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The most likely source of Mars's 'lakes' is clay rather than water

Pierre St-Jean

NEW ORLEANS, LA - A planetary scientist from Tulane University is part of a team of North American scientists working to disprove the theory that water exists beneath Mars's south polar cap.

Jennifer Whitten, a planetary scientist in Tulane's Department of Earth and Environmental Sciences, examined the Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS, radar data and found observations with high power values at the base of the south polar layered deposits, both in the assumed lake region and elsewhere.

The study, led by Isaac Smith, an assistant professor of earth and space science at from York University in Toronto and published in Geophysical Research Letters, appears to show for the first time that another material — a type of clay called smectites — is being attributed to the bright radar reflections that many scientists have mistakenly assumed to be water for years. Smectites are a type of clay formed when basalt, the volcanic rock that makes up the majority of Mars' surface, chemically breaks down in the presence of liquid water.

According to Smith, the scientific community has long been skeptical of the water theory, specifically that a lake or other body of water existed at the bottom of Mars' polar cap and discovered spectral evidence that smectites are present at the south polar cap's edges.

Researchers at York measured the radar properties of hydrated smectites at room and cryogenic temperatures. Two numbers represent the real and imaginary parts of the dielectric constant in the questionable radar characteristics. Both numbers are important for fully characterizing a material, but a 2018 study used modeling that only included the real part of the dielectric value, excluding certain classes of materials, namely clays.

Following the completion of the experimental measurements, the data was analyzed using code. Researchers discovered that frozen clays have numbers large enough to produce reflections in these simulations.

“I believe this study presents a viable alternative, and I am excited to see how it is received by the planetary science community,” Whitten said. “It's exciting to be a part of such an active discussion, where different groups are rapidly publishing papers on the subject.”

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