The European Space Agency’s Mars Express orbiter has estimated an extraordinary amount of ice beneath Mars’ surface, enough to imagine a shallow ocean covering the planet if the ice were to melt. This assessment comes from ESA’s official reporting on the mission’s radar data and analyses.
While previous missions hinted at water ice on Mars, the latest results from Mars Express represent the most extensive deposits identified to date. Radar readings indicate these ice-rich layers lie near the planet’s equator and extend down to a depth of about 3.5 kilometers. They are safeguarded by a crust of hardened ash and dust that sits hundreds of meters thick. Mars’ subterranean ice is not a single solid block; rather, it is layered and quite contaminated with dust particles, a signature of long-term geological and atmospheric processes.
Experts project that if these underground ice reserves were to melt, they would form a continuous sheet of liquid water that could range from 1.5 to 2.7 meters in depth on the Martian surface. At present, accessing these equatorial glaciers poses significant challenges for Earth-based missions and any planned rover or lander operations seeking to reach the subsurface regions.
The ice’s existence is thought to be tied to variations in Mars’ axial tilt over geologic timescales. Throughout the planet’s history, the tilt of the rotational axis has shifted in a chaotic pattern. Presently, the poles sit about 25 degrees relative to the ecliptic, slightly more than Earth’s 23-degree tilt. In the ancient past, this axial angle could swing from roughly 10 degrees to as much as 60 degrees, a wide range that would influence climate zones and the distribution of volatile materials. When the tilt climbs—placing more sunlight on higher latitudes—the equatorial region can accumulate large quantities of water ice, layered beneath volcanic ash and dust that later burial preserves for eons.
During periods when the axial tilt is higher, the Sun’s proximity to the poles increases, fostering the formation and preservation of ice along the equator. This ice can be hidden beneath layers of ash and dust, remaining effectively preserved in the near-subsurface until conditions allow it to be exposed again. The implications of such reservoirs are profound for understanding Mars’ climate history and its potential habitability in ancient epochs. Concurrently, ongoing geological activity inside Mars continues to modify the interior and surface, interacting with volatiles in ways that still puzzle scientists. [Citation: ESA]
These findings align with a broader narrative about Mars, where ice, dust, and volcanic history intertwine to shape the planet’s surface and subsurface architecture. The Mars Express mission demonstrates how radar sounding can reveal hidden water resources, offering a window into past climate cycles and the planet’s capacity to store volatiles far from the poles. While direct access to these equatorial ice deposits remains technically demanding, the data provide a crucial baseline for future mission planning and for refining models of Martian geology and climate. [Citation: ESA]
In summary, Mars Express has illuminated a substantial, layered, and dust-laden ice store beneath the equatorial region, likely formed and preserved through complex orbital dynamics and volcanic masking. If melted, this ice would create a shallow but persistent ocean-like layer, reshaping our understanding of Mars’ hydrological history and its potential for sustaining water at the surface under specific conditions. Ongoing analyses will continue to refine the volume, distribution, and state of this subterranean ice, guiding future exploration strategies and scientific inquiries about the red planet. [Citation: ESA]