The Runts of the Cosmic Litter

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Science  04 Jan 2002:
Vol. 295, Issue 5552, pp. 64-65
DOI: 10.1126/science.295.5552.64

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Brown dwarfs and other substellar bodies behave like giant planets, but most of them may form like stars. On the other hand, a few of the scores of known planets outside our solar system look more like brown dwarfs than planets. And some free-floating "planetary-mass objects" as light as 5 Jupiter masses have surfaced in surveys of young star clusters, the birthplaces of which are impossible to trace. Astronomers are beginning to suspect that brown dwarfs can form in either of two different ways: from very large planets or very small stars.

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