Post by Briony Horgan,
Postdoctoral Fellow, School of Earth and Space Exploration, Arizona State University, USA
Several large, overlapping basins dominate the northern hemisphere of Mars, and are collectively termed the northern lowlands. This ancient basin has been infilled by sediments and hosts some of the darkest terrains on the planet. A new spectral investigation of these dark terrains has revealed that they are almost entirely composed of iron-bearing glass. This is the first detection of glass on Mars, as most other martian surfaces exhibit a typical basaltic composition with abundant olivine and pyroxene. In total, glass-rich materials cover nearly ten million square kilometers in the northern lowlands (Horgan and Bell, 2012).
Large portions of the north polar sand sea also exhibit a glass-rich composition, and the glass-rich sediments appear to be sourced from an ancient indurated sand sea that lies underneath the polar cap (Image 3).
A possible terrestrial analog for the extensive glass-rich plains and sand dune fields on Mars are the similarly glass-rich dunes and plains that cover nearly a quarter of the surface of Iceland. These sediments are a byproduct of sub-glacial volcanism, and are emplaced through a combination of direct airfall, fluvial processes, and massive glacial outburst floods (jokulhlaups) (Image 4).
Explosive volcanism is the most plausible hypothesis for the origin of the martian glass-rich sediments, as impact processes are not expected to produce such glass-rich deposits. Furthermore, it is not likley that the glass was emplaced via airfall, as models of ash deposition from the major martian volcanic edifices have not been able to produce concentrations in the northern lowlands.
Ice-magma interactions are consistent with many characteristics of the martian glass. Both the high glass content and the large population of sand size grains are consistent with rapid fragmentation in a hydrovolcanic eruption, and the concentration of the glass in the northern basin could be consistent with deposition during jokulhlaup-like events originating at sites of ice-magma interactions in the surrounding highlands.
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