Building planets from protoplanetary discs

Planets and their stars form from the same reservoir of nebular material and their chemical compositions should therefore be correlated but the observed compositions of planets do not match completely those of their central stars. In our Solar system, for example, all the rocky planets and planetesimals contain near-solar proportions of refractory elements (elements like aluminum that condense from a gas when the temperature falls below about 1500 kelvin) but are depleted in volatile elements (t...