Today, the planet Mars presents itself as a cold, arid desert, but its soil retains the imprint of a far more welcoming past. Meandering valleys and water-altered minerals attest to a period when the Red Planet was wet and active. The manner in which this profound transition could have occurred is the subject of new investigations.
A study published in
Communications: Earth & Environment reports a novel and ongoing observation of a drying process. Researchers observed that an intense, though localized, dust storm had an unexpected function in transporting substantial amounts of water vapor to the high altitudes of the Martian atmosphere.
Mars was once covered in oceans.
Image ESO
Contrary to what was thought, this episode occurred during the northern hemisphere summer, a season previously considered unfavorable for water dissipation. Yet the instruments detected a water vapor concentration up to ten times higher than usual at mid-altitudes. This phenomenon was directly associated with the presence of suspended dust, which altered the local atmospheric circulation.
The increase in water vapor had an immediate repercussion: shortly afterwards, the amount of hydrogen measured at the atmospheric boundary more than doubled compared to previous years. This hydrogen comes from the dissociation of water molecules by solar radiation. Once released, it can escape more easily into space, irreversibly carrying away a portion of the planet's water.
Dust storms, although frequent on Mars, therefore exert a much greater influence on the climate than it seems. By locally warming the air, they can facilitate the ascent of humidity from the lower layers to the altitudes where solar radiation dissociates it. Regional episodes, like the one examined, are of particular interest because they are more common than global storms. Their effects, although localized, can repeat and thus contribute cumulatively to water loss. Their intensity and duration directly condition the volume of water vapor transported upward.
Diagram illustrating the atmospheric response to a localized dust storm in the northern hemisphere during the southern summer. A high dust concentration significantly increases the absorption of solar radiation, leading to increased atmospheric warming, particularly in the middle atmosphere. This thermal response affects the water ice cloud layer, which extends further vertically and becomes less opaque due to reduced condensation of water vapor. Furthermore, the enhanced atmospheric circulation associated with the dust storm intensifies the vertical transport of water vapor from the lower atmosphere, promoting the injection of water to high altitudes and accentuating hydrogen escape.
These observations show that isolated meteorological episodes can contribute notably to the climatic evolution of Mars. Models will now have to account for the effect of these local storms, which until now has been downplayed or even ignored. This advancement helps to reconstruct the journey of Martian water over billions of years.
The scientists behind this work, including Adrián Brines and Shohei Aoki, indicate that it provides an important missing piece for understanding the transformation of Mars. It opens new avenues for examining how the planet could have lost a large part of its liquid water, beyond mechanisms already identified such as general atmospheric escape.
By incorporating these events into their simulations, researchers are refining their understanding of Martian evolution. This approach allows for the fine-tuning of scenarios about how the planet could have changed and for estimating the conditions that allowed for the ancient presence of liquid water on its surface.