The minimum mass of a proto-solar system disk

Astronomers estimate that at the time the Solar system formed, its proto-planetary disk contained the equivalent of about twenty Jupiter-masses of gas and dust. This so-called "minimum mass solar nebula (MMSN)" is derived from the current masses of the rocky planets and calculations of how they formed; a minimum mass is used in case the planet formation mechanism is somehow less efficient than expected. (Some earlier estimates had MMSN values up to about 100 Jupiter-masses.) As a nebula ages and