Atmosphere of the Planets

by Abby Cessna on July 24, 2009

How did Mars lose its atmosphere? (NASA)

How did Mars lose its atmosphere? (NASA)


We take our atmosphere on Earth for granted; it’s all around us. But spend a second on any other planet in the Solar System and you’ll realize just how good we’ve got it here. Let’s take a look at the atmosphere of planets.

Mercury is reminiscent of the Moon – simply a ball of rock hotter than our satellite. Despite its appearance though, the planet actually does have an atmosphere. Some astronomers believe that Mercury originally had a thick atmosphere like Earth, but the planet is so small that it has very low gravity. As a result of the planet’s low gravity, Mercury’s atmosphere was blown away by strong solar winds. This barely existent atmosphere is made of a number of compounds including hydrogen, oxygen, water vapor, and potassium.

Venus has an extremely thick atmosphere, which covers the planet’s surface. Because of the planet’s thick atmosphere, astronomers were unable to view the surface of the planets, so scientists and writers alike speculated that the planet was covered with lush forests. Actually, the atmosphere hides a barren, burning planet. The thick clouds of Venus are composed mostly of toxic carbon dioxide.

Earth’s atmosphere is one of the reasons why life can survive on our planet. The thick atmosphere is composed of a number of different molecules. The most common elements in our atmosphere are nitrogen (78%), oxygen (21%), and argon (1%). The rest is comprised of very small amounts of neon, helium, methane, carbon dioxide, krypton, hydrogen, xenon, ozone, nitrous oxide, carbon monoxide, ammonia, and iodine. There is also water vapor in the lower part of Earth’s atmosphere.

Like Mercury, Mars has very little atmosphere. Even if you could breathe this atmosphere, it would not be a good idea. The atmosphere of Mars is poisonous because 95% of it is composed of carbon dioxide. The rest of it is nitrogen (3%), argon (1.6%), and very small amounts of water, methane, and oxygen.

Since gas giants do not actually have a surface, it is rather difficult to determine where their atmospheres end. Jupiter is composed of elements – hydrogen (90%) and helium (10%) – that are typically considered components of atmosphere. There are also some trace amounts of other molecules, such as methane, ammonia, water, and hydrogen sulfide. Scientists have defined the lower end of Jupiter’s atmosphere as the point where the pressure is 1 bar.  

Saturn is composed of mostly helium and hydrogen with traces of methane, ammonia, water ice, and other compounds. Saturn’s upper atmosphere is mostly ammonia crystals while the lower one is either water or ammonium hydrosulfide. Some of the different elements in the atmosphere combine to form what  we call smog in our atmosphere.

Uranus is a blue-green orb in space. The color comes from the methane in Uranus’ atmosphere; the substance absorbs red wavelengths, so they do not reflect back into space. Like other gas giants, Neptune is mostly composed of hydrogen and helium; however, unlike Jupiter and Saturn, Uranus has a higher concentration of what are known as “ices” – mixtures of compounds that include ammonia, ammonium, methane, and water.

Neptune is also a gas giant, but is has a higher proportion of ices than any other planet in our Solar System. Neptune is also blue as a result of the methane in its atmosphere. Like the other gas giants, Neptune’s atmosphere has different storms. At up to 2,400 km/hr, Neptune’s winds are the fastest of any of the planets.

Universe Today has a number of articles on atmosphere including the atmosphere of Neptune and the atmosphere of Mars

You should also check out water found on an extrasolar planet and atmosphere detected on an extrasolar planet.

Astronomy Cast has an episode on the source of the atmosphere.

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