Knowing the asteroid's composition isn't required to calculate the mass. This can be derived by the orbit. So, the total mass of the binary system (main and moo

Knowing the asteroid's composition isn't required to calculate the mass. This can be derived by the orbit. So, the total mass of the binary system (main and moonlet) is known, but the mass contribution of each isn't. Assuming though that they have the same bulk density, M2/M1 = (D2/D1)^3 ~ 0.0116 and considering Σ Mi = M, then M2 ~ 0.0115M.