Scientist unveils new evidence of salt water on Mars

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It may be known as a rocky, red planet, but there is growing evidence that salt water exists at the base of polar deposits on Mars.

Professor Graziella Caprarelli from the University of Southern Queensland is part of an international team studying light reflection signals below the Martian surface, first spotted in data acquired between 2010 and 2019 by the MARSIS radar sounder at aboard the Mars Express.

The mostly Italian team proposed that the reflections pointed to a mosaic of salt lakes, publishing their research in Science in 2018 and in Nature Astronomy in 2021. Recently, a new collaboration between the Italian team and US-based researchers provided new evidence further supporting this interpretation. .

The results of these studies were recently published in the prestigious journals Nature Communications and the Journal of Geophysical Research Planets.

Professor Caprarelli said new laboratory experiments and simulations have ruled out alternative interpretations.

“We explored questions such as ‘is it possible that strong radar signals could be produced by other types of materials like clays or salt ice, or by constructive interference,'” she said. .

“The latest papers address the long-standing issue of temperatures at the base of the southern polar ice cap: until now, these were considered too low even for the brines to be liquid.”

Professor Caprarelli, who is an assistant at the Center for Astrophysics at the University of Southern Queensland, developed the thermal models and calculated the temperature range at the base of Mars’ south polar cap, beneath the south polar stratified deposits ( SPLD).

“We decided to study the physical properties of the deposits themselves, by modeling the propagation of radar waves through water ice and dust.”

The new calculations limit the percentage of dust inclusions in the deposits to between 5 and 12%, further setting an upper limit of 230 K (-43°C) for the temperature at the base.

“Our studies show that the temperature at the base of the SPLD calculated so far by other researchers (around 170-180 K) has been greatly underestimated and can easily reach 200 K (-73°C), which is in the melting temperature range of perchlorate brines,” said Professor Caprarelli.

“New laboratory experiments conducted at the laboratories of Roma Tre University (Italy) and the Southwest Research Institute (USA) further demonstrate that the physical properties of brines at these revised temperatures are fully compatible with the strength of the signals radar acquired from the base of the Martian south polar deposits.

The research is the result of the joint efforts of teams from several institutions spread over three continents: Roma Tre University, University of Southern Queensland, the Southwest Research Institute, the Planetary Science Institute, the Institute for Electromagnetic Sensing of Environment of CNR (IREA- CNR) and IRA-INAF (National Institute of Astrophysics, Bologna, Italy).

The development and operations of the MARSIS radar sounder are supported by the Italian Space Agency (ASI), NASA and the European Space Agency (ESA).

Read “Using MARSIS Signal Attenuation to Assess the Presence of Subglacial Brines of the South Polar Layered Deposit” in Nature Communications and “Partially Saturated Brines in Basal Ice or Sediment May Explain Bright Basal Reflections in deposits in the southern polar layers” in the Journal of Geophysical Research Planets.

Explore the Astrophysics Center at the University of Southern Queensland.

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