Large wind ripples on Mars: A record of atmospheric evolution

M G A Lapotre, R C Ewing, M P Lamb, W W Fischer, J P Grotzinger, D M Rubin, K W Lewis, M J Ballard, M Day, S Gupta, S G Banham, N T Bridges, D J Des Marais, A A Fraeman, J A Grant, K E Herkenhoff, D W Ming, M A Mischna, M S Rice, D Y Sumner, A R Vasavada, R A Yingst

Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter- to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.