Description

HD 209458 b is an exoplanet, specifically a hot Jupiter, that orbits the solar analog HD 209458 in the constellation Pegasus, some 157 light-years from the Solar System. It is sometimes informally called Osiris. The radius of the planet's orbit is 0.047 AU, or one-eighth the radius of Mercury's orbit. This small orbital distance results in a year that is 3.5 Earth-days long and an estimated surface temperature of about 1,000 °C. Its mass is 220 times that of Earth and its volume is some 2.5 times greater than that of Jupiter. The high mass and volume of HD 209458 b indicate that it is a gas giant.