<P> and the Navier - Stokes equation for conservation of momentum is </P> <Dl> <Dd> D u D t = − ∇ p + ν ∇ 2 u + ρ ′ g + 2 Ω × u + Ω × Ω × R + J × B, (\ displaystyle (\ frac (D \ mathbf (u)) (Dt)) = - \ nabla p+ \ nu \ nabla ^ (2) \ mathbf (u) + \ rho' \ mathbf (g) + 2 \ mathbf (\ Omega) \ times \ mathbf (u) + \ mathbf (\ Omega) \ times \ mathbf (\ Omega) \ times \ mathbf (R) + \ mathbf (J) \ times \ mathbf (B),) </Dd> </Dl> <Dd> D u D t = − ∇ p + ν ∇ 2 u + ρ ′ g + 2 Ω × u + Ω × Ω × R + J × B, (\ displaystyle (\ frac (D \ mathbf (u)) (Dt)) = - \ nabla p+ \ nu \ nabla ^ (2) \ mathbf (u) + \ rho' \ mathbf (g) + 2 \ mathbf (\ Omega) \ times \ mathbf (u) + \ mathbf (\ Omega) \ times \ mathbf (\ Omega) \ times \ mathbf (R) + \ mathbf (J) \ times \ mathbf (B),) </Dd> <P> where ν (\ displaystyle \ nu) is the kinematic viscosity, ρ ′ (\ displaystyle \ rho') is the density perturbation that provides buoyancy (for thermal convection ρ ′ = α Δ T (\ displaystyle \ rho' = \ alpha \ Delta T)), Ω (\ displaystyle \ Omega) is the rotation rate of the Earth, and J (\ displaystyle \ mathbf (J)) is the electric current density . </P>

Which of the following has virtually no effect on the internal structure of a planet