal could be confirmed,” said David Bennett, the lead of the team that analyzed the Hubble data. Virginie Batista, leader of the Keck Observatory analysis, said:”The Keck and Hubble telescopes allow us to detect these faint planetary host stars and determine their properties.”

The planet in the OGLE system is probably an example of a “failed-Jupiter” planet, an object that begins to form a Jupiter-like core of rock and ice weighing around 10 Earth masses, but it doesn’t grow fast enough to accrete a significant mass of hydrogen and helium. So it ends up with a mass more than 20 times smaller than that of Jupiter.

The initial microlensing data of OGLE-2005-BLG-169 had indicated a combined system of foreground and background stars plus a planet. But due to the blurring effects of our atmosphere, a number of unrelated stars are also blended with the foreground and background stars in the very crowded star field in the direction of our galaxy’s center.

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