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We pass through it every moment of our lives; it is the air we breathe the rain that sustains our plants, the all-encompassing blanket that protects us from the lethal rays of the sun. All of this and more you may have known about our atmosphere---but did you know that our moon has an atmosphere? The kinds of planetary atmospheres are about as varied and vast as space itself.
A Look at Planetary Atmospheres
An atmosphere is the name given to the layer of gases that surround our planet, or any heavenly body with enough mass to generate the gravity needed to hold it in place. The fact that gravity is the linchpin that holds the atmosphere secure gives a clue to how neat gravity is—it is often assumed that gravity only works on solid objects.
The atmosphere of a planet is going to vary wildly depending on a number of factors, including the gravitational pull of the planet, the atmospheric temperature, what kinds of gases come from the planet’s core, geological change, the kind of star in the region, and whether or not the planet is terrestrial (rocky) or gas itself.
Even the stars have atmospheres, called “stellar atmospheres.” Our Sun, for example, has an atmosphere which starts at the photosphere (the part we can see from Earth) and extending outward.
Gas Bubble
An atmosphere is like a gas bubble that surrounds a planet, held in place by the gravity of the planet itself. How thick and deep the atmosphere is depends on two factors; the gravity, and the temperature. A high temperature means a thinner atmosphere, as does a low gravity.
Mercury, for example, has a relatively thin atmosphere made up primarily of sodium gas. (So, by the way, does our Moon.) Take a planet like Jupiter, which is a gas giant itself, and the high gravity and low temperature results in a very deep atmosphere.
The gas that makes up a planetary atmosphere is usually determined by the kinds of elements and chemical makeup of the solar nebula at the time of the planet’s formation, followed by escaping gases from the core.
The atmospheres of the major bodies in our Solar System are as follows:
Mercury
A thin atmosphere of sodium gas blankets the planet closest to the sun.
Venus
Our sister planet has a very different atmosphere to ours, being primarily carbon dioxide. There is oxygen to be found, but no where near the appropriate levels for a human to breathe.
Earth
Earth’s atmosphere is primarily nitrogen and oxygen and water vapour, with some carbon dioxide thrown in. There are lots of other gases to be found, especially around populated areas, but the composition of these trace elements changes constantly.
Mars
Like Venus, Mars’ atmosphere is mostly carbon dioxide with other trace gases.
Jupiter
This gas giant is composed mostly of hydrogen with a significant portion of helium.
Saturn
Hydrogen and helium.
Uranus
Hydrogen and helium, but also ice from water and methane.
Neptune
Hydrogen and helium, and enough methane to give Neptune its blue hue.
Pluto
A mostly frozen atmosphere of nitrogen and methane blankets this dwarf planet.
www.astronomyexpert.co.uk/PlanetaryAtmospheres.html