Analysis of the Cessation of Convection in Mercury's Mantle.

The question of whether the present‐day mantle of Mercury is undergoing convection remains unresolved. We address this issue by estimating the minimum value of the core‐mantle boundary (CMB) temperature needed to support mantle convection and considering the time required to cool the mantle below this threshold. A simple mathematical analysis of the cooling of the core, based on the assumption of a quasi‐steady‐state thermal equilibrium of Mercury's mantle, shows that the CMB temperature falls to the critical temperature for cessation of convection roughly halfway through the planet's evolutionary history. To first order, the duration of subsolidus convection does not depend on the absolute value of the viscosity. It depends primarily on parameters that control the viscosity function, such as the stress exponent and the activation energy. Our results based on conventional assumptions suggest the absence of present‐day mantle convection in Mercury, which is consistent with numerical models of Mercury's thermal history. However, because of large uncertainties in the controlling parameters, the possibility of still ongoing mantle convection on Mercury cannot be ruled out. Plain Language Summary: We address the question of whether Mercury's mantle is currently convecting. We start by applying recent constraints on the onset of convection in fluids with variable viscosity to estimate the critical mantle temperature below which convection in Mercury's mantle stops. Then we derive simple formulas for the time required for the mantle to cool down to this critical temperature. These formulas allow us to analyze various factors controlling the cooling time and assess the conditions under which mantle convection may occur on Mercury today. Key Points: We constrain the critical conditions for the cessation of convection in Mercury's mantleWe derive approximate formulas for the time it takes mantle convection to cease during Mercury's evolutionMercury's mantle is likely not convecting at present; however, the uncertainties remain large [ABSTRACT FROM AUTHOR]