In
cosmogony,
planetesimals are objects thought to exist within
solar nebulae. Planetesimals are thought to form from the coalescing (due to
gravity) of
particles,
orbiting within the
accretion disc of the solar nebula; an accumulation of planetesimals leads to the formation of a
protoplanetary disc, which in turn coalesce into
protoplanets/
planets. Some use the term to refer, in general, to objects such as
asteroids and
comets; other, such as
Comins[?] use the term to refer, specifically, to objects with
diameters of ~10km.
The Sol System
It is generally argued that by about 3.8 billion years ago most of the planetesimals, within Sol's system, had either left orbit or coalesced into larger objects. Most of the remaining planetesimals orbit within the asteroid belt.
See also: Giant impact theory
References
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