[4][8][9] The atmosphere of Mars is colder than Earth’s owing to the larger distance from the Sun, receiving less solar energy and has a lower effective temperature, which is about 210 K (−63 °C; −82 °F).

[2][4][10] 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.

A thicker, warmer and wetter atmosphere is required to explain several apparent features in the earlier history of Mars, such as the existence of liquid water bodies.

In general, the gases found on modern Mars are depleted in lighter stable isotopes, indicating the Martian atmosphere has changed by some mass-selected processes over its history.

However, the higher abundance of hydrogen in the Martian atmosphere and the high fluxes of extreme UV from the young Sun, together could have driven a hydrodynamic outflow and dragged away these heavy gases.

Assuming the three rocky planets have the same initial volatile inventory, then this low C / 84Kr ratio implies the mass of CO2 in the early Martian atmosphere should have been ten times higher than the present value.

[45] The hydrogen can be produced by the vigorous outgassing from a highly reduced early Martian mantle and the presence of CO2 and water vapor can lower the required abundance of H2 to generate such a greenhouse effect.

[48][49][50] However, other studies suggested that high solubility of SO2, efficient formation of H2SO4 aerosol and surface deposition prohibit the long-term build-up of SO2 in the Martian atmosphere, and hence reduce the potential warming effect of SO2.

[4] Despite the lower gravity, Jeans escape is not efficient in the modern Martian atmosphere due to the relatively low temperature at the exobase (≈200 K at 200 km altitude).

[65] The interaction of the solar wind and the interplanetary magnetic field with the Martian conductive ionosphere induces electrodynamic currents, that have been mapped and studied in detail, using MAVEN.

[67] These currents can drive the ionospheric species to high altitudes, where the solar wind is able to sweep them away from the planet, resulting to global scale ion outflows.

Although the sublimation and deposition of CO2 ice in the polar caps is the driving force behind seasonal cycles, other processes such as dust storms, atmospheric tides, and transient eddies also play a role.

In early 2016, Stratospheric Observatory for Infrared Astronomy (SOFIA) detected atomic oxygen in the atmosphere of Mars, which has not been found since the Viking and Mariner mission in the 1970s.

[91] In 2019, NASA scientists working on the Curiosity rover mission, who have been taking measurements of the gas, discovered that the amount of oxygen in the Martian atmosphere rose by 30% in spring and summer.

[93] Measurements showed that the total column of ozone can reach 2–30 μm-atm around the poles in winter and spring, where the air is cold and has low water saturation ratio.

[95] It is thought that the vertical distribution and seasonality of ozone in the Martian atmosphere is driven by the complex interactions between chemistry and transport of oxygen-rich air from sunlit latitudes to the poles.

[101] More recent measurements by Mars Express orbiter showed that the globally annually-averaged column abundance of water vapor is about 10–20 precipitable microns (pr.

[104][105] Measurements made by the Phoenix lander showed that water-ice clouds can form at the top of the planetary boundary layer at night and precipitate back to the surface as ice crystals in the northern polar region.

[121][122] However, a team led by scientists at NASA Goddard Space Flight Center reported detection of SO2 in Rocknest soil samples analyzed by the Curiosity rover in March 2013.

[142] Mars also has a complicated ionosphere that interacts with the solar wind particles, extreme UV radiation and X-rays from Sun, and the magnetic field of its crust.

Orbiter measurements suggest that the globally-averaged dust optical depth has a background level of 0.15 and peaks in the perihelion season (southern spring and summer).

[165] Atmospheric circulation models suggested repeated cycles of wind erosion and dust deposition can lead, possibly, to a net transport of soil materials from the lowlands to the uplands on geological timescales.

[170] On Mars, orbiters have observed a seasonally recurrent formation of huge water-ice clouds around the downwind side of the 20 km-high volcanoes Arsia Mons, which is likely caused by the same mechanism.

[189][190][191] A laboratory study showed that the air pressure on Mars is not favorable for charging the dust grains, and thus it is difficult to generate lightning in Martian atmosphere.

[192][191] Super-rotation refers to the phenomenon that atmospheric mass has a higher angular velocity than the surface of the planet at the equator, which in principle cannot be driven by inviscid axisymmetric circulations.

[193][194] Assimilated data and general circulation model (GCM) simulation suggest that super-rotating jet can be found in Martian atmosphere during global dust storms, but it is much weaker than the ones observed on slow-rotating planets like Venus and Titan.

[194] In 1784, German-born British astronomer William Herschel published an article about his observations of the Martian atmosphere in Philosophical Transactions and noted the occasional movement of a brighter region on Mars, which he attributed to clouds and vapors.

In 1894, though, spectral analysis and other qualitative observations by William Wallace Campbell suggested Mars resembles the Moon, which has no appreciable atmosphere, in many respects.

[198] In 1926, photographic observations by William Hammond Wright at the Lick Observatory allowed Donald Howard Menzel to discover quantitative evidence of Mars's atmosphere.

It has been proposed that human exploration of Mars could use carbon dioxide (CO2) from the Martian atmosphere to make methane (CH4) and use it as rocket fuel for the return mission.