Calculate the escape velocity (the minimum initial velocity that will take an object to infinity) from the surface of a planet of radius R. What is the value for (a) the Earth, R = 6.37 × 106 m, g = 9.81 m s-2, (b) Mars, R = 3.38 × 106 m, mMars/mEarth = 0.108. At what temperatures do H2, He, and O2 molecules have mean speeds equal to their escape speeds? What proportion of the molecules have enough speed to escape when the temperature is (a) 240 K, (b) 1500 K? Calculations of this kind are very important in considering the composition of planetary atmospheres.