Station: As the planetesimal clears its path around the star, it gains mass and can become a protoplanet.
Alkina: Let’s try getting into the server room through this crawl space.
Station: Protoplanets are massive enough that their gravity affects other planetesimals in the solar system.
Alkina: How much longer for you, Epo?
Epo: 80% complete.
Station: Occasionally, the planetesimals collide with the protoplanets, other times they become their satellites. Small planetesimals that aren’t swept up often become the asteroids and comets of the forming system.
Alkina: I think I see the opening up ahead.
In human speak please!
The computer tour-guide talks about objects clearing their paths around the star that they orbit. When a solar system begins to form, it does so from dust and gas. Planetesimals and protoplanets do not form standing still, they orbit their parent star through the dust and gas. In essence, the planetesimals and protoplanets are colliding with the dust and gas in their path. The dust and gas they don’t absorb will either start orbiting the planetesimal or protoplanet or it will get pushed out of the path (and possibly absorbed by another forming planet).
On the flip side, as planetesimals and protoplanets gain mass their gravitational pull increases. So they actually begin attracting dust and gas along the edges of their orbits. This ultimately causes the planetesimal or protoplanet to clear a path that is wider than itself.