May 10, 2012
Credits: NASA/JPL/University of Arizona - Credits for the additional process. and color.: Drr Gianluigi Barca and Paolo C. Fienga/Lunar Explorer Italia/IPF
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Both Martian Polar Ice Caps, as far as we know, are mainly made of Water Ice, even though a lot of frozen Carbon Dioxide (CO2 or Dry Ice) is present on their Surfaces. However, Dry Ice accumulates in the North Polar Regions (Planum Boreum) in Wintertime only (and then sublimates completely during the Martian Summer), while the South Polar Regions possess a permanent Dry Ice "blanket" (which is approx. 8 - eight - meters thick and that covers them up permanently). This difference is probably (and mainly) due to the higher elevation of the South Pole, as to the one of the North Pole; it is also remarkable to notice that the Martian Atmosphere can condense, at both Poles and during Wintertime, so much that even the Atmospheric Pressure can vary by up to one/third of its Mean Value. This Condensation and Evaporation Process can cause, among others, the proportion of the so-called "Non-Condensable Gases" which are present in the Martian Atmosphere, to change inversely. The Eccentricity of Mars' orbit also affects this Cycle, as well as other (minor) factors. The North Polar Cap of Mars has a diameter of approximately 1000 Km during the Northern Summer, and it likely contains about 1,6 Million Cubic Kilometres of Water Ice (which, assuming that it spreads-up evenly all over the Cap, should be about 2 Km thick). The South Polar Permanent Cap of Mars, instead, has a diameter of only 350 Km but an estimated Maximum Thickness of more than 3 Km. Both Polar Caps show Spiral Troughs, which were formerly believed to form as a result of differential Solar Heating, coupled with the Sublimation of Ice and Condensation of Water Vapor. A relatively recent analysis of the Ice Penetrating Radar data obtained by the SHARAD (---> such as the Mars SHAllow RADar Sounder: a Subsurface Sounding Radar located onboard the NASA - Mars Reconnaissance Orbiter which complements the MARSIS instrument that, on the other hand, is located onboard the ESA - Mars Express Orbiter - the latter providing lower penetration capabilities - just a few hundred meters - but a much finer resolution - 15 metres, untapered, in free space) has proven (but we believe that it would be better to say that such an analysis just speculated) that the Spiral Troughs may be the final result of a really unique situation in which the powerful action of High Density Katabatic Winds, descending from the Polar High and transporting Ice and Snow down to the Polar Plains, ended up to create these bizarre-looking Wavelength Landforms. It is also believed that these Spiral Troughs did not form at the same time of the Ice Caps (or even later), but they rather began their formation between 2,4 Millions and 500.000 years ago, such as when almost three/quarters of both Ice Caps were already in place. This speculation, if correct, suggests (once again, and just like many other theories) that some sort of Powerful Climatic Shift occurred on Mars in a relatively recent time (for reasons that, likely, shall remain unknown) and allowed, among other things, their onset. Both Polar Caps periodically shrink and regrow, according to the fluctuations of Temperature following the Martian Seasons; during the Southern Hemisphere Spring, the Solar Heating of Dry Ice Deposits may lead, in certain places, to the accumulation of some amount of pressurized CO2 Gas (flowing below the Surface of Semi-Transparent Ice sheets) that is warmed-up through the Absorption of Solar Radiation by the darker Substrate. Once the necessary Pressure is reached, the Gas bursts out through the Ice in Geyser-like Plumes. While the Eruptions have not (yet) been observed directly, it is known that they leave clear evidences of their occurrence on top of the Ice in the form of "Dark Dune Spots" and lighter "Fans", both made of Sand and Dust carried aloft by the Eruptions and, sometimes, a "spider-like" pattern of Grooves created just below the Ice, by the outrushing Gas. Eruptions of Nitrogen Gas observed by the NASA - Voyager 2 Probe on the Neptunian moon Triton, are thought to be triggered by a similar mechanism. Mars Local Time: 18:15 (Late Afternoon) This frame has been colorized in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Mars Reconnaissance Orbiter and then looked down, towards the South Polar Region of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.
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