Abstract
PETER VAN DE KAMP has an article with this title in Sky and Telescope of December 1944, in which he deals with the question of the criterion for stars and planets—a matter of considerable importance in view of the fact that recent discoveries have shown the existence of 'planets' fifteen or twenty times the mass of Jupiter. He accepts Russell's critical value of 1/20 of the sun's mass as a conventional borderline between visible stars and the invisible bodies which can be designated as 'planets'. This criterion defines a planet or star, therefore, by its mass, not by its size. Among the methods for detecting unseen companions of low mass is the photographic method applied to nearby stars, and if the determination of the orientation of the perturbation orbit were sufficiently accurate, good results would be obtained. Difficulties arise from the fact that photographic star images are 1"–3" in diameter, and most of the recently discovered perturbations have a total amplitude of less than 0·1". The gravitational method for discovering faint companions of low mass, while it is more powerful than the direct visual approach, has decided limitations for very low masses, and it would be extremely difficult by this method to find companion masses less than 1/100 times the sun's mass, even for the nearest stars. The star which seems unattended by dark companions may be the exception, and it is possible that the stars attended by massive companions, rather than by small planets, are in the decided majority. Our solar system may prove to be an extreme type of system, rather than an average type. Though generously endowed with planets, the sun is the only star known that has no close companion star.
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Stars or Planets?. Nature 155, 387–388 (1945). https://doi.org/10.1038/155387c0
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DOI: https://doi.org/10.1038/155387c0