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It is now thought that ice accumulated when Mars' orbital tilt was very different from what it is now. (The axis the planet spins on has considerable "wobble", meaning its angle changes over time.) [120] [121] [122] A few million years ago, the tilt of the axis of Mars was 45 degrees instead of its present 25 degrees. Its tilt, also called obliquity, varies greatly because its two tiny moons cannot stabilize it like Earth's moon. The large canyon, Valles Marineris (Latin for " Mariner Valleys", also known as Agathodaemon in the old canal maps [101]), has a length of 4,000 kilometres (2,500mi) and a depth of up to 7 kilometres (4.3mi). The length of Valles Marineris is equivalent to the length of Europe and extends across one-fifth the circumference of Mars. By comparison, the Grand Canyon on Earth is only 446 kilometres (277mi) long and nearly 2 kilometres (1.2mi) deep. Valles Marineris was formed due to the swelling of the Tharsis area, which caused the crust in the area of Valles Marineris to collapse. In 2012, it was proposed that Valles Marineris is not just a graben, but a plate boundary where 150 kilometres (93mi) of transverse motion has occurred, making Mars a planet with possibly a two- tectonic plate arrangement. [102] [103] Holes and caves Harrison, R.G.; Barth, E.; Esposito, F.; Merrison, J.; Montmessin, F.; Aplin, K.L.; Borlina, C.; Berthelier, J.; Deprez G.; Farrel, W.M.; Houghton, M.P.; Renno, N.O.; Nicoll, S.N.; Tripathi, N.; Zimmerman, M. (2016). "Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity". Space Sci. Rev. 203 (1–4): 299–345. Bibcode: 2016SSRv..203..299H. doi: 10.1007/s11214-016-0241-8. Archived from the original on September 2, 2019 . Retrieved September 2, 2019.
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.Oze, C.; Sharma, M. (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. S2CID 28981740. Many features on Mars, especially in the Ismenius Lacus quadrangle, are thought to contain large amounts of ice. The most popular model for the origin of the ice is climatic change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees. [123] [124] Large changes in the tilt explains many ice-rich features on Mars. When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust. [128] [129] The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind. [130] Note, that the smooth surface mantle layer probably represents only relative recent material. Below are images of layers in this smooth mantle that drops from the sky at times. One unique repeated weather phenomenon involving mountains is a spiral dust cloud that forms over Arsia Mons. The spiral dust cloud over Arsia Mons can tower 15 to 30km (49,000 to 98,000ft) above the volcano. [105] Clouds are present around Arsia Mons throughout the Martian year, peaking in late summer. [106]
Because the Mars Global Surveyor was able to observe Mars for 4 Martian years, it was found that Martian weather was similar from year to year. Any differences were directly related to changes in the solar energy that reached Mars. Scientists were even able to accurately predict dust storms that would occur during the landing of Beagle 2. Regional dust storms were discovered to be closely related to where dust was available. [134] Evidence for recent climatic change [ edit ] Pits in south polar ice cap (MGS 1999, NASA)
Mars's average distance from the Sun is roughly 230millionkm (143millionmi), and its orbital period is 687 (Earth) days. The solar day (or sol) on Mars is only slightly longer than an Earth day
Hargitai Henrik (2009). "Climate Zones of Mars" (PDF). Lunar and Planetary Institute. Archived (PDF) from the original on October 25, 2012 . Retrieved May 18, 2010.Colaprete, A; Barnes, JR; Haberle, RM; Hollingsworth, JL; Kieffer, HH; Titus, TN (May 12, 2005). "Albedo of the South Pole of Mars". Nature. 435 (7039): 184–188. Bibcode: 2005Natur.435..184C. doi: 10.1038/nature03561. PMID 15889086. S2CID 4413175. Archived from the original on July 28, 2020 . Retrieved July 5, 2019. a b Steinn Sigurðsson (October 5, 2005). "Global warming on Mars?". RealClimate. Archived from the original on March 6, 2007 . Retrieved February 21, 2007. Kok, Jasper F.; Renno, Nilton O. (2008). "Electrostatics in Wind-Blown Sand". Physical Review Letters. 100 (1): 014501. arXiv: 0711.1341. Bibcode: 2008PhRvL.100a4501K. doi: 10.1103/PhysRevLett.100.014501. PMID 18232774. S2CID 9072006. 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]
Jakosky, Bruce M.; Phillips, Roger J. (2001). "Mars' volatile and climate history". Nature. 412 (6843): 237–244. Bibcode: 2001Natur.412..237J. doi: 10.1038/35084184. PMID 11449285. review article a b c d Spiga, A. (August 1, 2011). "Elements of comparison between Martian and terrestrial mesoscale meteorological phenomena: Katabatic winds and boundary layer convection". Planetary and Space Science. Comparative Planetology: Venus-Earth-Mars. 59 (10): 915–922. Bibcode: 2011P&SS...59..915S. doi: 10.1016/j.pss.2010.04.025. ISSN 0032-0633. Niles, P.; etal. (2013). "Geochemistry of carbonates on Mars: implications for climate history and nature of aqueous environments" (PDF). Space Sci. Rev. 174 (1–4): 301–328. Bibcode: 2013SSRv..174..301N. doi: 10.1007/s11214-012-9940-y. S2CID 7695620. Archived (PDF) from the original on July 24, 2018 . Retrieved July 5, 2019.National Space Science Data Center: Atmospheric Structure". Archived from the original on July 28, 2020 . Retrieved September 14, 2014. 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. Geologically, Mars is fairly active, with dust devils sweeping across the landscape and marsquakes (Martian analog to earthquakes) trembling underneath the ground. The surface of Mars hosts a large shield volcano ( Olympus Mons) and one of the largest canyons in the Solar System ( Valles Marineris). Mars's significant orbital eccentricity and axial tilt cause large seasonal changes to the polar ice caps' coverage and temperature swings between −110°C (−166°F) to 35°C (95°F) on the surface. A Martian solar day ( sol) is equal to 24.5 hours and a Martian solar year is equal to 1.88 Earth years. Landforms visible on Mars strongly suggest that liquid water has existed on the planet's surface. Huge linear swathes of scoured ground, known as outflow channels, cut across the surface in about 25 places. These are thought to be a record of erosion caused by the catastrophic release of water from subsurface aquifers, though some of these structures have been hypothesized to result from the action of glaciers or lava. [146] [147] One of the larger examples, Ma'adim Vallis, is 700 kilometres (430mi) long, much greater than the Grand Canyon, with a width of 20 kilometres (12mi) and a depth of 2 kilometres (1.2mi) in places. It is thought to have been carved by flowing water early in Mars's history. [148] The youngest of these channels is thought to have formed only a few million years ago. [149] Mars once had a moderately dense atmosphere: Scientists suggest the fingerprints of early photochemistry provide a solution to the long-standing mystery". Archived from the original on March 27, 2018 . Retrieved March 9, 2018.
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