In 1943, the Soviet astronomer Otto Schmidt proposed that the Sun, in its present form, passed through a dense interstellar cloud, emerging enveloped in a cloud of dust and gas, from which the planets eventually formed. This solved the angular momentum problem by assuming that the Sun's slow rotation was peculiar to it, and that the planets did not form at the same time as the Sun.[7] Extensions of the model, together forming the Russian school, include Gurevich and Lebedinsky (in 1950), Safronov (in 1967,1969), Safronov and Vityazeff (in 1985), Safronov and Ruskol (in 1994), and Ruskol (in 1981), among others[12] However, this hypothesis was severely dented by Victor Safronov who showed that the amount of time required to form the planets from such a diffuse envelope would far exceed the Solar System's determined age.[7]