1. The problem statement, all variables and given/known data Calculate orbital radius of planet X using the given variables of its star: T=500 K, radius R=0.1 x Sun's radius, mass M=0.5 x Sun's mass and also its receives the same flux as the Earth receives from the Sun. I forgot to mention also that the orbit is circular, so the orbital radius=distance between planet X and its star. 2. Relevant equations Probably Newton's version of kepler's third planetary motion equation, but not really sure. 3. The attempt at a solution I have tried using various forms of keplers' third planetary motion equation, but I don't have the period of orbit, like in hours, so I have more than one missing variable. Besides that, I've tried looking for an equation to yield the orbital radius using the variables I'm given but I've got nothing so far. The other thing I thought of is that maybe I can use equations for a binary pair of stars to calculate Planet X's orbital radius, but I didn't know how to proceed with it.