page_title: Extraterrestrial atmosphere
section_title: Mars
hierarchical_section_title: Extraterrestrial atmosphere / Planets / Inner planets / Mars
caption_attribution_description: English: This Viking 1 orbiter image shows the thin atmosphere of Mars. The mountains of the southern Argyre Basin is visible, with Galle crater left of center. Viking image number is 040A63.
context_page_description: The study of extraterrestrial atmospheres is an active field of research, both as an aspect of astronomy and to gain insight into Earth's atmosphere. In addition to Earth, many of the other astronomical objects in the Solar System have atmospheres. These include all the gas giants, as well as Mars, Venus, and Pluto. Several moons and other bodies also have atmospheres, as do comets and the Sun. There is evidence that extrasolar planets can have an atmosphere. Comparisons of these atmospheres to one another and to Earth's atmosphere broaden our basic understanding of atmospheric processes such as the greenhouse effect, aerosol and cloud physics, and atmospheric chemistry and dynamics.
context_section_description: The Martian atmosphere is very thin and composed mainly of carbon dioxide, with some nitrogen and argon. The average surface pressure on Mars is 0.6-0.9 kPa, compared to about 101 kPa for Earth. This results in a much lower atmospheric thermal inertia, and as a consequence Mars is subject to strong thermal tides that can change total atmospheric pressure by up to 10%. The thin atmosphere also increases the variability of the planet's temperature. Martian surface temperatures vary from lows of approximately −140 °C (−220 °F) during the polar winters to highs of up to 20 °C (70 °F) in summers.
  Between the Viking and Mars Global Surveyor missions, Mars saw "Much colder (10-20 K) global atmospheric temperatures were observed during the 1997 versus 1977 perihelion periods" and "that the global aphelion atmosphere of Mars is colder, less dusty, and cloudier than indicated by the established Viking climatology," with "generally colder atmospheric temperatures and lower dust loading in recent decades on Mars than during the Viking Mission."  The Mars Reconnaissance Orbiter, though spanning a much shorter dataset, shows no warming of planetary average temperature, and a possible cooling.  "MCS MY 28 temperatures are an average of 0.9 (daytime) and 1.7 K (night- time) cooler than TES MY 24 measurements."  Locally and regionally, however, changes in pits in the layer of frozen carbon dioxide at the Martian south pole observed between 1999 and 2001 suggest the south polar ice cap is shrinking. More recent observations indicate that Mars' south pole is continuing to melt. "It's evaporating right now at a prodigious rate," says Michael Malin, principal investigator for the Mars Orbiter Camera. The pits in the ice are growing by about 3 meters (9.8 ft) per year. Malin states that conditions on Mars are not currently conductive to the formation of new ice. A web site has suggested that this indicates a "climate change in progress" on Mars. Multiple studies suggests this may be a local phenomenon rather than a global one.
  Colin Wilson has proposed that the observed variations are caused by irregularities in the orbit of Mars. William Feldman speculates the warming could be because Mars might be coming out of an ice age. Other scientists state the warming may be a result of albedo changes from dust storms.  The study predicts the planet could continue to warm, as a result of positive feedback.
  On June 7, 2018, NASA announced that the Curiosity rover detected a cyclical seasonal variation in atmospheric methane, as well as the presence of kerogen and other complex organic compounds.
caption: The tenuous atmosphere of Mars visible on the horizon.
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