XO-3b

XO-3b is an exoplanet with about 11.79 times the mass of Jupiter, and an orbit around its parent star in about 3.2 days. The radius of this object is 1.217 times that of Jupiter. Astronomers announced their discovery on May 30, 2007, at the American Astronomical Society in Honolulu, Hawaii. Its discovery is attributed to the combined effort of amateur and professional astronomers working together on the XO Project using a telescope located on the Haleakala summit in Hawaii.

Dubbed an "oddball" planet, the planet stands out from over 350 other extrasolar planets as the most massive planet found in close proximity to a star, yet the orbit is significantly elliptical instead of circular, as would be expected. It is also considered a transiting planet, passing in front of its parent star during each orbit. It is the third such planet to be found by the XO Project which was specifically created to locate them.