South polar midsummer ice cap (2000); the south cap has a permanent carbon dioxide ice cap covered with water ice. [158] 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.

Mumma, Michael; etal. (2010). "The Astrobiology of Mars: Methane and Other Candinate Biomarker Gases, and Related Interdisciplinary Studies on Earth and Mars" (PDF). Astrobiology Science Conference 2010. Astrophysics Data System. Greenbelt, MD: Goddard Space Flight Center . Retrieved July 24, 2010. Pettit, E.; etal. (September 1924). "Radiation Measures on the Planet Mars". Publications of the Astronomical Society of the Pacific. 36 (9): 269–272. Bibcode: 1924PASP...36..269P. JSTOR 40693334. Krauss, C.E.; Horanyi, M.; Robertson, S. (2006). "Modeling the formation of electrostatic discharges on Mars". J. Geophys. Res. Planets. 111 (E2): E2. Bibcode: 2006JGRE..111.2001K. doi: 10.1029/2004JE002313.Smith, Isaac B.; Holt, J. W. (2010). "Onset and migration of spiral troughs on Mars revealed by orbital radar". Nature. 465 (4): 450–453. Bibcode: 2010Natur.465..450S. doi: 10.1038/nature09049. PMID 20505722. S2CID 4416144. Search for 'Missing' Carbon on Mars Cancelled". Space.com. November 26, 2015. Archived from the original on November 29, 2015 . Retrieved December 1, 2015. 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]

Garisto, Dan (February 7, 2018). "Massive dust storms are robbing Mars of its water". Science News. Archived from the original on January 24, 2018 . Retrieved January 24, 2018. 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) Red Planet Heats Up: Ice Age Ending on Mars". Space.com. May 26, 2016. Archived from the original on July 6, 2019 . Retrieved July 6, 2019.

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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.

Antares project "Mars Small-Scale Weather" (MSW)". September 23, 2003. Archived from the original on March 3, 2006 . Retrieved July 6, 2019. Elsewhere on the planet, low latitude areas have more water ice than they should have given current climatic conditions. [138] [139] [140] Mars Odyssey "is giving us indications of recent global climate change in Mars", said Jeffrey Plaut, project scientist for the mission at NASA's Jet Propulsion Laboratory, in non-peer reviewed published work in 2003. 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. PMC 3382529. PMID 22679287. There have been regional changes around the south pole ( Planum Australe) over the past few Martian years. In 1999 the Mars Global Surveyor photographed pits in the layer of frozen carbon dioxide at the Martian south pole. Because of their striking shape and orientation these pits have become known as swiss cheese features. In 2001 the craft photographed the same pits again and found that they had grown larger, retreating about 3 meters in one Martian year. [135] These features are caused by the sublimation of the dry ice layer, thereby exposing the inert water ice layer. More recent observations indicate that the ice at Mars' south pole is continuing to sublimate. [136] MGS sees changing face of Mars". Astronomy.com. Archived from the original on April 19, 2021 . Retrieved April 20, 2021.Webster, C. R.; etal. (2013). "Isotope ratios of H, C, and O in CO 2 and H2O of the Martian atmosphere" (PDF). Science. 341 (6143): 260–263. Bibcode: 2013Sci...341..260W. doi: 10.1126/science.1237961. PMID 23869013. S2CID 206548962. Archived (PDF) from the original on October 29, 2021 . Retrieved August 30, 2020.

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. Main article: Volcanology of Mars Picture of the largest volcano on Mars, Olympus Mons. It is approximately 550km (340mi) across. a b "What happened to early Mars' atmosphere? New study eliminates one theory". Archived from the original on March 27, 2018 . Retrieved March 9, 2018.Mars Rovers Survive Severe Dust Storms, Ready For Next Objetives [sic]" (Press release). Jet Propulsion Laboratory. September 7, 2007. Aberle, R.M. (1998). "Early Climate Models". J. Geophys. Res. 103 (E12): 28467–79. Bibcode: 1998JGR...10328467H. doi: 10.1029/98je01396. S2CID 6353484. 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. Mars has an axial tilt of 25.2°. This means that there are seasons on Mars, just as on Earth. The eccentricity of Mars' orbit is 0.1, much greater than the Earth's present orbital eccentricity of about 0.02. The large eccentricity causes the insolation on Mars to vary as the planet orbits the Sun. (The Martian year lasts 687 days, roughly 2 Earth years.) As on Earth, Mars' obliquity dominates the seasons but, because of the large eccentricity, winters in the southern hemisphere are long and cold while those in the north are short and relatively warm. a b c d "Mars Pathfinder". mars.nasa.gov. Archived from the original on September 4, 2017 . Retrieved July 6, 2019.