Dancing dust devils trace raging winds on Mars

We have been observing dust devils for decades with Mars rovers and orbiters. This research goes even further, being the first to track the movement of so many of these tornadoes in order to discover how exactly they move across the surface of Mars.

The study was led by Valentin Bickel of the University of Bern in Switzerland. Their catalog is the first to include the speeds and directions of dust devil movements anywhere on Mars.

“Dust devils make the normally invisible wind visible,” explains Valentin. “By measuring their speed and direction of movement, we began to map the wind across the entire surface of Mars. This was impossible before because we did not have enough data to make this type of measurement on a global scale.”

Mars is a spectacular planet, with vast volcanoes and cavernous craters. Why should we focus on something as boring as dust?

Dust can provide protection from the sun to keep daytime temperatures cooler and act as a blanket to keep nighttime temperatures warmer. And dust particles can serve as the starting point for cloud formation, while dust storms can even force water vapor to escape into space.

Unlike Earth, where it is carried away by rain, dust can remain in Mars’ atmosphere for a long time and be blown all over the planet. So, for a better understanding of Mars’ climate, scientists want to understand when, where and how dust is lifted from the surface into the atmosphere.

More data, better picture

For this new study, researchers trained a neural network to recognize dust devils, then combed through images taken by Mars Express since 2004 and ExoMars TGO since 2016 to put together a catalog of 1,039 of them.

The map above shows the location of 1,039 dust devils and the direction of movement of 373. It confirms that although dust devils are found everywhere on Mars, even on its towering volcanoes, many vortices are swept up from certain “source regions.” For example, many of them were clustered in Amazonis Planitia (top left of the map), a huge area of ​​Mars covered in a thin layer of dust and sand.

By tracking how fast the dust devils were moving, the researchers discovered wind speeds of up to 44 m/s, or 158 km/h. That’s faster than we’ve ever measured with rovers on the ground – although it’s worth noting that Martian air is so thin that a human would barely notice a 60 mph wind on Mars.

The researchers found that, in most cases, the dust devils were blown across the landscape faster than our current Mars weather models would predict. In places where wind speeds are higher than expected, there may be more dust kicked up from the ground than we thought.

Like Earth, Mars has seasons. The catalog also points out that dust devils are more common in the spring and summer of each hemisphere. They last a few minutes and usually occur during the day, peaking between 11:00 a.m. and 2:00 p.m. local solar time.

This is very similar to what we observe on Earth, where dust devils are more common in dry, dusty places, in the late morning or early afternoon during the summer months.

Better picture, safer exploration

This type of overview requires a lot of data, which cannot be captured by rovers and landers alone. Until now, our models of Mars’ climate have been based on the limited data we have from missions that don’t really cover much of the planet’s surface.

Thanks to this study, we now have many new measurements from across Mars, helping to feed and refine the models. This improves our understanding and prediction of wind patterns around the Red Planet.

“Information on wind speed and direction is also very important for planning the arrival of future landers and rovers on Mars,” says Valentin. “Our measurements could help scientists better understand the wind conditions at a landing site before landing, which could help them estimate how much dust is likely to settle on a rover’s solar panels – and therefore how often they should self-clean.”

We are already using dust information to plan our future missions. Our ExoMars Rosalind Franklin rover is expected to land on Mars in 2030 to avoid landing during the planet’s global dust storm season.

Valentin points out that “this catalog of Dust Devil tracks is already public and anyone can use it for their own research. More entries are added over time – Mars Express and ExoMars TGO collect new images every day.”

“Now that we know where dust devils usually occur, we can direct more images to those specific locations and times. We also coordinate missions to image the same dust devils at the same time, so we can compare motion measurements and validate the data.”

From noise to gold

Mars Express and ExoMars TGO were never designed to measure wind speed on Mars. Valentin’s team used a normally unwanted feature of data to track dust devils.

For both spacecraft, a single image is created by combining views from separate channels (each channel views Mars either in a specific color or in a specific direction – or both). By design, there is a small delay between views. This delay is not a problem as long as the surface is static, but it can cause slight “color shifts” in the final image whenever something moves, such as clouds and dust swirls. These compensations were exactly what the researchers were looking for: in Valentin’s words, “we transformed image noise into valuable scientific measurements.”

A Mars Express imaging sequence combines up to nine channels of images taken with a delay of approximately 7 to 19 seconds between each. During these delays, any dust swirl passing below moves a short distance, allowing researchers to measure its speed. Since five separate image channels were used in this study, the team was even able to see how much the dust devil wobbled from left to right, as well as how its speed changed over time.

The GIF below shows a dust devil moving through all five channels in a Mars Express imaging sequence.

Images taken with the ExoMars TGO Color and Surface Stereo Imaging System (CaSSIS) combine two views taken at one second (for color images) or 46 seconds (for stereo images). Although we can’t see any oscillation or acceleration, the extra delay allows us to see the dust devils moving around a lot more between each frame.

The first GIF below shows a dust devil photographed by ExoMars TGO with a one-second delay between views. The second GIF shows the same dust devil photographed with a 46-second delay.

“It’s great to see researchers using Mars Express and ExoMars TGO for completely unexpected research,” says Colin Wilson, ESA project scientist for both missions. “Dust affects everything on Mars – from local weather conditions to the quality of our images from orbit. It’s hard to underestimate the importance of the dust cycle.”

Notes to editors

‘Dust Devil migration models reveal strong near-surface winds on Mars» by Bickel et al. is published today in Science Advances. DOI: 10.1126/sciadv.adw5170

For more information, please contact:

ESA Media Relations

media@esa.int