Minimum-mass solar nebula

The minimum-mass solar nebula estimates a primordial gas-and-solid protoplanetary disk by spreading planetary material into annuli and restoring a solar mixture. A common idealized surface density is proportional to $r^{-3/2}$. This reconstruction is a model of minimum material requirements, not a unique history of the Solar System. Extrapolating it far beyond the planetary region need not give a physically consistent disk.