Publication Abstracts

Cameron 1963

Cameron, A.G.W., 1963: Formation of the solar nebula. In Origin of the Solar System. R. Jastrow and A.G.W. Cameron, Eds. Academic Press, pp. 85-94.

I should like to start by discussing some of the difficulties that exist in the picture that has been presented in previous chapters by Fowler and by Hoyle. Let us see what seem to be the fundamental points of their analysis. Hoyle takes the minimum amount of mass in the solar nebula required to give the present amount of angular momentum to the planets. His whole cosmogony develops from this concept. It turns out, according to Fowler, that this is also an absolute upper limit on the mass that can be present and allow his nuclear transformations to take place. Fowler's nuclear arguments are based on the observation that there is a tremendous amount of deuterium in the earth and in the meteorites and that there are surprisingly small amounts of the isotopes Li6 and B10, which have the high neutron capture cross-sections, relative to the other lithium, beryllium, and boron isotopes. These statements seem to be the essence of the Fowler-Greenstein-Hoyle cosmogony.

I believe that Fowler's nuclear arguments certainly do not compel us to believe in the necessity for a solar nebula of very small mass. Thus, if a theory of the formation of the solar nebula gives us a very large amount of gas in the nebula, then one should not say that it is a strong argument against such a nebula that Fowler's nuclear reactions cannot take place in it.

Let us turn to the question of the formation of the solar nebula itself. Let me start with some comments on the picture that was outlined by Spitzer. He discussed the conditions required for an average interstellar cloud to become gravitationally unstable, and he went on to discuss the processes that come into operation during the collapse of such a cloud. He found that the magnetic energy density in such a cloud was too high to allow the fragmentation of it to carryon very far and for the fragments to approach stellar masses. Hence, in his view it is necessary that such a collapsing cloud hang up before it gets to the final stage of stellar fragmentation, and this period of suspended animation is supposed to continue long enough for most of the magnetic field to escape from the gas. Clearly this is one of the most interesting and also uncertain stages in Spitzer's discussion.

It has seemed somewhat unlikely that star formation should start from an average interstellar cloud such as is assumed by Spitzer. From the virial theorem we can see that it is much easier for a dense interstellar cloud to become gravitationally unstable than for an average one to do so. Much smaller total masses are required for gravitational instability in such a cloud. Hence I believe that we should more profitably :liscuss how star formation might start from an interstellar cloud possessing the highest observed density of material in space. There is observational evidence for gas densities as high as 1000 hydrogen atoms per cubic centimter or more in some clouds

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BibTeX Citation

@inproceedings{ca08120a,
  author={Cameron, A. G. W.},
  editor={Jastrow, R. and Cameron, A. G. W.},
  title={Formation of the solar nebula},
  booktitle={Origin of the Solar System},
  year={1963},
  pages={85--94},
  publisher={Academic Press},
  address={New York, N.Y.},
}

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RIS Citation

TY  - CPAPER
ID  - ca08120a
AU  - Cameron, A. G. W.
ED  - Jastrow, R.
ED  - Cameron, A. G. W.
PY  - 1963
TI  - Formation of the solar nebula
BT  - Origin of the Solar System
SP  - 85
EP  - 94
PB  - Academic Press
CY  - New York, N.Y.
ER  -

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