HD 209458 is a star with 1.23 times the mass of the Sun, and 1.19 times its radius. It is located 157.54 light years away from the solar system and is estimated to be 3.1 billion years old, as compared to the Sun which is roughly 4.6 billion years old.
HD 209458 is known to have 1 exoplanets in orbit around it.
HD 209458 b was discovered by the W. M. Keck Observatory observatory, in 2000-01, using the radial velocity method. Its semi-major axis is 0.05 astronomical units, as compared to Earth's which is 1 astronomical unit. The mass of HD 209458 b is 232.140 times the mass of Earth. The radius of HD 209458 b is 15.581 that of Earth. At more than 50 Earth masses, HD 209458 b is a gas giant, a planet whose mass is mostly made up of hydrogen and helium, like Jupiter and Saturn in our solar system.