THE ROLE OF AEOLIAN PROCESSES IN THE EVOLUTION OF PLANUM BOREUM, MARS

The processes that have shaped Planum Boreum, the ice-rich layered deposits at the north pole of Mars, have been debated since the early 1970’s when Mariner 9 provided the first glimpses of its unique morphology. One of the most enigmatic features of Planum Boreum is the system of spiral troughs. This giant, pinwheel-like structure imprints the entirety of Planum Boreum and is unlike anything observed on Earth. Other anomalies are associated with reentrants, including the largest of these, Chasma Boreale.

Multiple processes have been invoked to explain these features: brittle deformation, episodic ice flow, viscous relaxation, insolation, downcutting by winds, and subglacial volcanism with associated outflow. Using Viking imagery in a comprehensive analysis of surface albedo features and exposed stratigraphy, Alan Howard and colleagues proposed a major role for aeolian processes in the long-term evolution of both polar regions of Mars. Howard’s hypotheses, like the others, went largely untested for decades, until the recent advent of orbital radar sounding, which provided internal stratigraphy that could be compared to predictions.

For the spiral troughs, this radar stratigraphy is most consistent with Howard’s model calling upon solar ablation combined with Coriolis-deflected katabatic winds to transport ice across the surface. His prediction of the northward (upwind) migration of the troughs through time was also confirmed. Mesoscale atmospheric modeling further supports a dominant role for katabatic winds in this process. In a similar way, Abalos Mensa, found within a reentrant near Chasma Boreale, can be explained entirely by the construction of an independent mound of ice-rich material adjacent to Planum Boreum, with winds playing a strong role in its location and shape. This is again supported by a combination of three techniques: visible stratigraphy, radar-derived internal stratigraphy, and atmospheric modeling.

The view of dominant geologic processes at the poles of Mars is therefore undergoing a paradigm shift, away from a suite of possible exotic and/or catastrophic processes that alter otherwise uniform landscapes toward the persistent aeolian modification of deposition and erosion, shaping the polar deposits throughout their development.