One of many small solid celestial bodies thought to have existed at an early stage in the development of the solar system

Usage examples of planetesimal.

Around the fast-growing sun, grains of dust and ice had accreted into swarming planetesimals.

Or perhaps the meteorological abnormalities in the planetesimal ring bodies that orbit the seventeenth geochemical hybrid ventigrain of Ursalia VII?

Solar System was very young, and the crusts of Earth and other inner planets were still subject to bombardment from stray planetesimals - a ship came here.

In consequence of the inevitable intersection of the orbits of the planetesimals, nodes are formed where the flying particles meet, and at these nodes large masses are gradually accumulated.

It may be added that the authors of the theory do not insist upon the appulse of two suns as the only way in which the planetesimals may have originated, but it is the only supposition that has been worked out.

Even as an explanation of the spiral nebulæ, not as solar systems in process of formation, but as the birthplaces of stellar clusters, the Planetesimal Hypothesis would be open to many objections.

Battered by a supernova shock, the cloud quickly coalesced into planetesimals: loosely aggregated lumps of rock and ice that swam chaotically through the dark, like blind fish.

But for reasons that still were not entirely understood, star systems with poorly developed planetary systems also seemed to produce a large number of dark comets--and Inferno shared its star with only two planets barely large enough to qualify as gas giants, a wizened little asteroid belt, and the usual sorts of deep space debris--comets, asteroids, planetesimals, and so on.