 |
|
| Chemical species | mole fraction[1] |
| Carbon dioxide | 95.32% |
| Nitrogen | 2.7% |
| Argon | 1.6% |
| Oxygen | 1300 ppm |
| Carbon monoxide | 800 ppm |
| Water vapor | 210 ppm |
| Nitric oxide | 100 ppm |
| Neon | 2.5 ppm |
| HDO | 850 ppb |
| Krypton | 300 ppb |
| Xenon | 80 ppb |
| Ozone | 30 ppb |
| Methane | 10.5 ppb |
The atmosphere of Mars is, like that of Venus, composed mostly of carbon dioxide though far thinner. There has been renewed interest in its composition since the detection of traces of methane[2][3] that may indicate life but may also be produced by a geochemical process, volcanic or hydrothermal activity.[4]
The atmospheric pressure on the Martian surface averages 600 pascals (0.087 psi), about 0.6% of Earth's mean sea level pressure of 101.3 kilopascals (14.69 psi) and only .0065% that of Venus's 9.2 megapascals (1,330 psi). It ranges from a low of 30 pascals (0.0044 psi) on Olympus Mons's peak to over 1,155 pascals (0.1675 psi) in the depths of Hellas Planitia. Mars's atmospheric mass of 25 teratonnes compares to Earth's 5148 teratonnes with a scale height of about 11 kilometres (6.8 mi) versus Earth's 7 kilometres (4.3 mi). The Martian atmosphere is about 95% carbon dioxide, 3% nitrogen, 1.6% argon, and traces of free oxygen, carbon monoxide, water and methane, among other gases, for a mean molar mass of 43.34 g/mol.[1][5] The atmosphere is quite dusty, giving the Martian sky a light brown or orange color when seen from the surface; data from the Mars Exploration Rovers indicate that suspended dust particles within the atmosphere are roughly 1.5 micrometres across.[6]
Contents |
History [edit]
Mars's atmosphere is believed 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.[7] 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 less than 210 K (−63 °C; −82 °F), significantly lower than what is needed to sustain liquid water. However, early in its history Mars may have had conditions more conducive to retaining liquid water at the surface.
Possible causes for the depletion of a previously thicker Martian atmosphere include:
- Gradual erosion of the atmosphere by solar wind,[8] possibly helped by Mars's magnetic-field irregularities;[9]
- Catastrophic collision by a body large enough to blow away a significant percentage of the atmosphere;[9]
- Mars's low gravity allowing the atmosphere to "blow off" into space by gas-kinetic escape.[10]
Structure [edit]
| 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[11] | 33.7 kilopascals (4.89 psi) |
| Earth sea level | 101.3 kilopascals (14.69 psi) |
Mars's atmosphere is composed of the following layers:
- Lower atmosphere: This is a warm region affected by heat from airborne dust and from the ground.
- Middle atmosphere: Mars has a jetstream, which flows in this region.
- Upper atmosphere, or thermosphere: This region has 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.
- 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.
Observations and measurement from Earth [edit]
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."[12] Spectroscopic observations in the 1860s and 1870s[13][14] led many to believe 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.[13]
In 1926, photographic observations by William Hammond Wright at the Lick Observatory allowed Donald Howard Menzel to discover quantitative evidence of Mars's atmosphere.[15][16]
Composition [edit]
Carbon dioxide [edit]
The main component of the atmosphere of Mars is carbon dioxide (CO2) 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 CO2 condenses at the polar caps into solid CO2 ice (dry ice). When the pole is again exposed to sunlight during summer, the CO2 ice sublimates back into the atmosphere. This process leads to a significant annual variation in the atmospheric pressure and atmospheric composition around the Martian poles.
Argon [edit]
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.[19]
Water [edit]
Other aspects of the Martian atmosphere vary significantly. As carbon dioxide sublimates back into the atmosphere during the Martian summer, it leaves traces of water. Seasonal winds sweep off the poles at speeds approaching 400 kilometres per hour (250 mph) and 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.[20] NASA scientists working on the Phoenix Mars mission confirmed on July 31, 2008 that they had indeed found subsurface water ice at Mars's northern polar region. Further analysis by the Phoenix lander will confirm whether the water was ever liquid and if it contains organic materials necessary for life.
Methane [edit]
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.[3][21] In March 2004 the Mars Express Orbiter[22] and ground based observations from Canada–France–Hawaii Telescope[23] also suggested the presence of methane in the atmosphere with a mole fraction of about 10 nmol/mol.[24]
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 necessitates the existence of a source to continually replenish the gas.[25] Current photochemical models alone can explain neither the fast appearance nor the disappearance of the methane, or its reported variations in space and time.[26] It had been proposed that the methane might be replenished by meteorites entering the atmosphere of Mars,[27] 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.[28]
The methane occurs in extended plumes, and their profiles imply that the gas was released from sources in three discrete regions. In northern midsummer, the principal plume contained 19,000 metric tons of methane, with an estimated source strength of 0.6 kilogram per second.[29][30] The profiles suggest that there may be two local source regions, the first centered near 30°N 260°W / 30°N 260°W and the second near 0°N 310°W / 0°N 310°W .[29] It is estimated that Mars must produce 270 tons/year of methane.[29][31][32]
Research suggests that the implied methane destruction lifetime is as long as ~4 Earth years and as short as ~0.6 Earth years.[29][33] 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.[29] The rapid destruction of methane suggests 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×.[29][33] This unexplained fast destruction rate also suggests a very active replenishing source.[34] A possibility is that the methane is not consumed at all, but rather condenses and evaporates seasonally from clathrates.[35]
Although the methane could stem from a geological source, the lack of current volcanism, hydrothermal activity or hotspots are not favorable for a geological explanation. Living microorganisms, such as methanogens, are another possible source, but no evidence exists for the presence of such organisms anywhere on Mars. Roscosmos and ESA are planning to look for companion gases that may suggest which sources are most likely.[36][37] in the Earth's oceans, biological methane production tends to be accompanied by ethane, while volcanic methane is accompanied by sulfur dioxide.[37]
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.[38] It was also recently 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.[39] The required conditions for this reaction (i.e. high temperature and pressure) do not exist on the surface, but may exist within the crust.[40] To prove this process is occurring, serpentinite, a mineral by-product of the process would be detected. An analog on Earth suggests that low temperature production and exhalation of methane from serpentinized rocks may be possible on Mars.[41] Another possible geophysical source could be clathrate hydrates.[42]
The European Space Agency (ESA) found that the concentrations of methane in the Martian atmosphere were not even, but coincided with the presence of water vapor. In the upper atmosphere these two gases are uniformly distributed, but near the surface they concentrate in three equatorial regions, namely Arabia Terra, Elysium Planitia, and Arcadia Memnonia. Planetary scientist David H. Grinspoon of the Southwest Research Institute believes the coincidence of water vapor and methane increases the chance that the methane is of biological origin, but he cautions that it is uncertain how life could have survived so long on a planet as inhospitable as Mars.[21] It has been suggested that caves may be the only natural structures capable of protecting primitive life forms from micrometeoroids, UV radiation, solar flares and high energy particles that bombard the planet's surface.[43][44][45]
In contrast to the findings described above, studies by Kevin Zahnle, a planetary scientist at NASA's Ames Research Center, and two colleagues, conclude that "there is as yet no compelling evidence for methane on Mars". They argue that the strongest reported observations of the gas to date have been taken at frequencies where interference from methane in the Earth's atmosphere is particularly difficult to remove, and are thus unreliable. Additionally, they claim that the published observations most favorable to interpretation as indicative of Martian methane are also consistent with no methane being present on Mars.[46][47][48]
Ultimately, to determine the provenance of the Martian methane findings, a future probe or lander hosting a mass spectrometer must be sent to Mars.[49] Efforts to identify the sources of terrestrial methane have found that measurements of different methane isotopologues do not necessarily distinguish between possible geologic and biogenic sources, but the abundances of other cogenerated gases, such as ethane (C2H6), relative to methane do; the ethane/methane abundance ratio is < 0.001 for biogenic sources, while other sources produce nearly equivalent amounts of methane and ethane.[50] In June, 2012, scientists reported that measuring the ratio of hydrogen and methane levels on Mars may help determine the likelihood of life on Mars.[51][52] According to the scientists, low H2/CH4 ratios (less than approximately 40) would indicate that life is likely present and active.[51] Other scientists have recently reported methods of detecting hydrogen and methane in extraterrestrial atmospheres.[53][54]
The Curiosity rover, which landed on Mars in August 2012, is able to make measurements that distinguish between different isotopologues of methane;[55] but even if the mission is to determine that microscopic Martian life is the source of the methane, the life forms likely reside far below the surface, outside of the rover's reach.[56] The first measurements with the Tunable Laser Spectrometer (TLS) indicated that there is less than 5 ppb of methane at the landing site at the point of the measurement.[57][58][59][60] The Mars Trace Gas Mission orbiter planned to launch in 2016 would further study the methane,[61][62] as well as its decomposition products such as formaldehyde and methanol.
Potential for use by humans [edit]
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 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).
Martian sunset [edit]
See also [edit]
 |
- Climate of Mars
- Life on Mars
- Mars regional atmospheric modeling system
- Martian geyser
- MAVEN orbiter
- MetNet - a proposed widespread surface observation network in Mars.
- Seasonal flows on warm Martian slopes
- In Situ Resource Utilization
- Terraforming of Mars
References [edit]
- ^ a b Robbins, Stuart J.; et al. (14 September 2006). "Elemental composition of Mars' atmosphere". Case Western Reserve University Department of Astronomy. Archived from the original on 15 June 2011. Retrieved 5 April 2012.
- ^ Interplanetary Whodunit - Methane on Mars, David Tenenbaum, Astrobiology Magazine, NASA, July 20, 2005. (Note: part one of a four-part series.)
- ^ a b Mumma, M. J.; Novak, R. E.; DiSanti, M. A.; Bonev, B. P., "A Sensitive Search for Methane on Mars" (abstract only). American Astronomical Society, DPS meeting #35, #14.18.
- ^ Making Sense of Mars Methane (June 2008)
- ^ Seiff, A. and Kirk, D. (1977). "Structure of the atmosphere of Mars in summer at mid-latitudes" (abstract only). Journal of Geophysical Research, 82(28):4364–4378.
- ^ Lemmon et al., "Atmospheric Imaging Results from the Mars Exploration Rovers: Spirit and Opportunity"
- ^ "Gamma-Ray Evidence Suggests Ancient Mars Had Massive Oceans". Science Daily. University of Arizona. Archived from the original on 14 December 2009. Retrieved October 31, 2009.
- ^ "The Solar Wind at Mars". Science @ NASA. NASA. Retrieved October 31, 2009.
- ^ a b "Solar Wind Rips Up Martian Atmosphere". NASA Headlines. NASA. Retrieved October 31, 2009.
- ^ http://astronomynotes.com/solarsys/s10.htm
- ^ John B. West - Barometric pressures on Mt. Everest: new data and physiological significance (1998)
- ^ Dawes, W.R. (1865). "Physical Observations of Mars Near the Opposition in 1864". Astronomical Register.
- ^ a b Campbell, W.W. (1894). "Concerning an Atmosphere on Mars". Publications of the Astronomical Society of the Pacific.
- ^ Janssen, Huggins, Secchi, Vogel, and Maunder
- ^ Wright, W. H. (1925). "Photographs of Mars made with light of different colors". Lick Observatory bulletin.
- ^ Menzel, D. H. (1926). "The Atmosphere of Mars". Astrophysical Journal..
- ^ Webster, Guy (April 8, 2013). "Remaining Martian Atmosphere Still Dynamic". NASA. Retrieved April 9, 2013.
- ^ Wall, Mike (April 8, 2013). "Most of Mars' Atmosphere Is Lost in Space". Space.com. Retrieved April 9, 2013.
- ^ Francois Forgot. "Alien Weather at the Poles of Mars". Science. Retrieved February 25, 2007.
- ^ Clouds – December 13, 2004 NASA Press release. URL accessed March 17, 2006.
- ^ a b Michael J. Mumma. "Mars Methane Boosts Chances for Life". Skytonight.com. Archived from the original on 20 February 2007. Retrieved February 23, 2007.
- ^ V. Formisano, S. Atreya T. Encrenaz, N. Ignatiev, M. Giuranna (2004). "Detection of Methane in the Atmosphere of Mars". Science 306 (5702): 1758–1761. Bibcode:2004Sci...306.1758F. doi:10.1126/science.1101732. PMID 15514118.
- ^ V. A. Krasnopolskya, J. P. Maillard, T. C. Owen (2004). "Detection of methane in the Martian atmosphere: evidence for life?". Icarus 172 (2): 537–547. Bibcode:2004Icar..172..537K. doi:10.1016/j.icarus.2004.07.004.
- ^ ESA Press release. "Mars Express confirms methane in the Martian atmosphere". ESA. Archived from the original on 24 February 2006. Retrieved March 17, 2006.
- ^ Kazan, Casey (January 3, 2011). "Will Mars Be Our 'Rosetta Stone' in the Search for Life?". The Daily Galaxy. Retrieved 2011-08-06.
- ^ Mars Trace Gas Mission (September 10, 2009)
- ^ "Ultraviolet-radiation-induced methane emissions from meteorites and the Martian atmosphere". Nature. Published online 30 May 2012. doi: 10.1038/nature11203. Retrieved 2012-06-08.
- ^ "Life on Mars theory boosted by new methane study". Imperial College London. December 8, 2009. Retrieved December 9, 2009.
- ^ a b c d e f Mumma, Michael J.; et al. (February 20, 2009). "Strong Release of Methane on Mars in Northern Summer 2003". Science 323 (5917): pp. 1041–1045. Bibcode:2009Sci...323.1041M. doi:10.1126/science.1165243. PMID 19150811.
- ^ Hand, Eric (October 21, 2008). "Plumes of methane identified on Mars". Nature News. Retrieved August 2, 2009.
- ^ Vladimir A. Krasnopolsky (February 2005). "Some problems related to the origin of methane on Mars". Icarus 180 (2): 359–367. doi:10.1016/j.icarus.October+1,+20055.
- ^ Planetary Fourier Spectrometer website (ESA, Mars Express)
- ^ a b Franck, Lefèvre; François Forget (August 6, 2009). "Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics". Nature 460 (7256): 720–723. Bibcode:2009Natur.460..720L. doi:10.1038/nature08228. PMID 19661912. Retrieved October 23, 2009.
- ^ Burns, Judith (August 5, 2009). "Martian methane mystery deepens". BBC News. Archived from the original on 6 August 2009. Retrieved August 7, 2009.
- ^ Zahnle, Kevin; Richard Freedman and David Catling (2010). "Is there Methane on Mars?". 41st Lunar and Planetary Science Conference. Retrieved 2010-07-26
- ^ Inside ExoMars – Quarterly Newsletter (May 2012)
- ^ a b Docksai, Rick (July 2011). "A Chemical Mission to Mars". CBS. Retrieved 2011-08-05.
- ^ "THE ASTROBIOLOGY OF MARS: METHANE AND OTHER CANDIDATE BIOMARKER GASES, AND RELATED INTERDISCIPLINARY STUDIES ON EARTH AND MARS.". Astrobiology Science Conference 2010. Goddard Space Flight Center. Greenbelt, MD, USA.: Astrophysics Data System. 2010. Retrieved 2010-07-24
- ^ Oze, C., M. Sharma (2005). "Have olivine, will gas: Serpentinization and the abiogenic production of methane on Mars". Geophys. Res. Lett. 32 (10): L10203. Bibcode:2005GeoRL..3210203O. doi:10.1029/2005GL022691.
- ^ Rincon, Paul (March 26, 2009). "Mars domes may be 'mud volcanoes'". BBC News. Archived from the original on 29 March 2009. Retrieved April 2, 2009.
- ^ "Low temperature production and exhalation of methane from serpentinized rocks on Earth: A potential analog for methane production on Mars". Icarus. Online 14 May 2012. Retrieved 2012-06-08.
- ^ Thomas, Caroline; et al. (January 2009). "Variability of the methane trapping in Martian subsurface clathrate hydrates". Planetary and Space Science 57 (1): 42–47. arXiv:0810.4359. Bibcode:2009P&SS...57...42T. doi:10.1016/j.pss.2008.10.003. Retrieved August 2, 2009.
- ^ Langhoff, Stephanie, ed. (June 2008). "Workshop Report On Deep Mars" (PDF). Accessing The Subsurface Of Mars On Near Term Missions. NASA. PMID NASA/CP–2008-214586. Retrieved September 15, 2009
- ^ Rincon, Paul (March 17, 2007). "'Cave entrances' spotted on Mars". BBC News. Archived from the original on 30 September 2009. Retrieved September 15, 2009.
- ^ Than, Ker (April 2, 2007). "Possible New Mars Caves Targets in Search for Life". Space,com. Retrieved September 15, 2009.
- ^ "42nd Lunar and Planetary Science Conference" (PDF), Is there Methane on Mars? Part II, Lunar and Planetary Institute, 2011, retrieved 2011-08-06
- ^ "Methane on Mars. Now you see it. Now you don't...". The Economist. 29 December 2010. Retrieved 2011-08-06.
- ^ Kevin Zahnle, Richard S. Freedman and David C. Catling (2011). "Is there methane on Mars?". Icarus 212 (2): 493–503. Bibcode:2011Icar..212..493Z. doi:10.1016/j.icarus.2010.11.027.
- ^ Remote Sensing Tutorial, Section 19-13a – Missions to Mars during the Third Millennium, Nicholas M. Short, Sr., et al., NASA
- ^ "Report from the 2013 Mars Science Orbiter (MSO) – Second Science Analysis Group". Mars Exploration Program Analysis Group (MEPAG MSO-SAG-2). 2007. p. 16. Retrieved November 9, 2009
- ^ a b Oze, Christopher; Jones, Camille; Goldsmith, Jonas I.; Rosenbauer, Robert J. (June 7, 2012). "Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces". PNAS 109 (25): 9750–9754. Bibcode:2012PNAS..109.9750O. doi:10.1073/pnas.1205223109. Retrieved June 27, 2012.
- ^ Staff (June 25, 2012). "Mars Life Could Leave Traces in Red Planet's Air: Study". Space.com. Retrieved June 27, 2012.
- ^ Brogi, Matteo; Snellen, Ignas A. G.; de Krok, Remco J.; Albrecht, Simon; Birkby, Jayne; de Mooij, Ernest J. W. (June 28, 2012). "The signature of orbital motion from the dayside of the planet t Boötis b". Nature 486: 502–504. arXiv:1206.6109. Bibcode:2012Natur.486..502B. doi:10.1038/nature11161. Retrieved June 28, 2012.
- ^ Mann, Adam (June 27, 2012). "New View of Exoplanets Will Aid Search for E.T.". Wired (magazine). Retrieved June 28, 2012.
- ^ Tenenbaum, David (June 9, 2008):). "Making Sense of Mars Methane". Astrobiology Magazine. Archived from the original on 23 September 2008. Retrieved October 8, 2008.
- ^ Steigerwald, Bill (January 15, 2009). "Martian Methane Reveals the Red Planet is not a Dead Planet". NASA's Goddard Space Flight Center (NASA). Archived from the original on 17 January 2009. Retrieved January 24, 2009.
- ^ "Mars Curiosity Rover News Telecon -November 2, 2012".
- ^ Kerr, Richard A. (November 2, 2012). "Curiosity Finds Methane on Mars, or Not". Science (journal). Retrieved November 3, 2012.
- ^ Wall, Mike (November 2, 2012). "Curiosity Rover Finds No Methane on Mars — Yet". Space.com. Retrieved November 3, 2012.
- ^ Chang, Kenneth (November 2, 2012). "Hope of Methane on Mars Fades". New York Times. Retrieved November 3, 2012.
- ^ Rincon, Paul (July 9, 2009). "Agencies outline Mars initiative". BBC News. Retrieved July 26, 2009.
- ^ "NASA orbiter to hunt for source of Martian methane in 2016". Thaindian News. March 6, 2009. Retrieved July 26, 2009.
Further reading [edit]
- Mars Clouds Higher Than Any On Earth - Mars is home to the highest clouds ever discovered above the surface of a planet, Space.com
- Mikulski, Lauren (2000). "Pressure on the Surface of Mars". The Physics Factbook.
- Atmospheric pressure - summary of the Viking lander results
- Khan, Michael (December 4, 2009). "The Low Down on Methane on Mars". Archived from the original on 7 December 2009. Retrieved December 8, 2009.
External links [edit]
Media related to Atmosphere of Mars at Wikimedia Commons
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