A swarm of spherical rovers, blown by the wind like tumbleweeds, could enable large-scale and low-cost exploration of the martian surface, according to results presented at the Joint Meeting of the Europlanet Science Congress and the Division for Planetary Sciences (EPSC-DPS) 2025.
Recent experiments in a state-of-the-art wind tunnel and field tests in a quarry demonstrate that the rovers could be set in motion and navigate over various terrains in conditions analogous to those found on Mars.
Tumbleweed rovers are lightweight, 5-metre-diameter spherical robots designed to harness the power of martian winds for mobility. Swarms of the rovers could spread across the Red Planet, autonomously gathering environmental data and providing an unprecedented, simultaneous view of atmospheric and surface processes from different locations on Mars. A final, stationary phase would involve collapsing the rovers into permanent measurement stations dotted around the surface of Mars, providing long-term scientific measurements and potential infrastructure for future missions.
"Recent wind-tunnel and field campaigns have been a turning point in the Tumbleweed rover's development," said James Kingsnorth, Head of Science at Team Tumbleweed, who presented the results at EPSC-DPS2025 in Helsinki. "We now have experimental validation that Tumbleweed rovers could indeed operate and collect scientific data on Mars."
In July 2025, Team Tumbleweed conducted a week-long experimental campaign, supported by Europlanet, at Aarhus University's Planetary Environment Facility. Using scaled prototypes with 30-, 40- and 50-centimetre diameters, the team carried out static and dynamic tests in a wind tunnel with a variety of wind speeds and ground surfaces under a low atmospheric pressure of 17 millibars.
Results showed that wind speeds of 9-10 metres per second were sufficient to set the rover in motion over a range of Mars-like terrains including smooth and rough surfaces, sand, pebbles and boulder fields. Onboard instruments successfully recorded data during tumbling and the rover's behaviour matched fluid-dynamics modelling, validating simulations. The scale-model prototypes were able to climb up a slope of 11.5 degrees in the chamber – equivalent to approximately 30 degrees on Mars – demonstrating that the rover could traverse even unfavourable slopes.
"Experiments with the prototypes in the Aarhus Wind Tunnel have provided big insights into how Tumbleweed rovers would operate on Mars," said Mário João Carvalho de Pinto Balsemão, Team Tumbleweed's Mission Scientist, who led the experimental campaign. "The results are conservative, as the weights of the scaled prototypes used in the experiments are exaggerated compared to the real thing, so the threshold wind speeds for setting the rovers rolling could be even less."
Near-surface winds on Mars are currently not well understood due to the relatively sparse data collection. While data from rovers and landers on the surface show average wind speeds are generally in single digits, wind-generated vibrations recorded by NASA's Insight mission over more than two martian years, as well as measurements gathered during the flights of the Ingenuity helicopter, show that higher wind-speeds can occur near the surface quite frequently.
"Data from Insight suggests that in Mars's northern hemisphere during summer, daytime wind speeds are characterised by a wide distribution and are positively skewed toward higher wind speeds of around 10 metres per second, and while the nights are calmer, speeds of more 10 metres per second can sometimes be reached," said Balsemão. "The results from Aarhus support our modelling, which shows that an average Tumbleweed rover – following the daily shifts and day-night cycles of the wind – could travel about 422 kilometres over 100 martian sols, with an average overall speed of about 0.36 kilometres per hour. In favourable conditions, the maximum range could be as much as 2,800 kilometres."
Back in April, a 2.7-metre-diameter rover prototype, the Tumbleweed Science Testbed, was deployed in field tests in an inactive quarry in Maastricht in the Netherlands. The rover's modular payload bay carried a suite of off-the-shelf sensors including a camera, a magnetometer, an inertial measurement unit and a GPS. These experiments confirmed that the platform could successfully gather and process environmental data in real time while tumbling over natural terrain.
The organisation behind the rovers, Team Tumbleweed, is an interdisciplinary group of young, entrepreneurial scientists. With main branches in Vienna in Austria and Delft in the Netherlands, Team Tumbleweed brings together people from over 20 countries.
The next steps for the team will include integrating more sophisticated instruments into the Tumbleweed Science Testbed payload, including radiation sensors, soil probes and dust sensors, refining the rover's dynamics models, and scaling up the platform to higher technology readiness levels (TRLs). A further field campaign will take place in the Atacama Desert, Chile, in November, during which at least two Science Testbed rovers will carry instruments supplied by researchers from external partner organisations and will test swarm coordination strategies in Mars-like environments.
