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Composition of Earth's atmosphere by molecular count, excluding water vapor. Lower pie represents trace gases that together compose about 0.0434% of the atmosphere. [5] [6] [7] The three major constituents of Earth's atmosphere are nitrogen, oxygen, and argon. Water vapor accounts for roughly 0.25% of the atmosphere by mass.
The total mass of these heavier elements is estimated to be 19–31 times the mass of Earth, with a significant fraction located in Saturn's core region. [ 55 ] Trace amounts of ammonia, acetylene , ethane , propane , phosphine , and methane have been detected in Saturn's atmosphere.
Planets such as Jupiter and Saturn have primary atmospheres. Primary atmospheres are very thick compared to secondary atmospheres like the one found on Earth. The primary atmosphere was lost on the terrestrial planets due to a combination of surface temperature, mass of the atoms and escape velocity of the planet. [2]
The composition of Earth's atmosphere is determined by the by-products of the life that it sustains. Dry air (mixture of gases) from Earth's atmosphere contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and traces of hydrogen, helium, and other "noble" gases (by volume), but generally a variable amount of water vapor is ...
NASA's Cassini spacecraft, which explored Saturn and its icy moons, including the majestic Titan, ended its mission with a death plunge into the giant ringed planet in 2017. Cassini's radar ...
The smallest known extrasolar planet that is likely a "gas planet" is Kepler-138d, which has the same mass as Earth but is 60% larger and therefore has a density that indicates a thick gas envelope. [16] A low-mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. [17]
The two main constituents of the Jovian atmosphere are molecular hydrogen (H 2) and helium. [1] The helium abundance is 0.157 ± 0.004 relative to molecular hydrogen by number of molecules, and its mass fraction is 0.234 ± 0.005, which is slightly lower than the Solar System's primordial value. [1]
The number of particles able to escape depends on the molecular concentration at the exobase, which is limited by diffusion through the thermosphere. Three factors strongly contribute to the relative importance of Jeans escape: mass of the molecule, escape velocity of the planet, and heating of the upper atmosphere by radiation from the parent ...