HD 209458 b
HD 209458 b (sometimes unofficially called Osiris) is an exoplanet that orbits the solar analog HD 209458 in the constellation Pegasus, some 150 light-years from the Solar System. 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.
HD 209458 b represents a number of milestones in extraplanetary research. It was the first of many categories:
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