October 20, 2017

25.06.10- MRO and the Case of the Martian Spirals.


The NPC of Mars. (Credit: NASA/Caltech/JPL/E. DeJong/M. Stetson).

The NPC of Mars. (Credit: NASA/Caltech/JPL/E. DeJong/M. Stetson).


   Scientists may have solved the formation of one of the more curious features on Mars; the formation of its polar ice spirals. First spotted by NASA’s Mariner 9 spacecraft in 1972, these strange swirling patterns etched in the polar ice caps have remained a mystery. For example, the ice formation actually tends to form against and creep into the prevailing winds. Now Jack Holt and Isaac Smith at the University of Texas have used the Mars Reconnaissance Orbiters (MRO) Shallow Subsurface Radar to shed new light on the mystery. MRO’s radar can penetrate layers of ice that have accumulated over the millennia. During the Viking missions, researcher Alan Howard of the University of Virginia first proposed a mechanism for how these spirals could form via wind sweeping downslope and picking up water vapor and ice crystals and subsequently depositing them on the leeward or sun shadowed side on the opposite side of a trough. This process would be self replenishing as the spiral crept forward, much like glacial movement on Earth. This Sun-wind mechanism never gained wide spread acceptance, however, until close scrutiny by the MRO. The Coriolis force generated by the rotation of Mars adds the final touch, creating the final spiral structure. So why don’t we see similar structures in the polar regions of Earth? In the Arctic and Antarctic, more complex forces come into play; here, local topography overpowers the Coriolis force (remember, Mars, while having a day similar in length to the Earth, is much tinier) and shapes the force of the wind. The findings may also explain a prominent feature in the Martian northern polar cap; the Chasma Boreale, a long gash burrowed deep into the ice. It appears as if this canyon is related to a single ice melt event from 5 to 10 million years ago, and prevailing winds have not allowed for deposition of ice ever since. MRO has even discovered a second unknown chasm as well. The history of the formation of the polar caps all tie in to the Martian climate puzzle; a picture of the tiny world’s climate history is rapidly evolving into a unique story, one that parallels our own but diverges from it as well. What new mysteries does the Martian landscape hold?

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