Low temperature aqueous ferric sulfate solutions on the surface of Mars

• Published in: Geophysical research letters Vol. 35; no. 22; pp. L22101 - n/a
• Main Authors: Chevrier, Vincent F., Altheide, Travis S.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 01.11.2008; Blackwell Publishing Ltd
• Subjects: Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemical modeling; Geochemistry; Geomorphology and weathering; Global Change; gullies; Mars; Planetary Sciences; Solar System Objects; Thermodynamics; water; gullies; Mars; water; experimental studies; High latitude; models; thermodynamics; concentration; exhibits; sulfates; low temperature; subsurface; Modeling; brines; Water activity; solution; oxidizing environment; temperature; evaporation; low-water levels; Viscous flow
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2008GL035489

We have studied the low‐temperature properties of ferric sulfate Fe2(SO4)3 solutions as a model for potential liquid brines on the surface of Mars. Geochemical modeling demonstrates that concentrated ferric sulfate brines form through sulphur‐rich acidic evaporation processes in cold oxidizing environments. Experiments and thermodynamic calculations show that the Fe2(SO4)3 eutectic temperature is 205 ± 1 K for 48 ± 2 wt% concentration. As a result of low water activity, these solutions exhibit evaporation rates ranging from 0.42 mm h−1 (29.1 wt%) to 0.03 mm h−1 (58.2 wt%), thus down to 20 times lower than pure water. The combination of extremely low eutectic temperature and evaporation rates allow subsurface liquids to be stable at high latitudes, where the majority of gullies and viscous flow features are located. Therefore, we conclude that episodic releases of highly concentrated ferric sulfate brines are a potential agent for the formation of recent and present‐day gullies on Mars.