Osiris
Ownership: UCP?
System: HD 209458
Type: Gas giant
Temperature: +750 °C
Location: Alpha Quadrant
Also known as HD 209458 b, the gas planet Osiris is in the process of losing its atmosphere.
Orbital parameters
Semi-major axis (a): 0.045 AU
Eccentricity (e): 0.0
Orbital period (P): 3.52474541 ± 0.00000025 d
Inclination (i): 86.1 ± 0.1°
Time of periastron (τ): 2,452,854.825415 ± 0.00000025 JD
The radius of the planet's orbit is only 7 million kilometers, ~0.047 astronomical units. This small radius results in a year only 3.5 standard days long and an estimated surface temperature of about 1000°C.
Osiris' days are the same length as its years; is it rotates about its axis every time it rotates around its star. This means the planet is tidally locked, showing only one side to its star. This would result in uneven heating and therefore the possibility of very strong winds.
Atmospheric composition
Sodium is in the planet's atmosphere. It is also surrounded by an enormous ellipsoidal envelope of hydrogen, carbon and oxygen that reaches 10,000°C. At this temperature, the a significant 'tail' of atoms moving at speeds greater than the escape velocity emerges, and the planet is estimated to be losing about 1-5×108 kg of hydrogen per second. 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 main sequence stars closer than around 0.1 AU. Osiris will not evaporate entirely, although it may have lost up to about 7% of its mass over its estimated lifetime of 5 billion years.
