For the first time, scientists have observed that the ‘megaripples’ on Mars, huge sand waves seen on the Martian surface, are mobile structures and not ancient relics trapped in place from the distant past of the Red Planet.
Megaripples, which also occur in Earth’s deserts, are generally larger than the smallest sand waves, and are made up of thicker, coarser grains of sand that sit on top of their ridges, resting on grains. finer ones buried at the bottom.
The stiffness of the ridge grains, combined with the very thin and weak winds of the light atmosphere on Mars today, led scientists to think that these sediment structures must be static and immovable formations. Not so, new research shows.
A study led by planetary scientist Simone Silvestro of INAF’s Capodimonte Astronomical Observatory in Italy reveals that Martian megaripples are a phenomenon that flows after all, although you have to look closely to catch them on the spot.
By comparing images taken by the HiRISE (High Resolution Imaging Experiment) camera on NASA’s MARS Reconnaissance Orbiter over several years, Silvestro’s team discovered that Martin megaripples are definitely on the move, just very slow motion.
Between 2007 and 2016, megaripples at two Martian sites, Nili Fossae Crater and McLaughlin, switched at average speeds of up to 12 centimeters (4.7 inches) per year, with a recorded maximum speed of 19 centimeters (7.5 inches) per year.
At such slow rates of displacement, it is perhaps not surprising that these quicksands were considered static, and previous comparisons examining formations in shorter time periods of just two or three Martian years failed to detect subtle migration. Now, fortunately, we have more polling data to draw on, giving you a closer look at what’s happening.
“We had the opportunity to see these megaripples in motion because we now have more than 10 years of observations,” Silvestro told Inside Science.
However, not only our probe images are expanded. The same goes for our understanding of what is possible in the Martian atmosphere, as prior to this, the researchers did not believe that the winds from Mars were powerful enough within the thin atmosphere to move the megaripples, which are so large. that were spaced up to 35 meters. (115 feet) apart in the areas studied here (although the average is approximately 5 meters, or 16 feet).
It seems that the Martian wind can move the megaripples as long as it has some help. Researchers suggest that the proximity of the larger sand dunes located in the Nili Fossae and McLaughlin crater studied areas could be helping to change the megaripples, with the finer-grained dunes providing a high volume of sand flow that can help displace the coarse grains above the megaripple ridges.
Without that level of “impact-driven drag” of the neighboring dunes and salt flats, other Martian megaripples might not be able to move as much, or as fast, as the swift group glimpsed here.
While these megaripples can be slow, the fact that we can see them move not only represents a significant increase in our knowledge of atmospheric conditions on Mars, but it is also a very impressive science at work.
As the planetary scientist Ralph Lorenz of Johns Hopkins University, who was not involved in the research, said. Science: “We can now measure processes on the surface of another planet that are only a couple of times faster than our hair.”
The findings are reported in the Geophysical Research Magazine: Planets.