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HD 209458 and Osiris

The yellow star, which is a bit hotter as our Sun, is orbited by one of the most prominent exoplanets. This one, called Osiris, is very close to its star and therefore very hot. From our point of view it performs a transit, which means from time to time it is directly in front of the star, eclipsing a small part of it. It is the first exoplanet with a confirmed transit.
HD 209458b is the first discovered chthonian planet. This means it is so close to its star that this blows away the planets' atmosphere and will leave only the dead core behind. A tail of the planet containing much oxygen and carbon can be observed.

On March 23. 2005 Osiris' temperature was measured by the Spitzer Infrared Space Telescope: at least 1000 kelvin.

In February 2007 for the first time molecules have been discovered in exoplanets for HD 189733b and HD 209458b (with the Spitzer telescope). The atmosphere of these is quite thick, dry and dusty. HD 209458b even contains silicates, in the form of sand grains. This is a great step to the discovery of alien life, even though these two planets aren't suitable for this.

In April 2007 eventually water has been found in the atmosphere of this gas planet.

Constellation: Pegasus
Distance: 153 light-years
Planet orbit time: 3.5247 days

HD 209458

Spectral class: G0
Visual magnitude: 7.65
Mass: 1.05 * Sun


Planet Osiris

Mass: 0.69 * Jupiter
Diameter: 1.43 * Jupiter

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    HD 209458 and Osiris
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