Given the following approximations for planetary albedos and given approximate radii of their orbits, estimate the average effective temperature of the planets Mars and Neptune. (The effective temperature is the temperature at which the planet radiates thermal radiation in to space, which is not necessarily equal to the surface temperature). You may assume that the planets have circular orbits. Mars: albedo ≅ 0.16, r_orbit ≅ 2.28 × 10⁸ km; Neptune: albedo ≅ 0.29, r_orbit ≅ 4.5 × 10⁹ km.