Consider a small, spherical particle of radius r located in space a distance R = 3.90 1011 m from the Sun. Assume the particle has a perfectly absorbing surface and a mass density of rho = 1.40 g/cm3. Use S = 220 W/m2 as the value of the solar intensity at the location of the particle. Calculate the value of r for which the particle is in equilibrium between the gravitational force and the force exerted by solar radiation.