Active Ground Patterns Near Mars' Equator in the Glen Torridon Region of Gale Crater. Issue 10 (3rd October 2022)

• Record Type: Journal Article
• Authors: Hallet, Bernard; Sletten, Ronald S.; Malin, Michael; Mangold, Nicolas; Sullivan, Robert J.; Fairén, Alberto G.; Martínez, Germán; Baker, Mariah; Schieber, Juergen; Martin‐Torres, Javier; Zorzano, Maria‐Paz
• Is Part Of: Journal of geophysical research. Volume 127:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-10-03
• Subjects: patterned ground -- sorted patterns -- atmosphere‐regolith interactions -- granular systems -- active regolith processes -- self‐organization; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2021JE007126
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: On Mars, near the equator, much of the terrain in Gale Crater consists of bedrock outcrops separated by relatively smooth, uniform regolith surfaces. In scattered sites, however, distinct patterns—in the form and texture of the ground surface—contrast sharply with the typical terrain and with eolian bedforms. This paper focuses on these diverse, intriguing ground patterns. They include ∼1 to >10 m‐long linear disruptions of uniform regolith surfaces, alignments, and other arrangements of similar‐sized rock fragments and shallow, ∼0.1 m‐wide sandy troughs 1–10 m in length. Similar features were recognized early in the Mars Science Laboratory (MSL) mission, but they received only limited attention until Curiosity, the MSL rover, encountered striking examples in the Glen Torridon region. Herein, the ground patterns are illustrated with rover images. Potential mechanisms are briefly discussed in the context of the bedrock composition and atmospheric conditions documented by Curiosity. The evidence suggests that the patterns are active forms of spontaneous granular organization. It leads to the hypothesis that the patterns arise and develop from miniscule, inferred cyclic expansion and contraction of the bedrock and regolith, likely driven by oscillating transfers of energy and moisture between the atmosphere and the terrain. The hypothesis has significant implications for studies of contemporary processes on Mars on both sides of the atmosphere‐lithosphere interface. The ground patterns, as well as ripples and dunes formed by the wind, constitute remarkable extra‐terrestrial examples of granular self‐organization, complex phenomena well known in diverse systems on Earth. Plain Language Summary: Gale crater, which is near Mars' equator (4.5°S latitude), is generally rocky with sand and rocks scattered between extensive bedrock exposures. However, in a few local sites, distinct natural patterns mark the ground with ∼0.1 m‐wide, sand‐lined troughs and rocks arranged geometrically. We use detailed images from Curiosity, the Mars Science Laboratory rover, to illustrate these intriguing patterns in the Glen Torridon area, where they are widespread. We suggest they are currently active in the dry rock debris at the surface and driven by the sustained shrink‐swell activity of the underlying bedrock. This inferred activity, which likely results from variations in moisture and temperature in the lower Mars atmosphere, could generate these ground patterns, much like vibrations or analogous cyclic disturbances cause patterns to form naturally in diverse settings with granular materials of different sizes and shapes. The inferred cyclic shrink‐swell behavior of the shallow subsurface and underlying transfers of energy and mass may be of broad interest because of their potential implications for studies of processes shaping the Mars landscape and occurring in the lower atmosphere. These ground features, as well as ripples and dunes formed by the wind, are visible examples of extra‐terrestrial self‐organization. Key Points: Near Mars' equator, sandy troughs and organized rock fragments locally form distinct patterns suggestive of active ground deformation Unlike patterned ground on Earth, the ground patterns in Gale Crater form in thin, dry regolith overlying jointed bedrock Atmosphere‐surface exchange of energy and water vapor is inferred to drive self‐organization through cyclic subsurface volume changes