Misplaced Pages

This is an old revision of this page, as edited by SmackBot (talk | contribs) at 21:10, 11 August 2009 (Date maintenance tags and general fixes). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

It has been suggested that this article be merged with Dark dune spot and Talk:Martian spiders#Merger proposal. (Discuss) Proposed since August 2009.

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. The central point is sometimes, but not always, a crater. The formation is similar in its branching appearance to diffusion-limited aggregation.

It is thought that the Martian "spiders" and the Martian dark dune spots may be related features caused by the same phenomena.

Causes

Soon after the first detection in 2005, they were discovered to be negative topographical features - i.e. radial troughs or channels. This unusual shape and appearance of "spiders" caused a lot of speculation about their origin. The reasons for their geographic distribution is still unknown. Their boundary does not correlate with any other properties of the surface such as elevation, geological structure, chemical composition or thermal properties.

Some investigators have suggested that the "spiders" are dendritic drainage channels. But one characteristic that makes the formations so difficult to explain is the way they "work against" gravity. In fact, the branching occurs radially from a center, positively excluding a drainage function. Moreover, the spiders form in identical shapes irrespective of the terrain. Often, a single ravine is seen moving both uphill and down, and many of these radial patterns occur on a consistent incline.

Some theories include:

• Dry venting of carbon dioxide (CO₂) gas and sand. As the southern spring CO₂ ice receives enough Sun energy, it starts subliming the CO₂ ice from the bottom. This vapor accumulates under the slab rapidly increasing pressure and erupting. High-pressure gas roars through at speeds of 161 km/h (100 m/h) or more; 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. The dark material falls back to the surface, creating dark patches and patterns on the ice cap.
• Active water-driven erosive structures. Water derived from sub-surface layers is expelled up fissures eroding joints to create tributaries capped with mud-like material and/or ice.
• Modified clathrate hydrate model: Structures form as the outside of the flow chills.

It has also previously been suggested that these structures had a volcanic cause 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. NASA press release from August 16, 2006 states that an earlier theory proposed that the spots were patches of warm, bare ground exposed as the ice disappeared. However, the camera on Odyssey orbiter, 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. The morphology of these formations appears to be controlled by bedding and local jointing of the rocks; implying that expelled fluids are derived from within a few hundred meters of the surface. Some spider ravines modify, some destroy and others create crust in a dynamic near-surface process that extensively reworks the terrain creating and destroying surface layers. This process is rapid, happening in the space of a few days, weeks or months.

See also

• Arachnoid (astrogeology)
• Chaos terrain
• Mars' dark dune spots
• Geology of Mars
• Planetary geology
• Rille
• Swiss cheese features

References

1. ^ "Spiders on Earth and Mars (pp. 21)" (PDF). Australian Institute of Geoscientists. August 2006. Retrieved 2009-08-11.
2. Photographic examples: 1, 2, 3
3. ^ "NASA Findings Suggest Jets Bursting From Martian Ice Cap". Jet Propulsion Laboratory. NASA. August 16, 2006. Retrieved 2009-08-11. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
4. ^ "SIMULATIONS OF GEYSER-TYPE ERUPTIONS IN CRYPTIC REGION OF MARTIAN SOUTH" (PDF), Fourth Mars Polar Science Conference, 2006, retrieved 2009-08-11 {{citation}}: |editor-first= missing |editor-last= (help); |format= requires |url= (help); Cite has empty unknown parameters: |coeditors= and |coauthors= (help)
5. Spiders: Water-Driven Erosive Structures in the Southern Hemisphere of Mars. Prieto-Ballesteros, Olga et al. Astrobiology. August 2006, Vol. 6, No. 4. pp: 651-667
6. Prieto-Ballesteros, Olga (2005). "Martian Spiders as feasible water-driven erosive structures" (PDF). Centro de Astrobiología-INTA-CSIC. Retrieved 2009-08-11. {{cite journal}}: Cite has empty unknown parameter: |coauthors= (help)
7. [http://spsr.utsi.edu/articles/ness.pdf Peter K Ness and Greg M Orme. Spider-Ravine Models and Plant-like Features on Mars - Possible Geophysical and Biogeophysical Modes of Origin and Planet-like Features on Mars JBIS, Vol. 55, pp.85-108.]

External links

• Martian "Spiders" photo repository. 1, 2, 3
• Papers on Martian "Spiders" 1, 2, 3, 4, 5, 6, 7,
• Sir Arthur C. Clarke on Martian "Spiders" 1, 2, 3, 4, 5
• Fibonacci Numbers and Nature

• Articles to be merged from August 2009
• Planetary geology
• Mars