Thursday, May 26, 2022

Mysterious signal about hidden lakes on Mars may not be what we thought

The likelihood of liquid water lakes hidden under the south polar ice cap of Mars is diminishing before our eyes.

Last year, the paper found that temperatures were likely too cold for the region’s water to remain unfrozen. Now a new study has shown that the radar signal, interpreted as liquid water, was likely another resource abundant on Mars: volcanic rock.

“Here we aim to determine whether Martian landscapes today could produce strong basal echoes if they were covered by an entire planetary ice sheet,” the researchers write in their paper.

“We have found that some existing volcanic landscapes can produce a very strong basal signal, similar to what is seen in the south polar cap.”

The discovery of underground reservoirs of liquid water at the south pole of Mars was announced in 2018.

Radar signals reflected just below the planet’s surface revealed a patch of something with high radar reflectivity at a depth of 1.4 kilometers (0.87 miles) under the ice, the researchers said.

Subsequent searches revealed new shiny reflective spots, indicating the presence of a whole network of underground lakes.

It would be great. Here on Earth, underground water bodies are places where we can find microbial life surviving by chemical reactions rather than sunlight. If there is life on Mars, we might find it in a similar environment. But Mars is probably too, too cold for such liquid reservoirs.

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“For water to be maintained this close to the surface, you need both a very saline environment and a strong local heat source, but that doesn’t fit with what we know about this region,” says planetary scientist Cyril Grima from the University. Texas Institute of Geophysics.

The question arises: what are these shiny spots?

In a subsequent paper examining the data, it was found that frozen clay could produce reflectivity similar to the signal detected by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the European Space Agency’s Mars Express probe.

Grima and his colleagues took a different approach. They overlaid a virtual ice sheet over the entire Mars radar globe, including three years of MARSIS data showing what the red planet looks like through 1.4 kilometers (0.87 miles) of frozen water.

They then looked for reflective patches, similar to those interpreted as water, and found them scattered across all latitudes. Where they could, the researchers correlated these spots with the known geology of Mars. The spots are very neatly combined with the volcanic relief.

(Kirill Grima)

Above: Mars as it may appear covered in ice. Red spots are volcanic/reflective spots.

Just as frozen clay here on Earth reflects radar beams well, so volcanic rock is rich in metal, such as iron. We know that Mars has an abundance of volcanic rock, as well as a huge amount of iron.

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Future remote sensing missions could probe the ice cap to try to figure out if this interpretation is plausible – or, indeed, frozen clay could be the culprit.

But research also offers new opportunities for research. Namely, they can help us better understand the history of water on Mars.

“I think the beauty of Grima’s find is that while it debunks the idea that there might be liquid water under the planet’s south pole today, it also gives us really precise places to look for evidence of ancient lakes and riverbeds and test hypotheses. about the wider drying of the Martian climate over billions of years,” says planetary scientist Ian Smith of York University in Canada, who led the frozen clay study.

Now, the two scientists are set to work on mission proposals to use radar-based remote sensing to try to find water on Mars, both in future manned Martian missions and to learn more about Mars itself.

“Science cannot be reliable on the first try,” says Smith. “This is especially true in planetary science, where we study places that no one has ever visited and rely on instruments that sense everything from a distance.”

The study was published in Geophysical Research Letters.


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