3911 20190125173504.0 POSTER-2019-0036 Beuthe, Mikael Isostasy on Mercury in the presence of lateral variations of crustal density 2018 2018-12-11 AGU poster reference: P23F-3507 A good knowledge of Mercury’s crust is essential in fields as different as planetary formation, interior structure models, thermochemical evolution, volcanic history, surface mineralogy, or impact cratering. Although gravity anomalies and shape measured by the MESSENGER spacecraft can be converted into crustal thickness maps with unprecedented accuracy, these data do not directly constrain the average crustal thickness. Determining this crucial parameter requires additional assumptions about the mechanical equilibrium of the crust and mantle, often going under the name of isostasy. Previous studies of that kind predicted that Mercury’s crust is on the average rather thin, with a 2𝝈 range of 0 to 70 km. We investigate here the influence of three factors on these estimates. First, the accuracy of the gravity solution has improved in the meantime by a factor of two. Second, X-ray surface spectra acquired by MESSENGER show that surface composition, and thus also crustal grain density, varies significantly in the areas where isostasy is thought to be valid. Third, large-scale isostasy in the presence of internal crustal loads should be modeled in a self-consistent way with minimum stress isostasy. Integrating these three factors in our analysis, we derive new constraints on the average crustal thickness of Mercury. PRODEX/ 4000120791/ PlanetInterior NO Rivoldini, Attilio Van Hoolst, Tim Charlier, Bernard Namur, Olivier American Geophysical Union Fall Meeting, Washington D.C. mikael.beuthe@observatoire.be https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/430742 CPOSTER