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

Mars almost certainly had a considerable 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, by combining infrared, visible, and ultraviolet data from multiple Mars orbiters, we identify a new pathway for water loss, observed for the first time to our knowledge during the opposite season. Our findings show that a strong, localized, and short-lived dust storm in Martian Year 37 (August 2023) drove considerable 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. Observations compiled from several Mars observation missions suggest a significant but short-lived dust storm during the Northern hemisphere summer of Mars Year 37 drove substantial vertical transport of water vapor into the upper atmosphere.