CARBON and oxygen are streaming outwards in the atmosphere of a planet 150 light years away. It鈥檚 the first time anyone has observed these elements in a planet outside the solar system.
The planet, which orbits a star called HD 209458 in the constellation Pegasus, has been nicknamed Osiris, after the Egyptian god of the underworld. It is a Jupiter-like gas giant and orbits very close to its star, whipping around it every 3.5 days.
Osiris is one of only two extrasolar planets known to pass across the face of its star, as seen from Earth, during its orbit. Using the Hubble Space Telescope to analyse the starlight shining through its atmosphere, astronomers had already found the spectral signature of sodium. A team led by Alfred Vidal-Madjar of the Institute of Astrophysics in Paris also showed that hydrogen is evaporating from the planet鈥檚 upper atmosphere, which the star heats to 10,000 掳C.
Advertisement
By analysing observations Hubble made last autumn, Vidal-Madjar鈥檚 team has now shown that oxygen atoms and carbon ions are streaming out too. These elements are too heavy to evaporate from Osiris, so Vidal-Madjar concludes that the hydrogen wind is dragging them outwards like dust in a whirlwind, a process called 鈥渂low-off鈥�. ().
He thinks the planet is losing up to a million tonnes of mass every second.