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Sunday, July 29, 2012

Martian Large Polygon and Similarity With Earth

marine polygon
Terrestrial deep-water marine polygons (front, color image) are potential morphological and genetic analogs to large-scale Martian polygonal features (grayscale). Front: The terrestrial deep-water polygons are imaged using 3-D seismic-reflection data acquired by the oil and gas industry in offshore Norway (Brygge Fm.). Background: THEMIS imagery shows the character of large-scale Martian polygons in Acidalia Planitia (Vastitas Borealis Formation). See related article, p. 4–9. © The Geological Society of America, Inc.
The scientists found that the area in the northern polar region of Mars is divided into several portions of the polygon and reach large areas, but how they formed remains enigmatic. While the small size of the polygons that are found in Mars may come from the thermal contraction, and it is impossible to form a large polygon, similar to terrestrial permafrost. These findings have been inspected by Themis, Mola, Viking, data and images of the Mariner.

Previously, a heated debate among scientists about the origin of large-scale polygons in Mars has been occurring for several decades. Although in principle they acknowledge the existence of a geometric pattern similarities between Mars and Earth. But, Lorena Moscardelli and here friends give suggestion that terrestrial deep-water marine polygons are morphological and perhaps genetic analogs to large-scale Martian polygonal features.

In the August 2012 issue of GSA Today, Lorena Moscardelli and her colleagues from The University of Texas at Austin present a detailed comparison of the geometric features of these large Martian polygons and similar features found in deep-sea sediments here on Earth. Moscardelli and colleagues note striking similarities.

On Earth, polygon-shaped areas, with the edges formed by faults, are common in fine-grained deep-sea sediments. Some of the best examples of these polygon-fault areas are found in the North Sea and the Norwegian Sea. These are imaged using detailed, 3-D seismic surveys conducted to search for offshore oil and gas deposits. Images reproduced in this paper show that these deep-water polygons are also 1,000 meters or greater in diameter.

While the details of deep-sea polygon formation on Earth are complex, Moscardelli and her colleagues conclude that the majority of these polygons form in a common environment: sediments made up of fine-grained clays in ocean basins that are deeper than 500 meters, and when these sediments are only shallowly buried by younger sediments. A key observation -- also made recently by Michelle Cooke at the University of Massachusetts -- is that the physical mechanism of polygon formation requires a thick, wet, and mechanically weak layer of sediment.

Moscardelli and colleagues also conclude that the slope angle of the sea floor plays an important role in both the formation and preservation of these polygons. Where the seafloor slope is very gentle (slopes less than half a degree), the polygons have very regular shapes and sizes. In many locations where polygons have formed on top of buried topographic features on the seafloor, the shapes of the polygons were altered, and in some cases were broken up and disrupted where the slopes were steepest. Both observations are consistent with deformation of the soft marine sediments as they creep or flow downslope in these areas.

In the northern plains of Mars, where the surface is basically flat, the polygons have very regular shapes and sizes -- remarkably similar to the deep-sea polygons found on Earth. In places where the topography on Mars is more varied, and where there may be evidence for other sediment-transport features on the surface, areas of deformed and disrupted polygons can be found -- again similar to the disrupted polygons here on Earth.

On the basis of these striking similarities, the University of Texas at Austin team concludes that these features most likely share a common origin and were formed by similar mechanisms in a similar environment. The team argues that the Martian polygons were formed within a thick, wet, and weak layer of fine-grained sediments that were deposited in a deep-water setting, similar to the Earth polygons. Thus, these interesting geometric features may provide additional evidence for the existence of an ocean in the northern portion of Mars approximately three billion years ago.

This article had edited by authors of threelas
Source: Geosociety
Publication: GSA Today

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