Mars almost certainly once held abundant water. Until now, observations have shown that most atmospheric water loss occurs during the Red Planet’s southern summer, when warmer, dustier conditions allow water vapor to rise to high altitudes without condensing and escape into space. In new research, planetary scientists identified a previously unrecognized pathway for water loss — observed, for the first time, during the opposite season. Their results show that a strong, localized and short-lived dust storm in Martian Year 37 (August 2023) drove a surge of water vapor upward during the northern summer.
This close-up color image of a small-scale dust storm on Mars was acquired by the HRSC instrument on ESA’s Mars Express in April 2018. Image credit: ESA / DLR / FU Berlin / CC BY-SA 3.0 IGO.
“Our findings reveal the impact of this type of storm on the planet’s climate evolution and opens a new path for understanding how Mars lost much of its water over time,” said Dr. Adrián Brines, a researcher at the Instituto de Astrofísica de Andalucía and the University of Tokyo.
While dust storms have long been recognized as important for Mars’ water escape, previous discussions have mostly focused on large, planet-wide dust events.
In contrast, Dr. Brines and his colleagues shows that smaller, regional storms can also strongly enhance water transport to high altitudes, where it can be more easily lost to space.
Furthermore, previous research has focused on the warm, dynamic summers of the southern hemisphere, since it is typically the main period of water loss on Mars.
The current study detected an unusual increase in water vapor in the middle atmosphere of Mars during the northern hemisphere summer in Martian Year 37, caused by an anomalous dust storm.
Diagram illustrating the atmospheric response to a localized dust storm in the northern hemisphere during the local summer season; high dust concentrations significantly increase the absorption of solar radiation, leading to greater atmospheric warming, especially in the middle atmosphere; furthermore, the increased atmospheric circulation associated with the dust storm enhances the vertical transport of water vapor from the lower atmosphere, promoting water injection at higher altitudes and increasing hydrogen escape from the exobase. Image credit: Brines et al., doi: 10.1038/s43247-025-03157-5.
At these altitudes, the amount of water was up to ten times greater than usual, a phenomenon not observed in previous Martian years and not predicted by current climate models.
Shortly afterward, the amount of hydrogen in the exobase (a region where the atmosphere merges with space) increased significantly to 2.5 times that of the previous years during the same season.
One of the keys to understanding how much water Mars has lost is measuring how much hydrogen has escaped into space, since this element is readily released when water breaks down in the atmosphere.
“These results add a vital new piece to the incomplete puzzle of how Mars has been losing its water over billions of years, and shows that short but intense episodes can play a relevant role in the climate evolution of the Red Planet,” said Dr. Shohei Aoki, a researcher at the University of Tokyo and Tohoku University.
The results appear this week in the journal Communications: Earth & Environment.
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A. Brines et al. 2026. Out-of-season water escape during Mars’ northern summer triggered by a strong localized dust storm. Commun Earth Environ 7, 55; doi: 10.1038/s43247-025-03157-5
