|MadSci Network: Astronomy|
Kuiper's cosmic cloud theory dates back to the 1950s when Gerard Kuiper attempted to obtain a "satisfactory theory of the origin of the solar system" (1) which accounted "for the presence and the properties of the planets and the smaller bodies surrounding the sun, and preferably, but not necessarily, for the dynamical properties of the sun also" (1). Essentially, he was trying to determine the theory for the origin of the solar system and the mass of the nebula that formed our Sun and planets.
Back in 1951, we already knew that the composition of the Sun is typical for that of other stars and even for that of the interstellar medium, the space between the stars. In his 1951 paper, Kuiper defines this composition as "cosmic." He goes on to say that "the cloud from which the planets formed will almost certainly have been of cosmic composition." Additionally, he thought that by comparing planetary composition to cosmic composition, the mass of the nebula from which the planets condensed could be determined, and he found this mass to be 0.06 solar masses (1 solar mass = 10^33 grams). He thought that the total mass of the solar nebula was around 0.1 solar masses(1).
Molecular cloud cores, from which stars and their planets form, range in mass between 5 and 100,000 solar masses. Using today's astronomical definitions, we define the solar nebula as the phase immediately following formation of the Sun, when the planets form by accretion of planetesimals. The mass of the solar system's solar nebula was about 0.01 solar masses and the radius was about 100 AU (1 AU = 93 million miles, the distance between the Earth and the Sun). Today, we would call Kuiper's "solar nebula" a protoplanetary disk or proplyd. The mass of the outer disks of proplyds in the Orion nebula have been measured to be at least several times the mass of the Earth, and entire disks are 53 billion miles across, or 15 times the radius of our Solar System. The central star is about one fifth the mass of our Sun (0.20 solar masses) (2).
(1) Gerard P. Kuiper 1951, "On the Origin of the Solar System," Proceedings of the National Academy of Sciences (PNAS), vol. 37, pg. 1--14.
(2) Orion's proplyds
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