When mars first formed it had a very thick atmosphere. However, the gases have long since disappeared into space due to the planet’s weak gravity. Mars’ atmosphere is now very thin, and made mainly of carbon dioxide.
The atmosphere of Mars is the layer of gas surrounding Mars. It is primarily composed of carbon dioxide (95.32%), molecular nitrogen (2.6%) and argon (1.9%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen and other noble gases. The atmosphere of Mars is much thinner than Earth’s. The surface pressure is only about 610 Pascal’s (0.088 psi) which is less than 1% of the Earth’s value. The currently thin Martian atmosphere prohibits the existence of liquid water at the surface of Mars, but many studies suggest that the Martian atmosphere was much thicker in the past. The highest atmospheric density on Mars is equal to the density found 35 km above the Earth’s surface. The atmosphere of Mars has been losing mass to space throughout history, and the leakage of gases still continues today.
The atmosphere of Mars is colder than Earth’s. Owing to the larger distance from Sun, Mars receives less solar energy and has a lower effective temperature (about 210 K). The average surface emission temperature of Mars is just 215 K, which is comparable to inland Antarctica. The weaker greenhouse effect in the Martian atmosphere (5 °C, versus 33 °C on Earth) can be explained by the low abundance of other greenhouse gases. The daily range of temperature in the lower atmosphere is huge (can exceed 100 °C near the surface in some regions) due to the low thermal inertia. The temperature of the upper part of the Martian atmosphere is also significantly lower than Earth’s because of the absence of stratospheric ozone and the radiative cooling effect of carbon dioxide at higher altitudes.
Dust devils and dust storms are prevalent on Mars, which are sometimes observable by telescopes from Earth. Planet-encircling dust storms (global dust storms) occur on average every 5.5 earth years on Mars and can threaten the operation of Mars rovers. However, the mechanism responsible for the development of large dust storms is still not well understood.
The Martian atmosphere is an oxidizing atmosphere. The photochemical reactions in the atmosphere tend to oxidize the organic species and turn them into carbon dioxide or carbon monoxide. Although the most sensitive methane probe on the recently launched ExoMars Trace Gas Orbiter failed to find methane in the atmosphere over the whole Mars, several previous missions and ground-based telescope detected unexpected levels of methane in the Martian atmosphere, which may even be a bio signature for life on Mars. However, the interpretation of the measurements is still highly controversial and lacks a scientific consensus.
