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#REDIRECT [[Geysers on Mars]]
{{Use dmy dates|date=November 2012}}
[[File:Geysers on Mars.jpg|thumb|200px|Artist concept showing sand-laden jets erupting from Martian geysers. (Published by NASA; artist: [[Ron Miller (artist and author)|Ron Miller]].)]]
[[Image:Moc2 166b msss.gif|thumb|200px|Dark dune spots]]


{{R from move}}
'''Martian geysers''' (or '''{{chem|CO|2}} jets''') are putative sites of small gas and dust eruptions that occur in the [[Planum Australe|south polar region]] of [[Mars]] during the spring thaw. "Dark dune spots" and "spiders" – or araneiforms <ref name=Portyankina2014 >{{cite journal|title=Araneiform|journal=Encyclopedia of Planetary Landforms |page=1 |date=2014|first=Ganna|last=Portyankina|doi= 10.1007/978-1-4614-9213-9_540-1|url=https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_540-1|isbn=978-1-4614-9213-9 }}</ref> – are the two most visible types of features ascribed to these eruptions.

They are unlike any terrestrial geological phenomenon. The reflectance ([[albedo]]), shapes and unusual spider appearance of these features have stimulated a variety of hypotheses about their origin, ranging from differences in frosting reflectance, to explanations involving biological processes. However, all current geophysical models assume some sort of jet or [[geyser]]-like activity on Mars.<ref name=Piqueux2003 /><ref name=Manrubia /><ref name=Kieffer2000 >{{Cite journal|first=H. H. | last=Kieffer |title=Mars Polar Science 2000 - Annual Punctuated CO<sub>2</sub> Slab-ice and Jets on Mars.| date=2000| url=http://www.lpi.usra.edu/meetings/polar2000/pdf/4095.pdf| format=PDF| accessdate=6 September 2009 }}</ref><ref name=Kieffer2003 >{{Cite journal| first=Hugh H. |last=Kieffer |title=Third Mars Polar Science Conference (2003)- Behavior of Solid CO | date=2003 |url=http://www.lpi.usra.edu/meetings/polar2003/pdf/8083.pdf| accessdate=6 September 2009 }}</ref><ref name=Portyankina >{{Cite journal|title=Fourth Mars Polar Science Conference - Simulations of Geyser-Type Eruptions in Cryptic Region of Martian South| editor-first=G. |editor-last=Portyankina| date=2006| url=http://www.lpi.usra.edu/meetings/polar2006/pdf/8040.pdf| format=PDF| accessdate=11 August 2009 }}</ref><ref name=clathrate >{{Cite journal |title=Lunar and Planetary Science XXXV (2004) - Stratigraphy of Special Layers – Transient Ones on Permeable Ones: Examples| editor=Sz. Bérczi| display-editors=etal| date=2004| url=http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1317.pdf| format=PDF| accessdate=12 August 2009}}</ref><ref name=Hugh2006 /><ref name=2006-100 >{{cite news | title=NASA Findings Suggest Jets Bursting From Martian Ice Cap | date=16 August 2006 | publisher=NASA | url =http://www.jpl.nasa.gov/news/news.cfm?release=2006-100 | work=Jet Propulsion Laboratory | accessdate =11 August 2009 }}</ref><ref>{{cite journal | doi = 10.1016/j.icarus.2009.07.021 | title = HiRISE observations of gas sublimation-driven activity in Mars’ southern polar regions: I. Erosion of the surface | journal=Icarus | date = 2010 | authors = C.J. Hansen, N. Thomas, G. Portyankina, A. McEwen, T. Becker, S. Byrne, K. Herkenhoff, H. Kieffer, M. Mellon | volume = 205 | pages = 283–295| id = | url = http://www.lpl.arizona.edu/~shane/publications/hansen_etal_icarus_2010.pdf | accessdate =26 July 2010 | bibcode = 2010Icar..205..283H }}</ref> Their characteristics, and the process of their formation, are still a matter of debate.

These features are unique to the south polar region of Mars in an area informally called the 'cryptic region', at latitudes 60° to 80° south and longitudes 150°W to 310°W;<ref>Titus T. N. et al. (2003) Third Mars Polar Science Conference, Abstract #8081.</ref><ref>Kieffer, H. H. (2001) Second International Conf. On Mars Polar Sci. and Exploration, no. 1057.</ref><ref>Kieffer, H. H. (2003), Sixth International Conference on Mars, no. 3158.</ref> this 1 meter deep [[carbon dioxide]] (CO<sub>2</sub>) ice transition area—between the scarps of the thick polar ice layer and the permafrost—is where clusters of the apparent geyser systems are located.

The seasonal frosting and defrosting of carbon dioxide ice results in the appearance of a number of features, such dark dune spots with spider-like [[rille]]s or channels below the ice,<ref name=Manrubia>{{cite journal |title=Comparative Analysis of Geological Features and Seasonal Processes in Inca City and PittyUSA Patera Regions on Mars |journal=European Space Agency Publications (ESA SP) |date=2004 |first=S. C. |last=Manrubia |author2=O. Prieto Ballesteros |author3=C. González Kessler |author4=D. Fernández Remolar |author5=C. Córdoba-Jabonero |author6=F. Selsis |author7=S. Bérczi |author8=T. Gánti |author9=A. Horváth |author10=A. Sik |author11=E. Szathmáry |page=545 |url=http://www.colbud.hu/esa/publications/29ProcCAB-3ESASP-545pp77-80.pdf |deadurl=yes |archiveurl=https://web.archive.org/web/20110721105008/http://www.colbud.hu/esa/publications/29ProcCAB-3ESASP-545pp77-80.pdf |archivedate=21 July 2011 |df=dmy-all }}</ref> where spider-like radial channels are carved between the ground and the carbon dioxide ice, giving it an appearance of spider webs, then, pressure accumulating in their interior ejects gas and dark basaltic sand or dust, which is deposited on the ice surface and thus, forming dark dune spots.<ref name=Piqueux2003 /><ref name=Manrubia /><ref name="Kieffer2000"/><ref name="Kieffer2003"/><ref name="Portyankina"/><ref name="clathrate"/><ref name=Hugh2006 >{{cite journal|title=CO<sub>2</sub> jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap|journal=Nature|date=30 May 2006|first=Hugh H.|last=Kieffer|author2=Philip R. Christensen |author3=Timothy N. Titus |volume=442|issue=7104|pages=793–6 |doi=10.1038/nature04945|url=http://www.nature.com/nature/journal/v442/n7104/abs/nature04945.html|pmid=16915284 |bibcode = 2006Natur.442..793K }}</ref> This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology – especially for Mars.<ref name=Ness /> However, it would seem that multiple years would be required to carve the larger spider-like channels.<ref name=Piqueux2003 /> There is no direct data on these features other than images taken in the [[visible spectrum|visible]] and infrared [[Electromagnetic spectrum|spectra]].

== History ==
[[Image:Mars Global Surveyor 1.jpg|thumb|200px|Close up of dark dune spots obtained by the [[Mars Global Surveyor]] and discovered in 2000 by Greg Orme.]]
The geological features informally called '''dark dune spots''' and '''spiders''' were separately discovered on images acquired by the MOC camera on board the Mars Global Surveyor during 1998–1999.<ref name=Albee >{{cite journal|title=Mars Global Surveyor Mission: Overview and Status |journal=Science |date=1998 |first=A. L. |last=Albee |author2=F. D. Palluconi |author3=R. E. Arvidson |volume=279 |issue=5357 |pages=1671–5 |doi=10.1126/science.279.5357.1671 |url=http://www.sciencemag.org/cgi/content/full/279/5357/1671 |pmid= 9497277|bibcode = 1998Sci...279.1671A }}</ref><ref name=Malin1998 >{{cite journal|title=Early Views of the Martian Surface from the Mars Orbiter Camera of Mars Global Surveyor |journal=Science|date=13 March 1998|first=Michael C.|last=Malin|display-authors=etal|volume=279|issue=5357|pages=1681–5|doi = 10.1126/science.279.5357.1681 |url=http://www.sciencemag.org/cgi/content/full/279/5357/1681 |accessdate=3 September 2009|pmid=9497280|bibcode = 1998Sci...279.1681M }}</ref> At first it was generally thought they were unrelated features because of their appearance, so from 1998 through 2000 they were reported separately on different research publications (<ref name=Malin1998 /><ref name=basaltic >{{cite journal|title=Surface Properties of Mars’ Polar Layered Deposits and Polar Landing Sites.|journal=NASA|date=1999|first=A.|last=Vasavada |author2=K. E. Herkenhoff |url= http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6086.pdf |accessdate=21 August 2008 }}</ref> and<ref name=Channel >{{cite journal|title='Spiders' Channel Mars Polar Ice Cap.
|journal=Science|date=15 September 2000
|first=R. A.|last=Lovett|volume=289|issue=5486|pages=1853a–4a|pmid=17839924
|doi=10.1126/science.289.5486.1853a }}</ref> -respectively). "Jet" or "geyser" models were proposed and refined from 2000 onwards.<ref name="Kieffer2000"/><ref name="Kieffer2003"/>

The name 'spiders' was coined by [[Malin Space Science Systems]] personnel, the developers of the camera. One of the first and most interesting spider photos was found by Greg Orme in October 2000.<ref name=Orme>{{cite journal|title=Marsbugs |journal=The Electronic Astrobiology Newsletter |date=9 June 2003 |first=Greg M. |last=Orme |author2=Peter K. Ness |volume=10 |issue=23 |page=5 |url=http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |accessdate=6 September 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090327135109/http://www.lyon.edu/projects/marsbugs/2003/20030609.pdf |archivedate=27 March 2009 }}</ref> The unusual shape and appearance of these 'spider webs' and spots caused a lot of speculation about their origin. The first years' surveillance showed that during the following Martian years, 70% of the spots appear at exactly the same place, and a preliminary statistical study obtained between September 1999 and March 2005, indicated that dark dune spots and spiders are related phenomena as functions of the cycle of carbon dioxide (CO<sub>2</sub>) condensing as “[[dry ice]]” and sublimating.<ref name=LPS2006 /><br />

It was also initially suggested that the dark spots were simply warm patches of bare ground, but thermal imaging during 2006 revealed that these structures were as cold as the ice that covers the area,<ref name=2006-100 /><ref name=LPS2006 /> indicating they were a thin layer of dark material lying on top of the ice and kept chilled by it.<ref name=2006-100 /> However, soon after their first detection, they were discovered to be negative topographical features – i.e. radial troughs or channels of what today are thought to be geyser-like vent systems.<ref name=Piqueux2003 /><ref name=Manrubia /><ref name="Kieffer2000"/><ref name="Kieffer2003"/><ref name="Portyankina"/><ref name="clathrate"/><ref name=Hugh2006 />

==Morphology==
[[Image:Hirise dark dune spots.jpg|thumb|200px|Dark dune spots. High resolution color image by the [[HiRISE]] camera]]
[[Image:Dark dune spots - spider Mars.jpg|thumb|200px|'Spider' features shown in relationship to dark dune spots.]]
[[File:Darkdune spots emanating from Martian Spiders.jpg|thumb|200px|Dark sediment spots apparently emanating from 'spider' formations.]]
The geysers' two most prominent features (dark dune spots and spider channels) appear at the beginning of the Martian spring on dune fields covered with carbon dioxide (CO<sub>2</sub> or 'dry ice'), mainly at the ridges and slopes of the dunes; by the beginning of winter, they disappear. Dark spots' shape is generally round, on the slopes it is usually elongated, sometimes with streams—possibly of water—that accumulate in pools at the bottom of the dunes.<ref>{{cite journal|title=Annual change of Martian DDS-seepages|journal=Lunar and Planetary Science XXXVI |date=2005|first=A.|last=Horváth|author2=Kereszturi, Á. |author3=Bérczi, Sz. |display-authors=etal|url=http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1128.pdf|format=PDF|accessdate=24 November 2008 }}</ref><ref name=Andras >{{cite journal|title=Probable Evidences of Recent Biological Activity on Mars: Appearance and Growing of Dark Dune Spots in the South Polar Region|journal=32nd Annual Lunar and Planetary Science Conference, Houston, Texas, abstract no.1543|date=12–16 March 2001|first=Tibor|last=Gánti |author2=András Horváth |author3=Szaniszló Bérczi |author4=Albert Gesztesi |author5=Eörs Szathmáry|url=http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1543.pdf|format=PDF|accessdate=20 November 2008}}</ref> Dark dune spots are typically 15 to 46 metres (50 to 150 feet) wide and spaced several hundred feet apart.<ref name=2006-100 /> The size of spots varies, and some are as small as 20 m across,<ref name=Malin1998 /><ref name=Planetary >{{Cite journal |title=Lunar and Planetary Science XXXIII - Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation| editors=A. Horváth, T. Gánti, Sz. Bérczi, A. Gesztesi, E. Szathmáry| date=2002| url=http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1108.pdf| format=PDF| accessdate=24 November 2008 }}</ref>—however, the smaller size seen is limited by imaging resolution—and can grow and coalesce into formations several kilometres wide.

Spider features, when viewed individually, form a round lobed structure reminiscent of a spider web radiating outward in lobes from a central point.<ref name=AIG>{{cite web|url=http://www.aig.asn.au/pdf/AIGnews_Aug06.pdf |title=Spiders on Earth and Mars |page=21 |accessdate=11 August 2009 |date=August 2006 |format=PDF |publisher=Australian Institute of Geoscientists |deadurl=yes |archiveurl=https://web.archive.org/web/20091013121837/http://www.aig.asn.au/pdf/AIGnews_Aug06.pdf |archivedate=13 October 2009 |df=dmy }}</ref> Its radial patterns represent shallow channels or ducts in the ice formed by the flow of the sublimation gas toward the vents.<ref name=Manrubia /><ref name=Kieffer2000 /> The entire spider channel network is typically 160–300 m across, although there are large variations.<ref name=Piqueux2003 />

Each geyser's characteristic form appears to depend on a combination of such factors as local fluid or gas composition and pressure, ice thickness, underlying gravel type, local climate and meteorological conditions.<ref name=Ness /> The geysers' boundary does not seem to correlate with any other properties of the surface such as elevation, geological structure, slope, chemical composition or thermal properties.<ref name=Portyankina /> The geyser-like system produce low-albedo spots, fans and blotches, with small radial spider-like channel networks most often associated with their location.<ref name=Piqueux2003 >{{cite journal|title=Sublimation of Mars’s southern seasonal CO<sub>2</sub> ice cap formation of spiders|journal=[[Journal of Geophysical Research]]|date=8 August 2003| first=Sylvain|last=Piqueux |author2=Shane Byrne |author3=Mark I. Richardson |volume=180|issue= E8|pages=5084|doi= 10.1029/2002JE002007|url=http://www.lpl.arizona.edu/~shane/publications/piqueux_etal_jgr_2003.pdf |format=PDF| accessdate=5 September 2009|bibcode=2003JGRE..108.5084P}}</ref><ref name=Ness >{{cite journal|title=Spider-Ravine Models and Plant-like Features on Mars – Possible Geophysical and Biogeophysical Modes of Origin|journal=[[Journal of the British Interplanetary Society]] (JBIS) |date=2002 |first=Peter K.|last=Ness |author2=Greg M. Orme |volume=55|pages= 85–108|url=http://spsr.utsi.edu/articles/ness.pdf |accessdate=3 September 2009 }}</ref><ref name=LPS2006 >{{Cite journal |title=Lunar and Planetary Science XXXVII (2006) - Observation of the Martian Cryptic Region from Mars Orbiter Camera.| editor1=J. J. Jian|editor2=W. H. Ip | date=2006| url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1313.pdf| format=PDF| accessdate=4 September 2009| }}</ref> At first, the spots seem to be grey, but later their centres darken because they gradually get covered with dark ejecta,<ref name=Channel /> thought to be mainly [[basalt]]ic sand.<ref name=basaltic /> It should be noted that not all dark spots observed in early spring are associated with spider landforms, however, a preponderance of dark spots and streaks on the cryptic terrain are associated with the appearance of spiders later in the season.<ref name=Piqueux2003 />

Time-lapsed imagery performed by NASA confirms the apparent ejection of dark material following the radial growth of spider channels in the ice.<ref name=2006-100 /> Time-lapsed imaging of a single area of interest also shows that small dark spots generally indicate the position of spider features not yet visible; it also shows that spots expand significantly, including dark fans emanating from some of the spots, which increase in prominence and develop clear directionality indicative of wind action.<ref name=Piqueux2003 />

Some branching ravines modify, some destroy and others create crust in a dynamic near-surface process that extensively reworks the terrain creating and destroying surface layers. Thus, Mars seems to have a dynamic process of recycling of its near surface crust of carbon dioxide. Growth process is rapid, happening in the space of a few days, weeks or months, a growth rate rather unusual in geology – especially for Mars.<ref name=Ness /> A number of [[Geophysics|geophysical]] models have been investigated to explain the various colors and shapes' development of these geysers on the southern polar ice cap of Mars.

<gallery class="center" widths="190px" heights="180px" >
ESP 047609 0985spiders.jpg|Wide view of plumes, as seen by HiRISE under HiWish program Many of the plumes show spiders when enlarged.
47609 0985plumes.jpg|Plumes, as seen by HiRISE under HiWish program Arrow shows a double plume. This may have been because of shifting winds.

47609 0985spiderlong.jpg|Long plume, as seen by HiRISE under HiWish program
47609 0985spiderlongclose.jpg|Spiders, as seen by HiRISE under HiWish program

47609 0985spiders.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spidersclose.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spidersdark.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spiderswide.jpg|Wide view of plumes and spiders, as seen by HiRISE under HiWish program

47609 0985spidersdarkclose.jpg|Plumes and spiders, as seen by HiRISE under HiWish program

</gallery>

==Geyser mechanism models==
The strength of the eruptions is estimated to range from simple upsurges to high-pressure eruptions at speeds of {{convert|160|km/h}} or more,<ref name=Kieffer2000 /><ref name=Edgett>{{cite journal|title=Low-albedo surfaces and eolian sediment: Mars Orbiter Camera |journal=Journal of Geophysical Research |date=13 June 2002 |first=Kenneth S. |last=Edgett |volume=107 |issue=E6 |pages=5038 |url=http://www.msss.com/biographies/edgett/reprints/2001JE001587.pdf |format=PDF |accessdate=3 September 2009 |doi=10.1029/2001JE001587 |bibcode=2002JGRE..107.5038E |deadurl=yes |archiveurl=https://web.archive.org/web/20040505233200/http://www.msss.com/biographies/edgett/reprints/2001JE001587.pdf |archivedate=5 May 2004 }}</ref> carrying dark basaltic sand and dust plumes high aloft.<ref name=2006-100 /> The current proposed models dealing with the possible forces powering the geyser-like system are discussed next.

===Atmospheric pressure===
The surface atmospheric pressure on Mars varies annually around: 6.7–8.8 mbar and 7.5–9.7 mbar; daily around 6.4–6.8 mbar. Because of the pressure changes subsurface gases expand and contract periodically, causing a downward gas flow during increase of and expulsion during decrease of atmospheric pressure.<ref name=clathrate /> This cycle was first quantified with measurements of the surface pressure, which varies annually with amplitude of 25%.<ref name=Piqueux2003 />

;Clathrate hydrate model
This model proposes downward gas flow during increase of and upward flow during decrease of atmospheric pressure. In the defrosting process, ices (clathrate) may partly migrate into the soil and partly may evaporate.<ref name=clathrate /><ref name=Ness /> These locations can be in connection with the formation of dark dune spots and the arms of spiders as gas travel paths.<ref name=clathrate />

===Dry venting===
[[File:PIA11858 Starburst Spider.jpg|thumb|200px|A large 'spider' feature apparently emanating sediment to give rise to dark dune spots. Image size: {{convert|1|km|mi|abbr=on}} across.]]
[[File:Martian CO2 gas venting.jpg|thumb|200px|According to Sylvain Piqueux, sun light causes sublimation from the bottom, leading to a buildup of pressurized CO<sub>2</sub> gas which eventually bursts out, entraining dust and leading to dark fan-shaped deposits with clear directionality indicative of wind action.<ref name='Wind direction'/>]]
Some teams propose dry venting of carbon dioxide (CO<sub>2</sub>) gas and sand, occurring between the ice and the underlying bedrock. It is known that a CO<sub>2</sub> ice slab is virtually transparent to solar radiation where 72% of solar energy incident at 60 degrees off vertical will reach the bottom of a 1&nbsp;m thick layer.<ref name=Kieffer2000 /><ref>Mangold, N. 2011. Ice sublimation as a geomorphic process: A planetary perspective. Geomorphology. 126:1–17.</ref> In addition, separate teams from Taiwan and France measured the ice thickness in several target areas, and discovered that the greatest thickness of the CO<sub>2</sub> frost layer in the geysers' area is about 0.76–0.78&nbsp;m, supporting the geophysical model of dry venting powered by sunlight.<ref name=Hugh2006 /><ref>{{cite journal|title=Seasonal patterns of condensation and sublimation cycles in the cryptic and non-cryptic regions of the South Pole |journal=Advances in Space Research|date=5 January 2009 |first=Jeng-Jong|last=Jian |first2=Wing-Huen|last2=Ip |volume=43|issue=1|pages=138–142 |doi= 10.1016/j.asr.2008.05.002|url=https://www.sciencedirect.com/science/article/pii/S0273117708002603| bibcode=2009AdSpR..43..138J}}</ref><ref>{{cite journal | title = Dark spots and cold jets in the polar regions of Mars: New clues from a thermal model of surface CO2 ice | journal = Icarus | date = May 2011 | first = C. | last = Pilorget | volume = 213 | issue = 1| page = 131 | id = | url = http://www.sciencedirect.com/science/article/pii/S001910351100042X| doi=10.1016/j.icarus.2011.01.031 | bibcode=2011Icar..213..131P}}</ref> As the southern spring CO<sub>2</sub> ice receives enough solar energy, it starts [[Sublimation (chemistry)|sublimation]] of the CO<sub>2</sub> ice from the bottom.<ref name=Piqueux2003 /> This vapor accumulates under the slab rapidly increasing pressure and erupting.<ref name=Portyankina /><ref name=2006-100 /><ref name=Ness /><ref>{{cite journal|title=Active Polar Gullies on Mars and the Role of Carbon Dioxide|journal=Astrobiology|date=August 2002|first=Nick|last=Hoffman|volume=2|issue=3|pages=313–323|doi= 10.1089/153110702762027899|url=http://www.liebertonline.com/doi/abs/10.1089/153110702762027899|accessdate=7 September 2009|pmid=12530241 |bibcode = 2002AsBio...2..313H }}</ref><ref name=cold>{{cite journal |title=Bright Fans in Mars Cryptic Region Caused by Adiabatic Cooling of CO<sub>2</sub> Gas Jets. |journal=[[Eos (journal)|Eos, Transactions, American Geophysical Union]] |date=2007 |first=T. N. |last=Titus |author2=Kieffer, H H |author3=Langevin, Y |author4=Murchie, S |author5=Seelos, F |author6=Vincendon, M |author7=TEAM, C. |volume=88 |issue=52 (Fall Meet. Suppl.) |url=https://www.researchgate.net/publication/253157564_Bright_Fans_in_Mars_Cryptic_Region_Caused_by_Adiabatic_Cooling_of_CO2_Gas_Jets}}</ref> High-pressure gas flows through at speeds of {{convert|160|km/h}} or more;<ref name=Kieffer2000 /><ref name=Edgett /> under the slab, the gas erodes ground as it rushes toward the vents, snatching up loose particles of sand and carving the spidery network of grooves.<ref name=Hugh2006 /> The dark material falls back to the surface and may be taken up slope by wind, creating dark wind streak patterns on the ice cap.<ref name=LPS2006 /><ref name="Edgett"/> This model is consistent with past observations.<ref name=Edgett /><ref name=Titus2003 >{{Cite journal| first=T. N. | last=Titus| author2=H. H. Kieffer |author3=J. J. Plaut |author4=P. R. Christensen |author5=A. B. Ivanov |author6=the THEMIS Science Team. |title=Third Mars Polar Science Conference (2003) - South Polar Cryptic Region Revisited: THEMIS Observations.| date=2003| url=http://www.lpi.usra.edu/meetings/polar2003/pdf/8081.pdf| format=PDF| accessdate=4 September 2009 }}</ref> The location, size and direction of these fans
are useful to quantifying seasonal winds and sublimation activity.<ref name='Wind direction'>[https://arxiv.org/pdf/1803.10341.pdf Planet Four: Probing Seasonal Windson Mars by Mapping the Southern Polar CO2 Jet Deposits]. (PDF) K.-Michael Aye, Megan E. Schwamb, Ganna Portyankina, Candice J. Hansen, Adam McMaster, Grant R.M. Miller, Brian Carstensen, Christopher Snyder, Michael Parrish, Stuart Lynn, Chuhong Mai, David Miller, Robert J. Simpson, Arfon M. Smith. ''arXive''. 27 March 2018</ref>

It is clear that sublimation of the base of the seasonal ice cap is more than capable of generating a substantial overpressure,<ref name=Piqueux2003 /> which is four orders of magnitude higher than the ice overburden pressure and five orders of magnitude higher than atmospheric pressure as discussed above.<ref name=Piqueux2003 />

The observation that a few dark spots form before sunrise, with significant spot formation occurring immediately following sunrise, supports the notion that the system is powered by solar energy.<ref name=Morning>{{cite journal |title=Infrared and Visible Observations of South Polar Spots and Fans |journal=[[Eos (journal)|Eos, Transactions, American Geophysical Union]] |first=Christensen, P R |last=Kieffer, H H, Titus, T N |volume=86 |issue=52 (Fall Meet. Suppl.) |url=http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm05&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm05%2Ffm05&maxhits=200&="P23C-04" |accessdate=8 September 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090315074210/http://www.agu.org/cgi-bin/SFgate/SFgate |archivedate=15 March 2009 |df=dmy }}</ref> Eventually the ice is completely removed and the dark granular material is back on the surface;<ref name=Morning /> the cycle repeats many times.<ref name=LPS2006 /><ref name=Malin2000 /><ref name=Jeng >{{cite journal|title=Spatial distributions and seasonal variations of features related to a venting process at high southern latitudes observed by the MOC camera |journal=Planetary and Space Science|authors=Jeng-Jong Jian; Wing-Huen Ipa; Shin-Reu Sheu|volume=57|issue=7|pages=797–803 |doi= 10.1016/j.pss.2009.02.014|url=https://www.sciencedirect.com/science/article/pii/S0032063309000555|date=2009|bibcode=2009P&SS...57..797J}}</ref>

Laboratory experiments performed in 2016 were able to trigger dust eruptions from a layer of dust inside a {{chem|CO|2}} ice slab under Martian atmospheric conditions, lending support to the {{chem|CO|2}} jet and fan production model.<ref name='Wind direction'/>

=== Water-driven erosion ===
Data obtained by the [[Mars Express]] satellite, made it possible in 2004 to confirm that the southern polar cap has an average of {{convert|3|km|mi}} thick slab of CO<sub>2</sub> ice<ref name=NASAwater >{{cite news | title=Mars' South Pole Ice Deep and Wide | date=15 March 2007 | publisher=NASA | url =http://jpl.nasa.gov/news/news.cfm?release=2007-030 | work=Jet Propulsion Laboratory | accessdate =11 September 2009 }}</ref> with varying contents of frozen water, depending on its latitude: the bright polar cap itself, is a mixture of 85% CO<sub>2</sub> ice and 15% water ice.<ref name=ESAwater >{{cite news | title=Water at Martian south pole | date=17 March 2004 | publisher=European Space Agency (ESA) | url =http://www.esa.int/SPECIALS/Mars_Express/SEMYKEX5WRD_0.html | accessdate =11 September 2009 }}</ref> The second part comprises steep slopes known as 'scarps', made almost entirely of water ice, that fall away from the polar cap to the surrounding plains.<ref name=ESAwater /> This transition area between the scarps and the permafrost is the 'cryptic region', where clusters of geysers are located.

This model explores the possibility of active water-driven erosive structures, where soil and water derived from the shallow sub-surface layer is expelled up by CO<sub>2</sub> gas through fissures eroding joints to create spider-like radiating tributaries capped with mud-like material and/or ice.<ref name=Ness /><ref name=Spiders>{{cite journal|title=Spiders: Water-Driven Erosive Structures in the Southern Hemisphere of Mars|journal=Astrobiology|date=August 2006|first=Olga|last=Prieto-Ballesteros |volume=6|issue=4| pages=651–667|url=http://www.liebertonline.com/doi/pdfplus/10.1089/ast.2006.6.651 |doi=10.1089/ast.2006.6.651 |pmid=16916289 |last2=Fernández-Remolar|first2=DC|last3=Rodríguez-Manfredi|first3=JA|last4=Selsis|first4=F|last5=Manrubia|first5=SC |bibcode=2006AsBio...6..651P}}</ref><ref>{{cite journal|title=Martian Spiders as feasible water-driven erosive structures |journal=Centro de Astrobiología-INTA-CSIC |date=2005 |first=Olga |last=Prieto-Ballesteros |url=http://nai.nasa.gov/nai2005/abstracts/653%20-%20NAI2005-spiders.doc.pdf |accessdate=11 August 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090706072920/http://nai.nasa.gov/nai2005/abstracts/653%20-%20NAI2005-spiders.doc.pdf |archivedate=6 July 2009 |df=dmy }}</ref><ref>{{cite journal|title=Analysis of Dark Albedo Features on a Southern Polar Dune Field of Mars|journal=Astrobiology|date=February 2009|first=András|last=Horváth |author2=Ákos Kereszturi |author3=Szaniszló Bérczi |author4=András Sik |author5=Tamás Pócs |author6=Tibor Gánti |author7=Eörs Szathmáry |pmid=19203240|volume=9|issue=1|pages=90–103|doi= 10.1089/ast.2007.0212|url=http://www.liebertonline.com/doi/abs/10.1089/ast.2007.0212|accessdate=7 September 2009|bibcode=2009AsBio...9...90H}}</ref>

===Geothermal===
A European team proposes that the features could be a sign that non-solar energy source is responsible of the jets, subsurface heat wave for instance.<ref name=Ness /><ref>{{cite journal|title=Slab ice in the seasonal south polar cap of Mars|journal=European Planetary Science Congress (EPSC) – Abstracts|date=2009|authors=F. Schmidt, S. Dout´e, B. Schmitt , Y. Langevin , J.P. Bibring and the OMEGA Team|volume=4|issue=EPSC2009|pages=521–522|url=http://meetingorganizer.copernicus.org/EPSC2009/EPSC2009-521-2.pdf|format=PDF|accessdate=2 September 2009 }}</ref> This model is difficult to reconcile with the evidence collected in the form of thermal emission (infrared) imaging, which shows that the fans, spots and blotches are produced by expulsion of cold fluids or cold gases.<ref name=cold /><ref>{{cite journal|title=Viscous liquid film flow on dune slopes of Mars |journal=Icarus|date=5 January 2010 |first=Diedrich |last=Möhlmann |author2=Akos Kereszturi |doi= 10.1016/j.icarus.2010.01.002|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4Y6454S-1&_user=10&_coverDate=01%2F18%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1219231733&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=0d657806ae41ad8ed4683c55be7ab763|accessdate=23 February 2010 |volume=207|issue=2|pages=654|bibcode=2010Icar..207..654M}}</ref>

===Carbon dioxide and water cycling===
[[Image:Defrosting Sand.jpg|thumb|200px|Dark dune spots]]
[[Michael C. Malin]], a planetary scientist and designer of the cameras used by the Mars Global Surveyor that obtained the earliest images of the CO<sub>2</sub> geyser phenomenon, is studying the images acquired of specific areas and he tracks their changes over a period of a few years. In 2000, he modelled the fans and spots' dynamics as a complex process of carbon dioxide (CO<sub>2</sub>) and water sublimation and re-precipitation. The typical pattern of defrosting proceeds from the initiation of small, dark spots typically located at the margins of dunes; these spots individually enlarge and eventually all coalesce.<ref name=Malin2000 >{{Cite book| first=Michael C.| last=Malin |author2=K. S. Edgett| contribution=Frosting and Defrosting of Martian Polar Dunes| title=Lunar and Planetary Science XXXI| publisher=Malin Space Science Systems| date=2000| url=http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1056.pdf| format=PDF| accessdate=3 September 2009 }}</ref> The pattern the enlargement follows is distinct and characteristic: a dark nuclear spot enlarges slowly, often with a bright outer zone or 'halo'. As these are progressive, centripetal phenomena, each location of the light zone is overtaken by an expanding dark zone. Although initially developed along dune margins, spot formation quickly spreads onto and between dunes. As spring progresses, fan-shaped tails ('spiders') develop from the central spot. Defrosting occurs as the low albedo polar sand heats beneath an optically thin layer of frost, causing the frost to evaporate. This is the dark nucleus of the spots seen on dunes. As the vapor moves laterally, it encounters cold air and precipitates, forming the bright halo. This precipitated frost is again vaporized as the uncovered zone of sand expands; the cycle repeats many times.<ref name=LPS2006 /><ref name=Malin2000 /><ref name=Jeng />

==European Space Agency==
[[Image:Mars Global Surveyor Mars Orbiter Image E0701717.jpg|thumb|right|200px|Dark dune spots.]]
While the [[European Space Agency]] (ESA) has not yet formulated a theory or model, they have stated that the process of frost sublimation is not compatible with a few important features observed in the images, and that the location and shape of the spots is at odds with a physical explanation, specifically, because the channels appear to radiate downhill as much as they radiate uphill, defying gravity.<ref>{{cite news | title=Martian spots warrant a close look | date=13 March 2002 | publisher=European Space Agency | url =http://www.esa.int/esaCP/ASE4YZ9KOYC_FeatureWeek_1.html#subhead2 | accessdate =18 November 2008 }}</ref><ref>{{cite web|url=http://www.esa.int/esaCP/ASE4YZ9KOYC_FeatureWeek_0.html |title=Martian spots warrant a close look |accessdate=8 September 2009 |date=13 March 2002 |publisher=European Space Agency }}</ref>

==Hypothetical biological origin==
{{Section-Needs-Attention|This research is from a decade ago, needs update}}
[[Image:DDS MSO.jpg|thumb|right|200px|DDS-MSO hypothesis.]]
A team of Hungarian scientists propose that the dark dune spots and channels may be colonies of [[photosynthesis|photosynthetic]] Martian microorganisms, which over-winter beneath the ice cap, and as the [[sunlight]] returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesise and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. As this ice layer thins, the microorganisms show through grey. When it has completely melted, they rapidly desiccate and turn black surrounded by a grey aureole.<ref name=Andras /><ref>{{Cite book| author=Pócs, T. |author2=A. Horváth |author3=T. Gánti |author4=Sz. Bérczi |author5=E. Szathmáry |title=ESA SP-545 - Possible crypto-biotic-crust on Mars?| publisher=European Space Agency| date=2003| url=http://www.colbud.hu/esa/publications/28CBC8ESASP-545pp265-266.pdf| format=PDF| accessdate=24 November 2008 }}</ref><ref>{{cite journal|title=Dark Dune Spots: Possible Biomarkers on Mars?|journal=Origins of Life and Evolution of Biospheres|date=31 October 2003 |first=Tibor|last=Gánti|author2=András Horváth |author3=Szaniszló Bérczi |author4=Albert Gesztesi |author5=Eörs Szathmáry |volume= 33|issue=s 4–5|pages=515–557|doi=10.1023/A:1025705828948|url=http://www.springerlink.com/content/ut8r78131173254n/|accessdate=18 November 2008 }}</ref><ref>{{Cite journal|author=Pócs, T. |author2=A. Horváth |author3=T. Gánti |author4=S. Bérczi |author5=E. Szathmáry |title=38th Vernadsky-Brown Microsymposium on Comparative Planetology - Are the dark dune spots remnants of the crypto-biotic-crust of Mars? |place=Moscow, Russia |date=27–29 October 2003 |url=http://www.colbud.hu/esa/publications/26MosCBC10color.pdf |format=[[PDF]] |accessdate=7 September 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20110721104952/http://www.colbud.hu/esa/publications/26MosCBC10color.pdf |archivedate=21 July 2011 |df=dmy }}</ref> The Hungarian scientists think that even a complex sublimation process is insufficient to explain the formation and evolution of the dark dune spots in space and time.<ref name=Planetary /><ref>{{cite web|url=http://www.monochrom.at/dark-dune-spots/ |title=Dark Dune Spots – Could it be that it’s alive? |accessdate=4 September 2009 |author=András Sik |author2=Ákos Kereszturi |publisher=Monochrom }} (Audio interview, MP3 6 min.)</ref> Since their discovery, fiction writer [[Arthur C. Clarke]] promoted these formations as deserving of study from an [[astrobiology|astrobiological]] perspective.<ref name=Orme />

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, the structures might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from [[Ultraviolet|UV]] solar radiation.<ref name=Manrubia /> British and German teams also consider the possibility that [[organic matter]], [[microbe]]s, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a [[Geothermal gradient|geothermal]] energy source.<ref name=Ness /><ref>{{cite journal|title=Temporary liquid water in upper snow/ice sub-surfaces on Mars? |journal=Icarus|date=13 November 2009 |last1=Möhlmann |first=Diedrich T.F. |doi=10.1016/j.icarus.2009.11.013 |url=https://www.sciencedirect.com/science/article/pii/S0019103509004539|volume=207 |pages=140 |bibcode=2010Icar..207..140M}}</ref> However, they also remark that the majority of geological structures may be accounted for without invoking any organic "life on Mars" hypothesis.<ref name=Ness /> (See also: [[Life on Mars (planet)|Life on Mars]].)

==Lander mission==
There is no direct data on these features other than images taken in the [[visible spectrum|visible]] and infrared spectra, and development of the [[Mars Geyser Hopper]] [[Lander (spacecraft)|lander]] is under consideration to study the geyser-like systems.<ref>{{cite web | url = https://ntrs.nasa.gov/search.jsp?R=20120004036 | title = Design Study for a Mars Geyser Hopper | accessdate = 1 July 2012 | last1 = Landis | first1 = Geoffrey A. | last2 = Oleson | first2 = Steven J. | last3 = McGuire | first3 = Melissa | date = 9 January 2012 | format = PDF | work = Glenn Research Center | publisher = NASA}}</ref><ref name='Geyser Hopper'>{{citation | last1 = Landis | first1 = Geoffrey A. | last2 = Oleson | first2 = Steven J. | last3 = McGuire | first3 = Melissa | contribution = Design Study for a Mars Geyser Hopper | title = 50th AIAA Aerospace Sciences Conference | publisher = Glenn Research Center, NASA | date = 9 January 2012 | id = AIAA-2012-0631| url = https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120004036_2012004260.pdf | format = PDF | accessdate = 1 July 2012}}</ref> It has not yet been formally proposed nor funded.

==See also==
{{Portal|Mars}}
{{cmn|colwidth=30em|
* [[Arachnoid (astrogeology)]]
* [[Chaos terrain]]
* [[Geology of Mars]]
* [[Planetary geology]]
* [[Rille]]
* [[Swiss cheese features]]
}}

==References==
{{Reflist|30em}}

==External links==
{{Commons category|Dark Dune Spots}}
* [http://www.martianspiders.com Martian "Spiders"] photo repository.
* Arthur C. Clarke on "Martian Spider" features: [http://www.martianspiders.com/Arthur%20C_%20Clarke%20Stands%20By%20His%20Belief%20in%20Life%20on%20Mars.htm 1]

{{Astrobiology}}
{{Geography of Mars}}

{{DEFAULTSORT:Geyser (Mars)}}
[[Category:Astrobiology]]
[[Category:Extraterrestrial life]]
[[Category:Geography of Mars]]
[[Category:Geology of Mars]]
[[Category:Surface features of Mars]]

{{En-WP-Attrib}}

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