Mysterious reflections on Mars might come from something stranger than water

Scientists revisiting a mysterious signal from the south pole of Mars have suggested a new potential explanation, and it doesn’t bode well for hopes of finding liquid water on the Red Planet.

In 2018, scientists using data from the European Space Agency’s Mars Express orbiter’s Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument announced that they’d observed a radar signal that could be interpreted as evidence of liquid water. That signal, a strange bright reflection, came from the Martian south pole in a region known as Ultima Scopuli. Researchers investigating the reflection now suggest that the signal didn’t come from the ice itself, or even from liquid water, but from underlying geological layers made of minerals and frozen carbon dioxide. In particular, it turned out that the thickness of these layers, rather than what they’re made of, creates the otherworldly reflection.

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