Small particles might be blown out of solar systems by the radiation pressure of sunlight. Assume that the particles are spherical with a radius r and a density of 1 g/cm³ and that they absorb all the radiation in a crosssectional area of πr². They are a distance R from the sun, which has a power output of 3.83 × 10²⁶ W. What is the radius r for which the radiation force of repulsion just balances the gravitational force of attraction to the sun?