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HD 209458b, provisionally dubbed Osiris by its discoverers after the Egyptian god Osiris, 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. HD209458 is a 7th magnitude star, visible on Earth with binoculars. The radius of its orbit is only 7 million kilometers, ~0.047 astronomical units, one-eighth the radius of Mercury's orbit. This small radius results in a year only 3.5 Earth days long and an estimated surface temperature of about 1000°C. Its mass is 220 times that of Earth's (0.7 Jupiter masses), suggesting that it is probably a gas giant.
On November 27November 27 is the 331st day (332nd on leap years) of the year. There are 34 days remaining. Events 399 St. Anastius I becomes Pope. 1095 Pope Urban II declares the First Crusade at the Council of Clermont. 1703 The first Eddystone Lighthouse destroyed in 20012001 is a common year starting on Monday (see link for calendar), and also: The International Year of the Volunteer The United Nations Year of Dialogue Among Civilizations Events January January 1 A black monolith measuring approximately nine feet tall ap the Hubble Space TelescopeHubble Space Telescope Space Shuttle Discovery during the second servicing mission of the telescope, STS-82 Organization NASA, ESA Wavelength regimeoptical Orbit height600 km Orbit period100 min Launch date 24 April 1990 Deorbit datecirca 2010 Mass11,000 detected hydrogenhydrogen helium H Li Full table General Name, Symbol, NumberHydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1 (IA), 1 , s Density, Hardness 0. 0899 kg/m3, NA Appearance colorless Atomic properties Atomic weight 1. 00794 amu Atomic radius (ca in the planet's atmosphere, the first planetary atmosphere outside our solar system to be measured. In autumn of 2003 Hubble also detected oxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un and carbonAlternative meaning: Carbon (computing Carbon is a chemical element in the periodic table that has the symbol C and atomic number 6. An abundant nonmetallic, tetravalent element, carbon has several allotropic forms: diamonds (hardest known mineral). Bindi. These are not considered to be signs of life, however; the carbon and oxygen are in atomic form, ionized by the star's heat. Astronomers used the Hubble Space Telescope Imaging Spectrograph to discover an enormous ellipsoidDefinition In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. The equation of a standard ellipsoid in an x ''y ''z Cartesian coordinate system is : where a b and c are fixed positive real numbers determial envelope of tenuous atmosphere around the planet that reaches 10,000°C. At this temperature hydrogen atoms easily reach escape velocityFor the video game title, see Escape Velocity (computer game). In physics, for a given gravitational field and a given position, the escape velocity is the minimum speed an object without propulsion, at that position, needs to have to move away indefinite and the planet loses about 10,000 tonnes of hydrogen per second to this process. Analysis of the starlight passing through the envelope shows that the heavier carbon and oxygen atoms are being blown off of the planet by the extreme " hydrodynamic drag " created by its evaporating hydrogen atmosphere. The hydrogen tail streaming off of the planet is 200,000 kilometers long.
It is thought that this type of atmosphere loss may be common to all planets orbiting Sun-like stars closer than around 0.1 AU. The evaporation mechanism is so distinctive that a whole new class of extrasolar planets consisting of the cores of evaporated gas giants, called Cthonian planets, has been proposed. None have yet been detected.
" Osiris", the Egyptian god, lost part of his body — like HD 209458b — after having been killed and cut into pieces by his brother Set to prevent his return to life.
HD 209458b is the first transiting planet discovered, the first extrasolar planet known to have an atmosphere, the first extrasolar planet observed to have an evaporating hydrogen atmosphere, and now the first extrasolar planet found to have an atmosphere containing oxygen and carbon.