The majority of the exoplanets that astronomers have managed to look at in detail fall into the class of planet called ‘hot Jupiters’. The radius of the planet's orbit is 7 million kilometres, about 0.047 astronomical units, or one eighth the radius of Mercury' The planet orbits a yellow, Sun-like star called HD 209458, located 150 light-years away in the constellation Pegasus. 4.1 The hot ones: HD 189733 b, HD 209458 b and WASP-12 b. Like 51 Pegasi b, HD 209458 b is very unlike any planet in our Solar System. This envelope reaches temperatures of 10,000 K. The planet is estimated to be losing (1-5)×10 8 kg of hydrogen per second.

This artist's impression shows a dramatic close-up of the scorched extrasolar planet HD 209458b in its orbit 'only' 7 million kilometres from its yellow Sun-like star.

The radius of the planet's orbit is 7 million kilometers, ~0.047 astronomical units, one eighth the radius of Mercury's orbit.

[1] The radius of the planet's orbit is 7 million kilometers, about 0.047 astronomical units, or one eighth the radius of Mercury's orbit.

Later observations with the Hubble Space Telescope showed an enormous ellipsoidal envelope of hydrogen, carbon and oxygen around the planet. This means it’s extremely hot – like 51 Pegasi b, HD 209458 b is one of the new class of planets called hot Jupiters. HD 209458 b’s milestone discovery included a long and impressive list of firsts: It was the first planet discovered using the transit method, the first planet with a detectable atmosphere, the first planet with an evaporating hydrogen atmosphere, and the first exoplanet found with carbon and oxygen.

HD 209458 b is an extrasolar planet that orbits the Sun-like star HD 209458 in the constellation Pegasus, some 150 light-years from Earth's solar system, with evidence of water vapor. Therefore, HD 209458 b has an approximate radius of 1.2 R J based on this simple comparison with Jupiter. HD 209458 b, also given the nickname Osiris, is an exoplanet that orbits the solar analog HD 209458 in the constellation Pegasus, some 159 light-years from the Solar System. Sodium in the atmosphere of the planet HD 209458 b was detected during a set of four transits of the planet across its star. HD 209458 b orbits the star HD 209458, which is just a catalogue number. An introduction to exoplanets . … In fact, because the star HD 209458 is actually a bit bigger than the Sun, the real radius of HD 209458 b is about 1.3 R J. Its orbital period is just three and a half days so it orbits very close to its parent star. HD 209458 b is an extrasolar planet that orbits the Sun-like star HD 209458 in the constellation Pegasus, some 150 light-years from Earth's solar system. HD 209458 is a seventh-magnitude star about 150 light-years away in the constellation Pegasus. The star, which has physical characteristics similar to those of the Sun, was shown in late 1999 to have a planet, HD 209458b, by detection of the planet’s gravitational effects on the star’s motion.

Extrasolar Planet HD 209458 b (Osiris) The exoplanet HD 209458 b is one of only a handful that has a nickname (Osiris).It was one of the first transiting exoplanets to be discovered, and is one of the best-studied hot Jupiters.There are many results in the literature concerning the physical properties of HD 209458 b and the system in which it resides. HD 209458 is a 7th magnitude star, visible from Earth with binoculars.