An unusual dust storm on Mars reveals how the Red Planet lost some of its water

The Royal Belgian Institute for Space Aeronomy (BIRA-IASB) co-led a study published in Communications: Earth & Environment that demonstrates for the first time the impact of these anomalous episodes on the transformation of Mars into the arid planet we know today.

The findings are based on observations from the NOMAD instrument on ESA’s ExoMars Trace Gas Orbiter (TGO). NOMAD was developed by BIRA-IASB, who also manages the scientific lead of the instrument.

The current image of Mars as an arid and hostile planet contrasts sharply with the history revealed by its surface. Dry river beds, 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.

Now, a study jointly led by the Instituto de Astrofísica de Andalucía (IAA-CSIC) in Spain, the University of Tokyo in Japan and the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) in Belgium 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 University of Tokyo and visiting scientist at BIRA-IASB, and Frank Daerden, a researcher from BIRA-IASB.

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 Frank Daerden (BIRA-IASB) 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. This means that summers in the Southern Hemisphere are much warmer and more dynamic than those in the Northern Hemisphere.
As a result, the atmosphere during Southern Hemisphere summer becomes laden with dust and heats up, which allows water vapor to rise to very high altitudes.

There, 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 southern 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, co-led by BIRA-IASB, 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).

This water enhancement was caused by an anomalous, localized dust storm.

Explains Shohei Aoki (University of Tokyo).

The finding is based on data from the ExoMars Trace Gas Orbiter (TGO) and its NOMAD instrument— which was developed by BIRA-IASB and also its scientific lead is managed by BIRA-IASB — in combination with observations from other active missions in Martian orbit, such as NASA's Mars Reconnaissance Orbiter (MRO) and the Emirates Mars Mission (EMM) from the United Arab Emirates.

Thanks to the constant and systematic monitoring of these observations and the suitable computational tools of the IAA-CSIC for this type of atmospheric studies, we have been able to study not only the vertical distribution of water vapor, but also the distribution of dust in the atmosphere, the formation of water ice clouds and the escape of hydrogen into space.

Explains Adrián Brines (IAA-CSIC).

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.

This phenomenon was not observed in previous Martian years and is not predicted by current climate models.

Adds Frank Daerden (BIRA-IASB).

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.

The phenomenon was not limited to the middle atmosphere.

Shohei Aoki (University of Tokyo):

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.

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 Adrián Brines (IAA-CSIC).

References

Brines, A., Aoki, S., Daerden, F. et al. Out-of-season water escape during Mars' northern summer triggered by a strong localized dust storm. Commun Earth Environ 7, 55 (2026). https://doi.org/10.1038/s43247-025-03157-5