The atmosphere of Mars is the layer of gases surrounding
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
. It is primarily composed of
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
(95%), molecular
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(2.8%), and
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
(2%).
It also contains trace levels of
water vapor
(99.9839 °C)
, -
, Boiling point
,
, -
, specific gas constant
, 461.5 J/( kg·K)
, -
, Heat of vaporization
, 2.27 MJ/kg
, -
, Heat capacity
, 1.864 kJ/(kg·K)
Water vapor, water vapour or aqueous vapor is the gaseous pha ...
,
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
,
carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
,
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
, and
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemi ...
es.
The atmosphere of Mars is much thinner than
Earth's. The average
surface pressure is only about which is less than 1% of the Earth's value.
The currently thin Martian atmosphere prohibits the existence of liquid water on the surface of Mars, but many studies suggest that the Martian atmosphere was much thicker in the past.
The higher density during spring and fall is reduced by 25% during the winter when carbon dioxide partly freezes at the pole caps. The highest atmospheric density on Mars is equal to the density found above the Earth's surface and is ≈0.020 kg/m
3. The atmosphere of Mars has been losing mass to space since the planet's core slowed down, and the
leakage of gases still continues today.
The atmosphere of Mars is colder than Earth's. Owing to the larger distance from the Sun, Mars receives less solar energy and has a lower
effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...
, which is about .
The average surface emission temperature of Mars is just , which is comparable to inland Antarctica.
The weaker
greenhouse effect
The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
in the Martian atmosphere (, versus on Earth) can be explained by the low abundance of other
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
es.
The daily range of temperature in the lower atmosphere is huge due to the low thermal inertia; it can range from to near near the surface in some regions.
The temperature of the upper part of the Martian atmosphere is also significantly lower than Earth's because of the absence of
stratospheric ozone
The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in relat ...
and the radiative cooling effect of carbon dioxide at higher altitudes.
Dust devil
A dust devil is a strong, well-formed, and relatively short-lived whirlwind. Its size ranges from small (half a metre wide and a few metres tall) to large (more than 10 m wide and more than 1 km tall). The primary vertical motion is u ...
s and
dust storm
A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transporte ...
s are prevalent on Mars, which are sometimes observable by telescopes from Earth,
and in 2018 even with the naked eye as a change in colour and brightness of the planet. Planet-encircling dust storms (global dust storms) occur on average every 5.5 Earth years (every 3 Martian years) on Mars
and can threaten the operation of
Mars rover
A Mars rover is a motor vehicle designed to travel on the surface of Mars. Rovers have several advantages over stationary landers: they examine more territory, they can be directed to interesting features, they can place themselves in sunny pos ...
s. However, the mechanism responsible for the development of large dust storms is still not well understood.
It has been suggested to be loosely related to gravitational influence of both moons, somewhat similar to the creation of
tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravity, gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide t ...
s on Earth.
The Martian atmosphere is an
oxidizing atmosphere
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
. 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
The ExoMars Trace Gas Orbiter (TGO or ExoMars Orbiter) is a collaborative project between the European Space Agency (ESA) and the Russian Roscosmos agency that sent an atmospheric science, atmospheric research orbiter and the Schiaparelli EDM, ...
failed to find methane in the atmosphere over the whole of Mars,
several previous missions and ground-based telescope detected unexpected levels of methane in the Martian atmosphere, which may even be a
biosignature
A biosignature (sometimes called chemical fossil or molecular fossil) is any substance – such as an element, isotope, or molecule – or phenomenon that provides scientific evidence of past or present life. Measurable attribute ...
for
life on Mars
The possibility of life on Mars is a subject of interest in astrobiology due to the planet's proximity and similarities to Earth. To date, no proof of past or present life has been found on Mars. Cumulative evidence suggests that during the ...
.
However, the interpretation of the measurements is still highly controversial and lacks a scientific consensus.
History of atmospheric observations
In 1784, German-born British astronomer
William Herschel
Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
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 1809, French astronomer
Honoré Flaugergues
Pierre-Gilles-Antoine-Honoré Flaugergues, usually known as Honoré Flaugergues (16 May 1755 in Viviers, Ardèche – 26 November 1835 or 20 November 1830different sources give different years of death) was a French astronomer.
Biography
Flauger ...
wrote about his observation of "yellow clouds" on Mars, which are likely to be dust storm events.
In 1864,
William Rutter Dawes
William Rutter Dawes (19 March 1799 – 15 February 1868) was an English astronomer.
Biography
Dawes was born at Christ's Hospital then in the City of London (it moved to Horsham, West Sussex in 1902), the son of William Dawes, also an astro ...
observed that "the ruddy tint of the planet does not arise from any peculiarity of its atmosphere; it seems to be fully proved by the fact that the redness is always deepest near the centre, where the atmosphere is thinnest."
Spectroscopic observations in the 1860s and 1870s
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
William Wallace Campbell (April 11, 1862 – June 14, 1938) was an American astronomer, and director of Lick Observatory from 1901 to 1930. He specialized in spectroscopy. He was the tenth president of the University of California from 1923 to 1 ...
suggested Mars resembles the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, which has no appreciable atmosphere, in many respects.
In 1926, photographic observations by
William Hammond Wright at the
Lick Observatory allowed
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 atmosp ...
to discover quantitative evidence of Mars's atmosphere.
With an enhanced understanding of optical properties of atmospheric gases and advancement in
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
technology, scientists started to measure the composition of the Martian atmosphere in the mid-20th century. Lewis David Kaplan and his team detected the signals of water vapor and carbon dioxide in the spectrogram of Mars in 1964, as well as carbon monoxide in 1969. In 1965, the measurements made during
Mariner 4's flyby confirmed that the Martian atmosphere is constituted mostly of carbon dioxide, and the surface pressure is about 400 to 700 Pa. After the composition of the Martian atmosphere was known,
astrobiological
Astrobiology, and the related field of exobiology, is an interdisciplinary scientific field that studies the origins, early evolution, distribution, and future of life in the universe. Astrobiology is the multidisciplinary field that investig ...
research began on Earth to determine the viability of
life on Mars
The possibility of life on Mars is a subject of interest in astrobiology due to the planet's proximity and similarities to Earth. To date, no proof of past or present life has been found on Mars. Cumulative evidence suggests that during the ...
. Containers that simulated environmental conditions on Mars, called "
Mars jars", were developed for this purpose.
In 1976, two landers of the
Viking program
The ''Viking'' program consisted of a pair of identical American space probes, ''Viking 1'' and ''Viking 2'', which landed on Mars in 1976. Each spacecraft was composed of two main parts: an orbiter designed to photograph the surface of Mars f ...
provided the first ever in-situ measurements of the composition of the Martian atmosphere. Another objective of the mission included investigations for evidence of past or present life on Mars (see
Viking lander biological experiments
In 1976 two identical Viking program landers each carried four types of biological experiments to the surface of Mars. The first successful Mars landers, ''Viking 1'' and ''Viking 2'', then carried out experiments to look for biosignatures of mic ...
). Since then, many orbiters and landers have been sent to Mars to measure different properties of the Martian atmosphere, such as concentration of trace gases and isotopic ratios. In addition, telescopic observations and analysis of
Martian meteorite
A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. , 277 meteorites had been classified as Martian, less than half a percen ...
s provide independent sources of information to verify the findings. The imageries and measurements made by these spacecraft greatly improve our understanding of the atmospheric processes outside Earth. The rover ''
Curiosity
Curiosity (from Latin '' cūriōsitās'', from ''cūriōsus'' "careful, diligent, curious", akin to ''cura'' "care") is a quality related to inquisitive thinking such as exploration, investigation, and learning, evident by observation in humans ...
'' and the lander ''
InSight
Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings:
*a piece of information
*the act or result of understanding the inner nature of things or of seeing intu ...
'' are still operating on the surface of Mars to carry out experiments and report the local daily weather. The rover ''
Perseverance
Perseverance may refer to:
Behaviour
* Psychological resilience
* Perseverance of the saints, a Protestant Christian teaching
* Assurance (theology)
Geography
* Perseverance, Queensland, a locality in Australia
* Perseverance Island, Seychelles
...
'' and helicopter ''
Ingenuity'', which formed the
Mars 2020
Mars 2020 is a Mars rover mission forming part of NASA's Mars Exploration Program that includes the rover '' Perseverance'', the small robotic, coaxial helicopter '' Ingenuity'', and associated delivery vehicles. Mars 2020 was launched from ...
program, landed in February 2021. The rover ''
Rosalind Franklin
Rosalind Elsie Franklin (25 July 192016 April 1958) was a British chemist and X-ray crystallographer whose work was central to the understanding of the molecular structures of DNA (deoxyribonucleic acid), RNA (ribonucleic acid), viruses, co ...
'' is scheduled to launch in 2022.
Current chemical composition
Carbon dioxide
CO
2 is the main component of the Martian atmosphere. It has a mean volume ratio of 94.9%.
In winter polar regions, the surface temperature can be lower than the frost point of CO
2. CO
2 gas in the atmosphere can condense on the surface to form 1–2 m thick solid
dry ice
Dry ice is the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimates directly from the solid state to the gas state. It is used primarily a ...
.
In summer, the polar dry ice cap can undergo sublimation and release the CO
2 back to the atmosphere. As a result, significant annual variability in atmospheric pressure (≈25%) and atmospheric composition can be observed on Mars. The condensation process can be approximated by the
Clausius–Clapeyron relation for CO
2.
![Composition-comparison Mars-Venus-Earth](https://upload.wikimedia.org/wikipedia/commons/2/2c/Composition-comparison_Mars-Venus-Earth.png)
Despite the high concentration of CO
2 in the Martian atmosphere, the
greenhouse effect
The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...
is relatively weak on Mars (about 5 °C) because of the low concentration of water vapor and low atmospheric pressure. While water vapor in Earth's atmosphere has the largest contribution to greenhouse effect on modern Earth, it is present in only very low concentration in the Martian atmosphere. Moreover, under low atmospheric pressure, greenhouse gases cannot absorb infrared radiation effectively because the
pressure-broadening effect is weak.
In the presence of solar UV radiation (''hν'', photons with wavelength shorter than 225 nm), CO
2 in the Martian atmosphere can be
photolyzed via the following reaction:
: + ( < 225 nm) ⟶ .
If there is no chemical production of CO
2, all the CO
2 in the current Martian atmosphere would be removed by photolysis in about 3,500 years.
The
hydroxyl radical
The hydroxyl radical is the diatomic molecule . The hydroxyl radical is very stable as a dilute gas, but it decays very rapidly in the condensed phase. It is pervasive in some situations. Most notably the hydroxyl radicals are produced from the ...
s (OH) produced from the photolysis of water vapor, together with the other odd hydrogen species (e.g. H, HO
2), can convert carbon monoxide (CO) back to CO
2. The reaction cycle can be described as:
:
:
:
:
Mixing also plays a role in regenerating CO
2 by bringing the O, CO, and O
2 in the upper atmosphere downward.
The balance between photolysis and redox production keeps the average concentration of CO
2 stable in the modern Martian atmosphere.
CO
2 ice clouds can form in winter polar regions and
at very high altitudes (>50 km) in tropical regions, where the air temperature is lower than the frost point of CO
2.
Nitrogen
N
2 is the second most abundant gas in the Martian atmosphere. It has a mean volume ratio of 2.6%.
Various measurements showed that the Martian atmosphere is enriched in
15N.
The enrichment of heavy isotopes of nitrogen is possibly caused by mass-selective escape processes.
Argon
Argon is the third most abundant gas in the Martian atmosphere. It has a mean volume ratio of 1.9%.
In terms of stable isotopes, Mars is enriched in
38Ar relative to
36Ar, which can be attributed to hydrodynamic escape.
One of
Argon's isotopes,
40Ar, is produced from the radioactive decay of
40K. In contrast,
36Ar is primordial: It was present in the atmosphere after the formation of Mars. Observations indicate that Mars is enriched in
40Ar relative to
36Ar, which cannot be attributed to mass-selective loss processes.
A possible explanation for the enrichment is that a significant amount of primordial atmosphere, including
36Ar, was lost by impact erosion in the early history of Mars, while
40Ar was emitted to the atmosphere after the impact.
Oxygen and ozone
The estimated mean volume ratio of molecular oxygen (O
2) in the Martian atmosphere is 0.174%.
It is one of the products of the photolysis of CO
2, water vapor, and
ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
(O). It can react with atomic oxygen (O) to re-form ozone (O). In 2010, the
Herschel Space Observatory
The Herschel Space Observatory was a space observatory built and operated by the European Space Agency (ESA). It was active from 2009 to 2013, and was the largest infrared telescope ever launched until the launch of the James Webb Space Telesc ...
detected molecular oxygen in the Martian atmosphere.
Atomic oxygen is produced by photolysis of CO
2 in the upper atmosphere and can escape the atmosphere via dissociative recombination or ion pickup. In early 2016,
Stratospheric Observatory for Infrared Astronomy (SOFIA) detected
atomic oxygen
There are several known allotropes of oxygen. The most familiar is molecular oxygen (O2), present at significant levels in Earth's atmosphere and also known as dioxygen or triplet oxygen. Another is the highly reactive ozone (O3). Others are:
*A ...
in the atmosphere of Mars, which has not been found since the Viking and Mariner mission in the 1970s.
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.
Similar to stratospheric ozone in Earth's atmosphere, the ozone present in the Martian atmosphere can be destroyed by catalytic cycles involving odd hydrogen species:
:
:
: Net:
Since water is an important source of these odd hydrogen species, higher abundance of ozone is usually observed in the regions with lower water vapor content. 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. The actual reactions between ozone and odd hydrogen species may be further complicated by the heterogeneous reactions that take place in water-ice clouds.
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.
The UV/IR
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
on ''
Mars Express
''Mars Express'' is a space exploration mission being conducted by the European Space Agency (ESA). The ''Mars Express'' mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally ref ...
'' (SPICAM) 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 , 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 until midwinter, after which it slowly decreased to very low concentrations, with no layer detectable above .
Water vapor
![Pia24622-curiosity 1-1041](https://upload.wikimedia.org/wikipedia/commons/2/2a/Pia24622-curiosity_1-1041.jpg)
Water vapor is a trace gas in the Martian atmosphere and has huge spatial, diurnal and seasonal variability.
Measurements made by Viking orbiter in the late 1970s suggested that the entire global total mass of water vapor is equivalent to about 1 to 2 km
3 of ice. 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. μm).
Maximum abundance of water vapor (50-70 pr. μm) is found in the northern polar regions in early summer due to the sublimation of water ice in the polar cap.
Unlike in Earth's atmosphere, liquid-water clouds cannot exist in the Martian atmosphere; this is because of the low atmospheric pressure.
Cirrus
Cirrus may refer to:
Science
*Cirrus (biology), any of various thin, thread-like structures on the body of an animal
*Cirrus (botany), a tendril
* Infrared cirrus, in astronomy, filamentary structures seen in infrared light
*Cirrus cloud, a typ ...
-like water-ice clouds have been observed by the cameras on
''Opportunity'' rover and
''Phoenix'' lander. 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.
Dust
Under sufficiently strong wind (> 30 ms
−1), dust particles can be mobilized and lifted from the surface to the atmosphere.
Some of the dust particles can be suspended in the atmosphere and travel by circulation before falling back to the ground.
Dust particles can attenuate solar radiation and interact with infrared radiation, which can lead to a significant radiative effect on Mars. 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).
The local abundance of dust varies greatly by seasons and years.
During global dust events, Mars surface assets can observe optical depth that is over 4.
Surface measurements also showed the effective radius of dust particles ranges from 0.6 μm to 2 μm and has considerable seasonality.
Dust has an uneven vertical distribution on Mars. Apart from the planetary boundary layer, sounding data showed that there are other peaks of dust mixing ratio at the higher altitude (e.g. 15–30 km above the surface).
Methane
As a volcanic and biogenic species, methane is of interest to geologists and
astrobiologists.
However, methane is chemically unstable in an oxidizing atmosphere with UV radiation. The lifetime of methane in the Martian atmosphere is about 400 years.
The detection of methane in a planetary atmosphere may indicate the presence of recent geological activities or living organisms.
Since 2004, trace amounts of methane (range from 60 ppb to under detection limit (< 0.05 ppb)) have been reported in various missions and observational studies.
The source of methane on Mars and the explanation for the enormous discrepancy in the observed methane concentrations are still under active debate.
See also the section "detection of methane in the atmosphere" for more details.
Sulfur dioxide
Sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
(SO
2) in the atmosphere would be an indicator of current volcanic activity. It has become especially interesting due to the long-standing controversy of methane on Mars. If volcanoes have been active in recent Martian history, it would be expected to find SO
2 together with methane in the current Martian atmosphere. No SO
2 has been detected in the atmosphere, with a sensitivity upper limit set at 0.2 ppb.
However, a team led by scientists at
NASA Goddard Space Flight Center reported detection of SO
2 in
Rocknest soil samples analyzed by the
''Curiosity'' rover in March 2013.
[McAdam, A. C.; Franz, H.; Archer, P. D.; Freissinet, C.; Sutter, B.; Glavin, D. P.; Eigenbrode, J. L.; Bower, H.; Stern, J.; Mahaffy, P. R.; Morris, R. V.; Ming, D. W.; Rampe, E.; Brunner, A. E.; Steele, A.; Navarro-González, R.; Bish, D. L.; Blake, D.; Wray, J.; Grotzinger, J.; MSL Science Team (2013). "Insights into the Sulfur Mineralogy of Martian Soil at Rocknest, Gale Crater, Enabled by Evolved Gas Analyses". 44th Lunar and Planetary Science Conference, held 18–22 March 2013 in The Woodlands, Texas. LPI Contribution No. 1719, p. 1751]
Other trace gases
Carbon monoxide (CO) is produced by the photolysis of CO
2 and quickly reacts with the oxidants in the Martian atmosphere to re-form CO
2. The estimated mean volume ratio of CO in the Martian atmosphere is 0.0747%.
Noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemi ...
es, other than helium and argon, are present at trace levels (≈10 - 0.01 ppmv) in the Martian atmosphere. The concentration of helium, neon, krypton and xenon in the Martian atmosphere has been measured by different missions.
The isotopic ratios of noble gases reveal information about the early geological activities on Mars and the evolution of its atmosphere.
Molecular hydrogen (H
2) is produced by the reaction between odd hydrogen species in the middle atmosphere. It can be delivered to the upper atmosphere by mixing or diffusion, decompose to atomic hydrogen (H) by solar radiation and escape the Martian atmosphere.
Photochemical modeling estimated that the mixing ratio of H
2 in the lower atmosphere is about 15 ±5 ppmv.
Vertical structure
![Mars annotated-vertical-profiles](https://upload.wikimedia.org/wikipedia/commons/f/ff/Mars_annotated-vertical-profiles.png)
The vertical temperature structure of the Martian atmosphere differs from Earth's atmosphere in many ways. Information about the vertical structure is usually inferred by using the observations from thermal infrared
soundings,
radio occultation
Radio occultation (RO) is a remote sensing technique used for measuring the physical properties of a planetary atmosphere or ring system.
Atmospheric radio occultation
Atmospheric radio occultation relies on the detection of a change in a radio ...
,
aerobraking
Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit ( apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit ( periapsis). The resulting drag slows the spacecraft. Aerobraking ...
, landers' entry profiles. Mars's atmosphere can be classified into three layers according to the average temperature profile:
* Troposphere (≈0–40 km): The layer where most of the weather phenomena (e.g. convection and dust storms) take place. Its dynamics is heavily driven by the daytime surface heating and the amount of suspended dust. Mars has a higher
scale height
In atmospheric, earth, and planetary sciences, a scale height, usually denoted by the capital letter ''H'', is a distance ( vertical or radial) over which a physical quantity decreases by a factor of e (the base of natural logarithms, approxima ...
of 11.1 km than Earth (8.5 km) because of its weaker gravity.
The theoretical dry adiabatic
lapse rate
The lapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, falls with altitude. ''Lapse rate'' arises from the word ''lapse'', in the sense of a gradual fall. In dry air, the adiabatic lapse rate is ...
of Mars is 4.3 °C km
−1,
but the measured average lapse rate is about 2.5 °C km
−1 because the suspended dust particles absorb solar radiation and heat the air.
The
planetary boundary layer
In meteorology, the planetary boundary layer (PBL), also known as the atmospheric boundary layer (ABL) or peplosphere, is the lowest part of the atmosphere and its behaviour is directly influenced by its contact with a planetary surface. On Ear ...
can extend to over 10 km thick during the daytime.
The near-surface diurnal temperature range is huge (60 °C
) due to the low thermal inertia. Under dusty conditions, the suspended dust particles can reduce the surface diurnal temperature range to only 5 °C. The temperature above 15 km is controlled by radiative processes instead of convection.
Mars is also a rare exception to the "0.1-bar tropopause" rule found in the other atmospheres in solar system.
* Mesosphere (≈40–100 km): The layer that has the lowest temperature. CO
2 in the mesosphere acts as a cooling agent by efficiently radiating heat into space. Stellar occultation observations show that the
mesopause
The mesopause is the point of minimum temperature at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesosphere is the cold ...
of Mars locates at about 100 km (around 0.01 to 0.001 Pa level) and has a temperature of 100-120 K. The temperature can sometimes be lower than the frost point of CO
2, and detections of CO
2 ice clouds in the Martian mesosphere have been reported.
* Thermosphere (≈100–230 km): The layer is mainly controlled by
extreme UV heating. The temperature of the Martian thermosphere increases with altitude and varies by season. The daytime temperature of the upper thermosphere ranges from 175 K (at aphelion) to 240 K (at perihelion) and can reach up to 390 K, but it is still significantly lower than the temperature of
Earth's thermosphere. The higher concentration of CO
2 in the Martian thermosphere may explain part of the discrepancy because of the cooling effects of CO
2 in high altitude. It is thought that
aurora
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of bri ...
l heating processes is not important in the Martian thermosphere because of the absence of a strong magnetic field in Mars, but the
MAVEN
MAVEN is an American spacecraft orbiting Mars to study the loss of its atmospheric gases to space, providing insight into the history of
the planet's climate and water. The spacecraft name is an acronym for "Mars Atmosphere and Volatile Evolu ...
orbiter has detected several aurora events.
Mars does not have a persistent stratosphere due to the lack of shortwave-absorbing species in its middle atmosphere (e.g.
stratospheric ozone
The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet radiation. It contains a high concentration of ozone (O3) in relation to other parts of the atmosphere, although still small in relat ...
in Earth's atmosphere and organic haze in
Jupiter's atmosphere
The atmosphere of Jupiter is the largest planetary atmosphere in the Solar System. It is mostly made of molecular hydrogen and helium in roughly solar proportions; other chemical compounds are present only in small amounts and include methane, ...
) for creating a temperature inversion. However, a seasonal ozone layer and a strong temperature inversion in the middle atmosphere have been observed over the Martian south pole.
The altitude of the
turbopause
The turbopause, also known as the homopause, marks the altitude in an atmosphere below which turbulent mixing dominates. Mathematically, it is defined as the point where the coefficient of Eddy diffusion is equal to the coefficient of molecular d ...
of Mars varies greatly from 60 to 140 km, and the variability is driven by the CO
2 density in the lower thermosphere. 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. The
exosphere
The exosphere ( grc, ἔξω "outside, external, beyond", grc, σφαῖρα "sphere") is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the densit ...
of Mars starts at about 230 km and gradually merges with interplanetary space.
Dust and other dynamic features
Dust devils
Dust devils are common on Mars.
Like their counterparts on Earth, dust devils form when the convective vortices driven by strong surface heating are loaded with dust particles.
Dust devils on Mars usually have a diameter of tens of meter and height of several kilometers, which are much taller than the ones observed on Earth.
Study of dust devils' tracks showed that most of Martian dust devils occur at around 60°N and 60°S in spring and summer.
They lift about 2.3 × 10
11 kg of dust from land surface to atmosphere annually, which is comparable to the contribution from local and regional dust storms.
Dust storms
Local and regional dust storms are not rare on Mars.
Local storms have a size of about 10
3 km
2 and occurrence of about 2000 events per Martian year, while regional storms of 10
6 km
2 large are observed frequently in southern spring and summer.
Near the polar cap, dust storms sometimes can be generated by frontal activities and extratropical cyclones.
Global dust storms (area > 10
6 km
2 ) occur on average once every 3 Martian years.
Observations showed that larger dust storms are usually the result of merging smaller dust storms,
but the growth mechanism of the storm and the role of atmospheric feedbacks are still not well understood.
Although it is thought that Martian dust can be entrained into the atmosphere by processes similar to Earth's (e.g.
saltation), the actual mechanisms are yet to be verified, and electrostatic or magnetic forces may also play in modulating dust emission.
Researchers reported that the largest single source of
dust
Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in homes ...
on Mars comes from the
Medusae Fossae Formation
The Medusae Fossae Formation is a large geological formation of probable volcanic origin on the planet Mars. It is named for the Medusa of Greek mythology. "Fossae" is Latin for "trenches".
The formation is a collection of soft, easily eroded de ...
.
On 1 June 2018, NASA scientists detected
signs of a
dust storm
A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transporte ...
(see
image
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
) on Mars which resulted in the end of the
solar-powered
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic ef ...
''Opportunity'' rover's mission since the dust blocked the sunlight (see
image
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
) needed to operate. By 12 June, the storm was the most extensive 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). By 13 June, ''Opportunity'' rover began experiencing serious communication problems due to the dust storm.
Thermal tides
Solar heating on the day side and radiative cooling on the night side of a planet can induce pressure difference. Thermal tides, which are the wind circulation and waves driven by such a daily-varying pressure field, can explain a lot of variability of the Martian atmosphere.
Compared to Earth's atmosphere, thermal tides have a larger influence on the Martian atmosphere because of the stronger diurnal temperature contrast.
The surface pressure measured by Mars rovers showed clear signals of thermal tides, although the variation also depends on the shape of the planet's surface and the amount of suspended dust in the atmosphere. The atmospheric waves can also travel vertically and affect the temperature and water-ice content in the middle atmosphere of Mars.
Orographic clouds
![Mars elongated cloud – 21 September ESA401961](https://upload.wikimedia.org/wikipedia/commons/2/21/Mars_elongated_cloud_%E2%80%93_21_September_ESA401961.jpg)
On Earth, mountain ranges sometimes force an air mass to rise and cool down. As a result, water vapor becomes saturated and clouds are formed during the lifting process. 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
Arsia Mons is the southernmost of three volcanoes (collectively known as Tharsis Montes) on the Tharsis bulge near the equator of the planet Mars. To its north is Pavonis Mons, and north of that is Ascraeus Mons. The tallest volcano in the So ...
, which is likely caused by the same mechanism.
Wind modification of the surface
On Mars, the near-surface wind is not only emitting dust but also modifying the geomorphology of Mars over long time scales. Although it was thought that the atmosphere of Mars is too thin for mobilizing the sandy features, observations made by
HiRSE showed that the migration of dunes is not rare on Mars.
The global average migration rate of dunes (2 – 120 m tall) is about 0.5 meter per year.
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.
Acoustic environment
In April 2022, scientists reported, for the first time, studies of
sound waves
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
on Mars. These studies were based on measurements by instruments on the
''Perseverance'' rover. The scientists found that the
speed of sound
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...
is slower in the Martian atmosphere, 100 times thinner than the terrestrial atmosphere, than the
atmosphere on Earth; the speed of sound on Mars, within the
audible bandwidth between 20 Hz - 20 kHz, varies depending on
pitch, seemingly due to the low pressure and thermal turbulence of Martian surface air; and, as a result of these unique Martian conditions, sound is much quieter, and live music would be more variable, than on Earth.
Atmospheric evolution
The mass and composition of the Martian atmosphere are thought to have changed over the course of the planet's lifetime. 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. Observations of the Martian upper atmosphere, measurements of isotopic composition and analyses of Martian meteorites, provide evidence of the long-term changes of the atmosphere and constraints for the relative importance of different processes.
Atmosphere in the early history
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. Scientists often rely on these measurements of isotope composition to reconstruct conditions of the Martian atmosphere in the past.
While Mars and Earth have similar
12C /
13C and
16O /
18O ratios,
14N is much more depleted in the Martian atmosphere. It is thought that the photochemical escape processes are responsible for the
isotopic fractionation
Isotope fractionation describes fractionation processes that affect the relative abundance of isotopes, phenomena which are taken advantage of in isotope geochemistry and other fields. Normally, the focus is on stable isotopes of the same element. ...
and has caused a significant loss of nitrogen on geological timescales.
Estimates suggest that the initial partial pressure of N
2 may have been up to 30 hPa.
Hydrodynamic escape
Hydrodynamic escape refers to a thermal atmospheric escape mechanism that can lead to the escape of heavier atoms of a planetary atmosphere through numerous collisions with lighter atoms.
Description
Hydrodynamic escape occurs if there is a str ...
in the early history of Mars may explain the isotopic fractionation of argon and xenon. On modern Mars, the atmosphere is not leaking these two
noble gas
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemi ...
es to outer space owing to their heavier mass. 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.
Hydrodynamic escape also contributed to the loss of carbon, and models suggest that it is possible to lose of CO
2 by hydrodynamic escape in one to ten million years under much stronger solar extreme UV on Mars. Meanwhile, more recent observations made by the
MAVEN
MAVEN is an American spacecraft orbiting Mars to study the loss of its atmospheric gases to space, providing insight into the history of
the planet's climate and water. The spacecraft name is an acronym for "Mars Atmosphere and Volatile Evolu ...
orbiter suggested that
sputtering escape is very important for the escape of heavy gases on the nightside of Mars and could have contributed to 65% loss of argon in the history of Mars.
The Martian atmosphere is particularly prone to
impact erosion owing to the low escape velocity of Mars. An early computer model suggested that Mars could have lost 99% of its initial atmosphere by the end of
late heavy bombardment
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypoth ...
period based on a hypothetical bombardment flux estimated from lunar crater density. In terms of relative abundance of carbon, the ratio on Mars is only 10% of that on Earth and Venus. Assuming the three rocky planets have the same initial volatile inventory, then this low ratio implies the mass of CO
2 in the early Martian atmosphere should have been ten times higher than the present value. The huge enrichment of radiogenic
40Ar over primordial
36Ar is also consistent with the impact erosion theory.
One of the ways to estimate the amount of water lost by hydrogen escape in the upper atmosphere is to examine the enrichment of deuterium over hydrogen. Isotope-based studies estimate that 12 m to over 30 m
global equivalent layer of water has been lost to space via hydrogen escape in Mars' history. It is noted that atmospheric-escape-based approach only provides the lower limit for the estimated early water inventory.
To explain the coexistence of liquid water and
faint young Sun during early Mars' history, a much stronger greenhouse effect must have occurred in the Martian atmosphere to warm the surface up above freezing point of water.
Carl Sagan
Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on ext ...
first proposed that a 1 bar H
2 atmosphere can produce enough warming for Mars. The hydrogen can be produced by the vigorous outgassing from a highly reduced early Martian mantle and the presence of CO
2 and water vapor can lower the required abundance of H to generate such a greenhouse effect. Nevertheless, photochemical modeling showed that maintaining an atmosphere with this high level of H
2 is difficult. SO
2 has also been one of the proposed effective greenhouse gases in the early history of Mars. However, other studies suggested that high solubility of SO
2, efficient formation of H
2SO
4 aerosol and surface deposition prohibit the long-term build-up of SO
2 in the Martian atmosphere, and hence reduce the potential warming effect of SO
2.
Atmospheric escape on modern Mars
Despite the lower gravity,
Jeans escape
Atmospheric escape is the loss of planetary atmospheric gases to outer space. A number of different mechanisms can be responsible for atmospheric escape; these processes can be divided into thermal escape, non-thermal (or suprathermal) escape, and ...
is not efficient in the modern Martian atmosphere due to the relatively low temperature at the exobase (≈200 K at 200 km altitude). It can only explain the escape of hydrogen from Mars. Other non-thermal processes are needed to explain the observed escape of oxygen, carbon and nitrogen.
Hydrogen escape
Molecular hydrogen (H
2) is produced from the dissociation of H
2O or other hydrogen-containing compounds in the lower atmosphere and diffuses to the exosphere. The exospheric H
2 then decomposes into hydrogen atoms, and the atoms that have sufficient thermal energy can escape from the gravitation of Mars (Jeans escape). The escape of atomic hydrogen is evident from the UV spectrometers on different orbiters. While most studies suggested that the escape of hydrogen is close to diffusion-limited on Mars, more recent studies suggest that the escape rate is modulated by dust storms and has a large seasonality.
The estimated escape flux of hydrogen range from 10
7 cm
−2 s
−1 to 10
9 cm
−2 s
−1.
Carbon escape
Photochemistry of CO
2 and CO in ionosphere can produce CO
2+ and CO
+ ions, respectively:
: + ⟶
: + ⟶
An ion and an electron can recombine and produce electronic-neutral products. The products gain extra kinetic energy due to the
Coulomb attraction between ions and electrons. This process is called
dissociative recombination
Dissociative recombination is a chemical process where a positive polyatomic ion recombines with an electron, and as a result, the neutral molecule dissociates. This reaction is important for extraterrestrial and atmospheric chemistry. On Earth, ...
. Dissociative recombination can produce carbon atoms that travel faster than the escape velocity of Mars, and those moving upward can then escape the Martian atmosphere:
:
:
UV photolysis of carbon monoxide is another crucial mechanism for the carbon escape on Mars:
: + ( < 116 nm) ⟶ .
Other potentially important mechanisms include the
sputtering escape of CO
2 and collision of carbon with fast oxygen atoms.
The estimated overall escape flux is about 0.6 × 10
7 cm
−2 s
−1 to 2.2 × 10
7 cm
−2 s
−1 and depends heavily on solar activity.
Nitrogen escape
Like carbon, dissociative recombination of N
2+ is important for the nitrogen escape on Mars.
In addition, other photochemical escape mechanism also play an important role:
: + ⟶
:
Nitrogen escape rate is very sensitive to the mass of the atom and solar activity. The overall estimated escape rate of
14N is 4.8 × 10
5 cm
−2 s
−1.
Oxygen escape
Dissociative recombination of CO
2+ and O
2+ (produced from CO
2+ reaction as well) can generate the oxygen atoms that travel fast enough to escape:
:
:
:
However, the observations showed that there are not enough fast oxygen atoms the Martian exosphere as predicted by the dissociative recombination mechanism.
Model estimations of oxygen escape rate suggested it can be over 10 times lower than the hydrogen escape rate.
Ion pick and sputtering have been suggested as the alternative mechanisms for the oxygen escape, but this model suggests that they are less important than dissociative recombination at present.
Unexplained phenomena
Detection of methane
Methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...
(CH
4) is chemically unstable in the current oxidizing atmosphere of Mars. It would quickly break down due to ultraviolet radiation from the Sun and chemical reactions with other gases. Therefore, a persistent presence of methane in the atmosphere may imply the existence of a source to continually replenish the gas.
The
ESA-Roscomos Trace Gas Orbiter, which has made the most sensitive measurements of methane in Mars' atmosphere with over 100 global
soundings, has found no methane to a detection limit of 0.05
parts per billion
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...
(ppb).
However, there have been other reports of detection of methane by ground-based telescopes and Curiosity rover. Trace amounts of methane, at the level of several ppb, were first reported in Mars's atmosphere by a team at the NASA
Goddard Space Flight Center
The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
in 2003.
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.
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.
Before and after that, readings averaged around one-tenth that level.
On 7 June 2018, NASA announced a cyclical seasonal variation in the background level of atmospheric methane.
![PIA22328-MarsCuriosityRover-Methane-SeasonalCycle-20180607](https://upload.wikimedia.org/wikipedia/commons/2/22/PIA22328-MarsCuriosityRover-Methane-SeasonalCycle-20180607.jpg)
The principal candidates for the origin of Mars' methane include non-biological processes such as
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
-rock reactions,
radiolysis of water, and
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Iron, FeSulfur, S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic Luster (mineralogy), lust ...
formation, all of which produce
H2 that could then generate methane and other hydrocarbons via
Fischer–Tropsch synthesis with
CO and CO
2.
It has also been shown that methane could be produced by a process involving water, carbon dioxide, and the mineral
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
, which is known to be common on Mars.
Living
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s, such as
methanogen
Methanogens are microorganisms that produce methane as a metabolic byproduct in hypoxic conditions. They are prokaryotic and belong to the domain Archaea. All known methanogens are members of the archaeal phylum Euryarchaeota. Methanogens are com ...
s, are another possible source, but no evidence for the presence of such organisms has been found on Mars.
There are some suspicions about the detection of methane, which suggests that it may instead be caused by the undocumented
terrestrial contamination from the rovers or a misinterpretation of measurement raw data.
Lightning events
In 2009, an Earth-based observational study reported detection of large-scale electric discharge events on Mars and proposed that they are related to lightning discharge in Martian dust storms. However, later observation studies showed that the result is not reproducible using the radar receiver on ''
Mars Express
''Mars Express'' is a space exploration mission being conducted by the European Space Agency (ESA). The ''Mars Express'' mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally ref ...
'' and the Earth-based
Allen Telescope Array.
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.
Super-rotating jet over the equator
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.
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.
GCM experiments showed that the thermal tides can play a role in inducing the super-rotating jet. Nevertheless, modeling super-rotation still remains as a challenging topic for planetary scientists.
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
The idea of sending humans to Mars has been the subject of aerospace engineering and scientific studies since the late 1940s as part of the broader exploration of Mars. Some have also considered exploring the Martian moons of Phobos and Deim ...
could use
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
(CO
2) from the Martian atmosphere to make methane (CH
4) and use it as
rocket fuel
Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical ...
for the return mission. Mission studies that propose using the atmosphere in this way include the
Mars Direct
Mars Direct is a proposal for a human mission to Mars which purports to be both cost-effective and possible with current technology. It was originally detailed in a research paper by Martin Marietta engineers Robert Zubrin and David Baker in 1990 ...
proposal of
Robert Zubrin
Robert Zubrin (; born April 9, 1952) is an American aerospace engineer, author, and advocate for human exploration of Mars. He and his colleague at Martin Marietta, David Baker, were the driving force behind Mars Direct, a proposal in a 1990 res ...
and the NASA
Design Reference Mission study. Two major chemical pathways for use of the carbon dioxide are the
Sabatier reaction
The Sabatier reaction or Sabatier process produces methane and water from a reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures (perhaps 3 MPa ) in the presence of a nickel catalyst. It w ...
, converting atmospheric carbon dioxide along with additional hydrogen (H
2), to produce methane (CH
4) and oxygen (O
2), and
electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
, using a
zirconia
Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant sta ...
solid oxide electrolyte to split the carbon dioxide into oxygen (O
2) and carbon monoxide (CO).
In 2021, however, the NASA spaceship Perseverance was able to make oxygen on Mars. The process is complex and takes a lot of time to produce a small amount of oxygen.
Image gallery
Mars atmosphere 2.jpg, Mars's thin atmosphere, visible on the horizon.
Mars violet sky.jpg, ''Mars Pathfinder
''Mars Pathfinder'' (''MESUR Pathfinder'') is an American robotic spacecraft that landed a base station with a roving probe on Mars in 1997. It consisted of a lander, renamed the Carl Sagan Memorial Station, and a lightweight, wheeled robot ...
'' – Martian sky with water ice clouds.
PIA15567storm.jpg, A storm front moves in
Interactive Mars map
See also
*
Climate of Mars
The climate of Mars has been a topic of scientific curiosity for centuries, in part because it is the only terrestrial planet whose surface can be directly observed in detail from the Earth with help from a telescope.
Although Mars is smaller t ...
*
In situ resource utilization
In space exploration, in situ resource utilization (ISRU) is the practice of collection, processing, storing and use of materials found or manufactured on other astronomical objects (the Moon, Mars, asteroids, etc.) that replace materials that ...
*
Life on Mars
The possibility of life on Mars is a subject of interest in astrobiology due to the planet's proximity and similarities to Earth. To date, no proof of past or present life has been found on Mars. Cumulative evidence suggests that during the ...
*
Mars MetNet – proposed surface observation network
*
Mars regional atmospheric modeling system
*
MAVEN
MAVEN is an American spacecraft orbiting Mars to study the loss of its atmospheric gases to space, providing insight into the history of
the planet's climate and water. The spacecraft name is an acronym for "Mars Atmosphere and Volatile Evolu ...
orbiter
*
Seasonal flows on warm Martian slopes
Seasonal flows on warm Martian slopes (also called recurring slope lineae, recurrent slope lineae and RSL) are thought to be salty water flows occurring during the warmest months on Mars, or alternatively, dry grains that "flow" downslope of at le ...
*
Terraforming of Mars
The terraforming of Mars or the terraformation of Mars is a hypothetical procedure that would consist of a planetary engineering project or concurrent projects, with the goal of transforming Mars from a planet hostile to terrestrial life to on ...
References
Further reading
*
*
*
External links
*
NASA Mars Exploration Program* Mars Weather
''Perseverance''''Curiosity''''InSight''
!---()--->
Summary of weekly weather on Mars prepared by Malin Space Science systems
{{DEFAULTSORT:Atmosphere Of Mars
Mars
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
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