page_title: Gravity of Mars
section_title: Crustal thickness
hierarchical_section_title: Gravity of Mars / Geophysical implications / Crustal thickness
caption_attribution_description: English: Fig. 2. Histogram of crustal thickness versus area, adapted from Neumann et al., 2004.
context_page_description: The gravity of Mars is a natural phenomenon, due to the law of gravity, or gravitation, by which all things with mass around the planet Mars are brought towards it. It is weaker than Earth's gravity due to the planet's smaller mass. The average gravitational acceleration on Mars is 3.72076 ms⁻² and it varies laterally. In general, topography-controlled isostasy drives the short wavelength free-air gravity anomalies. At the same time, convective flow and finite strength of the mantle lead to long-wavelength planetary-scale free-air gravity anomalies over the entire planet. Variation in crustal thickness, magmatic and volcanic activities, impact-induced Moho-uplift, seasonal variation of polar ice caps, atmospheric mass variation and variation of porosity of the crust could also correlate to the lateral variations. Over the years models consisting of an increasing but limited number of spherical harmonics have been produced. Maps produced have included free-air gravity anomaly, Bouguer gravity anomaly, and crustal thickness. In some areas of Mars there is a correlation between gravity anomalies and topography.
context_section_description: No direct measurement of crustal thickness on Mars is currently available. Geochemical implications from SNC meteorites and orthopyroxenite meteorite ALH84001 suggested that mean crustal thickness of Mars is 100–250 km. Viscous relaxation analysis suggested that the maximum thickness is 50–100 km. Such thickness is critical in maintaining hemispheric crustal variations and preventing channel flow. Combination studies on geophysics and geochemistry suggested that average crustal thickness could be down to 50 ± 12 km.
  Measurement of gravity field by different orbiters allows higher-resolution global Bouguer potential model to be produced. With local shallow density anomalies and effect of core flattening eliminated, the residual Bouguer potential is produced, as indicated by the following equation,
  The residual Bouguer potential is contributed by the mantle. The undulation of the crust-mantle boundary, or the Moho surface, with mass of terrain corrected, should have resulted in varying residual anomaly. In turn, if undulating boundary is observed, there should be changes in crustal thickness.
  Global study of residual Bouguer anomaly data indicates that crustal thickness of Mars varies from 5.8 km to 102 km. Two major peaks at 32 km and 58 km are identified from an equal-area histogram of crustal thickness. These two peaks are linked to the crustal dichotomy of Mars. Almost all the crust thicker than 60 km are contributed by the southern highland, with generally uniform thickness. And the northern lowland in general has thinner crust. The crustal thickness of the Arabia Terra region and northern hemisphere are found to be latitude-dependent. The more southward towards the Sinai Planum and Lunae Planum, the more thickened the crust is.
  Among all regions, the Thaumasia and Claritis contain the thickest portion of crust on Mars that account for the histogram > 70 km. The Hellas and Argyre basins are observed to have crust thinner than 30 km, which are the exceptionally thin area in the southern hemisphere. Isidis and Utopia are also observed to have significant crustal thinning, with the center of Isidis basins believed to have the thinnest crust on Mars.
caption: Histogram of percentage area against crustal thickness of Mars: 32 km and 58 km are the two major peaks of the histogram.
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