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Climate of Mars

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The climate of Mars has been an issue of scientific curiosity for centuries, due not least to the fact that Mars is the only terrestrial planet whose surface can be directly observed in detail from the Earth. A lingering pre-scientific fascination with "the planet of war" also contributes to interest.

Although Mars is smaller and somewhat farther away from the Sun than the Earth, its climate has important similarities, such as the polar ice caps, seasonal changes and the observable presence of weather patterns. It has attracted sustained study from planetologists and climatologists. Although Mars's climate has similarities to Earth's, including seasons and periodic ice ages, there are also important differences such as the absence of liquid water and the much lower thermal inertia. Mars' atmosphere has a scale height of approximately 11 km (36,000 ft), 60% greater than that on Earth. The climate is of considerable relevance to the question of whether life is or was present on the planet, and briefly received more interest in the news due to NASA measurements indicating increased sublimation of the south polar icecap leading to some popular press speculation that Mars was undergoing a parallel bout of global warming.[1]

Martian climatic conditions have been reasonably well-studied. Data has been gathered by Earth-based instruments since as early as the 17th century but it is only since the exploration of Mars began in the mid-1960s that close-range observation has been possible. Flyby and orbital spacecraft have provided data from above, while direct measurements of atmospheric conditions have been provided by a number of landers and rovers. Advanced Earth orbital instruments today continue to provide some useful "big picture" observations of relatively large weather phenomena.

The first martian flyby mission was Mariner 4 which arrived in 1965. That quick two day pass (July 14-15, 1965) was limited and crude in terms of its contribution to the state of knowledge of martian climate. Later Mariner missions (Mariner 6, Mariner 7, and Mariner 9) filled in some of the gaps in basic climate information. Data based climate studies started in earnest with the Viking program in 1975 and continuing with such probes as the highly successful Mars Global Surveyor.

This observational work has been complemented by a type of scientific computer simulation called the Mars General Circulation Model.[2] Several different iterations of MGCM have led to an increased understanding of Mars as well as the limits of such models. Models are limited in their ability to represent atmospheric physics that occurs at a smaller scale than their resolution. They also may be based on inaccurate or unrealistic assumptions about how Mars works and certainly suffer from the quality and limited density in time and space of climate data from Mars.

Historical climate observations

Giancomo Miraldi determined in 1704 that the southern cap is not centered on the rotational pole of Mars.[3] During the opposition of 1719, Miraldi observed both polar caps and temporal variability in their extent.

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 two faint stars passed close to Mars with no effect on their brightness, Herschel correctly concluded that this meant that there was little atmosphere around Mars to interfere with their light.[3]

Honore Flaugergues 1809 discovery of "yellow clouds" on the surface of Mars is the first known observation of Martian dust storms.[4] Flaugergues also observed in 1813 significant polar ice waning during Martian springtime. His speculation that this meant that Mars was warmer than earth was inaccurate.

Martian paleoclimatology

Prior to any serious examination of Martian Paleoclimatology one has to agree on terms, especially broad terms of planetary ages. There are two extant age systems for Mars. The first is based on crater density and has three ages, Noachian, Hesperian, and Amazonian. An alternate minerological timeline has been proposed, also with three ages, Phyllocian, Theikian, and Siderikian.

Recent observations and modeling is 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 [5] 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.

The discovery of goethite on Mars by the Spirit rover has led to the conclusion that climatic conditions in the distant past allowed for free flowing water on Mars. The morphology of some crater impacts on Mars indicate that the ground was wet at the time of impact.

Weather

Mars temperature and circulation vary from year to year (as expected for any planet with an atmosphere). Mars lacks an ocean, a source of much inter-annual variation on earth. Mars Orbital Camera data beginning in March 1999 and covering 2.5 Martian years[6] shows that Martian weather tends to be more repeatable and hence more predictable than that of Earth. If an event occurs at a particular time of year in one year, the available data (sparse as it is) indicates that it is fairly likely to repeat the next year at nearly the same location give or take a week.

On September 29, 2008, the Phoenix lander took pictures of snow falling from clouds 4.5 km above its landing site near Heimdall crater. The precipitation vaporized before reaching the ground, a phenomenon called virga. [7]

Clouds

Animation of ice clouds moving above the Phoenix landing site

Mars' dust storms can kick up fine particles in the atmosphere around which clouds can form. These clouds can form very high up, up to 62 miles above the planet.[8]. The clouds are very faint and can only be seen reflecting sunlight against the darkness of the night sky. In that respect, they look similar to the mesospheric clouds, also known as noctilucent clouds on Earth, which occur about 50 miles (80 kilometers) above our planet.

Temperature

Differing values have been reported for the average temperature on Mars, [9] with a common value being −55 °C.[10] Surface temperatures have been estimated from the Viking Orbiter Infrared Thermal Mapper data; this gives extremes from a warmest of 27 °C to −143 °C at the winter polar caps. [11] Actual temperature measurements from the Viking landers range from −17.2 °C to −107 °C.

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 K)" but that the "daytime data, however, suggest a somewhat different story, with temperatures varying from year-to-year by up to 6 K in this season.[12]This day-night discrepancy is unexpected and not understood". In southern spring and summer variance is dominated by storms, which can generate increases of 30 °C; more years are needed (currently 5 martian years are available) before meaningful statistics can be made.

Atmospheric properties and processes

Low atmospheric pressure

The Martian atmosphere is composed mainly of carbon dioxide and has a mean surface pressure of about 600 pascals, much lower than the Earth's 101,000 Pa. One effect of this is that Mars' atmosphere can react much more quickly to a given energy input than can our atmosphere.[13] As a consequence, Mars is subject to strong thermal tides produced by solar heating rather than a gravitational influence. These tides can be significant, being up to 10% of the total atmospheric pressure (typically about 50 Pa). Earth's atmosphere experiences similar diurnal and semidiurnal tides but their effect is less noticeable because of Earth's much greater atmospheric mass.

Although the temperature on Mars can reach above nbk (0 °C), liquid water is unstable as the atmospheric pressure is below water's triple point and water ice simply sublimes into water vapor. An exception to this is in the Hellas Planitia impact crater, the largest such crater on Mars. It is so deep that the atmospheric pressure at the bottom reaches 1155 Pa, which is above the triple point, so if the temperature exceeded 0 °C liquid water could exist there.

Wind

The surface of Mars has a very low thermal inertia, which means it heats quickly when the sun shines on it. Typical daily temperature swings, away from the polar regions, are around 100 K. On Earth, winds often develop in areas where thermal inertia changes suddenly, such as from sea to land. There are no seas on Mars, but there are areas where the thermal inertia of the soil changes, leading to morning and evening winds akin to the sea breezes on Earth.[14] The Antares project "Mars Small-Scale Weather" (MSW) has recently identified some minor weaknesses in current global climate models (GCMs) due to the GCMs more primitive soil modeling "heat admission to the ground and back is quite important in Mars, so soil schemes have to be quite accurate. "[15] Those weaknesses are being corrected and should lead to more accurate assessments going forward but make continued reliance on older predictions of modeled Martian climate somewhat problematic.

At low latitudes the Hadley circulation dominates, and is essentially the same as the process which on Earth generates the trade winds. At higher latitudes a series of high and low pressure areas, called baroclinic pressure waves, dominate the weather. Mars is dryer and colder than Earth, and in consequence dust raised by these winds tends to remain in the atmosphere longer than on Earth as there is no precipitation to wash it out (excepting CO2 snowfall).[16] One such cyclonic storm was recently captured by the Hubble space telescope (pictured above).

One of the major differences between Mars' and Earth's Hadley circulations is their speed[17] which is measured on an overturning timescale. The overturning timescale on Mars is about 100 Martian days while on Earth, it is over a year.

Effect of dust storms

2001 Hellas Basin dust storm

When the Mariner 9 probe arrived at Mars in 1971, the world expected to see crisp new pictures of surface detail. Instead they saw a near planet-wide dust storm[18] with only the giant volcano Olympus Mons showing above the haze. The storm lasted for a month, an occurrence scientists have since learned is quite common on Mars. 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. This dust storm raised the temperature of the atmosphere of Mars by 30 °C. The low density of the Martian atmosphere means that winds of 40 to 50 mph (18 to 22 m/s) 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 4 °C below average. This was attributed to the global covering of dust that settled out of the dust storm, temporarily increasing Mars' albedo.[19]

In mid-2007 a series of planet-wide dust storms posed a serious threat to the Spirit and Opportunity Mars Exploration Rovers, greatly reducing the amount of energy provided by the solar panels and necessitating the shut-down of most science experiments while waiting for the storms to clear.[20]

Dust storms are most common during perihelion, when the planet receives 40 percent more sunlight than during aphelion. During aphelion water ice clouds form in the atmosphere, interacting with the dust particles and affecting the temperature of the planet.[21]

It has been suggested that dust storms on Mars could play a role in storm formation similar to that of water clouds on earth.[citation needed] 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.[22]

Saltation

The process of geological saltation is quite important on Mars as a mechanism for adding particulates to the atmosphere. Theory and real world observations have not agreed with each other, classical theory missing up to half of real-world saltating particles.[23] A new model more closely in accord with real world observations demonstrates that saltating particles create an electrical field that increases the saltation effect. Mars grains saltate in 100 times higher and longer trajectories and reach 5-10 times higher velocities than Earth grains do.[24]

Cyclonic storms

Hubble, colossal Polar Cyclone on Mars

First detected during the Viking orbital mapping program, cyclonic storms similar to hurricanes have been detected by various probes and telescopes. Images show them as being white in color, quite unlike the much more common dust storms. These storms tend to appear during the northern summer and only at high latitudes. Speculation is that this is due to unique climate conditions near the northern pole.[25]

Methane presence

Methane has been detected in the atmosphere of Mars by ESA's Mars Express probe at a level of 10 nL/L.[26][27][28] Since breakup of that much methane by ultraviolet light would only take 350 years under current Martian conditions, some sort of active source must be replenishing the gas.[29] Mars' current climate conditions may be destabilizing underground clathrate hydrates but there is at present no consensus on the source of Martian methane.

Carbon dioxide carving

Mars Reconnaissance Orbiter images suggest an unusual erosion effect occurs based on Mars' unique climate. Spring warming in certain areas leads to CO2 ice subliming and flowing upwards, creating highly unusual erosion patterns called "spider gullies".[30] Translucent CO2 ice forms over winter and as the spring sunlight warms the surface, it vaporizes the CO2 to gas which flows uphill under the translucent CO2 ice. Weak points in that ice lead to CO2 geysers.[30]

Mountains

Martian storms are significantly affected by Mars' large mountain ranges.[31] Individual mountains like record holding Olympus Mons (27 km) can affect local weather but larger weather effects are due to the larger collection of volcanoes in the Tharsis region.

One unique repeated weather phenomena involving Mountains is a spiral dust cloud that forms over Arsia Mons. The spiral dust cloud over Arsia Mons can tower 15 to 30 kilometers (9 to 19 miles) above the volcano. [32] Clouds are present around Arsia Mons throughout the Martian year, peaking in late summer. [33]

Clouds surrounding mountains display a seasonal variability. Clouds at Olympus Mons and Ascreaus Mons appear in northern hemisphere spring and summer, reaching a total maximum area of approximately 900,000 km2 and 1,000,000 km2 respectively in late spring. Clouds around Alba Patera and Pavonis Mons show an additional, smaller peak in late summer. Very few clouds were observed in winter. Predictions from the Mars General Circulation Model are consistent with these observations. [33]

Polar caps

An illustration of what Mars might have looked like during an ice age between 2.1 million and 400,000 years ago, when Mars's axial tilt is believed to have been much larger than today.

The polar regions of Mars, in particular the southern pole, are cold enough for carbon dioxide to condense and form polar ice caps together over the large accumulations of water ice. So much of the atmosphere can condense at the poles in summer and winter that the atmospheric pressure can vary by up to a third of its mean value. This condensation and evaporation will cause the proportion of the noncondensable gases in the atmosphere to change inversely.[34] The eccentricity of Mars's orbit affects this cycle, as well as other factors. In the spring and autumn wind caused by this sublimation process is so strong that it can be a cause of the global dust storms mentioned above.[35]

Mars possesses ice caps at both poles, which mainly consist of water ice; however, there is dry ice present on their surfaces. Frozen carbon dioxide (dry ice) accumulates in the northern polar region (Planum Boreum) in winter only, subliming completely in summer, while the south polar region additionally has a permanent dry ice cover up to eight metres (25 feet) thick.[36] This difference is due to the higher elevation of the south pole.

The northern polar cap has a diameter of approximately 1,000 km during the northern Mars summer,[37] and contains about 1.6 million cubic kilometres of ice, which if spread evenly on the cap would be 2 km thick.[38] (This compares to a volume of 2.85 million cubic kilometres for the Greenland ice sheet.) The southern polar cap has a diameter of 350 km and a maximum thickness of 3 km.[39] Both polar caps show spiral troughs, which are believed to form as a result of differential solar heating, coupled with the sublimation of ice and condensation of water vapor.[40][41] Both polar caps shrink and regrow following the temperature fluctuation of the Martian seasons as well as other processes which are not fully understood.

Solar wind

Mars lost most of its magnetic field about 4 billion years ago. As a result, the solar wind interacts directly with the Martian ionosphere. This keeps the atmosphere thinner than it would otherwise be by solar wind action constantly stripping away atoms from the outer atmospheric layer.[42] Most of the historical atmospheric loss on Mars can be traced back to this solar wind effect. Current theory posits a weakening solar wind and thus today's atmosphere stripping effects are much less than those in the past when the solar wind was stronger.

Seasons

See also Astronomy on Mars#Seasons

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 passes round 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 warm.

The seasons present unequal lengths are as follows:

Season Sols
(on Mars)		 Days
(on Earth)
Northern Spring, Southern Autumn: 193.30 92.764
Northern Summer, Southern Winter: 178.64 93.647
Northern Autumn, Southern Spring: 142.70 89.836
Northern Winter, Southern Summer: 153.95 88.997

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.[43]

Like Earth, the obliquity of Mars undergoes periodic changes which can lead to long-lasting changes in climate. Once again, the effect is more pronounced on Mars because it lacks the stabilizing influence of a large moon. As a result the obliquity can alter by as much as 45°. Jacques Laskar, of France's National Centre for Scientific Research, argues that the effects of these periodic climate changes can be seen in the layered nature of the ice cap on the planets north pole.[44] Current research suggests that Mars is in a warm interglacial period which has lasted more than 100,000 years.[45]

Evidence for recent climatic change

Pits in south polar ice cap, MGS 1999, NASA

There have been 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.[46]

These features are caused by the dry ice layer evaporating exposing the inert water ice layer.

More recent observations indicate that Mars' south pole is continuing to sublime. "It's evaporating right now at a prodigious rate," says Michael Malin, principal investigator for the Mars Orbiter Camera (MOC).[47] The pits in the ice continue to grow by about 3 meters per martian year. Malin states that conditions on Mars are not currently conductive to the formation of new ice. A NASA press release has suggested that this indicates a "climate change in progress"[48] on Mars.

Elsewhere on the planet, low latitude areas have more water ice than they should have given current climatic conditions.[49] 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.

Attribution theories

Causes of the polar changes

Colaprete et al. conducted simulations with the Mars General Circulation Model which show that the local climate around the Martian south pole may currently be in an unstable period. The simulated instability is rooted in the geography of the region, leading the authors to speculate that the subliming of the polar ice is a local phenomenon rather than a global one.[50] The researchers showed that even with a constant solar luminosity the poles were capable of jumping between states of depositing or losing ice. The trigger for a change of states could be either increased dust loading in the atmosphere or an albedo change due to deposition of water ice on the polar cap.[51] This theory is somewhat problematic due to the lack of ice depositation after the 2001 global dust storm[52] Another issue is that the accuracy of the Mars General Circulation Model decreases as the scale of the phenomenon becomes more local.

It has been argued that "observed regional changes in south polar ice cover are almost certainly due to a regional climate transition, not a global phenomenon, and are demonstrably unrelated to external forcing."[43] Writing in a Nature news story, Chief News and Features Editor Oliver Morton said "The warming of other solar bodies has been seized upon by climate sceptics; but oh how wrong they are... On Mars, the warming seems to be down to dust blowing around and uncovering big patches of black basaltic rock that heat up in the day"[53][54]

Assertion that solar irradiance is causing global warming on Mars

Despite the absence of a time series for martian global temperatures, K.I. Abdusamatov has proposed that "parallel global warmings — observed simultaneously on Mars and on Earth some global warming skeptics think this is proof that human are not casing global warming— can only be a straightline consequence of the effect of the one same factor: a long-time change in solar irradiance."[55] Abdusamatov's hypothesis has yet to be published in the peer-reviewed literature, and requires more clarity as to what time period he is referring. His assertion have received mixed review by other scientists, who have stated that "the idea just isn't supported by the theory or by the observations" and that it "doesn't make physical sense."[56] Other scientists have proposed that the observed variations are caused by irregularities in the orbit of Mars or a possible combination of solar and orbital effects.[57]

Current missions

The Mars Reconnaissance Orbiter is currently taking daily weather and climate related observations from orbit. One of its instruments, the Mars climate sounder is specialized for climate observation work.

Future missions

MetNet is an atmospheric science mission to Mars, initiated and defined by the Finnish Meteorological Institute and scheduled for 2011. The mission includes sending several tens of MetNet Landers (MNL) on the Martian surface. The objective is to establish a wide-spread surface observation network in Mars to investigate the planet's atmospheric structure, physics and meteorology.

MSL is scheduled for 2009, followed by the Mars Scout mission in 2013. Both candidates (MAVEN and Great Escape) for the 2013 mission were to have climate study implications as they are upper atmosphere scientific packages with the MAVEN spacecraft being the final choice.

The People's Republic of China is launching a Mars probe called Yinghuo-1 in 2009. Its mission is not entirely clear but will focus mainly on the study of the external environment of Mars and should thus gain some data of interest to Mars climatologists.

Russia will simultaneously launch Phobos-Grunt on the same rocket. Its destination and main focus will be Phobos but certain Mars climate related data are scheduled to be coming back from this probe as well.

See also

References

  1. ^ Francis Reddy (23 September 2005). "MGS sees changing face of Mars". Astronomy Magazine. Retrieved 2007-09-06.
  2. ^ NASA. "Mars General Circulation Modeling". NASA. Retrieved 2007-02-22.
  3. ^ a b Exploring Mars in the 1700s
  4. ^ Exploring Mars in the 1800s
  5. ^ "Clay studies might alter Mars theories". Science Daily. 19 July 2007. Retrieved 2007-09-06.
  6. ^ "Weather at the Mars Exploration Rover and Beagle 2 Landing Sites". Malin Space Science Systems. Retrieved 2007-09-08.
  7. ^ "NASA Mars Lander Sees Falling Snow, Soil Data Suggest Liquid Past". 2008-09-29. Retrieved 2008-10-03.
  8. ^ Mars Clouds Higher Than Any On Earth
  9. ^ Eydelman, Albert (2001). "Temperature on the Surface of Mars". The Physics Factbook.
  10. ^ "Focus Sections :: The Planet Mars". MarsNews.com. Retrieved 2007-09-08.
  11. ^ "What is the typical temperature on Mars?". Astronomy Cafe. Retrieved 2007-09-08.
  12. ^ Liu, Junjun (15 August 2003). "An assessment of the global, seasonal, and interannual spacecraft record of Martian climate in the thermal infrared" (PDF). Journal of Geophysical Research. 108 (5089): 5089. doi:10.1029/2002JE001921. Retrieved 2007-09-08. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  13. ^ Mars General Circulation Modeling Group. "Mars' low surface pressure. ." NASA. Retrieved 2007-02-22.
  14. ^ Mars General Circulation Modeling Group. "Mars' desert surface…". NASA. Retrieved 2007-02-25.
  15. ^ Antares project "Mars Small-Scale Weather" (MSW)
  16. ^ François Forget. "Alien Weather at the Poles of Mars" (PDF). Science. Retrieved 2007-02-25.
  17. ^ Mars General Circulation Modeling Group. "The Martian tropics…". NASA. Retrieved 2007-09-08.
  18. ^ NASA. "Planet Gobbling Dust Storms". NASA. Retrieved 2007-02-22.
  19. ^ Global warming and climate forcing by recent albedo changes on Mars
  20. ^ Mars Exploration Rover Status Report Concern Increasing About Opportunity
  21. ^ "Duststorms on Mars". whfreeman.com. Retrieved 2007-02-22.
  22. ^ Zurek, Richard W. (1993). "Interannual variability of planet-encircling dust storms on Mars". 98 (E2). Journal of Geophysical Research: 3247–3259. Retrieved 2007-03-16. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  23. ^ Kok, Jasper F. (2008). "Electrostatics in Wind-Blown Sand". Physical Review Letters. 100: 014501. doi:10.1103/PhysRevLett.100.014501. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  24. ^ Almeida, Murilo P. (2008). "Giant saltation on Mars". PNAS. 105: 6222. doi:10.1073/pnas.0800202105. {{cite journal}}: Cite has empty unknown parameter: |month= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  25. ^ David Brand and Ray Villard (19 May 1999). "Colossal cyclone swirling near Martian north pole is observed by Cornell-led team on Hubble telescope". Cornell News. Retrieved 2007-09-06.
  26. ^ Francis Reddy (7 March 2006). "Titan, Mars methane may be on ice". Astronomy Magazine. Retrieved 2007-09-06.
  27. ^ V. Formisano, S. Atreya, T. Encrenaz, N. Ignatiev, M. Giuranna (2004). "Detection of Methane in the Atmosphere of Mars". Science. 306: 1758–1761. doi:10.1126/science.1101732. PMID 15514118.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  28. ^ "Mars Express confirms methane in the Martian atmosphere". ESA. March 30, 2004. Retrieved 2008-08-19.
  29. ^ Martin Baucom (2006). "Life on Mars?". American Scientist. 94 (2). Retrieved 2007-02-26.
  30. ^ a b Mars Rover Finding Suggests Once Habitable Environment - New York Times, "In the spring, sunlight warms the ground, vaporizing carbon dioxide at the base of the ice layer. The gas flows uphill, carving channels in the underlying soil. At weak points in the ice, the gas erupts in small geysers."
  31. ^ Mars General Circulation Modeling Group. "The Martian mountain ranges…". NASA. Retrieved 2007-09-08.
  32. ^ "PIA04294: Repeated Clouds over Arsia Mons". NASA. Retrieved 2007-09-08.
  33. ^ a b Benson; et al. (2006). "Interannual variability of water ice clouds over major martian volcanoes observed by MOC". Icarus. 184: 365–371. doi:10.1016/j.icarus.2006.03.014. {{cite journal}}: Explicit use of et al. in: |author= (help)
  34. ^ François Forget. "Alien Weather at the Poles of Mars" (PDF). Science. Retrieved 2007-02-25.
  35. ^ Mars General Circulation Modeling Group. "Mars' dry ice polar caps…". NASA. Retrieved 2007-02-22.
  36. ^ Darling, David. "Mars, polar caps, ENCYCLOPEDIA OF ASTROBIOLOGY, ASTRONOMY, AND SPACEFLIGHT". Retrieved 2007-02-26.
  37. ^ "MIRA's Field Trips to the Stars Internet Education Program". Mira.org. Retrieved 2007-02-26.
  38. ^ Carr, Michael H. (2003). "Oceans on Mars: An assessment of the observational evidence and possible fate". Journal of Geophysical Research. 108 (5042): 24. doi:10.1029/2002JE001963. {{cite journal}}: |access-date= requires |url= (help); |format= requires |url= (help)
  39. ^ Phillips, Tony. "Mars is Melting, Science at NASA". Retrieved 2007-02-26.
  40. ^ Pelletier, J. D. (2004). "How do spiral troughs form on Mars?". Geology. 32: 365–367. doi:10.1130/G20228.2. Retrieved 2007-02-27.
  41. ^ "Mars Polar Cap Mystery Solved". Mars Today. 25 March 2004. Retrieved 2007-01-23.
  42. ^ The Solar Wind at Mars
  43. ^ a b Steinn Sigurðsson. "Global warming on Mars?". RealClimate. Retrieved 2007-02-21.
  44. ^ Jacques Laskar. "Martian 'wobbles' shift climate". BBC. Retrieved 2007-02-24.
  45. ^ Francis Reddy. "Titan, Mars methane may be on ice". Astronomy Magazine. Retrieved 2007-03-16.
  46. ^ "MOC Observes Changes in the South Polar Cap". Malin Space Science Systems. Retrieved 2007-02-22.
  47. ^ "Evaporating ice". Astronomy.com. Retrieved 2007-02-22.
  48. ^ Orbiter's Long Life Helps Scientists Track Changes on Mars
  49. ^ Mars Emerging from Ice Age, Data Suggest
  50. ^ "Albedo of the South Pole of Mars. .". Nature. 435: 184–188. 2005-05-12. {{cite journal}}: |access-date= requires |url= (help)
  51. ^ Jakosky, Bruce M. (1990). "Year-to-year instability of the Mars Polar Cap". J.Geophys Res. 95: 1359–1365. doi:10.1029/JB095iB02p01359.
  52. ^ Fenton, Lori K. (5 April 2007). "Global warming and climate forcing by recent albedo changes on Mars" (PDF). Nature. 446: 646–9. doi:10.1038/nature05718. Retrieved 2007-09-06. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  53. ^ Access : Hot times in the Solar System : Nature News
  54. ^ Fenton, Lori K.; Geissler, Paul E.; Haberle, Robert M. (2007), "Global warming and climate forcing by recent albedo changes on Mars" (PDF), Nature, 446, doi:10.1038/nature05718
  55. ^ "Look to Mars for the truth on global warming". National Post. Retrieved 2007-03-02.
  56. ^ Ker Than (12 March 2007). "Sun Blamed for Warming of Earth and Other Worlds". Live Science. Retrieved 2007-09-06.
  57. ^ Kate Ravilious. "Mars Melt Hints at Solar, Not Human, Cause for Warming, Scientist Says". National Geographic Society. Retrieved 2007-03-02.

External links

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