Several years ago, astronomers announced the incredible discovery of lakes of liquid water on Mars, buried under an ice cap at the South Pole. Three new studies refute this claim, and new experiments show that the “water” signal most likely came from frozen clay.
While there is abundant evidence indicating that there was water on Mars in the past, the discovery of its liquid form, which has survived to this day, inspired scientists. In 2018, the Mars Express orbiter returned radar signals corresponding to the water interface. Scientists have come to the conclusion that the lake with liquid water lies under 1.5 km of solid ice and extends for 20 km. Further observations showed that there are several such reservoirs on Mars.
Radar signals that can penetrate rocks and ice change as they bounce off various materials. In this case, they produced particularly bright signals under the polar cap that could be interpreted as liquid water.
However, after years of studying data and experiments in terrestrial laboratories, scientists have come to a disappointing conclusion. They hypothesized that clay, rather than water, could create such signals. Over the past month, three new studies on this topic came out at once, which destroy the hypothesis about lakes.
So, in particular, it is noted that many of these signals were detected in areas close to the surface. And there the temperatures are too low for the water to continue to remain in a liquid state, even taking into account the fact that it mixed with salts, which can lower the freezing point of water.
After analyzing the available signals for what else could generate them, the scientists identified possible options, which included clays, metal-containing minerals, and salt ice.
All three studies were published in Geophysical Research Letters.