Definition 1 of 1 is: The area surrounding a planet, which contains measurable amounts of various substances.
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Planets with known atmosphere are:
Pluto, number 9. -- The composition of its atmosphere is methane, probably mixed with nitrogen. The surface may be icy water and methane. Below that may be an icy mantle.
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Neptune, number 8. -- Probably the most abundant gases in the atmosphere are hydrogen, 85 per cent, and helium, 13 per cent. Methane amounts to only 2 per cent. The gaseous envelope is 3,000 kilometers (roughly 2,000 miles) deep. Below that is an ice layer 10,000 kilometers (roughly 6,000 miles) thick.
Above Neptune's clouds is a haze of hydrocarons. Methane cirrus clouds rise 25 miles above the main cloud deck. The main cloud deck is blown by winds at speeds of about 1,200 miles per hour. Below that are darker clouds of hydrogen sulfide. There are three atmospheric features of note: Great Dark Spot, an anticyclonic wind storm; Small Dark Spot, a cyclonic wind storm; and Scooter, a cirrus cloud.
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Uranus, number 7. -- Probably the most abundant gases in the atmosphere are hydrogen, 85 per cent, and helium, 12 percent. Methane amounts to only 3 per cent. It is thought to consist of a dense mixture of different types of ice and gas around a solid core. Its atmosphere contains traces of methane, giving the planet a blue-green hue, and the temperature at the cloud tops is about minus 550 degrees Fahrenheit.
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Saturn, number 6. -- Atmospheric composition: hydrogen about 94 per cent; helium about 6 per cent; traces of ammonia, methane, and water vapor. The stratosphere contains a haze of ammonia crystals. The troposphere contains white clouds of ammonia crystals, dark orange clouds of ammonium hydrosulfide crystals, and blue clouds of water ice and water vapor.
Outside the inner mantle is an outer mantle of liquid hydrogen that merges into a gaseous atmosphere. Saturn's clouds form belts and zones similar to those on Jupiter, but obscured by overlying haze. Storms and eddies, seen as red or white ovals, occur in the clouds. Ribbon-shaped striation, caused by winds of up to 335 miles per hour, has also been observed.
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Jupiter, number 5. -- Atmospheric composition: hydrogen about 90 per cent; helium about 10 per cent; traces of ammonia, methane, and water vapor. The troposphere contains white clouds of ammonia crystals, dark orange clouds of ammonium hydrosulfide crystals, and bluish clouds of water ice and water droplets.
Outside the inner mantle is an outer mantle of of liquid hydrogen and helium that merges into the gaseous atmosphere. Jupiter's rapid rate of rotation causes the clouds in its atmosphere to form zones and belts that encircle the planet parallel to the equator. Zones are bright, high'altitude, cooler cloud layers. Belts are dark, low-lying, relatively warm cloud layers. Within the zones and belts, turbulence causes the formation of cloud features such as white ovals and red spots, both of which are huge storm systems. The most prominent cloud feature is a storm called the Great Red Spot, which consists of a spiraling column of clouds three times wider than the Earth, that rises about five miles above the upper cloud layer.
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Last update of this page:
2000 MAR 02 Pronunciation added.
1999 JUL 20