Investigator: Jordan Ober Recurring Slope Lineae Processes 5/16/16 Advisor: Paul Fisher at Elysium Mons, Mars Morristown-Beard School

Abstract

The focus of our research is present day water dynamics in the near surface of Mars. Our research area is a complex rectilinear depression, likely a modified graben, located at the basal slope break on the north west flank of Elysium Mons (27.4515°N, 143.1744°E). We hypothesize that this feature was initially of tectonic origin, due to compressional and tensional stresses related to volcanic activity at Elysium Mons, and subsequently altered through fluvial, glacial and mass wasting processes. A primary source of alteration is likely to have been caused by magma and ice-water interactions. (Mouginis-Mark et al, 1984; Wilson and Head, 2002; Head and Wilson, 2002) We propose that such processes are continuing today through permafrost surface heating resulting in the formation of Recurring Slope Lineae (RSL) on steep slope terrain of interior graben walls. We further propose that CRISM spectra can be used to estimate how recently an RSL formed by modeling the effect of sublimation and evaporation processes on the CRISM IR spectra of the RSL feature.

The Elysium Mons volcano and surrounding regions have ample evidence for previously containing permafrost. Weak regions under tension could have collapsed leaving box-like depression. Permafrost could have melted during more temperate conditions, leading to flowing water that eroded the depression through fluvial erosion. However, as we know from earth analogues such as Svalbard (Hauber et al, 2011), such terrain is also prone to sapping processes that create landforms similar to those seen here. Other factors like eroded ash flow, lava flow, lahars and wall collapses, would have enlarged and smoothed the depression.

We propose that, as stated in Ojha, et al (2015), RSLs are created by the seasonal release of water. We further propose that, in the Elysium Mons region, the source of this water is permafrost undergoing active layer processes unique to Mars. Recent RSLs will be significantly darker than the surrounding terrain due to the strong absorption caused by bound and liquid water seeping through the volcanic ash deposits of Elysium Mons. We suggest that over time, evaporation and sublimation of the water will result in a lightening of the surface feature and will result in unique changes in the IR spectra that can further refine our understanding of this process and also be used to study the dynamics of RSL evolution.

To test this hypothesis we have identified three possible RSLs within a single CRISM cube (frt000061d1_07_if166l_trr3), all occurring along the same south facing graben wall. Image 1 depicts these features and labels the referenced RSL’s that will be discussed by A, B, and C. Feature A was first identified using HiRISE image PSP_004046_2080 collected at the same time as the CRISM data.

Area A is approximately 60 meters wide and 360 meters long; in the shape of an isosceles triangle. Area B and Area C are roughly similar in geometric shape and size to that of Area A. There is uncertainty in our ability to confidently verify the size and geometry of features B and C as they are not within the HiRISE field of view. We have obtained two spectra for each of these features and subtracted the spectra of a background area near feature A. If A our hypothesis is correct we expect that comparing these difference spectra will show a B progression of spectral features consistent with the evaporation and sublimation of water C from the surface material.

An alternative explanation for the brightening and softening of the RSL features would be the formation of the RSL through removal of light colored sediment from the surface Image 1: CRISM Image through small landslides and the subsequent deposition of light colored material through FRT000061D1_07_IF166L_TRR3 wind action. We expect the spectral changes to be different between these two processes NASA/Johns Hopkins University Applied and allow for a determination of which process is in action.

Our preliminary results, based on six RSL spectra (two per feature) and one background spectra, are encouraging in depicting that the spectral differences between the RSLs seem larger than the spectral variation within an RSL. We have not yet demonstrated these difference have statistical significance. Whether the differences between RSL spectra is consistent with our hypothesis of evaporation and sublimation of water remains an area of active study.

A significant challenge with this analysis is the accurate collection and processing of the RSL spectra. At this point we have only completed a limited ‘proof of concept’ study. A more accurate analysis will require the collection of many more spectra per RSL and a careful characterization of the average spectra per feature, the variation of the spectra within a feature and the significance of the differences in spectra between features.

It would also be valuable, but certainly beyond our time constraints, to perform a mixing model for the RSLs based on laboratory spectra as was performed in Ojha, et al. Such a model would allow quantitative analysis of varying components of the surface spectra and address quite convincingly our hypothesis.