What critically defines a protoplanet, setting it apart from a smaller, kilometer-sized planetesimal?
Answer
Its gravity being powerful enough to systematically clear out kilometer-sized bodies
While both planetesimals and protoplanets are large enough to be influenced by gravity, the defining difference lies in the scale and effectiveness of that influence. A planetesimal's gravity is localized, leading mainly to direct, gentle impacts. A protoplanet, having undergone significant runaway accretion, develops a much larger sphere of gravitational influence. This superior gravitational dominance allows the protoplanet to systematically incorporate or gravitationally scatter all other kilometer-sized bodies in its orbital neighborhood, signifying a much higher degree of maturation.
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