Polar caps of Mars

from Wikipedia, the free encyclopedia
The north polar region of the planet Mars, captured by the Viking 1 spacecraft in the late 1970s

The planet Mars has striking, permanent ice caps at both of its poles , which are composed of frozen carbon dioxide and water ice . During the winter season, the poles are immersed in complete darkness, which lasts half a Martian year (or 343.5 days). Due to the extreme cold, 25-30% of the gaseous carbon dioxide in the thin Martian atmosphere resublimate to dry ice . When the sunlight returns in the summer, the frozen CO 2 sublimes . This creates enormous gusts of wind that blow down from the polar region at up to 400 km / h. These seasonal storms create earth-like frost conditions and carry vast amounts of dust and water vapor . Cirrus clouds move through the higher atmosphere . In 2004, the Rover Opportunity photographed clouds containing water ice.

history

Christian Huygens discovered the polar caps of Mars with his telescope in 1672. Friedrich Wilhelm Herschel observed Mars from 1781 onwards. In addition to their variability, he noticed the eccentric position of the polar caps. It has been known since the 1960s that the polar ice caps, which change with the seasons, consist of carbon dioxide on their surface. Carbon dioxide sublimes during the polar winter half-year at temperatures below 148 K (or −125 ° C). Infrared measurements by Viking 2 then confirm in 1976 that at least the northern polar cap is made up of water ice and dry ice.

Northern polar cap

The North Pole Cap of Mars as captured by Mars Global Surveyor on March 13, 1999
"Cottage cheese" structures of the North Pole Cap

There are seasons on Mars similar to those on Earth, as Mars' current inclination angle of 25.19 ° is very close to Earth's 23.43 °. However, due to the more elliptical orbit of Mars, the seasons in its southern hemisphere are much more pronounced than in the northern hemisphere.

The northern polar cap has a diameter of around 1100 kilometers during the northern Martian summer. It is arranged more or less symmetrically around the polar axis and reaches down to about 65 ° north latitude in winter. Its ice volume is 1.6 million cubic kilometers, which corresponds to an average total thickness of 2 km. (For comparison, the Greenland Ice Sheet has a total volume of 2.85 million cubic kilometers.) About half of it consists of water ice. Radar measurements from Mars Reconnaissance Orbiter showed 0.821 million cubic kilometers of water ice, or just under 30% of the Greenland inland ice.

In the course of a winter the northern hemisphere accumulates on the northern pole cap seasonal ice cap ( English seasonal ice cap ), to a relatively thin dry layer thickness of 1.5 to 2 meters, which then sublimated in the summer half-year. Their mass is determined by Kieffer u. a. (1992) given 3.5 × 10 15 kilograms. This dry ice layer is surrounded on its outer edge by a ring of water ice.

Every Mars year, around a third of the thin Martian atmosphere condenses into dry ice. This process has been proven by scientists as tiny changes in the gravitational field of Mars.

The northern polar cap is lower than the southern. Its highest point at - 1950 ± 50 meters is in the immediate vicinity of the geographic North Pole. Their thickness is 2950 ± 200 meters, since the surrounding lowlands represent a deep depression falling towards the pole and a level between - 4800 meters and - 5200 meters.

The temperatures are therefore higher, so that all dry ice disappears again in the Martian summer. What remains is the so-called residual ice cap ( Northern residual ice cap or NRIC ), which mainly consists of water ice. Their thickness is estimated at up to 3 kilometers in places. In contrast to the conditions at the South Pole, the underlying layer deposits are almost completely covered by the residual ice cap. The dry ice layer begins its growth in late summer or early autumn, when various cloud formations cover the polar region and bring precipitation . This phenomenon is called polar cap (engl. Polar hood ), respectively.

The spiral furrows running through it are characteristic of the North Pole Cap. High-resolution images from Mars Global Surveyor show that the northern polar cap is littered in detail with depressions, cracks, small waves and bumps, in addition to the large-scale spiral furrows, which leave behind a cottage cheese effect . Compared to the southern polar cap, which also has characteristic depressions, these structures are arranged much more closely.

Internal structure

Radar sounding of the northern polar cap using SHARAD

Use the radar soundings of SHARAD was won a good insight into the internal structure of an average of 2,000 meters thick pole cap. Their stratigraphy is relatively homogeneous and can be divided into four units ( summarized in the figure as English internal layers ). The 200-meter-thick unit A, which traces the irregularities of the subsurface, conforms to the basal unit BU ( Basal Unit ). The overlying unit B shows strong fluctuations in thickness and wedges laterally. Above this is unit C, which makes up the main part of the ice cap. It also shows fluctuations in thickness because it has sunk into the underlying unit B. Their uppermost parts can be affected by shallow faults . The final 300 to 500 meter thick unit D is very reflective, especially on its immediate surface. In addition to the also flat faults, it shows a very badly disturbed structure in the area of ​​the spiral furrows and at the edge of the ice. Unit B, the only below Gemina Lingula (ice tongue south of Chasma Boreale is found) is interpreted by Holt and Safaeinili (2009) as representing an Paläoeiskappe that due to the applied load of the overlying units to the creep came and dodged sideways. These lateral evasive movements caused the dislocations in the overlying units. Cracks formed in the ice, which were then expanded to today's Chasmata due to the abrasive effect of the downwind.

Southern polar cap

The South Pole Cap of Mars as captured by Mars Global Surveyor on April 17, 2000

With a diameter of 400 km and an average thickness of 1.5 km, the southern polar cap is far less extensive. In the southern winter it covers the southern hemisphere up to 50 ° south latitude. It is higher than the northern polar cap and is therefore colder. Like the northern polar cap, it also shows spiral incisions, the way in which they originated has not yet been fully clarified. The total volume of the southern polar cap is also estimated at 1.6 million cubic kilometers (including 0.2 million cubic kilometers of water ice), although the layer deposits surrounding the south pole are also included.

As with the northern polar cap, 1.5 to 2 meters of dry ice accumulate in the course of the southern winter due to precipitation from the polar cap , which largely sublimes again in summer. Overall, the seasonal ice cap of the South Pole is much more inhomogeneous and also more porous (with a porosity of up to 70% in places). Water ice occurs only in patches and is locally limited.

The southern residual ice cap ( SRIC ) is a permanent layer of dry ice about 8 meters thick. Compared to the northern polar cap, the southern residual cap is eccentric after 315 °. The fresh annual deposits are, however, centered over the geographic South Pole. The eccentricity of the residual cap can be explained by a stationary low pressure system over the Hellas basin , which receives more precipitation in the form of snow. The remote side, on the other hand, receives far less snow overall and is also colder and more frozen. In summer, snow reflects more sunlight and sublimation is reduced (under the climatic conditions of Mars, snow does not melt, but evaporates). Frozen surfaces, on the other hand, are rougher and store solar radiation. As a result of the heating that takes place, the sublimation increases.

In 2004, Mars Express was able to measure the thickness of the ice cap with its MARSIS radar probe, which covered 3.7 kilometers. His OMEGA probe found that the southern polar cap region was divided into three:

  • The light polar cap (seasonal and residual polar cap with high albedo) is a mixture of 85% dry ice and 15% water ice.
  • The steep edge slopes of the layer deposits consist almost entirely of water ice.
  • Strictly speaking, the surrounding plains no longer belong to the ice cap, but due to their composition and their permafrost , which can withstand a distance of several tens of kilometers, they must be added.

NASA scientists have calculated that if the southern polar cap melted completely, the surface of Mars would be covered with 11 meters of water. A melting of both polar regions, including permafrost areas, would cause an increase of 35 meters.

Swiss cheese and fingerprint terrain

Changes in the ice cream of Swiss cheese between 1999 and 2001
Dry ice landscape at the South Pole in late summer

Just as the plate, pitted surface of the northern ice cap as a cottage cheese like etched acting, much larger holes, troughs and flattened can be described, so bring mesas of southern polar cap more the impression of a Swiss cheese (Engl. Cheese Swiss ). This structure was first described by Sharp in 1973. In turn, circular depressions were eroded out of the flattened mesas of the top layer. Ultimately, the way in which they emerged is likely to be based on a combination of ablation and deflation . Recordings from the Mars orbiter camera from 2001, when compared with 1999, showed an average retraction of the trough walls by 3 meters per Mars year (the retreat rate could even be up to 8 meters in places). Over time, this led to the merging of individual troughs and the disappearance of the mesas. The attempt to explain the high retreat rate of the trough walls is the low position of the sun, which irradiates the walls all day in the summer but not the trough floor. The dust sediment released as a result is then blown out.

In addition to the typical terrain of the Swiss cheese of southern Residualkappe still occurs on the surface of the fingerprint-Terrain (Engl. Fingerprint terrain on). This consists of a series of elongated backs and intervening depressions, the pattern of which is similar to the papillary ridges .

Geysers

The seasonal freezing of the seasonal ice cap at the South Pole and its surrounding regions leads to the formation of thick, transparent dry ice sheets near the ground. With the beginning of spring, the top soil layer is warmed by the sun. The CO 2 in the overlying dry ice layer sublimes from below. This process builds up overpressure, which lifts the layer and finally causes it to burst. This results in geyser- like outbreaks of carbon dioxide mixed with dark basalt sand or dust. The sublimation process can take place within a few days, weeks, or months - a relatively short period of time for geological dimensions and especially for Mars. The gas flowing to the center of departure chiseled radial, spider-like grooves in the subsurface of the ice sheet.

Star-shaped channels

Spider-like grooves near the South Pole, the structure is a total of 500 meters wide and 1 meter deep

The network of channels radiating outwards runs out like a feather. The cobweb-like structures are usually 500 meters wide and 1 meter deep. They are caused by a gas leak to which dust is mixed. With the onset of warming in spring, gas collects under transparent ice. Observable changes in the shape of the star-shaped canals can occur within days. The following model concept offers a possible explanation for the observed phenomenon: “The rays of the sun warm up dust particles trapped in the ice. These then melt through to the subsurface, with the melt holes that have been left welding back together. As the dust sinks to the bottom, the ice is lightened. The dark, dust-enriched soil layer then also heats up, so that the dry ice layer above sublimes and the gas that is generated flows off to higher areas in the ice. Dark dust is entrained here. Surface winds blow away the dust-laden, released gas and deposit the sediment load again in dark, fan-like structures that could be picked up by satellites. ”The physical approaches of this model are similar to the attempts to explain the dark eruption clouds on the surface of Triton .

Layer deposits

Layer deposits at the South Pole with a polygonal fissure system, recorded by Mars Reconnaissance Orbiter

Both residual polar caps are underlain and framed by thick, areologically very young layer deposits ( English polar layered deposits or PLD ), which were formed by the seasonal cycle of sublimation and condensation and from an alternating layer of water ice, silicate dust (2 to 10 percent by volume) and dry ice (minimal) or mixtures thereof. Their density was calculated to be 1220 to 1271 kg / m 3 .

The layers, which can be traced over hundreds of kilometers, largely follow the contours and are therefore horizontal. Individual members of the shift can be easily distinguished based on their different albedo . The albedo values ​​in turn depend on the ratio of dust to ice, on grain size variations in the dust deposits and on the composition of the dust. They also show different degrees of solidification, recognizable by their susceptibility to erosion by wind, sublimation and creep processes.

The layer deposits of the North Pole Cap ( NPLD ) have a volume of 1.14 million cubic kilometers and those of the South Pole Cap 1.6 million cubic kilometers. The two together have roughly the same volume as the Greenland ice sheet with around 2.6 million cubic kilometers.

Also unconformities can locally be observed, often associated with impact structures. They refer to local settlement and flow phenomena in the ice cap. Arch-shaped structures can also be seen, which can be traced back to flow movements in the ice due to increasing load in the central part of the polar cap.

The thickness of the layer packages varies between 10 and 50 meters, but individual layers can be considerably thinner. The thickness of the individual layers is possibly controlled by changes in the axis inclination angle. Under the newly formed ice layers are layers of dust that originate from dust storms. At the North Pole, the layer deposits form the Planum Boreum - a 3-kilometer-high plateau area with a diameter of 1,000 kilometers. Its counterpart at the South Pole is the Planum Australe with comparable dimensions. The rhythmic alternation of the two planes made of water ice and dust is based on climate changes that were triggered by slowly changing parameters of the Mars orbit (see also Milanković cycles ). For a future investigation of the paleoclimate on Mars, these locations should contain extremely valuable information, roughly comparable to the annual ring pattern of trees and the ice cores on Earth.

At the southern polar cap, the layer deposits are traversed by the large, east-trending canyon Chasma Australe . At 90 ° East the deposits lie over a large depression, the Prometheus Basin .

At the South Pole, extensive, polygonal rift systems can often be recognized by the layer deposits . It is believed that the right-angled clefts are due to the cyclical expansion and contraction of the subsurface water ice.

Spiral furrows

Chasma Boreale

Both polar caps are traversed by spiral-like trenches or furrows (English spiral troughs ) that expose the layer deposits on their slopes and side walls. The spiral pattern of these furrows is arranged much more symmetrically in the North Pole Cap than in the South Pole Cap and shows an anticyclonic rotation in a clockwise direction. Opposite conditions prevail at the South Pole, here the spiral pattern rotates cyclonically counterclockwise.

The origin of the spiral furrows is likely due to ablation in association with wind flow patterns. The dust content of the Martian atmosphere is likely to have played a decisive role here due to a positive feedback . The more dust there is, the darker the surface becomes. Since dark surfaces absorb more light , the rate of sublimation inevitably increases.

But there are other theories that explain spiral furrows. Fisher (1993) sees the cause in a combination of asymmetrical flow movements of the ice with ablation. Recently, SHARAD's radar soundings have shown the spiral furrows to be the result of catabatic winds driven by the Coriolis force .

An extremely large trench furrow is Chasma Boreale . The 100 km wide incision crosses almost half of the northern polar cap. With a depth of 2 kilometers, it exceeds the Grand Canyon . Chasma Australe on the southern polar cap is roughly comparable in terms of size, but it is not in contact with the surface ice. She is accompanied by the somewhat smaller Promethei Chasma and Ultimum Chasma .

Asymmetry of the polar ice caps

Asymmetry in water content

The water ice content of the North Pole Cap is around four times that of the South Pole. This is due to the not inconsiderable difference in altitude between the two polar caps (the area around the south pole is on average 6 km higher than that around the north pole). This difference in height triggers large-scale differences in the atmospheric circulation, which ultimately lead to an increase in the water vapor concentration in the North Pole area.

Asymmetry in the surface distribution

The centers of symmetry of the polar cap surfaces do not coincide with the current axis of rotation of Mars. The center of symmetry of the North Pole Cap is offset by about 3 ° to 0 ° longitude, but that of the South Pole Cap is shifted antipodal (in the opposite direction) by almost 5 ° to 170 ° Longitude. The topographically highest point of the North Pole Cap with - 2000 meters is located above the pole of rotation, that of the South Pole Cap with + 3500 meters is again eccentric and lies at 86–87 ° latitude and 0 ° longitude (for comparison: the lowland around the North Pole takes - 5000 Meters, whereas the foreland of the South Pole at least reaches heights of + 1000 to + 1500 meters). The reasons for the observed asymmetries are not clear and various attempts at explanation have been made (pole wandering, changing the axis inclination, topography of the contact surface). The antipodal offset may only mean the recording of a paleo-axis position. The rheologically very sluggishly reacting ice caps are therefore likely to lag significantly behind the current axis position in their eccentric surface configuration.

Influence of the axis inclination angle

Changes in the axis inclination angle (and thus the obliquity) have a very large influence on the expansion of the polar caps. At the maximum axis inclination angle, the poles receive significantly more solar radiation because the duration of the irradiation increases. This in turn leads to an increased rate of sublimation.

Since Mars does not have a stabilizing moon like Earth ( Phobos and Deimos are too small to have any significant influence), the spatial position of the axis of rotation changes in a chaotic way over time, i.e. H. Mars is tumbling , as corresponding simulation calculations show. These changes have a serious impact on the large-scale atmospheric circulation and thus also on the intensity of global dust storms.

Withdrawal or relocation of the polar ice caps

Fishbaugh and Head (2000) advocate a previously far greater expansion of the northern polar ice caps in the direction of Olympia Planitia (up to 78 ° north latitude and 180 ° longitude). They justify this with typical ice edge structures such as kames and dead ice basins and the presence of a lobe of polar layer deposits, now hidden beneath the linear dunes of the Olympia Undae . In this case, the North Pole Cap would very well have been aligned symmetrically around today's North Pole. The reasons for the retreat of the ice masses to their current position are, however, in the dark.

For comparison, Head and Pratt (2001) interpret structures such as Esker and meltwater courses in the area of ​​the Dorsa-Argentea Formation (at 77 ° south latitude and 320 ° longitude) as well as collapse holes over former gas accumulations of the Cavi Angusti and the Cavi Sisyphi as proglacial and imply at the South Pole thus a much further expansion of the South Pole Cap. Esker have recently been suspected to be much further north in Argyre Planitia (at 55 ° south and 315 ° longitude).

Areology

Areological map of Mars, north pole top left, south pole top right

The polar caps of Mars have a long areological past that can be traced back over 3.7 billion years to the early Hesperian . In terms of their base, they are diametrically opposed to each other - the northern polar cap, which was essentially formed from the late Amazonian around 0.6 billion years ago, lies on lowland sediments of the Vastitas Borealis , whereas the southern polar cap extends over much older highland units of the Noachian (4.1 to 3.7 billion years).

The northern polar cap shows the following stratigraphic structure (from young to old):

  • Ice cap lApc - late Amazon
  • Layer deposition at Apu - outgoing middle and late Amazon
  • Hesperian layer deposits Hpu - Hesperium and at the same time
  • rough Hesperian constructs Hpe - Hesperium.
  • The dunes of the Olympia Undae lApd - late Amazonian - surround the ice cap between 240 ° and 120 ° in length and lie on the two layer deposition units. Between 310 ° and 270 ° in length, isolated dune deposits overlay the lowland sediments lHl of the vastitas boreales from the late Hesperian.

The southern polar cap can be broken down as follows:

  • Ice cap lApc
  • Layer deposits Apu
  • polar plains formation Ap - Late Hesperian to Late Amazonian
  • Hesperian plane formation Hp - hesperium as well as at the same time
  • harsh imperious constructs Hpe .

Dune formations are missing on the southern polar cap. The formations Ap , Hp and Hpe are mainly found between 240 ° and 30 ° longitude. The layer deposits Apu preferably spread after a length of 160 °.

Age of the ice caps

The polar ice caps are areologically very young. Stratigraphically they have a late Amazonian age. Relative age estimates based on crater counts originally yielded a little less than a hundred thousand years for the North Pole Cap and a few hundred thousand years for the somewhat older South Pole Cap. Later research revised these ages to less than 10 million years for the North Pole and 7 to 15 million years for the South Pole.

Individual evidence

  1. ↑ Michael T. Mellon, William C. Feldman, Thomas H. Prettyman: The presence and stability of ground ice in the southern hemisphere of Mars . In: Icarus . tape 169 , no. 2 , June 1, 2004, p. 324-340 , doi : 10.1016 / j.icarus.2003.10.022 .
  2. ^ Seymour L. Hess, Robert M. Henry, James E. Tillman: The seasonal variation of atmospheric pressure on Mars as affected by the south polar cap . In: Journal of Geophysical Research: Solid Earth . tape 84 , B6, June 10, 1979, ISSN  2156-2202 , pp. 2923-2927 , doi : 10.1029 / JB084iB06p02923 .
  3. ^ Mars Exploration Rover Mission: Press Release Images: Opportunity. marsrovers.jpl.nasa.gov, 2004, accessed June 2, 2016 .
  4. ↑ William Sheehan: The planet Mars. A history of observation & discovery . University of Arizona Press, Tucson 1996, ISBN 0-8165-1640-5 , pp. 25 .
  5. ^ Robert B. Leighton, Bruce C. Murray: Behavior of Carbon Dioxide and Other Volatiles on Mars . In: Science . tape 153 , no. 3732 , July 8, 1966, ISSN  0036-8075 , p. 136-144 , doi : 10.1126 / science.153.3732.136 .
  6. ↑ CB Farmer, inter alia: Mars. Water vapor observations from the Viking orbiters . In: Journal of Geophysical Research . tape 82 , 1977, pp. 4225-4248 .
  7. ↑ Michael H. Carr, James W. Head: Oceans on Mars. An assessment of the observational evidence and possible fate . In: Journal of Geophysical Research: Planets . tape 108 , E5, May 20, 2003, ISSN  2156-2202 , p. 5042 , doi : 10.1029 / 2002JE001963 ( planetary.brown.edu [PDF]).
  8. ↑ Keith Cowing: Radar Map of Buried Mars Layers Matches Climate Cycles. spaceref.com, archived from the original on April 22, 2014 ; accessed on June 2, 2016 .
  9. ^ KL Wagstaff, among others: Observations of the north polar water ice annulus on Mars using THEMIS and TES . In: Planet. Space Sci. tape 56 , 2008, p. 256-65 .
  10. ^ Maria T. Zuber, David E. Smith, Sean C. Solomon, James B. Abshire, Robert S. Afzal, Oded Aharonson, Kathryn Fishbaugh, Peter G. Ford, Herbert V. Frey, James B. Garvin, James W. Head, Anton B. Ivanov, Catherine L. Johnson, Duane O. Muhleman, Gregory A. Neumann, Gordon H. Pettengill, Roger J. Phillips, Xiaoli Sun, H. Jay Zwally, W. Bruce Banerdt, Thomas C. Duxbury: Observations of the North Polar Region of Mars from the Mars Orbiter Laser Altimeter . In: Science . tape 282 , no. 5396 , December 11, 1998, ISSN  0036-8075 , p. 2053-2060 , doi : 10.1126 / science.282.5396.2053 , PMID 9851922 .
  11. ↑ Fisher, D .: Internal layers in an “accublation” ice cap: A test for flow . In: Icarus . tape 144 , 2000, pp. 289-294 .
  12. Jump up ↑ JW Holt, A. Safaeinili: Northern Polar Layered Deposits, Mars: Structural Relationships between Gemina Lingula, the Main Lobe and Chasma Boreale from SHARAD Radar Stratigraphy . In: Lunar and Planetary Science Conference . tape 40 , no. 1721 , 2009 ( lpi.usra.edu [PDF]).
  13. ↑ CJ Hansen, inter alia: HiRISE observations of gas sublimation-driven activity in Mars' southern polar regions: I. Erosion of the surface . In: Icarus . tape 205 , 2010, p. 283-295 , doi : 10.1016 / j.icarus.2009.07.021 .
  14. ↑ a b Jeffrey J. Plaut, Giovanni Picardi, Ali Safaeinili, Anton B. Ivanov, Sarah M. Milkovich, Andrea Cicchetti, Wlodek Kofman, Jérémie Mouginot, William M. Farrell, Roger J. Phillips, Stephen M. Clifford, Alessandro Frigeri , Roberto Orosei, Costanzo Federico, Iwan P. Williams, Donald A. Gurnett, Erling Nielsen, Tor Hagfors, Essam Heggy, Ellen R. Stofan, Dirk Plettemeier, Thomas R. Watters, Carlton J. Leuschen, Peter Edenhofer: Subsurface Radar Sounding of the South Polar Layered Deposits of Mars . In: Science . tape 316 , no. 5821 , April 6, 2007, ISSN  0036-8075 , p. 92-95 , doi : 10.1126 / science.1139672 .
  15. ^ RM Haberle, B. Mattingly, TN Titus: Reconciling different observations of the CO2 ice mass loading of the Martian north polar cap . In: Geophys. Res. Lett. tape 31 , 2004, p. 5702 .
  16. ↑ D. Darling: Mars, polar caps . In: Encyclopedia of Astrobiology, Astronomy, and Spaceflight . ( daviddarling.info ).
  17. ↑ NG Barlow: Mars: an introduction to its interior, surface and atmosphere . Cambridge University Press, Cambridge, UK 2011, ISBN 978-0-521-85226-5 .
  18. ^ European Space Agency (ESA): Water at Martian south pole . 2004.
  19. ↑ V.-P. Kostama, MA Kreslavsky, JW Head: Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement . In: Geophysical Research Letters . tape 33 , no. June 11 , 2006, ISSN  1944-8007 , p. L11201 , doi : 10.1029 / 2006GL025946 .
  20. ^ PR Christensen: Water at the Poles and in Permafrost Regions of Mars . In: GeoScienceWorld Elements . tape 3 (2) , 2006, pp. 151-155 .
  21. ^ RP Sharp: Mars: south polar pits and etched terrains . In: Journal of Geophysical Research . tape 78 , 1973, p. 4222-4230 .
  22. ^ W. Hartmann: A Traveler's Guide to Mars . Workman Publishing, New York 2003.
  23. ^ HH Kieffer: Annual Punctuated CO2 Slab-ice and Jets on Mars. Mars Polar Science 2000 . 2000 ( lpi.usra.edu [PDF]).
  24. ↑ G. Portyankina: Simulations of Geyser-type Eruptions in Cryptic Region of Martian South. Fourth Mars Polar Science Conference . Ed .: G. Portyankina. 2006 ( lpi.usra.edu [PDF]).
  25. ^ A b Hugh H. Kieffer, Philip R. Christensen, Timothy N. Titus: CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap . In: Nature . tape 442 , no. 7104 , p. 793-796 , doi : 10.1038 / nature04945 .
  26. ^ Hansen, C., McEwen, A. and HiRISE Team: AGU Press Conference Spring at the South Pole of Mars . 2007.
  27. ↑ LA Soderblom, SW Kieffer, TL Becker, RH Brown, AF Cook, CJ Hansen, TV Johnson, RL Kirk, EM Shoemaker: Triton's Geyser-Like Plumes. Discovery and Basic Characterization . In: Science . tape 250 , no. 4979 , October 19, 1990, ISSN  0036-8075 , p. 410-415 , doi : 10.1126 / science.250.4979.410 .
  28. ^ MA Wieczorek: Constraints on the composition of the martian south polar cap from gravity and topography . In: Icarus . tape 196 , 2008, p. 506-17 .
  29. ↑ DE Smith, among others: Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars . In: Journal of Geophysical Research . tape 106 , 2001, pp. 23689-722 .
  30. ↑ a b Herkenhoff, K .: Geology, composition, age, and stratigraphy of the polar layered deposits on Mars . In: 1st International Conference on Mars Polar Science and Exploration (Ed.): LPI Contribution . tape 953 , 1998, pp. 18-19 .
  31. ^ Carr, Michael H .: The Surface of Mars . Cambridge University Press, 2006, ISBN 0-521-87201-4 .
  32. ↑ DA Fisher: If Martian ice caps flow - Ablation mechanisms and appearance . In: Icarus . tape 105 , 1993, pp. 501 .
  33. ↑ Isaac B. Smith, John W. Holt: Onset and migration of spiral troughs on Mars revealed by orbital radar . In: Nature . tape 465 , no. 7297 , May 27, 2010, p. 450–453 , doi : 10.1038 / nature09049 .
  34. ↑ KE Fishbaugh, JW Head: Comparison of North and South Polar Caps of Mars: New Observations from MOLA Data and Discussion of Some Outstanding Questions . In: Icarus . tape 154 , 2001, p. 145-161 .
  35. ^ Ward, WR: Large-scale variations in the obliquity of Mars . In: Science . tape 181 , 1973, p. 260-62 .
  36. ↑ Fishbaugh, K. and Head, J .: North polar region of Mars: Topography of circumpolar deposits from Mars Orbiter Laser Altimeter (MOLA) data and evidence for asymmetric retreat of the polar cap . In: Journal of Geophysical Research . tape 105 , 2000, pp. 22.455-22.486 .
  37. ^ Head, J. and Pratt, S .: Extensive Hesperian-aged south polar ice cap on Mars: Evidence for massive melting and retreat, and lateral flow and ponding of meltwater . In: Journal of Geophysical Research . tape 106 , 2001, pp. 12.275-299 .
  38. ↑ Tanaka, KL et al.: Geologic map of Mars . US Geological Survey Scientific Investigations Map 3292, 2014, doi : 10.3133 / sim3292 .
  39. ↑ Hartmann, W. and Neukum, G .: Cratering chronology and the evolution of Mars . In: Space Science Revue . tape 95 , 2001, p. 167-196 .
  40. ↑ P. Thomas, among others: Polar deposits of Mars . In: HH Kieffer, et al. (Ed.): Mars . Univ. of Arizona Press, Tucson 1992, pp. 767-795 .