Scientists reveal further evidence of salt water on Mars

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

Professor Graziella Caprarelli from the University of Southern Queensland is part of an international team investigating bright reflectance signals beneath the surface of Mars, first observed in data obtained between 2010 and 2019 by the MARSIS radar sounder aboard Mars Express.

The mainly Italian team suggested that the reflections pointed to a patchwork of saline lakes, and published their research in Science in 2018 and in Natural Astronomy in 2021. Recently, a new collaboration between the Italian team and US-based researchers yielded new evidence that further confirms this interpretation.

The results of these studies were recently published in the journals nature communication and the Journal of Geophysical Research: Planets.

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

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

“The latest articles address the long-standing question regarding temperatures at the base of the southern polar cap: until now, these have been considered too low even for brine to be liquid.”

Professor Caprarelli, of the Center for Astrophysics at the University of Southern Queensland, developed the thermal models and calculated the temperature range at the base of the southern polar cap of Mars, under the South Polar Layered Deposits (SPLD).

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

The new calculations limit the percentage of dust inclusions in the deposits between 5% and 12%, which is a further 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 (about 170-180 K) have been greatly underestimated and can instead easily reach 200 K (-73 °C), which is within the range of the melting temperatures of perchlorate brine,” said Professor Caprarelli.

“New laboratory experiments conducted in the laboratories of Roma Tre University (Italy) and the Southwest Research Institute (USA) further demonstrate that the physical properties of brine at these revised temperatures are fully consistent with the strength of the radar signals obtained from the base of the south pole deposits of Mars.”