By David Bressan
(Click here for original article.)
"No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intelligences greater than man's and yet as mortal as his own; that as men busied themselves about their various concerns they were scrutinised and studied, perhaps almost as narrowly as a man with a microscope might scrutinise the transient creatures that swarm and multiply in a drop of water."
H.G. Well's Martians greatest problem in 1898 was the slow cooling of the planet and a certain death in a frozen wasteland, but modern research showed that it is in fact ice that holds Mars alive (in geological and maybe even biological sense). From all the objects of the solar system maybe the planet Mars shows the most similarities to Earth, especially to the periglacial regions characterized by the presence of permafrost - perennially frozen soil that can contain ground ice.
The presence of ice on Mars was never questioned. Even the first modern maps by the American astronomer Richard Antony Proctor (1867) located two huge ice caps on the poles. However today we know that the polar ice caps contain only a core of water ice, less than many authors speculated needed for a Martian civilisation.
Could water ice exist also in other regions on Mars? Computer models showed that a cover of debris could prevent the ice to sublimate into the thin Martian atmosphere. In theory deposits of ground ice, maybe even liquid water, could be hidden under the red rubble of the Martian surface.
The Viking orbiters mapping Mars provided in 1976 an overwhelming gallery of features resembling landforms indicative of ground ice on Earth: patterned ground, thermokarst, various types of mass movement, glacial cirques and horns, valleys filled with moraine-like material.
Many Martian craters and mountains are filled or surrounded by curious and very large features, hundreds of kilometres long lobes or tongue-shaped flows, or when inside a crater resembling a gigantic pancake.
Various explanations were proposed - ancient lava flows, rock avalanches or submarine landslides. Research on terrestrial rock glaciers and debris-covered glaciers in the last decades offered an ulterior explanation - the rock glacier like features on Mars are - according to the duck test - rock glaciers.
Rock Glaciers are important landforms formed by active permafrost and defined as "an accumulation of angular rock debris that contains either interstitial ice or an ice core and shows evidence of movement through creep and deformation of the ice-part". A terrestrial rock glacier can be active - containing enough ice to show creep and deformation, inactive - still containing ice, but with no movement and relictic - containing no more ice but still displaying the morphology of past movements.
Under modern Martian climatic condition, and considering modern terrestrial rock glaciers in Antarctica, the rock glaciers on Mars could possibly be still active and be composed of water ice and dry ice.
MOC (Mars Global Surveyor Camera) Orbiter images showed that the surface of these features are practically uncratered, indicating likely emplacement and formation within the past several million years. By counting the craters on the lobes that surround the escarpment of Olympus Mons these possible rock glaciers were estimated to be 280-130, 60-20 and -surprisingly- 4 million years old. At current Martian surface temperatures and the recent accumulation rate of debris the flow velocity of such large ice masses is very low, research based on these considerations proposed an age of 1 to 10 millions years for the rock glaciers. Assuming higher temperatures in "recent" times a young age of less than 5 million years, as the crater density suggests, could still be possible. Overlapping tongues seen on some lobes even suggest that these features were periodically active, implying the occurrence of glacial and interglacial periods on Mars.
The discovery of microbial activity inside active terrestrial rock glaciers has given room for speculations that Martian rock glaciers could be still today a habitat for primitive live forms. The pressure of the overlaying debris - with an average thickness of 200-300 meters - maybe melts some of the water ice forming pockets of liquid water. Could be these hypothetical oases the cradle of real Martians?
DEGENHARDT Jr., J.J. & GIARDINO, J.R. (2003): Subsurface investigation of a rock glacier using ground-penetrating radar: Implications for locating stored water on Mars. Journal of Geophysical Research, 108: 8036-8053
GASSELT, S. (2007): Cold-Climate Landforms on Mars. PhD University of Berlin
MAHANEY, W.C.; MIYAMOTO, H.; DOHM, J.M.; BAKER, V.R. & CABROL, N.A. (2007): Rock glaciers on Mars: Earth-based clues to Mars recent paleoclimatic history. Planetary and Space Science 55: 181-192
WHALLEY, W.B. & AZIZI, A. (2003): Rock glaciers and protalus landforms: Analogous forms and ice sources on Earth and Mars. Journal of Geophysical Research 108: 8032 - 8045
WILLIAMS, M. (2004): CU-BOULDER research team discovers first evidence of life in Rock Glaciers. Marsbugs: The Electronic Astrobiology Newsletter 11(47)
About the Author: Freelance geologist dealing with quaternary outcrops interested in the history and the development of geological concepts trough time. Follow on Twitter @David_Bressan.
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