English: PIA19345: How to Make a Helium Atmosphere – fossil state

http://photojournal.jpl.nasa.gov/catalog/PIA19345

NASA's Spitzer Space Telescope observed a proposed helium planet, GJ 436b. This diagram illustrates how hypothetical helium atmospheres might form. These would be on planets about the mass of Neptune, or smaller, which orbit tightly to their stars, whipping around in just days. They are thought to have cores of water or rock, surrounded by thick atmospheres of gas.

Both water and methane consist in part of hydrogen. Eventually, billions of years later (a "Gyr" equals one billion years), the abundances of the water and methane would be greatly reduced. Since hydrogen would not be abundant, the carbon would be forced to pair with oxygen, forming carbon monoxide.

Helium Atmospheres on Warm Neptunes Spitzer Space Telescope

For more information about Spitzer, visit http://spitzer.caltech.edu and http://www.nasa.gov/spitzer.