Cornell University researchers have provided a simple and comprehensive -- if less dramatic -- explanation for bright radar reflections initially interpreted as liquid water beneath the ice cap on Mars' south pole.

Their simulations show that small variations in layers of water ice -- too subtle for ground-penetrating radar instruments to resolve -- can cause constructive interference between radar waves. Such interference can produce reflections whose intensity and variability match observations to date -- not only in the area proposed to be liquid water, but across the so-called south polar layered deposits.

"I can't say it's impossible that there's liquid water down there, but we're showing that there are much simpler ways to get the same observation without having to stretch that far, using mechanisms and materials that we already know exist there," said Daniel Lalich, research associate in the Cornell Center for Astrophysics and Planetary Science. "Just through random chance you can create the same observed signal in the radar."

Lalich is the first author of "Small Variations in Ice Composition and Layer Thickness Explain Bright Reflections Below Martian Polar Cap Without Liquid Water," published June 7 in Science Advances.

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