Chloride-bearing deposits on Mars

Across the southern highlands of Mars, approximately 640 sites of chloride-bearing deposits have been identified using the Thermal Emission Imaging System (THEMIS).

[3] Chlorides contain the anion Cl− and are soluble in water, meaning they provide evidence of past aqueous processes, which helps to constrain the type of environment at a particular region.

[3] Further investigation of these deposits using the High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) showed the features to be light-toned and irregularly shaped fractures overlying small, degraded craters.

[3] Spectra from the Compact Reconnaissance Imaging Spectrometer (CRISM) on MRO was also used for comparison in lab experiments to explain the featureless slope observed in the THEMIS data.

[1] Terra Sirenum is a region in the southern highlands of Mars[5] (approximately at 38.8°S, 221°E), with a distinguishing feature of a higher brightness as compared to the typical background soils.

[6][7] One study has interpreted six regions of chloride deposits (10 – 50 km2) in the lowest topographical levels of an inter-crater basin (300 – 400 km) as individual salt flats.

Locations of chloride-bearing deposits (black) overlain on a Mars Orbiter Laser Altimeter (MOLA) elevation map (grayscale). Inset is of a region in Terra Sirenum investigated by Davila et al. (2011). Color represents elevation as determined by MOLA (red is higher elevation, yellow is lower elevation).
Upper Left) Chloride deposits shown in blue as observed by THEMIS in Terra Sirenum A) HiRISE image of black box in upper left B) HiRISE image showing the polygonal fractures (inset of Box B in Box A) C) HiRISE image showing the chloride deposits overlying degraded craters (inset of Box C in Box A)