Martian regolith: from cryolithosphere to atmosphere

Caprarelli, Graziella1

1Centre for Astrophysics, School of Sciences, University of Southern Queensland, Toowoomba, QLD 4350, Australia

Regolith is: “everything, from fresh rock to fresh air”1. The term indicates the layers of loose material that mantle bedrock, although there is disagreement among regolith experts between the camp that subscribes to the broad definition given above, and the camp that discriminates between the material formed in place as a product of weathering, and sediments formed elsewhere, transported and deposited on bedrock which was not the parent material2. We now know that regolith mantles the surface of all rocky bodies in the solar system: on many of these objects there are no geological processes leading to sedimentary erosion and deposition such as on Earth. Thus, here I use the term in its broader sense.

Mars is a hyperarid planet3, with water stored as ice in its polar caps and in the ground. The uppermost layers of the martian crust are thus termed the ‘cryolithosphere’. Meteoritic “gardening” since early Noachian times (~ 4.0 Ga) has produced the thick layer of broken rocky material covering Mars’s surface globally. Wind erosion and mass wasting also act on a global scale, while chemical processes have led to the deposition of hydrous minerals in the soil. The martian regolith thus comprises dust, sandy soils and sediments, pebbles, rocks, secondary minerals, and may include water ice at mid- to high latitudes, where permafrost landforms are observed4, and where additional disintegration of bedrock occurs owing to thaw/freeze cycles. Aeolian processes move solids across the martian surface: dust particles (< 10 mm) may remain in suspension indefinitely; dust and silt (< 60 mm) are lifted and may be deposited at great distance by atmospheric currents; sand particles (up to a few hundred mm) move by saltation, breaking into smaller fragments that may then be lifted; coarse grained material (1-5 mm in size) is dragged or accumulates as lag deposits. A way to study the distribution of these materials is through satellite thermophysical data: mapping based on thermal inertia and albedo classification5 shows links between type of material and geology.

My colleagues and I have investigated the spatial distribution and vertical composition of the martian cryolithosphere through impact processes6 and by ground penetrating radar7. Here, I show and discuss the main outcomes of our work in relation to: (a) the spatial distribution of the martian regolith and its composition; (b) ground ice and regolith; (c) the link between cryolithosphere and atmosphere. These aspects underpin part of the geological and climatological history of the planet, with far reaching implications about the selection of landing sites and possible future human missions to Mars.       

1Eggleton RA, Ed. (2001) CRC LEME, ISBN 0-7315-3343-7, 144 pp.

2Pain and Ollier (1996) AGSO J Austral Geol Geophys 16(3), 197-202. 

3Baker VR (2001) Nature 412, 228-236. 

4Lasue et al. (2013) Space Sci Rev 174, 155-212.

5Jones et al. (2014) Remote Sensing 6, 5184-5237.

6Jones et al. (2016) JGR Planets 121, 986-1015.

7Orosei et al. (2017) JGR Planets 122, 1405-1418.


Dr Graziella Caprarelli FAIG is Adjunct Research Fellow with the Centre for Astrophysics at the University of Southern Queensland, Adjunct Research Professor at the International Research School of Planetary Sciences (Italy), and member of MARSIS science team. She explores the martian subsurface geology looking for water.

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