On the difficulty to detect Mercury's mantle convection from future gravity data

Abstract

Thermo-chemical evolution and convection models of Mercury suggest that its thin mantle may still exhibit thermal convection. To confirm or disregard this assumption, future gravity and topography data can be in principle used. In the case of present-day mantle convection the dynamic flow in the mantle not only generates a gravity signal possibly detectable above the surface of the planet, but also modifies the observed planetary topography. To estimate the possible amplitudes of these dynamic signatures self- consistently, we have employed a viscous mantle flow model coupled with an overlaying thick elastic lithosphere. For a wide range of present-day elastic thicknesses obtained using a parameterized thermal evolution model and maximal temperature anomalies in the present mantle of Δ T =± 100 K, we find that the dynamic geoid and topography do not exceed significantly ± 10 and ± 250 meters, respectively. Unless the present-day elastic thickness is significantly smaller than the results of thermal- evolution models suggest, we will not be able to distinguish between a convecting or a non-convecting mantle. This is in contrast to earlier findings of Spohn et al. [2001], Breuer et al. [2007] and Redmond and King [2007]. References: Spohn et al. (2001), Planet. Space Sci., 49, 1561--1570. Redmond and King (2007), Phys. Earth Planet. Int., 164, 221--231. Breuer et al. (2007), Space Sci. Rev., 132(2-4), 229--260.