Spin of the planet due to PA as a function of planet mass. The more massive the planet, the less spin reaches the planet’s surface. For planets of 0.5 Earth masses and above, the atmosphere absorbs all incoming spin. In the absence of an atmosphere, there is a large domain of retrograde spin for planets larger than 0.1–0.2 Earth masses. An atmosphere could prevent this strong retrograde spin build-up and leave the planet with prograde spin at the end of its evolution.