Martian Ice: A Find Just a Meter Deep express
Beneath a thin layer of red dust on Mars lies water ice. Its presence was confirmed by the Phoenix lander and orbital instruments, but the mystery remained: why is the ice always just a few centimeters below the surface?
The answer lies in the wobbles of Mars' axial tilt. When the tilt is high, water vapor from the poles falls as frost in the mid-latitudes. As the tilt decreases, the frost sublimates, leaving behind dust. A porous crust forms — a dust blanket that slows the evaporation of the remaining ice.
Climate modeling revealed: ice deposited around 630,000 years ago now sits at a depth of 25–150 cm, matching observations. The conclusion: subsurface ice is young — less than 4 million years old. Without the dust blanket, it would vanish in centuries. But the crust acts as a self-regulator: the stronger the evaporation, the thicker the protection, and the ice persists for millions of years. For colonists, this means: water is nearby, no need to dig deep.
Original abstract
as written by the authors arXiv:2602.18847
On Mars, a relatively pure water ice layer lies beneath several centimeters of dry soil at mid-latitudes. Its widespread presence poleward of 60{\deg} latitude was detected by remote neutron spectroscopy and confirmed by the Phoenix lander at 68{\deg}N. Recent observations of exposed ice indicate that the near-surface ice layer extends to 35{\deg} latitude and exhibits pronounced spatial structure. However, previous models did not capture the observed spatial structure of the midlatitude ice layer. Here, on the basis of improved calculations using the Mars Planetary Climate Model, we show that mid-latitude buried ice could be the remnant of a ice layer deposited on the surface when the obliquity was higher than today. Assuming that the ice subsequently sublimated and became buried beneath a sublimation lag, we estimate that surface ice emplaced 630 kyr (4.18 Myr) ago at 35{\deg} obliquity (40{\deg}), at latitudes of 40-55{\deg}N, would today reside at depths of 25-150 (41-255) cm, depending on the regolith and ice properties. For ice emplaced 630 kyr ago, the modeled burial depths align with observations and capture the observed longitudinal depth variations, in contrast to ice emplaced 4.18 Myr ago. We therefore infer that the mid-latitude subsurface ice is younger than 4 Myr.
On Mars, ice behaves like dry ice on a theater stage: it slowly evaporates, skipping the liquid phase, leaving only a dusty trail.
In the movie 'The Martian,' the hero extracts water from the soil — exactly as can be done with subsurface ice on Mars.