Using NASA’s Hubble Space Telescope and the W. M. Keck Observatory in Hawaii, two teams of astronomers have independently confirmed the existence of a gas giant exoplanet orbiting far from its parent star, OGLE-2005-BLG-169L. The planet was discovered through a technique called gravitational microlensing.

Dubbed OGLE-2005-BLG-169Lb, the planet is thought to be an example of a ‘failed-Jupiter,’ an object that begins to form a Jupiter-like core of rock and ice weighing about ten 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.

“Failed-Jupiter planets, like OGLE-2005-BLG-169Lb, are predicted to be more common than Jupiters, especially around stars less massive than the Sun, according to the preferred theory of planet formation. So this type of planet is thought to be quite common,” said Prof David Bennett from the University of Notre Dame, lead member of the team that analyzed the data from Hubble.

The system OGLE-2005-BLG-169L lies around 8,800 light-years from Earth, in the constellation Sagittarius.

It 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.

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

The initial microlensing data of OGLE-2005-BLG-169L 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 Milky Way Galaxy’s center.

The sharp Hubble and Keck images allowed the astronomers to separate out the background source star from its neighbors in the very crowded star field in the direction of Galaxy’s center.

“It is the first time we were able to completely resolve the source star and the lensing star after a microlensing event,” said Dr Virginie Batista of the Ohio State University, who is the leader of the Keck Observatory analysis.

The results will appear in two papers in the July 30 edition of the Astrophysical Journal.