High Quality Content by WIKIPEDIA articles! HD 209458 b is an extrasolar planet (unofficially referred to as Osiris) that orbits the Solar analog star HD 209458 in the constellation Pegasus, some 150 light-years from Earth`s solar system, with evidence of water vapor. The radius of the planet`s orbit is 7 million kilometres, about 0.047 astronomical units, or one eighth the radius of Mercury`s orbit. This small radius results in a year that is 3.5 Earth days long and an estimated surface temperature of about 1,000 °C (about 1,800 °F). Its mass is 220 times that of Earth (0.69 Jupiter masses) and its volume is some 2.5 times greater than that of Jupiter. The high mass and great volume of HD 209458 b indicate that it is a gas giant.