![]() ![]() (2017) and Supplementary Information for more information on several of the products): The following data products are provided through this webpage (see Goossens et al. An example of Mars' crustal thickness using our lower crustal density (while applying a higher density of 2900 kg/m 3 to volcanic complexes). The Mars results are further described in Goossens et al. The lower bulk crustal density also has implications for models of the crustal thickness of Mars. The difference between the average density and the density for the volcanoes indicates strong lateral variations for Mars' crustal density. The density for the volcanic complexes is higher: from our model we find a density for Pavonis of 3231 kg/m 3, in good agreement with earlier estimates ( e.g., Belleguic et al., 2005). ![]() We find a bulk crustal density for Mars of 2582 +/- 209 kg/m 3, lower than generally assumed. We have applied this constraint to gravity field determination using the data from Mars orbiters that were also used for the GMM-3 gravity field model (see Genova et al. The RM1 constraint was applied with varying damping factors λ. Effective density ( A) and correlations between gravity and gravity-from-topography ( B) for various Mars gravity models. Thus, even for systems that are resolved not nearly as well as GRAIL’s, and therefore have an effective resolution well below the degree where the admittance becomes asymptotic ( e.g., Wieczorek et al., 2013), we can still obtain a reliable estimate of the bulk density.įigure 2. Using the data system of the pre-GRAIL lunar gravity model SGM150J (Goossens et al., 2011), we can robustly and independently determine the average bulk crustal density directly from the tracking data, using the admittance between topography and gravity: with the SGM150J data system and our RM1 constraint we find the same result as GRAIL. Our RM1 constraint model matches the results of the independent GRAIL model GRGM900C (Lemoine et al., 2014), showing that we can derive the crustal density robustly. Effective density ( A) and correlations between gravity and gravity-from-topography ( B) for various models based on the SGM150J data matrix system. The constraint is described in detail in Goossens et al. In this way, we can estimate the bulk crustal density directly from the satellite tracking data. Using the effective density spectrum ( e.g., Wieczorek et al., 2013), we interpret this factor as describing the bulk crustal density, if we choose x a to be gravity from uncompensated topography ( e.g., Wieczorek and Phillips, 1998). This factor α is the scale factor that is fully determined by the data. The constraint is applied with a damping factor λ, and it can be shown that for λ -> ∞, the solution for the gravity field model x will be α x a. It thus has one degree of freedom, and we call our constraint rank-minus-1 (RM1). The constraint assumes some description of the gravity field model, which we call x a, and it assigns infinite variance in this x a direction. ![]() This makes the constraint, and thus the resulting gravity field model, independent of some model crustal density. We have derived a constraint for use in gravity field determination from satellite tracking data that improves correlations of the gravity field with topography, while a scale factor between the two is determined completely by the data. As a consequence, the crustal density is assumed in geophysical studies, and a conservative range (e.g., spanning 2700-3100 kg/m 3) is adopted. For other terrestrial planets, the resolution of the models of the gravity field is often deemed too low to reliably estimate the bulk crustal density. Yet even with in-situ samples it is difficult to determine, as exemplified by the results of the Gravity Recovery And Interior Laboratory (GRAIL) mission: owing to the combination of high-resolution topography and high-resolution gravity, the bulk crustal density was found to be lower than assumed. The average bulk density of the crust is an important geophysical parameter, for example in studies of the planet's crustal thickness, its topographic support, and of its thermo-chemical evolution. Knowledge of the crust of a planet is important to constrain its formation and evolution. Mars Crust Density from Gravity & Topography Sander Goossens
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