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| '''Martian "spiders"''' are geological formations thus far unique to the ] of Mars. These structures have not been found in the ] or any other region of Mars to date. They appear as the ] ice cap at the Martian south pole ] into carbon dioxide gas during the Martian spring and the surface below is revealed. | |||
| The formations, when viewed individually, form a round lobed structure reminiscent of a spider web. They generally radiate outward in lobes from a central point <ref> (''Spiders on Earth and Mars''. AIG News #85, page 21.) </ref>. The central point is sometimes, but not always, a crater <ref> Photographic examples: , , </ref>. The formation is similar in its branching appearance to ]. Similar branching patterns are also seen in watershed erosion regimes as well as the branches, roots and leaf veins of plants. | |||
| ==Causes== | |||
| It is not yet fully understood how the formations occur, or why they appear to only form in the south polar region. However, several explanations have been offered by ], astrophysicists, astrogeologists and astrobiologists including water erosion in Mars' history <ref> , , </ref>, carbon dioxide / sand geysers <ref> , </ref> | |||
| It has also previously been suggested that these structures had a volcanic cause {{Fact|date=February 2007}} or were simply warm patches of bare ground, however recent thermal imaging by NASA has revealed that these structures are generally as cold as the dry ice that covers the area during the Martian southern hemispheric winter <ref> [http://www.jpl.nasa.gov/news/news.cfm?release=2006-100 NASA Findings Suggest Jets Bursting From Martian Ice Cap | |||
| ] </ref>. | |||
| From the NASA press release (dated Aug 16, 2006) "''An earlier theory proposed that the spots were patches of warm, bare ground exposed as the ice disappeared. However, the camera on Odyssey, which sees in both infrared and visible-light wavelengths, discovered that the spots are nearly as cold as the carbon dioxide ice, suggesting they were just a thin layer of dark material lying on top of the ice and kept chilled by it.''" | |||
| ==Additional Information== | |||
| It is not known why the "spider" formations appear to occur only in specific regions of Mars' south pole, but not in corresponding regions of Mars' north pole or other regions of the planet. There are, however, several differences between the Martian north and south poles which may factor in. | |||
| ]' orbit around the ] is not ], nor circular. Mars has an ]. At ] (the point in its orbit furthest from the sun), Mars is 249,228,730 km (154,863,553 mi) away from the sun. At ] (the point in its orbit closest to the sun), Mars is 206,644,545 km (128,402,967 mi) away from the sun. Mars reaches perihelion during the south polar summer and north polar winter. Mars reaches aphelion during the north polar summer and south polar winter. For this reason, the south pole receives considerably more direct energy from the sun during its summer than the north pole receives during its summer. The difference in energy received is due to the difference in ] of radiated energy per square unit of surface area at the considerably different distances. One theory as to why the south pole develops "spiders" but the north does not relates to the difference in heating patterns of the ] ice in the polar CO2 ice caps during the respective south and north polar springs and/or summers. | |||
| Recent imaging of auroras on Mars have led to a correlation between auroras and remnant magnetization of susceptible minerals in Mars' crust, that create miniature magnetospheres. From observations, it appears that the majority of remaining magnetization of Mars' crustal minerals occurs in the southern hemisphere <ref>, , , , </ref>, with little to no remnant magnetization in the northern hemisphere. Another theory as to why the "spiders" formed in the southern region and not in the northern relates to how charged particles from solar radiation interact with magnetic field lines. Charged particles tend to flow along magnetic field lines. Due to the south polar remnant magnetic fields being significantly stronger than the small or non-existent northern magnetic fields, charged particles would interact different with the south pole than the north <ref></ref>. The fact that the south pole is aligned closer to the sun at perihelion, thus receiving more solar radiation and charged particles could factor in as well. | |||
| == Cultural References == | |||
| David Bowie's Martian character Ziggy Stardust has a band named the 'Spiders from Mars' in ]. The two terms, however, are unrelated as the band was around long before the "spider" formations were discovered on Mars. | |||
| ==References== | |||
| <references/> | |||
| ==See also== | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| * ] | |||
| == External links == | |||
| * photo repository. , , | |||
| * Papers on Martian "Spiders" , , , , , , , | |||
| * Sir Arthur C. Clarke on Martian "Spiders" , , , , | |||
| * | |||
| ] | |||
| ] | |||
| ] | |||
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