University of South Queensland professor Graziella Caprelli is part of an international team investigating the signals reflected from Mars’ internal structures, which were first detected in data collected between 2010 and 2019 by the MARSIS radar echo sounder aboard Mars Express.
The Italian team suggested they point to salt lakes and published their study in Science in 2018 and Nature Astronomy in 2021.
Recently, a new collaboration between an Italian team and American researchers has provided new evidence to support this interpretation.
Professor Caprelli said new laboratory experiments and simulations have ruled out alternative interpretations.
“We explored issues such as the possibility that strong radar signals could be generated by other types of materials, such as clay or salt ice, or by structural interference,” she said.
“Recent work addresses a long-standing issue related to temperatures at the base of the south polar cap: until now they were considered too low even for brines to remain liquid.”
Professor Caprelli has developed thermal models and calculated the temperature range at the base of the south polar cap of Mars, under the south polar layered deposits (SPLD).
“We decided to study the physical properties of the deposits themselves by simulating the propagation of radar waves through water ice and dust,” she said.
The new calculations limit the percentage of dust inclusions in the deposits to between 5% and 12%, additionally placing an upper limit on the base temperature of 230 K (-43°C).
“Our research indicates that the temperature at the base of the SPLD as calculated by the researchers (approximately 170-180 K) has been greatly underestimated, and instead it can easily reach 200 K (-73°C), which is within the melting points of perchlorate brines.” said Professor Caprelli.
“New laboratory experiments conducted at the laboratories of the University of Roma Tre (Italy) and the Southwest Research Institute (USA) additionally demonstrate that the physical properties of the brines at these revised temperatures are fully consistent with the strength of the radar signals received from the Martian south polar deposits.”
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