Martian spiders
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Martian "spiders" are geological formations thus far unique to the south polar region of Mars. These structures have not been found in the north polar region or any other region of Mars to date. They appear as the carbon dioxide ice cap at the Martian south pole sublimates 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 [1]. The central point is sometimes, but not always, a crater [2]. The formation is nearly identical to Lichtenberg figures, which can be formed by the branches, roots and the leaf veins of plants in nature, or by electrical processes in the lab [3].
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[edit] 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 NASA, astrophysicists, astrogeologists and astrobiologists including water erosion in Mars' history [4], carbon dioxide / sand geysers [5] (due to the black streaking and rounded pattern of ejecta), some form of plant or other biological life [6] (inferred due to the similarity to the Fibonacci number branching structure of plants in nature [7]), and electrical causation (inferred due to the similarity of the structures to Lichtenberg figures created by electricity in the lab) [8] [9].
It has also previously been suggested that these structures had a volcanic cause[citation needed] 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 [10].
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."
[edit] 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.
Mars' orbit around the sun is not symmetrical, nor circular. Mars has an elliptic orbit. At aphelion (the point in its orbit furthest from the sun), Mars is 249,228,730 km (154,863,553 mi) away from the sun. At perihelion (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 intensity 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 carbon dioxide 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 [11], 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 [12]. 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.
[edit] Cultural References
David Bowie's Martian character Ziggy Stardust has a band named the 'Spiders from Mars' in The Rise and Fall of Ziggy Stardust and the Spiders from Mars.
[edit] References
- ^ [1] (Spiders on Earth and Mars. AIG News #85, page 21.)
- ^ Photographic examples: 1, 2, 3
- ^ Lichtenberg figure [2]
- ^ Simulations of Geyser-Type Eruptions in Cryptic Region of Mars' South Polar Cap, Spiders: Water Driven Erosive Structures in the Southern Hemisphere of Mars, Martian Spiders as feasible water-driven erosive structures.
- ^ NASA Findings Suggest Jets Bursting From Martian Ice Cap, Simulation of Geyser-Type Eruptions in Cryptic Region of Mars' South Pole
- ^ Martian Spiders (Greg M. Orme and Peter K. Ness, in consultation with Sir Arthur C. Clarke)
- ^ Fibonacci Numbers and Nature
- ^ [3]
- ^ The Baffling Martian "Spiders" 1, 2, 3
- ^ [4]
- ^ Hundreds Of Auroras Detected On Mars, [5], [6], [7], [8]
- ^ [9]
[edit] See also
- Arachnoid (astrogeology)
- Chaos terrain
- Geology of Mars
- Martian spherules
- Planetary geology
- Rille
- Swiss cheese features
