Unobserved processes on Earth play a major role in the movement of sand on Mars

The wind has shaped the face of Mars for millennia, but its exact role in stacking sand dunes, forming rocky escarpments or filling impact craters has so far escaped scientists.

In the most detailed analysis of how the sands are moving on Mars, a team of planetary scientists led by Matthew Chojnacki of Lunar and the Planetary Lab of the University of Arizona s 39; is committed to discovering the conditions that govern the movement of sand on Mars and how they differ Earth.

The results, published in the last issue of the journal Geology, reveal that processes not involved in the control of sand motion on Earth play a major role on Mars, especially the large-scale features of the landscape and differences in surface temperature of terrain.

"Because large sand dunes are found in distinct regions of Mars, these are good places to look for change," said Chojnacki, associate researcher at AU and lead author of the article, "The border imposes controls on the high sand". Mars flow regions. "" If you do not move sand, it means that the surface is simply besieged by ultraviolet and gamma rays that would destroy complex molecules and any ancient Martian biosignature. "

Compared to the Earth's atmosphere, the Martian atmosphere is so thin that its average surface pressure represents only 0.6% of the atmospheric pressure of our planet at sea level. As a result, sediments on the Martian surface move more slowly than their terrestrial counterparts.

The Martian dunes observed in this study ranged from 6 to 400 feet in height and were found to slide at a fairly uniform average velocity of two feet per earth year. For comparison, some of the fastest land-based sand dunes on Earth, such as those in North Africa, migrate at 100 feet per year.

"On Mars, there is simply not enough wind energy to move a substantial amount of material to the surface," Chojnacki said. "It could take two years on Mars to see the same movement that you would typically see in a season on Earth."

Planetary geologists have been wondering if the sand dunes on the red planet were relics from a distant past, when the atmosphere was much thicker, or if drifting sands were still reshaping the face of the planet today, and to what extent.

"We wanted to know: is the movement of sand uniform across the planet or is it strengthened in some areas relative to others?" Chojnacki said. "We have measured the speed and volume at which the dunes are moving on Mars."

The team used footage taken by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter, which has been monitoring the neighboring neighbor of Earth since 2006. HiRISE, which stands for "high-resolution imaging science experiment," is led by the lunar and planetary planetary laboratory about three percent of the Martian surface in breathtaking detail.

The researchers mapped sand volumes, dune migration rates, and heights of 54 dune fields, including 495 individual dunes.

"This work could not have been done without HiRISE," said Chojnacki, a member of the HiRISE team. "The data does not come only from the images, but comes from our photogrammetry lab that I co-manage with Sarah Sutton.We have a small army of undergraduate students who work part-time and build these terrain models. digital that provide topography. "

The survey detected layers of active sand and dust in the form of wind in structural pits (craters, canyons, fissures and fissures) as well as volcanic remains, polar basins and plains surrounding the craters.

In the most surprising discovery of the study, researchers found that the largest sand movements in terms of volume and velocity are limited to three distinct regions: Syrtis Major, a dark spot larger than Arizona located directly west of the vast basin of Isidis; Hellespontus Montes, a mountain range about two-thirds the length of the Cascades; and North Polar Erg, a sea of ​​sand around the northern polar ice cap. The three zones are distinguished from other parts of Mars by conditions that are not known to affect the dunes: abrupt transitions of topography and surface temperatures.

"These are not factors that you will find in earth geology," Chojnacki said. "On Earth, the factors at play are different from those of Mars, for example, groundwater near the surface or plants growing in the area are delaying the movement of dune sand."

On a smaller scale, ponds filled with shiny dust also had higher rates of sand movement.

"A bright pool reflects sunlight and heats the air above much faster than the surrounding areas, where the ground is dark," said Mr. Chojnacki. with her, the sand. "

Understanding how sand and sediments move on Mars could help scientists plan future missions in areas that are difficult to monitor and have implications for studying potentially habitable old environments.