(A) Polar stereographic map of the south polar region of Mars, showing where reflection-free zones (RFZ) were mapped on 118 SHARAD ground tracks, overlain on a Mars Orbiter Laser Altimeter (MOLA) shaded relief map. Analysis shows 30 times moer CO2 ice than prior estimates.
Shallow Radar soundings from the Mars Reconnaissance Orbiter reveal a buried deposit of CO2 ice within the south polar layered deposits of Mars with a volume of 9,500 to 12,500 km3, about 30 times that previously estimated for the south pole residual cap. The deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior CO2 volatile release. If released into the atmosphere at times of high obliquity, the CO2 reservoir would increase the atmospheric mass by up to 80%, leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling.
CO2 ice is about the red lines
Using radar data from the Mars Reconnaissance Orbiter, scientists have now found a potential resting place for some material that was once in the Martian atmosphere: a huge deposit at the south pole that holds nearly as much CO2 as the planet’s current atmosphere.
Mars’ south pole has extensive ice deposits, but most of that material is thought to be water, with only a thin coating of carbon dioxide on top. However, the MRO’s radar instrument identified several reflection-free zones, where most of the radar signal went entirely through the icy material to the planet’s surface itself. Based on the authors’ calculations, this can’t be water ice, but it does have very similar reflective properties to dry ice, or frozen carbon dioxide. The area also has features that indicate that some of the dry ice has sublimated to a gaseous form, resulting in areas where the surface has collapsed.
Even with the possible melting of the polar ice caps and enhanced greenhouse effect, the total of the changes don’t seem to be sufficient to get us to anything like Mars’ watery past, which suggests that some of the planet’s carbon dioxide and water may now be trapped in geological features.