Atmosphere of Mars

The atmosphere of the planet Mars is composed mostly of carbon dioxide. The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi; 6.0 mbar), about 0.6% of Earth's mean sea level pressure of 101.3 kilopascals (14.69 psi; 1.013 bar). It ranges from a low of 30 pascals (0.0044 psi; 0.30 mbar) on Olympus Mons's peak to over 1,155 pascals (0.1675 psi; 11.55 mbar) in the depths of Hellas Planitia. This pressure is well below the Armstrong limit for the unprotected human body. Mars's atmospheric mass of 25 teratonnes compares to Earth's 5148 teratonnes; Mars has a scale height of 11.1 kilometres (6.9 mi)[2] versus Earth's 8.5 kilometres (5.3 mi).[3]

The Martian atmosphere consists of approximately 96% carbon dioxide, 1.9% argon, 1.9% nitrogen, and traces of free oxygen, carbon monoxide, water and methane, among other gases,[1] for a mean molar mass of 43.34 g/mol.[4][5] There has been renewed interest in its composition since the detection of traces of methane in 2003[6][7] that may indicate life but may also be produced by a geochemical process, volcanic or hydrothermal activity.[8]

The atmosphere is quite dusty, giving the Martian sky a light brown or orange-red color when seen from the surface; data from the Mars Exploration Rovers indicate suspended particles of roughly 1.5 micrometres in diameter.[9]

On 16 December 2014, NASA reported detecting an unusual increase, then decrease, in the amounts of methane in the atmosphere of the planet Mars. Organic chemicals have been detected in powder drilled from a rock by the Curiosity rover. Based on deuterium to hydrogen ratio studies, much of the water at Gale Crater on Mars was found to have been lost during ancient times, before the lakebed in the crater was formed; afterwards, large amounts of water continued to be lost.[10][11][12]

On 18 March 2015, NASA reported the detection of an aurora that is not fully understood and an unexplained dust cloud in the atmosphere of Mars.[13]

On 4 April 2015, NASA reported studies, based on measurements by the Sample Analysis at Mars (SAM) instrument on the Curiosity rover, of the Martian atmosphere using xenon and argon isotopes. Results provided support for a "vigorous" loss of atmosphere early in the history of Mars and were consistent with an atmospheric signature found in bits of atmosphere captured in some Martian meteorites found on Earth.[14] This was further supported by results from the MAVEN orbiter circling Mars, that the solar wind is responsible for stripping away the atmosphere of Mars over the years.[15][16][17]

In September 2017, NASA reported radiation levels on the surface of the planet Mars were temporarily doubled, and were associated with an aurora 25 times brighter than any observed earlier due to a massive, and unexpected, solar storm in the middle of the month.[18]

On 1 June 2018, NASA scientists detected signs of a dust storm (see image) on the planet Mars which resulted in the end of the solar-powered Opportunity rover's mission since the dust blocked the sunlight (see image) needed to operate; as of 12 June, the storm is the worst ever recorded at the surface of the planet, and spanned an area about the size of North America and Russia combined (about a quarter of the planet); as of 13 June, Opportunity was reported to be experiencing serious communication problems due to the dust storm;[19] a NASA teleconference about the dust storm was presented on 13 June 2018 at 01:30 pm/et/usa and is available for replay.[20][21][22][23] In July 2018, researchers reported that the largest single source of dust on the planet Mars comes from the Medusae Fossae Formation.[24]

On 7 June 2018, NASA announced a cyclical seasonal variation in atmospheric methane.[25][26][27][28][29][30][31][32]

Atmosphere of Mars
Image of Mars with sandstorm visible, taken by the Hubble Space Telescope on 28 October 2005
General information[1]
Chemical speciesMole fraction
Carbon dioxide95.32%
Carbon monoxide0.08%
Martian Methane Map
One mystery is the source of Mars methane, detection shown here
Mars dust storm – optical depth tau – May to September 2018
(Mars Climate Sounder; Mars Reconnaissance Orbiter)
(1:38; animation; 30 October 2018; file description)


Pressure comparison
Where Pressure
Olympus Mons summit 0.03 kilopascals (0.0044 psi)
Mars average 0.6 kilopascals (0.087 psi)
Hellas Planitia bottom 1.16 kilopascals (0.168 psi)
Armstrong limit 6.25 kilopascals (0.906 psi)
Mount Everest summit[33] 33.7 kilopascals (4.89 psi)
Earth sea level 101.3 kilopascals (14.69 psi)
The solar wind accelerates ions from the Mars upper atmosphere into space
(video (01:13); 5 November 2015)

Mars's atmosphere is composed of the following layers:

  • Exosphere: Typically stated to start at 200 km (120 mi) and higher, this region is where the last wisps of atmosphere merge into the vacuum of space. There is no distinct boundary where the atmosphere ends; it just tapers away.
  • Upper atmosphere, or thermosphere: A region with very high temperatures, caused by heating from the Sun. Atmospheric gases start to separate from each other at these altitudes, rather than forming the even mix found in the lower atmospheric layers.
  • Middle atmosphere: The region in which Mars's jetstream flows.
  • Lower atmosphere: A relatively warm region affected by heat from airborne dust and from the ground.

There is also a complicated ionosphere,[34] and a seasonal ozone layer over the south pole.[35] The MAVEN spacecraft determined in 2015 that there is a substantial layered structure present in both neutral gases and ion densities.[36]

Initial analyses by the MAVEN orbiter[37] and the ExoMars Trace Gas Orbiter, have shown high thermal and density variability in the atmosphere with a slightly lower average density than predicted by existing models.[38]

Observations and measurement from Earth

Comparison of the atmospheric compositions of Venus, Mars, and Earth.

In 1864, William Rutter Dawes observed "that the ruddy tint of the planet does not arise from any peculiarity of its atmosphere seems to be fully proved by the fact that the redness is always deepest near the centre, where the atmosphere is thinnest."[39] Spectroscopic observations in the 1860s and 1870s[40][41] led many to think the atmosphere of Mars is similar to Earth's. 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.[40]

In 1926, photographic observations by William Hammond Wright at the Lick Observatory allowed Donald Howard Menzel to discover quantitative evidence of Mars's atmosphere.[42][43]


PIA16460 Mars Atmosphere Gases 20121102
Most abundant gases on Mars.

Carbon dioxide

The main component of the atmosphere of Mars is carbon dioxide (CO
) at 95.9%. Each pole is in continual darkness during its hemisphere's winter, and the surface gets so cold that as much as 25% of the atmospheric CO
condenses at the polar caps into solid CO
ice (dry ice). When the pole is again exposed to sunlight during summer, the CO
ice sublimes back into the atmosphere. This process leads to a significant annual variation in the atmospheric pressure and atmospheric composition around the Martian poles.

It has been suggested that Mars had a much thicker, warmer, and wetter atmosphere early in its history.[44] Much of this early atmosphere would have consisted of carbon dioxide. Such an atmosphere would have raised the temperature, at least in some places, to above the freezing point of water.[45] With the higher temperature, running water could have carved out the many channels and outflow valleys that are common on the planet. It also might have gathered to form lakes and maybe an ocean.[46] Some researchers have suggested that the atmosphere of Mars may have been many times as thick as the present one of Earth; however, research published in fall 2015 advanced the idea that perhaps the early Martian atmosphere was not as thick as previously thought.[47] Currently, the atmosphere is very thin. For many years, it was assumed that as with Earth, most of the early carbon dioxide was locked up in minerals, called carbonates. However, despite the use of many orbiting instruments that looked for carbonates, very few carbonate deposits have been found.[47][48] Today, it is thought that much of the carbon dioxide in the Martian air was removed by the solar wind. Researchers have discovered a two-step process that sends the gas into space.[49] Ultraviolet light from the sun could strike a carbon dioxide molecule, breaking it into carbon monoxide and oxygen. A second photon of ultraviolet light could subsequently break the carbon monoxide into oxygen and carbon which would receive enough energy to escape the planet. In this process the light isotope of carbon (12C) is most likely to leave the atmosphere. Hence, the carbon dioxide left in the atmosphere would be enriched with the heavy isotope (13C).[50] This higher level of the heavy isotope is what was recently found by the Curiosity rover that sits on the surface of Mars.[51][52]


The atmosphere of Mars is enriched considerably with the noble gas argon, in comparison to the atmosphere of the other planets within the Solar System. Unlike carbon dioxide, the argon content of the atmosphere does not condense, and hence the total amount of argon in the Mars atmosphere is constant. However, the relative concentration at any given location can change as carbon dioxide moves in and out of the atmosphere. Recent satellite data shows an increase in atmospheric argon over the southern pole during its autumn, which dissipates the following spring.[55]


Some aspects of the Martian atmosphere vary significantly. As carbon dioxide sublimes back into the atmosphere during the Martian summer, it leaves traces of water. Seasonal winds transport large amounts of dust and water vapor giving rise to Earth-like frost and large cirrus clouds. These clouds of water-ice were photographed by the Opportunity rover in 2004.[56] NASA scientists working on the Phoenix Mars mission confirmed on 31 July 2008 that they had indeed found subsurface water ice at Mars's northern polar region.


Volatile gases on Mars.

Trace amounts of methane (CH4), at the level of several parts per billion (ppb), were first reported in Mars's atmosphere by a team at the NASA Goddard Space Flight Center in 2003.[7][57] In March 2004, the Mars Express Orbiter and ground-based observations by three groups also suggested the presence of methane in the atmosphere at a concentration of about 10 ppb (parts per billion).[58][59][60] Large differences in the abundances were measured between observations taken in 2003 and 2006, which suggested that the methane was locally concentrated and probably seasonal.[61]

Because methane on Mars would quickly break down due to ultraviolet radiation from the Sun and chemical reactions with other gases, its reported persistent presence in the atmosphere also implies the existence of a source to continually replenish the gas. Current photochemical models alone can not explain the rapid variability of the methane levels.[62][63] It had been proposed that the methane might be replenished by meteorites entering the atmosphere of Mars,[64] but researchers from Imperial College London found that the volumes of methane released this way are too low to sustain the measured levels of the gas.[65]

Research suggests that the implied methane destruction lifetime is as long as ≈4 Earth years and as short as ≈0.6 Earth years.[66][67] This lifetime is short enough for the atmospheric circulation to yield the observed uneven distribution of methane across the planet. In either case, the destruction lifetime for methane is much shorter than the timescale (≈350 years) estimated for photochemical (UV radiation) destruction.[66] The rapid destruction (or "sink") of methane suggests that another process must dominate removal of atmospheric methane on Mars, and it must be more efficient than destruction by light by a factor of 100 to 600.[67][66] This unexplained fast destruction rate also suggests a very active replenishing source.[68] In 2014 it was concluded that presence of strong methane sinks are not subject to atmospheric oxidation.[69] A possibility is that the methane is not consumed at all, but rather condenses and evaporates seasonally from clathrates.[70] Another possibility is that methane reacts with tumbling surface sand quartz (SiO
) and olivine to form covalent Si–CH

Possible methane sources and sinks on Mars.

The principal candidates for the origin of Mars' methane include non-biological processes such as water–rock reactions, radiolysis of water, and pyrite formation, all of which produce H2 that could then generate methane and other hydrocarbons via Fischer–Tropsch synthesis with CO and CO2.[72] It has also been shown that methane could be produced by a process involving water, carbon dioxide, and the mineral olivine, which is known to be common on Mars.[73] The required conditions for this reaction (i.e. high temperature and pressure) do not exist on the surface, but may exist within the crust.[74][75] A detection of the mineral by-product serpentinite would suggest that this process is occurring. An analog on Earth suggests that low-temperature production and exhalation of methane from serpentinized rocks may be possible on Mars.[76] Another possible geophysical source could be ancient methane trapped in clathrate hydrates that may be released occasionally.[77] Under the assumption of a cold early Mars environment, a cryosphere could trap such methane as clathrates in stable form at depth, that might exhibit sporadic release.[78]

A group of Mexican scientists performed plasma experiments in a synthetic Mars atmosphere and found that bursts of methane can be produced when a discharge interacts with water ice. A potential source of the discharges can be the electrification of dust particles from sand storms and dust devils. The ice can be found in trenches or in the permafrost. The electrical discharge ionizes gaseous CO2 and water molecules and their byproducts recombine to produce methane. The results obtained show that pulsed electrical discharges over ice samples in a Martian atmosphere produce about 1.41×1016 molecules of methane per joule of applied energy.[79][80]

Living microorganisms, such as methanogens, are another possible source, but no evidence for the presence of such organisms has been found on Mars. In Earth's oceans, biological methane production tends to be accompanied by ethane, whereas volcanic methane is accompanied by sulfur dioxide.[81] Several studies of trace gases in the Martian atmosphere have found no evidence for sulfur dioxide in the Martian atmosphere, which makes volcanism unlikely to be the source of methane.[82][83]

In 2011, NASA scientists reported a comprehensive search using ground-based high-resolution infrared spectroscopy for trace species (including methane) on Mars, deriving sensitive upper limits for methane (<7 ppbv), ethane (<0.2 ppbv), methanol (<19 ppbv) and others (H2CO, C2H2, C2H4, N2O, NH3, HCN, CH3Cl, HCl, HO2 – all limits at ppbv levels).[84] The data were acquired over a period of 6 years and span different seasons and locations on Mars, suggesting that if organics are being released into the atmosphere, these events were extremely rare or currently non-existent, considering the expected long lifetimes for some of these species.[84]

Methane measurements in the atmosphere of Mars by the Curiosity rover.

In August 2012, the Curiosity rover landed on Mars. The rover's instruments are capable of making precise abundance measurements, which can be used to distinguish between different isotopologues of methane.[8][85] The first measurements with Curiosity's Tunable Laser Spectrometer (TLS) in 2012 indicated that there was no methane or less than 5 ppb of methane at the landing site,[86][87][88][89][90] later calculated to a baseline of 0.3 to 0.7 ppb.[91] On 2013, NASA scientists again reported no detection of methane beyond a baseline.[92][93][94] But in 2014, NASA reported that the Curiosity rover detected a tenfold increase ('spike') in methane in the atmosphere around it in late 2013 and early 2014. Four measurements taken over two months in this period averaged 7.2 ppb, implying that Mars is episodically producing or releasing methane from an unknown source.[95] Before and after that, readings averaged around one-tenth that level.[10][11][95]

The Indian Mars Orbiter Mission, which entered orbit around Mars on 24 September 2014, is equipped with a Fabry–Pérot interferometer to measure atmospheric methane, but after entering Mars orbit it was determined that it was not capable of detecting methane,[96][97]:57 so the instrument was repurposed as an albedo mapper.[96][98] The ExoMars Trace Gas Orbiter, which entered orbit on 19 October 2016, will further study the methane, as well as its decomposition products such as formaldehyde and methanol starting in April 2018.[81][99][100][101]

Measuring the ratio of hydrogen and methane levels on Mars may help determine the likelihood of life on Mars.[102][103] According to the scientists, "...low H2/CH4 ratios (less than approximately 40)" would "indicate that life is likely present and active."[102] The observed ratios in the lower Martian atmosphere were "approximately 10 times" higher "suggesting that biological processes may not be responsible for the observed CH4."[102] The scientists suggested measuring the H2 and CH4 flux at the Martian surface for a more accurate assessment.

On 7 June 2018, NASA announced a cyclical seasonal variation in atmospheric methane.[28][31][32]

Curiosity detected a cyclical seasonal variation in atmospheric methane.

Sulfur dioxide

Sulfur dioxide in the atmosphere is thought to be a tracer of current volcanic activity. It has become especially interesting due to the long-standing controversy of methane on Mars. If methane on Mars were being produced by volcanoes (as it is in part on Earth) we would expect to find sulfur dioxide in large quantities. Several teams have searched for sulfur dioxide on Mars using the NASA Infrared Telescope Facility. No sulfur dioxide was detected in these studies, but they were able to place stringent upper limits on the atmospheric concentration of 0.2 ppb.[82][83] In March 2013, a team led by scientists at NASA Goddard Space Flight Center reported a detection of SO2 in Rocknest soil samples analyzed by the Curiosity rover.[104]


Mars rotation simulation december 2007
Rotation of Mars near opposition in Dec 2007. Ecliptic south is up.

As reported by the European Space Agency (ESA) on 29 September 2013, a new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone (O
) above Mars's southern pole in winter. Ozone was most likely difficult to detect on Mars because its concentration is typically 300 times lower than on Earth, although it varies greatly with location and time. The SPICAM —an UV/IR spectrometer— on board Mars Express has shown the presence of two distinct ozone layers at low-to-mid latitudes. These comprise a persistent, near-surface layer below an altitude of 30 km, a separate layer that is only present in northern spring and summer with an altitude varying from 30 to 60 km, and another separate layer that exists 40–60 km above the southern pole in winter, with no counterpart above the Mars's north pole. This third ozone layer shows an abrupt decrease in elevation between 75 and 50 degrees south. SPICAM detected a gradual increase in ozone concentration at 50 km until midwinter, after which it slowly decreased to very low concentrations, with no layer detectable above 35 km. The reporting scientists think that the observed polar ozone layers are the result of the same atmospheric circulation pattern that creates a distinct oxygen emission identified in the polar night and also present in Earth's atmosphere. This circulation takes the form of a huge Hadley cell in which warmer air rises and travels toward the south pole before cooling and sinking at higher latitudes. Mars is on a quite elliptical orbit and has a large axial tilt, which causes extreme seasonal variations in temperature amongst the northern and southern hemispheres. Mars's temperature difference greatly influences the amount of water vapor in the atmosphere, because warmer air can contain more moisture. This, in turn, affects the production of ozone-destroying hydrogen radicals.[105]


In 2010, the Herschel Space Observatory detected molecular oxygen the martian atmosphere.[106]

In early 2016, Stratospheric Observatory for Infrared Astronomy (SOFIA) detected atomic oxygen in the atmosphere of Mars.[107] This was the first time in forty years it was detected, the last time being the Viking and Mariner missions in the 1970s.[107]


Molecular nitrogen (N2) is present in the atmosphere at 1.9%.[1] Measurements by various robotic missions,[108] and analyses of Martian meteorites, show that the atmosphere is enriched in the isotope 15N.[109] The enrichment is attributed to selective escape by electron impact dissociation of N2 and by dissociative recombination of N2+.[110] Estimates suggest that the initial partial pressure of N2 may have been up to 30 millibars.[109][111]

Potential for use by humans

The atmosphere of Mars is a resource of known composition available at any landing site on Mars. It has been proposed that human exploration of Mars could use carbon dioxide (CO2) from the Martian atmosphere to make rocket fuel for the return mission. Mission studies that propose using the atmosphere in this way include the Mars Direct proposal of Robert Zubrin and the NASA Design reference mission study. Two major chemical pathways for use of the carbon dioxide are the Sabatier reaction, converting atmospheric carbon dioxide along with additional hydrogen (H2), to produce methane (CH4) and oxygen (O2), and electrolysis, using a zirconia solid oxide electrolyte to split the carbon dioxide into oxygen (O2) and carbon monoxide (CO).

Early atmosphere

Mars's atmosphere is thought to have changed over the course of the planet's lifetime, with evidence suggesting the possibility that Mars had large oceans a few billion years ago.[112] As stated in the Mars ocean hypothesis, atmospheric pressure on the present-day Martian surface only exceeds that of the triple point of water (6.11 hectopascals (0.0886 psi)) in the lowest elevations; at higher elevations water can exist only in solid or vapor form. Annual mean temperatures at the surface are currently < 210 K (−63 °C; −82 °F), significantly lower than that needed to sustain liquid water. However, early in its history Mars may have had conditions more conducive to retaining liquid water at the surface. In 2013, a team of scientists proposed that Mars once had "oxygen-rich" atmosphere billions of years ago.[113][114]

Possible causes for the atmospheric escape of a previously thicker Martian atmosphere include:

  • Gradual erosion of the atmosphere by solar wind. On 5 November 2015, NASA announced that data from MAVEN shows that the erosion of Mars' atmosphere increases significantly during solar storms. This shift took place between about 4.2 to 3.7 billion years ago, as the shielding effect of the global magnetic field was lost when the planet's internal dynamo cooled.[15][16][115][116]
  • Catastrophic collision by a body large enough to blow away a significant percentage of the atmosphere;[117]
  • Mars’ low gravity allowing the atmosphere to "blow off" into space by Jeans escape.[118]
Mars's escaping atmosphere—carbon, oxygen, hydrogen—made by MAVEN UV spectrograph).
Mars's escaping atmosphere—carbon, oxygen, hydrogen—made by MAVEN UV spectrograph).[119]


Mars atmosphere

Mars's thin atmosphere, visible on the horizon.

Mars violet sky

Mars Pathfinder – Martian sky with water ice clouds.

A storm front moves in

Martian sunset by Spirit rover at Gusev crater (May, 2005).
Martian sunset by Spirit rover at Gusev crater (May, 2005).
Martian sunset by Pathfinder at Ares Vallis (July, 1997).
Martian sunset by Pathfinder at Ares Vallis (July, 1997).

Interactive Mars map

Acidalia PlanitiaAcidalia PlanitiaAlba MonsAmazonis PlanitiaAonia TerraArabia TerraArcadia PlanitiaArcadia PlanitiaArgyre PlanitiaElysium MonsElysium PlanitiaHellas PlanitiaHesperia PlanumIsidis PlanitiaLucas PlanumLyot (crater)Noachis TerraOlympus MonsPromethei TerraRudaux (crater)Solis PlanumTempe TerraTerra CimmeriaTerra SabaeaTerra SirenumTharsis MontesUtopia PlanitiaValles MarinerisVastitas BorealisVastitas BorealisMap of Mars
The image above contains clickable linksInteractive imagemap of the global topography of Mars. Hover your mouse to see the names of over 25 prominent geographic features, and click to link to them. Coloring of the base map indicates relative elevations, based on data from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor. Reds and pinks are higher elevation (+3 km to +8 km); yellow is 0 km; greens and blues are lower elevation (down to −8 km). Whites (>+12 km) and browns (>+8 km) are the highest elevations. Axes are latitude and longitude; Poles are not shown.
(See also: Mars Rovers map) (view • discuss)

See also


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Further reading

External links

Astronomy on Mars

In many cases astronomical phenomena viewed from the planet Mars are the same or similar to those seen from Earth but sometimes (as with the view of Earth as an evening/morning star) they can be quite different. For example, because the atmosphere of Mars does not contain an ozone layer, it is also possible to make UV observations from the surface of Mars.

Dawes (Martian crater)

Dawes Crater is located in the Sinus Sabaeus quadrangle of Mars, at 9.2 S and 38 E. It is about 191 km (119 mi) in diameter, and was named after William R. Dawes, a British astronomer (1799–1868) who was ahead of his time in believing that Mars only had a thin atmosphere. Dawes presumed that the atmosphere of Mars was thin because surface markings on the planet could easily be seen.

Donald Howard Menzel

Donald Howard Menzel (April 11, 1901 – December 14, 1976) was one of the first theoretical astronomers and astrophysicists in the United States. He discovered the physical properties of the solar chromosphere, the chemistry of stars, the atmosphere of Mars, and the nature of gaseous nebulae. The minor planet 1967 Menzel was named in his honor, as well as a small lunar crater located in the southeast of Mare Tranquilitatis, the Sea of Tranquility.

Firsoff (Martian crater)

Firsoff is an impact crater in the region called Meridiani Planum in the Oxia Palus quadrangle of Mars, located at 2.66°N latitude and 9.42°W longitude. It is 90 km in diameter. It was named after British astronomer Axel Firsoff, and the name was approved in 2010.Parts of the crater display many layers, as do some of the other craters in the region. Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers. There is much evidence that at least some of the layers seen on Mars especially in Firsoff crater involve groundwater.There are mounds in the crater that may have formed from springs. They show breccia sometimes a pit at the top. Some of the mounds are lined up along straight fractures. The mound's composition and shape suggest water came out of the mounds and then minerals were precipitated.A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars.At a conference in May 2014, Firsoff Crater was picked to be one of 26 locations being considered for the 2020 Rover. Some of the layers in the crater contain sulfates which have a good chance of preserving traces of life. This Rover will look for signs of life and gather samples for return to Earth in another mission. A microscope will look for cells and other signs of life. It will also test a device to extract oxygen from the carbon-dioxide atmosphere of Mars. This is a technology needed for future human exploration.

George C. Pimentel

George Claude Pimentel (May 2, 1922 – June 18, 1989) was the inventor of the chemical laser. He also developed the technique of matrix isolation in low-temperature chemistry. In theoretical chemistry, he proposed the three-center four-electron bond which is now accepted as the best simple model of hypervalent molecules. In the late 1960s, Pimentel led the University of California team that designed the infrared spectrometer for the Mars Mariner 6 and 7 missions that analyzed the surface and atmosphere of Mars.An alumnus of University of California, Los Angeles (B.S. 1943) and University of California, Berkeley (Ph.D. 1949), Pimentel began teaching at Berkeley in 1949, where he remained until his death in 1989.

History of Mars observation

The recorded history of observation of the planet Mars dates back to the era of the ancient Egyptian astronomers in the 2nd millennium BCE. Chinese records about the motions of Mars appeared before the founding of the Zhou Dynasty (1045 BCE). Detailed observations of the position of Mars were made by Babylonian astronomers who developed arithmetic techniques to predict the future position of the planet. The ancient Greek philosophers and Hellenistic astronomers developed a geocentric model to explain the planet's motions. Measurements of Mars' angular diameter can be found in ancient Greek and Indian texts. In the 16th century, Nicolaus Copernicus proposed a heliocentric model for the Solar System in which the planets follow circular orbits about the Sun. This was revised by Johannes Kepler, yielding an elliptic orbit for Mars that more accurately fitted the observational data.

The first telescopic observation of Mars was by Galileo Galilei in 1610. Within a century, astronomers discovered distinct albedo features on the planet, including the dark patch Syrtis Major Planum and polar ice caps. They were able to determine the planet's rotation period and axial tilt. These observations were primarily made during the time intervals when the planet was located in opposition to the Sun, at which points Mars made its closest approaches to the Earth.

Better telescopes developed early in the 19th century allowed permanent Martian albedo features to be mapped in detail. The first crude map of Mars was published in 1840, followed by more refined maps from 1877 onward. When astronomers mistakenly thought they had detected the spectroscopic signature of water in the Martian atmosphere, the idea of life on Mars became popularized among the public. Percival Lowell believed he could see a network of artificial canals on Mars. These linear features later proved to be an optical illusion, and the atmosphere was found to be too thin to support an Earth-like environment.

Yellow clouds on Mars have been observed since the 1870s, which Eugène M. Antoniadi suggested were windblown sand or dust. During the 1920s, the range of Martian surface temperature was measured; it ranged from −85 to 7 °C (−121 to 45 °F). The planetary atmosphere was found to be arid with only trace amounts of oxygen and water. In 1947, Gerard Kuiper showed that the thin Martian atmosphere contained extensive carbon dioxide; roughly double the quantity found in Earth's atmosphere. The first standard nomenclature for Mars albedo features was adopted in 1960 by the International Astronomical Union. Since the 1960s, multiple robotic spacecraft have been sent to explore Mars from orbit and the surface. The planet has remained under observation by ground and space-based instruments across a broad range of the electromagnetic spectrum. The discovery of meteorites on Earth that originated on Mars has allowed laboratory examination of the chemical conditions on the planet.

Ice cloud

An ice cloud is a colloid of ice particles dispersed in air. The term has been used to refer to clouds of both water ice and carbon dioxide ice on Mars.

Such clouds can be sufficiently large and dense to cast shadows on the Martian surface.Clouds on Earth can contain ice particles.

Mariner 6 and 7

As part of NASA's wider Mariner program, Mariner 6 and Mariner 7 (Mariner Mars 69A and Mariner Mars 69B) completed the first dual mission to Mars in 1969. Mariner 6 was launched from Launch Complex 36B at Cape Canaveral Air Force Station and Mariner 7 from Launch Complex 36A at Cape Kennedy. The craft flew over the equator and south polar regions, analyzing the atmosphere and the surface with remote sensors, and recording and relaying hundreds of pictures. The mission's goals were to study the surface and atmosphere of Mars during close flybys, in order to establish the basis for future investigations, particularly those relevant to the search for extraterrestrial life, and to demonstrate and develop technologies required for future Mars missions. Mariner 6 also had the objective of providing experience and data which would be useful in programming the Mariner 7 encounter five days later.

Mars 2M No.521

Mars 2M No.521, also known as Mars M-69 No.521 and sometimes identified by NASA as Mars 1969A, was a Soviet spacecraft which was lost in a launch failure in 1969. It consisted of an orbiter. The spacecraft was intended to image the surface of Mars using three cameras, with images being encoded for transmission back to Earth as television signals. It also carried a radiometer, a series of spectrometers, and an instrument to detect water vapour in the atmosphere of Mars. It was one of two Mars 2M spacecraft, along with Mars 2M No.522, which was launched in 1969 as part of the Mars programme. Neither launch was successful.The Mars 2M probes were originally intended to consist of both an orbiter and a lander. Time constraints did not permit the development of a soft lander, so engineers decided to simply use a hard lander that would crash into the Martian surface but gather data during its descent. At first, a modified Luna E-8 bus was to be used for the spacecraft, however it had a number of limitations that made it unsuitable for the long journey to Mars. Halfway through the project, Lavochkin Bureau design chief Georgi Babakin decided to simply discard the Luna E-8 derived probe and design a completely new one from scratch.

However, the 2M probes ended significantly heavier than intended and engineers also ran out of time to conduct drop tests of the lander, so that part was abandoned which left only the orbiter. If successful, this would still be a major propaganda success for the Soviets as NASA was nearly three years away from attempting a Mars orbiter.

As 1968 drew to a close, the project was lagging behind schedule and the US was also making significant headway in the space race with Mariner 6 and 7 scheduled to launch to Mars early in the next year and Apollo 8 taking astronauts into lunar orbit. The Kremlin wanted the Mars probes readied as soon as possible and the second of the two probes was completed in the middle of January. Despite doubts that the probes were ready to fly, they were delivered to Baikonour.

Mars 2M No.522

Mars 2M No.522, also known as Mars M-69 No.522 and sometimes identified by NASA as Mars 1969B, was a Soviet spacecraft which was lost in a launch failure in 1969. It consisted of an orbiter. The spacecraft was intended to image the surface of Mars using three cameras, with images being encoded for transmission back to Earth as television signals. It also carried a radiometer, a series of spectrometers, and an instrument to detect water vapour in the atmosphere of Mars. It was one of two Mars 2M spacecraft, along with Mars 2M No.521, which was launched in 1969 as part of the Mars program. Neither launch was successful.

Mars aircraft

A Mars aircraft is a vehicle for flying in the atmosphere of Mars. So far, Mars lander entry, descent, and landing systems have passed through the atmosphere. Aircraft may provide in situ measurements of the atmosphere of Mars, as well as additional observations over extended areas. A long-term goal is to develop piloted Mars aircraft.Compared to Earth, the air is thinner at the surface (with pressure less than 1% of Earth's at sea level) but the gravity is lower (less than 40%). Mars air, consisting mostly of CO2 gas, is over 50% denser than Earth air adjusted to equal pressure.

Mars atmospheric entry

Mars atmospheric entry is the entry into the atmosphere of Mars. High velocity entry into Martian air creates a CO2-N2 plasma, as opposed to O2-N2 for Earth air. Mars entry is affected by the radiative effects of hot CO2 gas and Martian dust suspended in the air. Flight regimes for entry, descent, and landing systems include aerocapture, hypersonic, supersonic, and subsonic.

Mars general circulation model

The Mars general circulation model (MGCM) is the result of a research project by NASA to understand the nature of the general circulation of the atmosphere of Mars, how that circulation is driven and how it affects the climate of Mars in the long term.

Mars regional atmospheric modeling system

The Mars Regional Atmospheric Modeling System (MRAMS) is a computer program that simulates the circulations of the Martian atmosphere at regional and local scales. MRAMS, developed by Scot Rafkin and Timothy Michaels, is derived from the Regional Atmospheric Modeling System (RAMS) developed by William R. Cotton and Roger A. Pielke to study atmospheric circulations on the Earth.Key features of MRAMS include a non-hydrostatic, fully compressible dynamics, explicit bin dust, water, and carbon dioxide ice atmospheric physics model, and a fully prognostic regolith model that includes carbon dioxide deposition and sublimation. Several Mars exploration projects, including the Mars Exploration Rovers, the Phoenix Scout Mission, and the Mars Science Laboratory have used MRAMS to study a variety of atmospheric circulations.

Nadir and Occultation for Mars Discovery

Nadir and Occultation for MArs Discovery (NOMAD) is a 3-channel spectrometer on board the ExoMars Trace Gas Orbiter (TGO) launched to Mars orbit on 14 March 2016.

NOMAD is designed to perform high-sensitivity orbital identification of atmospheric components, concentration and temperature, their sources, loss, and cycles. It measures the sunlight reflected from the surface and atmosphere of Mars, and it analyses its wavelength spectrum to identify the components of the Martian atmosphere that may suggest a biological source. The Principal Investigator is Ann Carine Vandaele, from the Belgian Institute for Space Aeronomy, Belgium.

Niger Vallis

Niger Vallis is a valley on Mars that appears to have been carved by water. It has been identified as an outflow channel. It merges with Dao Vallis which runs southwestward into Hellas Planitia from the volcanic Hadriacus Mons. Like Dao, it was formed around the Late Noachian and Early Hesperian Epochs. It is named after the Niger River in Africa.


The Noachian is a geologic system and early time period on the planet Mars characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water. The absolute age of the Noachian period is uncertain but probably corresponds to the lunar Pre-Nectarian to Early Imbrian periods of 4100 to 3700 million years ago, during the interval known as the Late Heavy Bombardment. Many of the large impact basins on the Moon and Mars formed at this time. The Noachian Period is roughly equivalent to the Earth’s Hadean and early Archean eons when the first life forms likely arose.Noachian-aged terrains on Mars are prime spacecraft landing sites to search for fossil evidence of life. During the Noachian, the atmosphere of Mars was denser than it is today, and the climate possibly warm enough to allow rainfall. Large lakes and rivers were present in the southern hemisphere, and an ocean may have covered the low-lying northern plains. Extensive volcanism occurred in the Tharsis region, building up enormous masses of volcanic material (the Tharsis bulge) and releasing large quantities of gases into the atmosphere. Weathering of surface rocks produced a diversity of clay minerals (phyllosilicates) that formed under chemical conditions conducive to microbial life.

Tader Valles

Tader Valles is a set of small channels in the Phaethontis quadrangle found at

49.1° south latitude and 152.5° west longitude. it is named after the ancient name for present Segura River, Spain.


WAVAR, short for water-vapor adsorption reactor, is a process that has been studied for its potential in directly extracting water from the atmosphere of Mars by alternately blowing air over a zeolite adsorption bed and heating the bed to extract the adsorbed water. An advantage of this process is its mechanical simplicity and applicability to any point on Mars's surface. Its output is not sufficient for industrial purposes such as fuel manufacture, but it may be a useful supplement to life support in some architectures.

Dwarf planet
See also

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