EXPERIMENTAL SIMULATIONS OF RECURRING SLOPE LINEAE ON THE SURFACE OF MARS

Recurring Slope Lineae (RSL) are active surface features found on rocky Martian slopes commonly in the southern hemisphere equatorial to mid-latitude regions and have been observed in HiRISE images taken by the Mars Reconnaissance Orbiter. These low albedo, dark streaks on Mars demonstrate seasonal characteristics; they appear and grow darker and longer in warm months and fade to possible disappearance in colder months. One proposed mechanism for the formation and evolution of these features is the melting of subsurface water on Mars. The goal in this study was to reconstruct features similar to RSL in the lab that display the same seasonal characteristics as a result of freezing and thawing cycles creating a source of subsurface liquid. Laboratory experiments were conducted at both the Arkansas Center for Space and Planetary Sciences and at Connecticut College using small open-topped and insulated boxes filled with saturated sediment. These boxes were put through cycles of freezing and thawing while observations were made of the features generated during the thawing process on various slopes. Two different sediment sizes were investigated: playground sand and wind deposited loess containing 60% sand, 30% silt and 10% clay. Preliminary results showed that dark wet streaks could appear along the slope as a result of capillary rise through a thin dry overburden of sediment. However, there must be some sort of anisotropy introduced into the system in order for the dark line to occur in a linear trend, such as the generation of a small channel extending down the slope. The lack of recurrence of these slope lines suggests a need for larger scale varying topography experiments or a possible limitation due to the size of the small boxes not reaching the critical length necessary for features to form. Additional experiments were not able to generate slope lines without the implementation of a small channel in the system before the start of the cycles, and so other processes such as those associated with periglacial environments are considered and reviewed as potential mechanisms for the formation of RSL.