Spiral trough diversity on the north pole of Mars, as seen by Shallow Radar (SHARAD)

We combine observations from ground penetrating radar and optical instruments to conduct a comprehensive survey of spiral troughs on the north polar layered deposits of Mars. Our survey reveals that all north polar troughs have common characteristics, but there is strong regional diversity. We divide the north polar layered deposits (NPLD) into eight regions based on observations of morphology and stratigraphy in order to classify the spiral troughs. Morphologic features that separate the regions include central promontories, topographic undulations, bedrock floors, and trough asymmetry among others. We demonstrate here that the troughs formed during two periods. The first generation of troughs formed on the main lobe and in part of Gemina Lingula during accumulation of ∼600 m of ice and dust. The second generation of troughs formed stratigraphically higher and immediately after large-scale erosion in Gemini Scopuli, which we conclude created the slopes necessary for troughs to form. We test scenarios of trough evolution and find that only three concurrent processes are required for their formation: wind transport, insolation-induced sublimation, and atmospheric deposition. Our observations are inconsistent with other hypothesized processes to produce spiral troughs, including incision after the formation of the NPLD, fracturing due to flowing ice, and sublimation-driven patterns from insolation.