M. Woolfson did some work in the 1960's in developing a new theory for the origin of the solar system involving the capture of material from a passing dwarf star. This material settled into orbit around the Sun and collected into the planets we now see. As for why this material did not just evaporate, the 'Woolfson Capture Theory' proposed that the gradiant of the gravitational field of the Sun was strong enough to stabalize this evaporating gas, which rapidly cooled to 50 - 100 K and condensed into planets. Aside for some anecdotal historical references, this theory is no longer viable since infrader astronomers have discovered so many circumstellar disks which could not have been created by infrequent '2-body' tidal encounters. For more details, see the paper in The Monthly Notices of the ROyal Astronomical Society 1971, vol. 151, page 307.