  If dark matter is efficiently captured by a planet, energy released in its
annihilation can exceed that planet's total heat output. Building on prior
work, we treat Earth's composition and dark matter capture in detail and
present improved limits on dark matter-nucleon scattering cross sections for
dark matter masses ranging from 0.1 to $10^{10}$ GeV. We also extend Earth
limits by applying the same treatment to Mars. The scope of dark matter models
considered is expanded to include spin-dependent nuclear interactions including
isospin-independent, proton only, and neutron only interactions. We find that
Earth and Mars heating bounds are alleviated for dark matter s-wave
self-annihilation cross sections $\lesssim 10^{-44}~{\rm cm^2}$.
