Rover Curiosity exploring the dark dunes

For two long years, Curiosity did not dare approach the mountain of Sharpe, although it was sent to study it. The sediments of dark sand, which blocked the path, prevented, so they had to get round. The rover moved along the mountain, and the black dunes constantly loomed at the foot, sometimes resembling a frozen sea, sometimes - an old highway.

The longer they sailed away, the more they wanted to get closer to them, examine the MAHLI macro camera, touch the APXS spectrometer, run the bucket in them, microwave the SAM chromatograph and illuminate the CheMin diffractometer with X- rays .


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The rover since the summer of 2013 moved along a dark dune spit to a break in the sands, where on solid ground it was possible to get to the mountain slopes and the canyon, which was once cut into the mountain by streams of thawed water. While Curiosity was far from being a scientist, we had to be content with high-resolution satellite images of the HiRise MRO camera. Pictures of this camera convey the image in "extended" colors, in which the dark sand seemed blue or greenish.



In part, this effect is not accidental. The CRISM satellite hyperspectrometer showed a high content of pyroxene and olivine volcanic minerals. Pyroxen is responsible for virtually all the dark rocks of Mars that are observed from space. It is the pyroxene "seas" that look like dark spots if viewed through a telescope.

Thanks to olivine, also a volcanic rock, which got its name, for its green color, like the olives, the dark dunes of Mars become blue-green hues.

In the first months of Curiosity's stay in the Gale crater, the question remained about the density of these sands. Are they a fossil monolith long preserved in the shape of an ancient desert (or seabed), or are they ordinary sand? At first, engineers did not dare to touch the wheel of the rover and touch it so as not to waste time. But the dunes began to be observed from the satellite, and compared with the pictures that were taken four years before landing Curiosity. And the answer was received - they are "alive".



The moving dunes in the Gale crater are not unique to Mars. Scientists have been watching dunes in several regions of the planet for several years.

Here it is necessary to clarify that dust storms are not uncommon on Mars, but not sandy. The difference in size and mass of particles. A thin atmosphere and a gentle breeze can lift fine dust high, and the sand can only be moved by centimeters, as a result of which the dunes crawl by about a meter per year.

The isolated position of these dunes from other sand and dust is explained by the size, mass, and possibly the shape of the particles. Despite the fact that they seem to be gathered and held together by some magical force, when viewed from above, it is clear that the dark sands are quite far from the dunes, and the terrain is tinged with dark colors on the approaches.

This partly explains why from a distance the dunes stood out sharply against the background of the surrounding area, and as they approached, the contrast was reduced. Another possible effect is “black-blue / white-gold”.



While Curiosity went on detour along the mountain, its movement was relatively frisky, by marshalling standards - about 6 kilometers per year. When his course changed and a gradual rise began, the speed of advancement was sharply reduced due to long stops for a detailed survey of soils.

Sharpe Mountain has attracted the attention of scientists for a long time due to its layered structure . The upward movement of Curiosity, with the analysis of all geological layers, is its priority task, so it flew here. Therefore, the remaining two kilometers from the foot to the dune fields had to wait another year.

Finally we are here!


On the desktop.

The Dune Spit, which stretches near the mountain, was named the Dunes of Bagnold , in honor of the explorer of the Sahara. The next two heaps of sand, the study of which began Curiosity, called Namib, in honor of the earthly desert.

Last half a kilometer to the Namib dunes, the rover drivers seem to be in a hurry themselves, wanting to quickly examine the dark dumps. However, the rush did not prevent them from discovering on the way interesting deposits of soil with a high silicon content. How it was deposited there remains to be learned, and Curiosity has already passed to the study of sand.

Dropping accumulated soil with a high content of silicon, the rover created an entertaining still life of three “varieties” of Mars: gray-blue soil extracted by a borer from a depth of 5 cm, laid down on solid sedimentary rocks covered with a layer of light red dust. Nearby is a scree of dark sand disturbed by the wheels of a rover.



Dark sand was examined using the MAHLI macro camera.



For comparison, we can recall the deposits of another sand - red, which was investigated by the rover in the first year of its expedition.



You can see that the dark sand is more “granular” particle size is about the same, interspersed with larger ones. Red sand consists of two fractions - relatively large sand grains mixed with dust (more precisely, aleurite - a transitional form between dust and sand).

The difference in the physical properties of the sand and explains the fact that the dark and red dunes are not mixed. Although the behavior of sand interacting with the wind is now the leading direction in research, and there are still many unknowns. The rover can stand in one place for several months just to see from the surface how the dunes crawl.



At first, Curiosity approached a small lowland filled with dark sand. Primary studies were carried out here, and it became clear that the dunes here are the most common, with no signs of petrification. Then the rover moved to a more impressive dune, a few meters high. First, a careful examination was carried out, and then Curiosity unceremoniously disturbed the tranquility of the dune and dug a small trench with his wheel.

This place was recognized as promising enough to allow an in-depth study of the samples. The rover used his bucket to produce alternately three soil samples.



In the process, Curiosity made a self-portrait, which can be viewed on an impressive panorama, which was filmed by a camera on the rover's manipulator and reduced to an interactive panorama by photo artist Andrei Bodrov.



The first samples went to the laboratory SAM device to determine the chemical and isotopic composition of sand minerals.

But then a problem arose: it seems that the Chimra tool, which is located in the manipulator and used for sifting the ground, is stuck. The screening of the soil is a necessary procedure before loading samples into the internal laboratory instruments. Research with devices is possible only for small particles of not more than 0.15 mm. In order to weed out unnecessary, larger grains of sand, Chimra is used - this is a set of several cavities and gratings with different cell sizes that allow cleaning the soil to the required parameters.



The malfunction arose after the third time Curiosity scooped dark sand with a bucket and was going to prepare it for research. Because of the “anomaly” of Chimra, the rover stopped exploring the sand of a dark dune and continued to explore the surrounding area with the help of APXS and ChemCam spectrometers.

It is too early to say how malfunctioning can harm the scientific mission of the rover and when it can be managed. Previous experience shows that engineers are creative in overcoming such difficulties, but so far even the cause of the failure is not known, so you just have to wait and hope for the best.

We will also learn about the results of the study of dark sand, its composition and possible origin later, when geologists finish processing the results.