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Beyond Earthly Skies

Detection of an Oxygen Atmosphere around Callisto

21 May 2015, 22:00 UTC
Detection of an Oxygen Atmosphere around Callisto
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Of all the moons in the Solar System, Saturn’s moon Titan has by far the densest atmosphere. The atmospheric pressure on the surface of Titan is 1.4 times greater than at sea-level on Earth. Titan’s atmosphere is so thick that it obscures its entire surface. From space, Titan appears as a fuzzy orange orb with no visible indication of any surface features. After Titan, the moon with the next thickest atmosphere is Neptune’s moon Triton. Triton’s atmosphere is so rarefied that it is only ~1/20,000th the density of Earth’s atmosphere. Nevertheless, its atmosphere is still thick enough to have winds, clouds and weather.Like Earth, the atmospheres of Titan and Triton are thick enough that their gas molecules collide with one another before travelling any appreciable distance. Such atmospheres are known as collisional atmospheres. In contrast, some other moons in the Solar System, including Earth’s Moon, have extremely tenuous atmospheres known as exospheres. The gas particles in an exosphere are spaced so far apart that they rarely collide with each other. An exosphere is basically a non-collisional atmosphere.Besides Titan and Triton, Jupiter’s moon Io is the third moon in the Solar System with a collisional atmosphere. The atmospheric pressure on Io ...

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