Scientists Say: Atmosphere

An atmosphere is a jacket of gas surrounding a planetary body

This picture of Earth’s atmosphere at sunset was taken from the International Space Station. The lowest layer of the atmosphere, the troposphere, appears reddish brown. Other layers of the atmosphere above it appear in light and dark shades of blue.

Image courtesy of the Earth Science and Remote Sensing Unit, NASA Johnson Space Center

Atmosphere (noun, “AT-muss-fear”)

An atmosphere is a mix of gases that surrounds a planetary body. Earth’s atmosphere extends from the ground to more than 10,000 kilometers (6,200 miles) high. It’s about 78 percent nitrogen. Another 21 percent is oxygen. The rest is trace amounts of water vapor, methane, argon, carbon dioxide and other gases. Earth’s atmosphere contains five distinct layers, which get thinner higher up — until the atmosphere fades into outer space.

The atmosphere makes life possible on Earth. We breathe its oxygen. Plants use its carbon dioxide to grow. Ozone in the atmosphere shields life on the ground from the sun’s harmful ultraviolet rays. Clouds and weather play a central role in Earth’s water cycle. Carbon dioxide and other “greenhouse gases” in the atmosphere trap some of the sun’s heat. This makes Earth warm enough to live on. (Note: This “greenhouse effect” is natural. But human industry has pumped lots of extra carbon into the atmosphere, ramping the effect up. This is now driving climate change.)

Earth is not the only world with an atmosphere. Other planets, dwarf planets and moons do, too. Their atmospheres contain different mixes of gases. The dwarf planet Pluto has a wispy atmosphere made mostly of nitrogen, methane and carbon monoxide. Saturn and Jupiter, meanwhile, are padded with thick atmospheres of hydrogen and helium. These gas giants’ thick atmospheres, like Earth’s, can whip up dazzling storms and auroras. Astronomers have even glimpsed the atmospheres of planets orbiting other stars. And some of those exoplanets might just have weather similar to our own.

In a sentence

Astronomers are using what they know about atmospheres to predict the weather on distant moons and planets.

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Maria Temming is the assistant editor at Science News for Students. She has bachelor's degrees in physics and English, and a master's in science writing.

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