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Recent planetary geology research has brought significant attention to peculiar surface features on Mars known as boxwork formations. These geological structures, first identified in terrestrial caves like those of Wind Cave National Park in South Dakota, are intricate networks of intersecting ridges that form angular, often polygonal patterns on rock surfaces. On Mars, these formations provide intriguing evidence of the planet’s aqueous and diagenetic history, and they continue to fuel ongoing debates about Mars’ past habitability and climate.

Boxwork formations on Mars refer to polygonal or lattice-like patterns of raised ridges that commonly appear to crisscross the surface of sedimentary rocks. They are most often observed in eroded areas where the surrounding, less-resistant matrix has been stripped away, leaving behind the more resilient mineralized veins. These features resemble fossilized skeletons of a once-buried fracture network, now exposed by aeolian (wind-driven) erosion. The ridges are typically centimeters to meters in height and can span several meters in length, forming grid- or honeycomb-like patterns.

Boxwork-like features were first clearly documented on Mars by high-resolution imaging instruments aboard NASA’s Mars Reconnaissance Orbiter (MRO), particularly by the High Resolution Imaging Science Experiment (HiRISE) and the Context Camera (CTX). Notable observations include:

Gale Crater, explored by the Curiosity rover, where polygonal fracture patterns in sedimentary rocks were observed and interpreted as evidence of past fluid movement through rock.

Nilosyrtis region and Northeast Syrtis, both imaged by HiRISE, show spectacular examples of boxwork-like ridges.

Murray Buttes, inside Gale Crater, features boxwork textures that suggest extensive fracture-filling and mineral precipitation processes.

More recently, the Perseverance rover, exploring Jezero Crater since 2021, has detected similar linear ridges within ancient deltaic deposits, although their exact classification as boxwork is still under study.

These features are often associated with hydrated minerals, especially sulfates and clays, suggesting an interaction between water and rock over extended periods.

The most widely accepted model for the formation of boxwork on Mars involves mineral-filled fractures, a process consistent with what is observed in analogous terrestrial environments. The prevailing theory includes several key stages:

Fracturing of Host Rock: Martian bedrock, likely composed of volcanic or sedimentary materials, develops a network of fractures due to tectonic stress, desiccation (drying), or thermal contraction.

Fluid Infiltration and Mineral Precipitation: Subsurface fluids, likely brines or groundwater, percolate through the fractures, depositing minerals such as hematite, silica, sulfates, or carbonates along the walls of the fractures.

Cementation: Over time, these mineral deposits harden and cement the fracture walls.

Erosion of Host Matrix: Wind erosion or chemical weathering preferentially removes the surrounding, softer rock, leaving behind the more resistant mineral veins as raised ridges—creating the boxwork pattern.

In some cases, researchers hypothesize that the mineralization may have occurred during early diagenesis (sediment-to-rock transformation), potentially linked to hydrothermal systems or long-standing subsurface aquifers. The distribution and composition of these ridges support the idea that groundwater was once active and persistent in Martian history.

Boxwork structures are crucial for reconstructing Mars’ environmental history. They serve as indirect evidence for past water activity and reveal subsurface fluid pathways, potentially pointing to habitats that could have supported microbial life. Their mineralogical composition, especially when hydrated phases are present, offers insights into the chemical conditions that prevailed during their formation.

Moreover, the preservation of such delicate structures indicates limited subsequent geological disturbance, suggesting that some regions on Mars have remained relatively unchanged for billions of years. As such, they are prime targets for future in-situ analysis and sample return missions, especially those seeking biosignatures or geochemical proxies of past life.

Video credit: NASA Jet Propulsion Laboratory