Evidence for a low bulk crustal density for Mars from gravity and topography

Abstract

Knowledge of the average density of the crust of a planet is important in determining its interior structure. The combination of high‐resolution gravity and topography data has yielded a low density for the Moon's crust, yet for other terrestrial planets the resolution of the gravity field models has hampered reasonable estimates. By using well‐chosen constraints derived from topography during gravity field model determination using satellite tracking data, we show that we can robustly and independently determine the average bulk crustal density directly from the tracking data, using the admittance between topography and imperfect gravity. We find a low average bulk crustal density for Mars, 2582 ± 209 kg m−3. This bulk crustal density is lower than that assumed until now. Densities for volcanic complexes are higher, consistent with earlier estimates, implying large lateral variations in crustal density. In addition, we find indications that the crustal density increases with depth.

The Gravitational Signature of Martian Volcanoes

“…Neumann et al () have estimated the pore‐free density of this soil‐free rock to be 3,060 kg/m 3 . With a porosity of 10%, the bulk density becomes 2,754 kg/m 3 , which is close to the average bulk density given in Goossens et al (). Conversely, as the depth sensitivity of admittance analysis is difficult to evaluate, it is possible that the estimate of Goossens et al () is only sensitive to a portion of the upper crust that has been reworked by sedimentary processes and which has a high intrinsic porosity (see Lewis et al, , for an estimate of the density of near‐surface sedimentary deposits in Gale crater).…”

“…Note that in both cases, the degree of divergence is generally close to the maximum investigated degree of this study and should not affect the result (Table ). We think that these are due to the regularization procedure applied to small wavelengths for the model of Goossens et al (). No significant differences were found using the JGMRO_120 model.…”

“…Admittance (left) and correlation (right) spectra of the gravity field and topography of Mars using the gravity solutions JGMRO_95 of Konopliv et al (), JGMRO_110 of Konopliv et al (), JGMRO_120 of Konopliv et al (), GMM3_120 of Genova et al (), and GMM3‐GOOSSENS_120 of Goossens et al ().…”

High‐Resolution Gravity Field Models from GRAIL Data and Implications for Models of the Density Structure of the Moon's Crust

“…This effective density was also employed in (Besserer et al, ) and Han et al () to infer vertical variations in addition to the lateral variations. In Goossens et al (), we showed that applying this constraint to a pre‐GRAIL data system results in a bulk density estimate for the Moon close to that obtained from GRAIL data, 2550 kg m −3 (Wieczorek et al, ). The effective density spectrum for the RM1‐constrained solution presented in that work stays stable for its entire degree range.…”

The Thermal State and Interior Structure of Mars

“…However, gamma-ray measurements can only map the uppermost 10 cm of the crust, and little is known about the HPE distribution in deeper layers. In addition, the difference in crustal thickness between the northern and southern hemispheres (the so-called crustal thickness dichotomy) can be reduced if the crustal density varied between the two hemispheres (Goossens et al, 2017;Plesa et al, 2016). The results are non-unique; inferred crustal thicknesses vary between 30 and 87 km for uniform crustal densities between 2,700 and 3,200 kg/m 3 Wieczorek & Zuber, 2004).…”