Sculpting of Martian brain terrain reveals the drying of ancient Mars

The Martian brain terrain (MBT), characterized by its unique brain-like morphology, is a potential geological archive for finding hints of paleoclimatic conditions during its formation period. The morphological similarity of MBT to self-organized patterned ground on Earth suggests a shared formation mechanism. However, the lack of quantitative descriptions and robust physical modeling of self-organized stone transport jointly limits the study of the thermal and aqueous conditions governing MBT’s formation. Here we established a specialized quantitative system for extracting the morphological features of MBT, taking a typical region located in the northern Arabia Terra as an example, and then employed a numerical model to investigate its formation mechanisms. Our simulation results accurately replicate the observed morphology of MBT, matching its key geometric metrics with deviations $<10%$. Crucially, however, we find that the self-organized transport can solely produce relief $<0.5$ m, insufficient to explain the formation of MBT with average relief of $3.29 \pm 0.65$ m. We attribute this discrepancy to sculpting driven by late-stage sublimation, constraining cumulative subsurface ice loss in this region to $\sim 3$ meters over the past $\sim 3$ Ma. These findings demonstrate that MBT’s formation is a multi-stage process: initial patterning driven by freeze-thaw cycles (implying liquid water) followed by vertical sculpting via sublimation (requiring a dry environment). This evolution provides physical evidence for the transition of the ancient Martian climate from a wetter period to a colder hyper-arid state.

💡 Research Summary

The paper investigates the origin of Martian Brain Terrain (MBT), a distinctive, brain‑like patterned surface that occurs in the mid‑latitudes of both hemispheres. The authors first note that MBT’s morphology closely resembles self‑organized patterned ground on Earth, suggesting a common formation mechanism involving stone transport driven by freeze‑thaw cycles. However, previous work lacked quantitative morphological descriptors and robust physical modeling, limiting the ability to infer the thermal and aqueous conditions that produced MBT.

To address this gap, the authors selected a representative area in northern Arabia Terra and employed high‑resolution HiRISE imagery together with a digital terrain model (DTM) to extract three key geometric metrics: depression‑area fraction (DAF), depression spacing (DS), and depression width (DW). An automated pipeline identified DAF values ranging from ~5 % to ~40 %, with mean DS = 27.2 ± 2.3 m and mean DW = 7.9 ± 0.9 m. The DS‑DAF relationship is non‑monotonic (DS decreases then increases with DAF), while DW increases monotonically with DAF, providing a detailed statistical description of MBT’s surface pattern.

Next, the authors built a physics‑based model of self‑organized stone transport. The model treats stone concentration as a scalar field that evolves under a phase‑separation framework, incorporating parameters such as the stone‑movement rate (v), a characteristic length scale (λ), a coupling constant (c), and the number of simulation steps (t). By scanning λ, c, v, and t, they identified a region of parameter space where “brain‑pattern” formation occurs. Using v ≈ 3.3–3.9 mm per freeze‑thaw cycle and t ≈ 2 × 10⁹ steps, the simulated terrain reproduces the observed MBT morphology with deviations under 10 % for all three metrics. The model also reproduces the observed DAF values (≈17–29 %) across three simulated cases, matching the field measurements.

A critical finding is that the simulated relief (vertical height difference) never exceeds ~0.5 m, even when varying the angle of repose (θ) between 30° and 60° and packing densities (η) between 50 % and 70 %. In contrast, the actual MBT in the study area exhibits an average relief of 3.29 ± 0.65 m, an order of magnitude larger. This discrepancy indicates that self‑organized stone transport alone cannot generate the full topographic amplitude of MBT.

The authors argue that a second, later stage must have amplified the relief. They evaluate possible external processes—impact cratering, aeolian erosion, and sublimation—and reject impacts (random, localized) and aeolian erosion (tends to smooth rather than deepen depressions). Sublimation of subsurface ice, a process known to operate widely across Martian mid‑latitudes, emerges as the most plausible mechanism. In the early stage, freeze‑thaw cycles require subsurface ice, which later provides the material for sublimation. During sublimation, ice‑rich low‑stone‑concentration zones lose volume faster than ice‑poor high‑stone‑concentration zones, producing differential subsidence that can increase relief by several meters. The authors estimate that ~3 m of ice loss over the past ~3 Ma would be sufficient to generate the observed relief.

From a climatic perspective, the two‑stage model implies a transition in Martian environmental conditions. The first stage requires temperatures above the melting point of water and sufficient atmospheric pressure to permit liquid water, indicating a relatively warmer, wetter climate. The second stage operates under cold, hyper‑arid conditions where ice sublimates directly to vapor, reflecting the modern Martian climate. Thus, MBT records a shift from a thawing, potentially habitable epoch to a cold, desiccated one.

In conclusion, the study provides a comprehensive, quantitative framework that couples detailed morphological extraction with a physically grounded self‑organization model and a subsequent sublimation‑driven modification phase. This dual‑process explanation not only resolves the long‑standing debate over MBT formation but also offers a new proxy for reconstructing ancient Martian climate evolution. The methodology can be extended to other icy planetary surfaces, opening avenues for deciphering paleoenvironments across the Solar System.