Water on Mars, With a Grain of Salt: Local Heat Anomalies Are Required for Basal Melting of Ice at the South Pole Today. Issue 3 (12th February 2019)

• Record Type: Journal Article
• Authors: Sori, Michael M.; Bramson, Ali M.
• Is Part Of: Geophysical research letters. Volume 46:Issue 3(2019)
• Page Start: 1222
• Page End: 1231
• Publication Date: 2019-02-12
• Subjects: basal melting -- water -- magmatism -- thermal modeling -- Mars -- salts; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL080985
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Recent analysis of radar data from the Mars Express spacecraft has interpreted bright subsurface radar reflections as indicators of local liquid water at the base of the south polar layered deposits (SPLD). However, the physical and geological conditions required to produce melting at this location were not quantified. Here we use thermophysical models to constrain parameters necessary to generate liquid water beneath the SPLD. We show that no concentration of salt is sufficient to melt ice at the base of the SPLD in the present day under typical Martian conditions. Instead, a local enhancement in the geothermal heat flux of >72 mW/m 2 is required, even under the most favorable compositional considerations. This heat flow is most simply achieved via the presence of a subsurface magma chamber emplaced 100 s of kyr ago. Thus, if the liquid water interpretation of the observations is correct, magmatism on Mars may have been active extremely recently. Plain Language Summary: Recent radar observations from the European Space Agency's Mars Express spacecraft have been interpreted as evidence for melting beneath the ice at the south pole of Mars. We model the temperatures in the subsurface to determine the necessary conditions to achieve liquid water at the base of the ice cap. Salts lower the melting point of ice, with calcium‐perchlorate generating the lowest temperatures at which melting can be achieved. However, even if there are local concentrations of large amounts of these salts at the base of the south polar ice, typical Martian conditions are too cold to melt the ice. We find that a local heat source within the crust is needed to increase the temperatures, and a magma chamber within 10 km of the ice could provide such a heat source. This result suggests that if the liquid water interpretation of the observations is correct, magmatism on Mars may have been active extremely recently. Key Points: No amount of salt is sufficient to cause basal melting of south polar ice on Mars under typical conditions Under an ideal composition of an ice‐perchlorate mixture, basal melting may occur if the geothermal heat flux is >72 mW m −2 A subsurface magma chamber may provide sufficient heat for local, transient melting of basal polar ice