Madrid. New analyzes from the Southwest Research Institute (SwRi) support that salty water likely exists between ice grains or sediments beneath the ice cap at the south pole of Mars.
Laboratory measurements of the properties of ice-brine mixtures at temperatures of -100 degrees Celsius, by SwRI geophysicist Dr. David Stillman, support the eerily bright reflections detected by the MARSIS subsurface sounding radar aboard the Mars Express orbiter. of the ESA.
With a 40 meter antenna, MARSIS flies over the planet, bouncing radio waves over a selected area and then receiving and analyzing the echoes or reflections. Any liquid water near the surface should send out a bright, strong signal, while the radar signal for ice and rock would be much smaller.
Because conventional models assume that the south polar cap of Mars experiences temperatures much lower than the melting point of water, many scientists have questioned the presence of liquid water. Clays, hydrated salts, and salt ices have been proposed as possible explanations for the origin of the bright basal reflections. The Italian-led team investigating the proposed phenomena since 2018 used previously published data, simulations and new laboratory measurements.
“Liquid water lakes actually exist under glaciers in the Arctic and Antarctic regions, so we have terrestrial analogs for finding liquid water under ice,” said Stillman, a specialist in detecting water in any format (liquid, ice or absorbed) on planetary bodies and co-authored a paper describing these findings. “The exotic salts that we know exist on Mars have incredible ‘antifreeze’ properties that allow brines to remain liquid down to -75 degrees Celsius. We studied these salts in our lab to understand how they would respond to radar.”
Stillman has more than a decade of experience measuring the properties of materials at low temperatures to detect and characterize subsurface ice, unfrozen water, and the potential for life throughout the solar system. For this project, Stillman measured the properties of perchlorate brines in an SwRI environmental chamber that produces near-liquid nitrogen temperatures at pressures similar to those on Mars.
“My Italian colleagues reached out to see if the data from my lab experiments would support the presence of liquid water beneath the Martian ice sheet,” Stillman said. “The research showed that perchlorate and chloride brine lakes do not need to be present, but that these brines could exist between ice grains or sediments and are sufficient to exhibit a strong dielectric response. This is similar to how seawater saturates the grains of sand on the coast or how the flavor permeates a slushie, but at -75 degrees Celsius below a mile of ice near the South Pole of Mars.”
The search for water in the cosmos is rooted in the search for potential habitability, because all known life requires water. “In this case, ‘following the water’ has taken us to a place so cold that life as we know it could not flourish,” Stillman said. “But it’s still interesting, and who knows what evolutionary paths extraterrestrial life might have taken.”
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