CRATER RETENTION TIMESCALES OF MARTIAN BRAIN TERRAIN

Martian brain terrain is a conspicuous landform consisting of ridges and troughs sorted to form decameter-scale arcuate cells reminiscent of the human brain or aquatic brain coral. Many patterned surface features on Mars, including brain terrain, are hypothesized to result from repeated freeze-thaw cycles of rock-bearing soil, and may thus record the locations of occasionally stable near-surface liquid water, particularly during eras of high planetary obliquity. The identification and characterization of these terrains is thus important for understanding Mars’ past and present potential habitability.

Previous workers have used crater statistics to derive surface ages of brain terrain within individual craters, but to date there has not been a larger-scale analysis of brain terrains across Mars. This is important not only for identifying potential spatial trends, but also because brain terrains generally cover small areas, so larger counting areas are necessary to obtain robust age estimates.

We approach this problem by using a convolutional neural network to search for and identify brain terrain in more than 52,000 HiRISE images. Using these automated detections as guide, we manually map brain terrain and superposed impact craters. We classify craters as being either fresh, partially degraded, or heavily degraded in order to derive detailed surface degradation timescales. Because individual brain terrain fields are small and craters <50 m diameter are difficult to resolve against the similar scale of brain terrain cells, we assume that the brain terrains in each of three geographic areas - Northern Arabia/Sabaea, Utopia Planitia, and Arcadia Planitia - have a similar age and resurfacing history.

Results indicate that while brain terrains themselves are 50-100 Ma, they have undergone complex partial resurfacing during the past 5 Myr. Preliminary analysis of the fresh crater population indicates that for brain terrain along the dichotomy north of Terras Arabia and Sabaea, crater degradation rates increased at ~15 Ma, and craters with diameters smaller than ~100 m were preferentially eroded. This era of increased crater degradation ceased ~3 Ma. These ages correspond with a shift in Mars’ mean obliquity from ~35° to ~25° at ~4 Ma.