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Brown Dwarfs
The dividing line between planets and brown dwarfs occurs with objects that have
masses below about 1 percent of the mass of the Sun, or 10 times the mass of
Jupiter. These objects cannot fuse deuterium. It is also thought that planets
form by a different mechanism from brown dwarfs. Planets form through the
coalescence of small rocky or icy bodies in a disk around a star, whereas brown
dwarfs form by collapsing from a cloud of dust and gas. Recent discoveries of
large gaseous planets near stars may have cast some doubt on this distinction,
however.
Because it has no strong central nuclear energy source, the interior of a brown
dwarf is in a rapid boiling, or convective motion. When combined with the rapid
rotation that most brown dwarfs exhibit, convection sets up conditions for the development of a
strong, tangled magnetic field
near the surface.
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