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How did Titan’s nitrogen-rich atmosphere likely form from ammonia ice?
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Titan
Titan, moon of Saturn, photographed by Voyager 2 on August 25, 1981, at a distance of 907,000 km (564,000 miles). Green and violet images were combined to make this photograph, which shows the extended atmosphere of the satellite.
Titan’s nitrogen-rich atmosphere is considered a secondary atmosphere rather than a primordial one. It is believed to have formed through the photochemical dissociation of ammonia, which is an abundant ice found in the outer solar system. Through this process, ammonia was broken down into molecular nitrogen and hydrogen.1
While Titan was able to retain the heavier nitrogen molecules due to its surface gravity and cold temperatures, the lighter hydrogen molecules escaped into space. This retention depends on a balance between the moon's gravity, the mass of the atmospheric molecules, and solar heating.1