Water under the frozen cap | Science and life

Once upon a time, it rained on Mars, rivers flowed, and even a small ocean splashed. Since then, a lot of water has flowed in every sense, and now only canyons and valleys that have preserved traces of water flows, sedimentary rocks, and ice deposits at the poles speak of the watery past of the Red Planet. Liquid water, with the exception of small salty streams that briefly form on the heated slopes, is not currently on Mars. At least it hasn’t been found yet. But that doesn’t mean they aren’t looking for it.

In 2018 using radar MARSIS, installed on the Mars Express orbiter, under a kilometer and a half of ice at the south pole, something interesting was discovered. Right under the layer of ice, something gave a strong reflection of the radio signal, and in its properties this something was similar to liquid water. On Earth, water under ice is not at all uncommon: from lakes and ponds frozen in winter to subglacial lakes in Antarctica. But Mars is too cold for liquid water to survive even under a thick ice cap. At the very least, the researchers were very skeptical of these data, offering several explanations for the observed phenomenon, for example, that a bright picture on the radar could have arisen due to the superposition of the reflected signal from layers of ice and rocks of different composition.

However, as researchers write in a recent article in Nature Astronomywhat the radar “saw” MARSIS under the polar cap, after all, really liquid water. The scientists based their conclusion not on the notorious radar data, but on the results of the analysis of the height map in the region of the southern Martian pole. The fact is that the existence of an under-ice reservoir does not pass without a trace for the ice layer located on top. Over liquid water, the mass of ice moves (and ice moves under the influence of gravity) faster than over a “dry” area, where the glacier scrapes its “belly” against the rocky firmament, and this is reflected in the surface topography. In other words, the ice surface located above the subglacial lake, even if it is very deep, and above the area where there is no subglacial liquid, looks different. And if this “works” with ice on Earth, then why not be the same phenomenon on Mars?

The researchers built a model of ice movement at the south pole of Mars, taking into account the existence of subglacial lakes and without them, and compared the results with real relief maps of the surface of this area. And, indeed, where MARSIS I saw something at a depth, and on the surface there was a relief characteristic of an ice lake. Here we can recall the so-called “duck test”: if something looks like a duck, swims like a duck and quacks like a duck, then it is probably a duck. Just not a duck, an under-ice Martian lake. And getting to it would be very interesting.

Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.

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