A new international study published in Communications: Earth & Environment brings scientists closer to solving this mystery. Researchers found that an unusually intense but localized dust storm was able to push water vapor high into Mars' atmosphere during the Northern Hemisphere summer, a season previously thought to play little role in this process.

"The 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," 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.

Small Storms With Big Effects

Dust storms have long been linked to the loss of water from Mars, but most studies have focused on massive, planet-wide events. This new research shows that smaller, regional storms can also play a powerful role by lifting water to higher altitudes, where it can escape more easily into space. Earlier work also emphasized the Southern Hemisphere summer as the primary period of water loss, making this Northern Hemisphere finding especially surprising.

During Martian year 37 (2022-2023 on Earth), scientists observed a sharp rise in water vapor in the middle atmosphere linked to this unusual storm. At those heights, water levels reached up to ten times the normal amount. This dramatic increase had not been seen in previous years and was not predicted by existing climate models.

Hydrogen Escape Reveals Water Loss

Soon after, researchers detected a major increase in hydrogen at the exobase -- the boundary where Mars' atmosphere transitions into space. Hydrogen levels rose to 2.5 times those recorded in earlier years during the same season. Tracking escaping hydrogen is critical because it forms when water molecules break apart, offering a direct clue to how much water Mars is losing.

"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," concludes Aoki (University of Tokyo and Tohoku University).

Data From Multiple Mars Missions

The study is based on data collected through an international collaboration involving several Mars missions. These include the Trace Gas Orbiter (TGO) from the ESA's ExoMars mission (2016) and its NOMAD instrument, along with observations from NASA's Mars Reconnaissance Orbiter (MRO) and the Emirates Mars Mission (EMM), all currently operating in orbit around Mars.