Out-of-season water escape during Mars’ northern summer triggered by a strong localized dust storm

Mars almost certainly had a significant amount of water in its past. Recent observations reveal that during southern summer, when the atmosphere is warmer and dustier, water vapor can reach high altitudes without condensing, leading to water loss to space. Here, we identify a new pathway for water loss, for the first time observed during the opposite season. Our findings show that a strong, localized, and short-lived dust storm in Martian Year 37 (August 2023) drove significant vertical transport of water vapor in the northern summer season. Just days after the storm, enhanced water vapor concentrations were observed at altitudes over 40 km across northern high latitudes, followed by an increase in escaping hydrogen detected at the exobase. These results suggest that water loss on Mars can be triggered by strong local dust storms at any time of year, potentially making total water loss greater than previously estimated.