Astronomers have unraveled the nature of “streams” on Mars

It seems that astronomers have understood how mysterious strips are formed, traced the Martian slopes. The most intriguing in them is a change from season to season: they gradually lengthen in the warm season and disappear into the cold season. A new study shows that these are not streams, as previously thought, but streams of moist soil.

In 2011, interesting details were found on the surface of Mars. Planetologists called them repeating lines on the slopes (in English recurring slope lineae, RSL).

As the name implies, mysterious lines traced the slopes of the Martian landscape. In the warm season they gradually lengthen, grow from the top of the slope to its foot, disappear in winter, and spring again. On the Earth, similarly, only thawed water behaves. Corresponding explanation and proposed by planetologists.

The hypothesis is intriguing. Especially considering the scale of the phenomenon: the bands are found more than half a hundred Martian slopes scattered from the equator to the mid-latitudes in both hemispheres. Many thousands of such bands are known. Where does the liquid water come from on a powdery planet? And is it really water?

November 20, 2017 in the journal Nature Geoscience published an article by a scientific group led by Colin Dundas of the Center for Astrogeology in the United States. The authors seem to have unraveled the nature of the mysterious bands.

Researchers relied on the data of high-resolution cameras HiRISE on board the orbital probe MRO. Using several images of the same slope, they created its three-dimensional model. In this way scientists studied 151 streams in ten different points of Mars.

The researchers found that RSLs do not resemble their behavior on liquid water. That, as is known, flows at the slightest slope of the surface. And almost all the Martian streams studied were completely indifferent to the areas where the slope was less than 27 degrees.

This phenomenon has long been known to geologists studying sand dunes on Earth. For them, too, there is a critical angle, which experts call the angle of rest. If the slope is more flat, then the sand does not move, it is held by the force of friction.

It turns out, mysterious RSL – just crumbling sand, nothing unusual? Whence then seasonal behavior? Why do they gradually lengthen in the warm season and disappear in the winter? Why change the color over time? Why, finally, do the orbital spectrometers show in them the presence of hydrated, that is, water-rich rocks?

The authors suggest that without water it was all right. According to their hypothesis, salts contained in Martian rocks are drawn from the atmosphere by water vapor, which leads to the formation of crystalline hydrates and even drops of liquid water. Seasonal changes in wetting mode can be a “trigger” for ground movement down. Changes in water content can also explain the change in color.

It turns out that all the riddles are solved? Again, no. Water vapor is everywhere in the atmosphere. The slopes of a suitable steepness on Mars are more than enough. Why are the flows not observed on all such slopes?

This question has not yet been answered. As noted in the press release, the mechanism of the formation of RSL, it seems, is specific to Mars. To study it more accurately will help research carried out with the help of vehicles moving on the surface of the planet.

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