The planet Mars continues to reveal intriguing mysteries, particularly the potential presence of buried ice in its equatorial regions, an area where such reserves wouldn't be expected.
Recent observations from the Mars Odyssey and ExoMars Trace Gas Orbiter spacecraft have detected high concentrations of hydrogen near the surface in Martian equatorial zones. These signals could indicate the presence of preserved water ice beneath layers of dust or volcanic debris. Unlike the well-documented polar ice caps, this equatorial ice raises questions about its origin and persistence in an environment where surface conditions are normally unfavorable for its preservation.
Water ice detected near the Medusae Fossae formation on the Martian equator, observed by the European Space Agency's Mars Express probe
Credit: Planetary Science Institute/Smithsonian Institution Researchers have developed climate models to simulate the explosive volcanic eruptions that marked Mars' ancient history, between 4.1 and 3 billion years ago. Their simulations reveal that a single three-day eruption could eject enormous quantities of water vapor into the upper atmosphere. This vapor, encountering the freezing temperatures of the Martian atmosphere, would then condense into ice particles and fall back to the ground, forming deposits that could reach up to 16 feet (5 meters) thick around volcanoes.
Saira Hamid, a planetary scientist at Arizona State University and lead author of the study, emphasizes that repeated eruptions over millions of years could have accumulated considerable amounts of ice mixed with volcanic ash. These deposits beneath a protective layer would explain the detected hydrogen signals. However, she notes that these signals could also come from hydrated minerals, requiring additional investigations.
Ancient volcanic eruptions also injected sulfuric acid into the Martian atmosphere, creating aerosols that reflected sunlight. This phenomenon would have caused global cooling of the planet, extending cold periods favorable to ice accumulation. Meanwhile, the heat and chemical compounds released by volcanism could have created temporarily habitable environments, opening perspectives for the search for past life traces.
The discovery of these icy reservoirs would have major implications for future human exploration. Volcanic equatorial regions could become priority targets for crewed missions, offering both water resources and potential sites for the search of biological clues. This work opens new avenues for understanding Mars' climate evolution and locating the most promising areas for future investigations.
Martian explosive volcanism
Explosive volcanism on Mars fundamentally differs from the effusive eruptions observed on Earth. These cataclysmic events occurred when gas-rich magma encountered aquifers or underground water pockets, generating violent explosions that ejected materials to altitudes of dozens of miles (kilometers).
Unlike volcanoes like Olympus Mons that slowly release lava flows, explosive Martian volcanoes created massive eruptive plumes capable of injecting enormous quantities of ash and gas into the atmosphere. These fine particles could remain suspended for months, radically altering the planet's albedo and thermal balance.
Explosive volcanic activity was particularly intense during the Noachian eon, over 3.5 billion years ago, when Mars' interior was still very hot and liquid water was more abundant on the surface. The calderas of these ancient Martian supervolcanoes have diameters that can reach several hundred miles (kilometers), testifying to the phenomenal scale of these events.
The ash deposits from these eruptions now form sedimentary layers that preserve a unique record of the Red Planet's geological and climatic history. Studying these formations allows reconstruction of the environmental conditions that prevailed during periods when Mars was potentially habitable.
Ice preservation on Mars
The preservation of water ice on Mars represents a delicate balance between atmospheric conditions, sunlight exposure, and the insulating properties of the soil. In equatorial regions where temperatures can exceed 68°F (20°C) during the day, ice exposed at the surface sublimates directly into water vapor without passing through the liquid phase, due to the low atmospheric pressure.
The secret of preservation lies in the formation of a protective insulating layer. Volcanic ash falls, dust deposits, or rock debris create a thermal barrier that prevents temperature variations from reaching the underlying ice. This insulation can maintain ice stable for billions of years, even at latitudes normally too warm.
The microstructure of the Martian regolith also plays a crucial role. Soils rich in perchlorates form porous structures that trap water vapor and facilitate its condensation into ice during cold nights. These processes create diurnal cycles where water changes state without being lost to the atmosphere.
Climate models show that slight variations in Mars' obliquity - the tilt of its rotation axis - can considerably modify ice distribution. During periods of high tilt, polar ice migrates toward equatorial regions, where it can be trapped and preserved under protective layers until the next cycle.