The current image of Mars as an arid and hostile desert contrasts sharply with the history revealed by its surface. Channels, minerals altered by water, and other geological traces indicate that the Red Planet was, in its early days, a much wetter and more dynamic world. Reconstructing how this water-rich environment disappeared remains one of the great challenges of planetary science: although several processes are known that can explain some of this loss, the fate of much of Martian water remains a mystery.

IMAGE_ONE. Composite images of Mars taken by the Hubble Space Telescope in 2024. Thin clouds of water ice, visible in ultraviolet light, give the Red Planet an icy appearance. The frigid north polar ice cap was experiencing the beginning of Martian spring. Credit: NASA, ESA, STScI

Now, a study adds a significant piece to this puzzle. For the first time, the work, published in Communications: Earth & Environment , demonstrates that an anomalous, intense, but localized dust storm was able to drive the transport of water to the upper layers of the Martian atmosphere during the Northern Hemisphere summer, a time when this process was not considered relevant. “The finding reveals 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,” says Adrián Brines, a researcher at the Instituto de Astrofísica de Andalucía (IAA-CSIC) and co-lead author of the study along with Shohei Aoki, a researcher from the Graduate School of Frontier Sciences at the University of Tokyo  and the Graduate School of Science at Tohoku University.

HYDROGEN ESCAPE ON THE RED PLANET

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. Current measurements show that the planet has lost an enormous amount of water over billions of years, enough to cover much of its surface to a depth of hundreds of meters.

Researcher Brines explains that, like Earth, Mars has four seasons due to a similar axial tilt. “However, its orbit is more elliptical, so for part of its year the planet is closer to the Sun and receives more energy.” He adds that “this is compounded by a marked difference in elevation between the two hemispheres—lower in the north than in the south—which means that summers in the Southern Hemisphere are much warmer and more dynamic than those in the Northern Hemisphere.”

In this context, during the Southern Hemisphere summer—or austral summer—the atmosphere becomes laden with dust and heats up, which allows water vapor to rise to very high altitudes, where solar radiation breaks it down and allows hydrogen to escape into space. In contrast, during the northern summer, water remains confined to lower altitudes, and the loss is much less. This seasonal cycle makes the austral summer the main period of water loss on Mars, a process that, repeated year after year, has been key to the transformation of the Red Planet.

AN UNEXPECTED EPISODE

This new study has detected an unusual increase in water vapor in the middle atmosphere of Mars during the Northern Hemisphere summer in Martian year 37 (2022-2023 on Earth), caused by an anomalous dust storm.

The finding is based on the combination of data from the Trace Gas Orbiter (TGO) of the ESA's ExoMars mission (2016) and its NOMAD instrument with observations from other active missions in Martian orbit, such as NASA's Mars Reconnaissance Orbiter (MRO) and the Emirates Mars Mission (EMM).

In this instance, an atypical dust storm triggered a sudden and intense injection of water vapor that reached heights of up to 60–80 kilometers, particularly in the high latitudes of the Northern Hemisphere. 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.

This excess of water vapor was not localized: it was detected simultaneously at all longitudes, indicating that the water was rapidly distributed around the planet. After a few weeks, the amount of dust in the atmosphere returned to normal levels, and consequently, the water vapor once again confined in the lower layers.

IMAGE_TWO. Daily MRO-MARCI global map images of the initial growth of a rare regional dust storm in northwestern Syrtis Major, observed on August 21, 2023, at Ls = 107.6° (left) and August 22, 2023, at Ls = 108.0° (right), reaching an extent of 1.2 × 10⁶ km². Credit: Brines, Aoki et al., 2026, Communications: Earth & Environment

The phenomenon was not limited to the middle atmosphere. Independent observations from the EMM and MRO missions showed that, shortly afterward, the amount of hydrogen in the exobase—the region where the atmosphere merges with space—increased significantly. As a result, hydrogen escaping into space increased approximately 2.5 times compared to previous years during the same season.

Although this episode was brief and not as intense as the major hydrogen loss events associated with the austral summer and global dust storms, it demonstrates that Mars can lose water significantly even during traditionally quiet periods.

 

IMAGE_THREE. 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. Credit: Brines, Aoki et al., 2026, Communications: Earth & Environment.

“These results add a new piece to the incomplete picture of how Mars has been losing its water over billions of years and show that short but intense episodes can play a relevant role in the climate evolution of the Red Planet,” concludes Aoki (UTokyo).

 

REFERENCES:

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

https://doi.org/10.1038/s43247-025-03157-5

 

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