HD 209458 – one of the first few exoplanets discovered (by the Hubble Space telescope). It was named ‘Osiris’, after the Egyptian god of the underworld.

This planet is large, as large as Jupiter and orbits it’s star every three and a half days.

What allowed scientists to discover it was that its spectral signature contained hydrogen, oxygen and carbon. The atmosphere is heated to 10,000 oC by the sun. It is thought that a hydrogen wind of evaporating gas drags away the oxygen and carbon as they are too heavy to evaporate. It is estimated that the planet looses 1,000,000 tonnes of mass every second!

This blog posting was adapted from an article in New Scientist magazine, ‘Our best glimpse yet into an alien atmosphere’ published on page 17 of the edition, 14th February 2004.