Animation of the orbit of the extrasolar planet HD 209458b, showing the trail of gas it leaves during its orbit. This planet is a so_called hot Jupiter , a gas giant planet that orbits very close to its star, just seven million kilometres in this case the Earth is roughly 150 million kilometres from the Sun. This proximity leads to it having a very hot atmosphere, which is boiling off the planet as it orbits. Astronomers also detected a cloud and trail of atmospheric gases extending up to 200,000 kilometres from the planet itself. As the planet transits the star as seen from Earth, its atmosphere can be probed spectroscopically, which led to the discovery of water its atmosphere. HD 209458b orbits its star every 3.5 days, and is 1.3 times as massive as Jupiter. The parent star, HD 209458, is a Sun_like star lying 150 light years from Earth in the constellation Pegasus.brRestrictions: