Viscous relaxation of craters within the martian south polar layered deposits

The South Polar Layered Deposits (PLD) are of fundamental importance to martian climatology, as they may comprise the largest reservoir of near-surface water on Mars. The South PLD exhibit relatively young crater retention surface ages, which are widely attributed to recent resurfacing. However, we show that both constructional and destructional resurfacing mechanisms (such as dust deposition and water ice sublimation, respectively) are inconsistent with the size, depth, and spatial distributions of South PLD craters. We demonstrate that another process—viscous creep relaxation of dusty water ice—is more compatible with the observed cratering of South PLD surfaces. The results of our finite element relaxation simulations suggest that, despite their apparent youthfulness, the PLD have been stable for at least several hundred million and perhaps even over a billion years. Consequently, our modeling implies that the time scales for the formation and preservation of the layers characteristic of the South (and possibly North) PLD are much longer than generally assumed.