planetesimal

As nouns the difference between planetesimal and protostar

is that planetesimal is planetesimal while protostar is (star) a collection of gas and dust in space with high temperature that usually grows to the point of beginning nuclear fusion and becoming a star.

As nouns the difference between comet and planetesimal

is that comet is (astronomy) a celestial body consisting mainly of ice, dust and gas in a (usually very eccentric) orbit around the sun and having a "tail" of matter blown back from it by the solar wind as it approaches the sun while planetesimal is planetesimal.

As nouns the difference between planetessimal and planetesimal

is that planetessimal is while planetesimal is planetesimal.

As nouns the difference between planetesimal and preplanetesimal

is that planetesimal is planetesimal while preplanetesimal is (astronomy) a conglomeration of material that will form a planetesimal.