Fig. 1
Feasibility of running a dynamo in a liquid silicate mantle in Mars as a function of mid-mantle heat flux Q m . The heat flux is scaled relative to the present-day heat flux Q m,n o w as estimated by Sohl and Spohn (1997). ν T , ν MAC, and ν CIA show three families of potential dynamos driven by different types of flows (see text). Thick and thin lines of each pair denote low and high estimates of silicate electrical conductivity, σ (8.9–22.9 S m −1). R m values greater than 40 (horizontal dotted line) indicate feasible range for dipolar dynamos. Turbulent flow speeds are capable of running dynamos at any mantle heat flow provided that the mantle is liquid. Magnetostropic dynamos are also feasible in the high heat flux epoch early in Mars evolution (vertical dotted lines; 0–1 Gyr according to Breuer et al. (2010)). Geostrophic dynamos do not seem feasible under any realistic heat flow scenario