Seasonal formation rates of martian slope streaks

Abstract

Slope streaks are gravity-driven dark or light-toned features that form throughout the martian year in high-albedo and low-thermal inertia equatorial regions on Mars. These distinctive features have never been observed in a terrestrial environment although some analogs have been proposed. Based on diverse orbital observations, a number of mechanisms including granular and aqueous flows have been proposed to explain their formation. Using multi-temporal images taken by the Context Camera (CTX) aboard the Mars Reconnaissance Orbiter (MRO), we identified newly formed streaks in multiple martian years and estimated seasonal streak formation rates at intermediate latitudes, as well as at the equator. We found seasonal variations in streak activity in multiple consecutive martian years, including high formation rates during autumn (solar longitude LS ~190°). During this time, slope streak activity exceeds the long-term formation rate multiple times. The highest seasonal formation rate of 0.16% per streak per martian day was observed in the Olympus Mons aureole in autumn (LS ~210°) of Mars year 30. In some sites, slope streak formation rate at slopes of opposite orientation peaks at different seasons. The seasonal variations of the formation rate are inconsistent with sporadic trigger mechanisms and revealed that changing conditions at the slopes affect the formation of the streaks throughout the martian year. Modelled environmental parameters at the streak-bearing slopes indicate a correlation between seasonal streak activity and surface temperature, as well as wind velocity. Seasonal variations of streak activity could be a result of varying intensities of both dry and wet mechanisms or could be explained by the interaction of multiple mechanisms.