Which Planet Is Closest to Earth's Atmosphere?

Types

• There are two main types of planetary atmospheres: the thin atmospheres around rocky planets and the thick atmospheres of the gas giants. Mercury, Venus, Earth and Mars have thin atmospheres, while Jupiter, Saturn, Uranus and Neptune have much thicker atmospheres.

Features

• The Earth's atmosphere consists mainly of nitrogen (78 percent), oxygen (21 percent) and trace amounts of other gases, notably water vapor and carbon dioxide. Mercury's sparse atmosphere contains mostly hydrogen, oxygen, water vapor and potassium. Venus and Mars both have carbon dioxide-rich atmospheres. All of the gas giants have atmospheres composing mainly of hydrogen and helium, along with other gases and ices.

Size

• The gas giant planets are almost all atmosphere: no solid surface can be observed beneath their thick atmospheric clouds. Mercury, in contrast, has almost no atmosphere. Venus has an atmosphere much thicker than that of Earth, while Mars has only 1 percent of the atmospheric pressure that Earth has.

Considerations

• The blue colors of Uranus and Neptune do not come from the presence of water, the source of the blue color of Earth. On those planets, methane and other trace gases in the atmosphere reflect blue. Although they may look like watery Earth, their composition is very different.

Function

• No other planet's atmosphere could support life. Oxygen, needed for animal life to breathe, exists only in trace amounts in all other atmospheres. Gases toxic to human life, such as carbon dioxide, ammonia and methane, are common features elsewhere in the solar system.