The bright white region of this image, captured by Europe's Mars Express spacecraft in December 2012, shows the icy cap that covers Mars’ south pole, composed of frozen water and frozen carbon dioxide.Doubt has been cast on the possibility of a lake of liquid water buried beneath Mars' southern ice cap by new computer simulations, which suggest that closely compacted layers of ice could produce the same radar reflections that liquid water would.
"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 observations without having to stretch that far, using mechanisms and materials that we already know exist there," said Cornell's Daniel Lalich in a. Lalich is the lead author of new research that suggests compacted ice layers could return a strong radar signal that looks just like the radar echo from a layer of liquid.
The trick is"constructive interference" of the radar waves. The spatial resolution on MARSIS is limited, and if ice layers are too thin, the radar instrument cannot distinguish them. Each layer would reflect back some of the radar beam, and because the layers are crushed so tightly together, the radar echoes overlap and combine, amplifying their strength and making them seem brighter.
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