Giant sand waves spotted for the first time moving on Mars

For the first time, an international team of planetary scientists, including David Vaz from the Centre for Earth and Space Research of the University of Coimbra (CITEUC), has observed the movement of giant waves of sand called megaripples ("megaondulations") on the planet Mars.

This discovery, the result of about a decade of observations (between 2007 and 2016), is particularly important because until now it was assumed that these structures - made up of thicker sand particles - were not active (the wind would not be able to move these particles at present). "Since there was no evidence that they were moving, they were thought to be "relics" of the strongest wind activity that could have existed on Mars in the past. However, our observations are quite conclusive and contradict this view: the megaripples on Mars are definitely active," explains David Vaz.

To reach the conclusion that the "megaripples" are moving around the Red Planet, albeit slowly (about 10 centimetres per year), the team led by Simone Silvestro of the INAF-Osservatorio Astronomico di Capodimonte (Italy) analysed more than a thousand of these sedimentary structures using high-resolution images taken by NASA's Mars Reconnaissance Orbiter in two regions of Mars: McLaughlin Crater and Nili Fossae.

The CITEUC researcher's contribution to this discovery focused on "processing the surface images obtained by the orbiter and using various previously developed techniques to measure with great precision the sediment flows (speed and amount of sediment transported by the wind) on the surface of Mars".

"In this study, it was particularly important to measure the speed and manner in which megaripples, a specific type of ripple formed by the transport of sediment by the action of the wind, moved over a period of almost 10 Earth years," Vaz points out.

David Vaz also contributed with a series of measurements of the migration velocity and sediment flows in dunes from other regions of Mars, "which served to frame and explain the observations made in the two areas on which the study focused". He also participated in the work carried out in the Moroccan desert in 2017 and 2019, where "terrestrial megaripples" were studied, "a work that served as preparation and inspiration for the discoveries we made later on Mars". This is because the phenomenon observed on Mars is also registered on Earth, albeit at very different scales and speeds.

This study is also important because it shows for the first time that these sedimentary structures (megaripples) are active and that the wind on the Martian surface is strong enough to move larger particles; in other words, this discovery confirms that Mars is a very active planet from a geological point of view," says David Vaz, who holds a doctorate in geology from the Faculty of Sciences and Technology of the University of Coimbra (FCTUC). Even at much lower speeds than on Earth, geological processes continue to shape the planet's surface.

The team includes scientists from Università degli Studi "Gabriele d'Annunzio" (Italy), Lunar and Planetary Laboratory, University of Arizona (USA), Planetary Science Institute (USA) and Ben-Gurion University of the Negev (Israel).

The study, which was recently published in the Journal of Geophysical Research: Planets, was highlighted and commented on in Science last week. The video with examples of the movement of the dunes and megaripples is available at: https://www.youtube.com/watch?v=hvTnTsZOZGs&feature=emb_logo and the scientific paper at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020JE006446.

^{Translation by Diana Taborda}