<P> In 1944 the German chemist and physicist Arnold Eucken considered the thermodynamics of Earth condensing and raining - out within a giant protoplanet at pressures of 100--1000 atm . In the 1950s and early 1960s discussion of planetary formation at such pressures took place, but Cameron's 1963 low - pressure (c. 4--10 atm .) model largely supplanted the idea . </P> <P> Jeans, in 1931, divided the various models into 2 groups: those where the material for planet formation came from the Sun and those where it didn't and may be concurrent or consecutive . </P> <P> William McCrea, in 1963, divided them into 2 groups also: those that relate the formation of the planets to the formation of the Sun and those where it is independent of the formation of the Sun, where the planets form after the Sun becomes a normal star . </P> <P> Ter Haar and Cameron distinguished between those theories that consider a closed system, which is a development of the Sun and possibly a solar envelope, that starts with a protosun rather than the Sun itself, and state that Belot calls these theories monistic; and those that consider an open system, which is where there is an interaction between the Sun and some foreign body that is supposed to have been the first step in the developments leading to the planetary system, and state that Belot calls these theories dualistic . </P>

Who proposed some early models of the solar system