Raging Winds On Mars
Despite the very thin Martian atmosphere, there are also winds on Mars that are central to the climate and the distribution of dust.
The wind movements and the whirling up of dust also create so-called dust devils, rotating columns of dust and air that move across the surface. In images of Mars, the wind itself is invisible, but dust devils are clearly visible. Due to their movement, they are valuable indicators for researchers to determine the otherwise invisible winds.
A new study led by Dr. Valentin Bickel from the Center for Space and Habitability at the University of Bern shows that the dust devils and the winds that surround them reach significantly higher speeds than previously assumed. The stronger winds could be responsible for a large part of the dust uplift on Mars, which in turn has a major influence on the weather and climate of Mars. The study, in which researchers from the Department of Space Research and Planetology at the Physics Institute at the University of Bern, the Open University in the UK and the German Aerospace Center (DLR) are also involved, has just been published in the journal Science Advances.
Dust devils are whirlwinds of dust that are blown across Mars’ surface. The Colour and Stereo Surface Imaging System (CaSSIS) on board ESA’s ExoMars Trace Gas Orbiter (TGO) and the High Resolution Stereo Camera on board ESA’s Mars Express captured these three dust devils tracking across the martian surface. ExoMars TGO and Mars Express create colour images and stereo products by combining views from separate channels. By nature, there is a delay between the individual views, so moving objects like dust devils appear in different positions in the different views. The researchers used this delay to measure the dust devils’ speed and direction. © CC BY SA 3.0 IGO, ESA/DLR/FU Berlin for HRSC, ESA/TGO/CaSSIS for CaSSIS
Movement of dust devils studied with the help of deep learning
“Using a state-of-the-art deep learning approach, we were able to identify dust devils in over 50,000 satellite images,” explains first author Valentin Bickel. The team used images from the Bern-based Mars camera CaSSIS (Color and Stereo Surface Imaging System) and the stereo camera HRSC (High Resolution Stereo Camera). CaSSIS is on board the European Space Agency’s (ESA) ExoMars Trace Gas Orbiter, while the HRSC camera is on board the ESA orbiter Mars Express. “Our study is therefore based exclusively on data from European Mars exploration,” Bickel continues.
In a next step, the research team examined stereo images for around 300 of the identified dust devils in order to measure their directions of movement and velocities. Co-author Nicolas Thomas, under whose leadership the CaSSIS camera system was developed and built at the University of Bern and
which is funded by SERI’s Swiss Space Office through ESA’s PRODEX program (see info box), explains: “Stereo images are images of the same spot on the surface of Mars, but taken a few seconds apart. These images can therefore be used to measure the movement of dust devils.”
(C) Global map of dust devil distribution (n = 1039), symbol color indicates season of occurrence (N-Sp, northern spring; N-Su, northern summer; S-Sp, southern spring; S-Su, southern summer); histograms indicate longitudinal and latitudinal distribution. Teal dots represent CTX-derived dust devil detections recorded by an earlier survey [n = 12,828 (58)]. Locations of landed missions (white stars) and the Medusae Fossae Formation (MFF) indicated. Viking color mosaic in the background. Spacecraft badges mark data derived by different missions/instruments. Image credit: ESA/TGO/CaSSIS CC -BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) IGO, ESA/DLR/FU Berlin CC -BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en) IGO; the shown images were cropped from the original CaSSIS and HRSC images. — Science
Bickel emphasizes: “If you put the stereo images together in a sequence, you can observe how dynamically the dust devils move across the surface.” (see the images on the website of the University of Bern)
Winds on Mars stronger than previously assumed
The results show that the dust devils and the winds surrounding them on Mars can reach speeds of up to 44 m/s, i.e. around 160 km/h, across the entire planet, which is much faster than previously assumed (previous measurements on the surface had shown that winds mostly remain below 50 km/h and – in rare cases – can reach a maximum of 100 km/h).
The high wind speed in turn influences the dust cycle on the Red Planet: “These strong, straight-line winds are very likely to bring a considerable amount of dust into the Martian atmosphere – much more than previously assumed,” says Bickel. He continues: “Our data show where and when the winds on Mars seem to be strong enough to lift dust from the surface. This is the first time that such findings are available on a global scale for a period of around two decades.”
Future Mars missions can benefit from the research results
The results obtained are also particularly important for future Mars missions. “A better understanding of the wind conditions on Mars is crucial for the planning and execution of future landed missions,” explains Daniela Tirsch from the Institute of Space Research at the German Aerospace Center (DLR) and co-author of the study. “With the help of the new findings on wind dynamics, we can model the Martian atmosphere and the associated surface processes more precisely,” Tirsch continues. These models are essential to better assess risks for future missions and adapt technical systems accordingly. The new study thus provides important findings for a number of research areas on Mars, such as research into the formation of dunes and slope streaks, as well as the creation of weather and climate models of Mars.
The researchers plan to further intensify the observations of dust devils and supplement the data obtained with targeted and coordinated observations of dust devils using CaSSIS and HRSC. “In the long term, our research should help to make the planning of Mars missions more efficient,” concludes Bickel.
Dust Devil Migration Patterns Reveal Strong Near-surface Winds across Mars, Science Advances (open access)
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