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The hypothesis that the planets and satellites of the solar system were formed by gravitational aggregation of planetesimals.
(Astronomy) the discredited theory that the close passage of a star to the sun caused many small bodies (planetesimals) to be drawn from the sun, eventually coalescing to form the planets
[C20: planetesimal, from planet + infinitesimal]
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|Noun||1.||planetesimal hypothesis - (cosmology) the theory that the solar system was formed by the gravitational accumulation of planetesimals|
scientific theory - a theory that explains scientific observations; "scientific theories must be falsifiable"