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Martian Spiders
Hi All,
FYI: I just assembled a two-image animation showing a unique variety of Martian surface feature known as "spiders" that are found in the cryptic region of the south pole of Mars: http://www.geocities.com/iamgoddard/spiders01.gif The "spiders" seen therein are huge branching radial ravines miles in length on the Martian surface. The CO2 icecap covers the ravines and the region for part of the year before evaporating. The looping- animation contains two satellite images that show the same area at two different times of the year. The first image shows the naked surface with spider ravines. The second which is the darker image shows the same area near the end of the annual icecap recession. The best theory about the Martian-spider ravines (Kieffer's theory) is that they were etched into the surface by pressurized gas rushing to escape holes in the CO2 icecap during seasonal icecap evaporations. While frozen water melts into liquid, CO2 ice vaporizes into gas that builds under the icecap as it evaporates during its annual recession. Spider ravines are slowly etched into the regolith surface over many years by pressurized CO2 gas rushing to holes in the thinning icecap. Acting as gas-escape channels, spiders are associated with geysers of CO2 gas escaping from under the evaporating icecap. In this next satellite image the fallout (known as "fans") of dark debris carried by CO2 gas that escaped through geysers can be seen deposited on the thinning icecap through which underlying spider ravines can be seen: http://www.msss.com/moc_gallery/m07_...7/M0703150.jpg According to Kieffer those ravines seen through the ice are acting as gas-escape channels. Here is a study that tested the Kieffer CO2-geyser-channel theory (a must-read for all interested): http://www.gps.caltech.edu/~shane/2002JE002007.pdf Figure 3 in that study contains a composite of satellite images showing the same area over the annual transition from total CO2- icecap coverage (seen in A) to total surface exposure (seen in F): A: http://www.msss.com/moc_gallery/ab1_.../M0305867.html B: http://www.msss.com/moc_gallery/ab1_.../M0403488.html C1: http://www.msss.com/moc_gallery/m07_.../M0702549.html C2: http://www.msss.com/moc_gallery/m07_.../M0705081.html D: http://www.msss.com/moc_gallery/m07_.../M0807709.html E: http://www.msss.com/moc_gallery/m07_.../M0900570.html F: http://www.msss.com/moc_gallery/m07_.../M1100280.html Select the hi-resolution images. In C1 and C2, spiders begin to become visible through the thinning ice as geysers and their wind-blown dark fans become most prolific. In F, the icecap has totally evaporated and the spider-ravine-etched surface is fully exposed. Ian Goddard's Journal: http://iangoddard.net/journal.htm "When we have lived any time, and have been accustomed to the uniformity of nature, we acquire a general habit, by which we always transfer the known to the unknown, and conceive the latter to resemble the former." David Hume |
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