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Di Renzo, M.; Urzay, J. (2018). "Aerodynamic generation of electric fields in turbulence laden with charged inertial particles". Nature Communications. 9 (1): 1676. Bibcode: 2018NatCo...9.1676D. doi: 10.1038/s41467-018-03958-7. PMC 5920100. PMID 29700300. Because Mars has no oceans and hence no " sea level", a zero-elevation surface had to be selected as a reference level; this is called the areoid [80] of Mars, analogous to the terrestrial geoid. [81] Zero altitude was defined by the height at which there is 610.5 Pa (6.105 mbar) of atmospheric pressure. [82] This pressure corresponds to the triple point of water, and it is about 0.6% of the sea level surface pressure on Earth (0.006 atm). [83] Precession in the alignment of the obliquity and eccentricity lead to global warming and cooling ('great' summers and winters) with a period of 170,000 years. [131] Recent observations and modeling are producing information not only about the present climate and atmospheric conditions on Mars but also about its past. The Noachian-era Martian atmosphere had long been theorized to be carbon dioxide–rich. Recent spectral observations of deposits of clay minerals on Mars and modeling of clay mineral formation conditions [4] have found that there is little to no carbonate present in clay of that era. Clay formation in a carbon dioxide–rich environment is always accompanied by carbonate formation, although the carbonate may later be dissolved by volcanic acidity. [5] On June 26, 2001, the Hubble Space Telescope spotted a dust storm brewing in Hellas Basin on Mars (pictured right). A day later the storm "exploded" and became a global event. Orbital measurements showed that this dust storm reduced the average temperature of the surface and raised the temperature of the atmosphere of Mars by 30K. [29] The low density of the Martian atmosphere means that winds of 18 to 22m/s (65 to 79km/h) are needed to lift dust from the surface, but since Mars is so dry, the dust can stay in the atmosphere far longer than on Earth, where it is soon washed out by rain. The season following that dust storm had daytime temperatures 4K below average. This was attributed to the global covering of light-colored dust that settled out of the dust storm, temporarily increasing Mars' albedo. [62]
Observation since the 1950s has shown that the chances of a planet-wide dust storm in a particular Martian year are approximately one in three. [69] Mike Wall (August 17, 2019). "Elon Musk Floats 'Nuke Mars' Idea Again (He Has T-Shirts)". Space.com. Archived from the original on January 22, 2023 . Retrieved January 22, 2023. NASA. "Mars General Circulation Modeling". NASA. Archived from the original on February 20, 2007 . Retrieved February 22, 2007.
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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 easily directly observed in detail from the Earth with help from a telescope. A 2023 study shows evidence, based on the orbital inclination of Deimos (a small moon of Mars), that Mars may once had a ring system 3.5 billion years to 4 billion years ago. [30] This ring system may have been formed from a moon, 20 times more massive than Phobos, orbiting Mars billions of years ago; and Phobos would be a remnant of that ring. [31] [32]
a b c Spiga, Aymeric; Forget, François; Madeleine, Jean-Baptiste; Montabone, Luca; Lewis, Stephen R.; Millour, Ehouarn (April 1, 2011). "The impact of martian mesoscale winds on surface temperature and on the determination of thermal inertia". Icarus. 212 (2): 504–519. Bibcode: 2011Icar..212..504S. doi: 10.1016/j.icarus.2011.02.001. ISSN 0019-1035. Bandfield, J. L.; etal. (2013). "Radiometric Comparison of Mars Climate Sounder and Thermal Emission Spectrometer Measurements". Icarus. 225 (1): 28–39. Bibcode: 2013Icar..225...28B. doi: 10.1016/j.icarus.2013.03.007. William Herschel was the first to deduce the low density of the Martian atmosphere in his 1784 paper entitled On the remarkable appearances at the polar regions on the planet Mars, the inclination of its axis, the position of its poles, and its spheroidal figure; with a few hints relating to its real diameter and atmosphere. When Mars appeared to pass close by two faint stars with no effect on their brightness, Herschel correctly concluded that this meant that there was little atmosphere around Mars to interfere with their light. [2]Smith, I. (May 27, 2016). "An Ice Age Recorded in the Polar Deposits of Mars". Science. 352 (6289): 1075–8. Bibcode: 2016Sci...352.1075S. doi: 10.1126/science.aad6968. PMID 27230372. Jacques Laskar (September 25, 2002). "Martian 'wobbles' shift climate". BBC. Archived from the original on July 8, 2007 . Retrieved February 24, 2007. Pelletier, Jon D. (April 2004). "How do spiral troughs form on Mars?" (PDF). Geology. 32 (4): 365–367. Bibcode: 2004Geo....32..365P. doi: 10.1130/G20228.2. Archived (PDF) from the original on July 31, 2020 . Retrieved November 4, 2019. Francis Reddy. "Titan, Mars methane may be on ice". Astronomy Magazine. Archived from the original on September 27, 2007 . Retrieved March 16, 2007. If Mars had an Earth-like orbit, its seasons would be similar to Earth's because its axial tilt is similar to Earth's. The comparatively large eccentricity of the Martian orbit has a significant effect. Mars is near perihelion when it is summer in the Southern Hemisphere and winter in the north, and near aphelion when it is winter in the Southern Hemisphere and summer in the north. As a result, the seasons in the Southern Hemisphere are more extreme and the seasons in the northern are milder than would otherwise be the case. The summer temperatures in the south can be warmer than the equivalent summer temperatures in the north by up to 30°C (54°F). [135]
Eden, H.F.; Vonnegut, B. (1973). "Electrical breakdown caused by dust motion in low-pressure atmospheres: considerations for Mars". Science. 180 (4089): 39–87. Bibcode: 1973Sci...180..962E. doi: 10.1126/science.180.4089.962. PMID 17735929. S2CID 38902776. It has been reported that "On the basis of the nighttime air temperature data, every northern spring and early northern summer yet observed were identical to within the level of experimental error (to within ±1°C)" but that the "daytime data, however, suggests a somewhat different story, with temperatures varying from year-to-year by up to 6°C in this season. [27] This day-night discrepancy is unexpected and not understood". In southern spring and summer, variance is dominated by dust storms which increase the value of the night low temperature and decrease the daytime peak temperature. [28] This results in a small (20°C) decrease in average surface temperature, and a moderate (30°C) increase in upper atmosphere temperature. [29] Both polar caps are currently accumulating, confirming predicted Milankovich cycling on timescales of ~400,000 and ~4,000,000 years. Soundings by the Mars Reconnaissance Orbiter SHARAD indicate total cap growth of ~0.24km 3/year. Of this, 92%, or ~0.86mm/year, is going to the north, [118] as Mars' offset Hadley circulation acts as a nonlinear pump of volatiles northward. Schorghofer, N (2007). "Dynamics of ice ages on Mars". Nature. 449 (7159): 192–194. Bibcode: 2007Natur.449..192S. doi: 10.1038/nature06082. PMID 17851518. S2CID 4415456.Although better remembered for mapping the Moon, Johann Heinrich Mädler and Wilhelm Beer were the first areographers. They began by establishing that most of Mars's surface features were permanent and by more precisely determining the planet's rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars. [72] Aplin, K.L.; Fischer, G. (2017). "Lightning detection in planetary atmospheres". Weather. 72 (2): 46–50. arXiv: 1606.03285. Bibcode: 2017Wthr...72...46A. doi: 10.1002/wea.2817. S2CID 54209658.
Before and after the Viking missions, newer, more advanced Martian temperatures were determined from Earth via microwave spectroscopy. As the microwave beam, of under 1 arcminute, is larger than the disk of the planet, the results are global averages. [30] Later, the Mars Global Surveyor's Thermal Emission Spectrometer and to a lesser extent 2001 Mars Odyssey's THEMIS could not merely reproduce infrared measurements but intercompare lander, rover, and Earth microwave data. The Mars Reconnaissance Orbiter's Mars Climate Sounder can similarly derive atmospheric profiles. The datasets "suggest generally colder atmospheric temperatures and lower dust loading in recent decades on Mars than during the Viking Mission," [31] although Viking data had previously been revised downward. [32] The TES data indicates "Much colder (10–20 K) global atmospheric temperatures were observed during the 1997 versus 1977 perihelion periods" and "that the global aphelion atmosphere of Mars is colder, less dusty, and cloudier than indicated by the established Viking climatology," again, taking into account the Wilson and Richardson revisions to Viking data. [33] Mars General Circulation Modeling Group. "Mars' desert surface". NASA. Archived from the original on July 7, 2007 . Retrieved February 25, 2007. Mars lost its magnetosphere 4billion years ago, [108] possibly because of numerous asteroid strikes, [109] so the solar wind interacts directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer. [110] Both Mars Global Surveyor and Mars Express have detected ionised atmospheric particles trailing off into space behind Mars, [108] [111] and this atmospheric loss is being studied by the MAVEN orbiter. Compared to Earth, the atmosphere of Mars is quite rarefied. Atmospheric pressure on the surface today ranges from a low of 30 Pa (0.0044 psi) on Olympus Mons to over 1,155Pa (0.1675psi) in Hellas Planitia, with a mean pressure at the surface level of 600Pa (0.087psi). [112] The highest atmospheric density on Mars is equal to that found 35 kilometres (22mi) [113] above Earth's surface. The resulting mean surface pressure is only 0.6% of Earth's 101.3kPa (14.69psi). The scale height of the atmosphere is about 10.8 kilometres (6.7mi), [114] which is higher than Earth's 6 kilometres (3.7mi), because the surface gravity of Mars is only about 38% of Earth's. [115] NASA Mars Rovers Braving Severe Dust Storms" (Press release). Jet Propulsion Laboratory. July 20, 2007. a b Benson; etal. (2006). "Interannual variability of water ice clouds over major martian volcanoes observed by MOC". Icarus. 184 (2): 365–371. Bibcode: 2006Icar..184..365B. doi: 10.1016/j.icarus.2006.03.014.A large intensifying dust storm began in late-May 2018 and had persisted as of mid-June. By June 10, 2018, as observed at the location of the rover Opportunity, the storm was more intense than the 2007 dust storm endured by Opportunity. [66] On June 20, 2018, NASA reported that the dust storm had grown to completely cover the entire planet. [67] [68] Fairén, A. G.; etal. (2004). "Inhibition of carbonate synthesis in acidic oceans on early Mars". Nature. 431 (7007): 423–426. Bibcode: 2004Natur.431..423F. doi: 10.1038/nature02911. PMID 15386004. S2CID 4416256. The northern polar cap has a diameter of approximately 1,000km during the northern Mars summer, [109]
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