accretion - growth of a body by accumulation of surrounding material

asteroid - small, rocky body in orbit around the Sun

asteroid belt - region of the solar system bounded by the orbits of Mars and Jupiter which is occupied by the vast majority of minor planets

Chicxulub crater - a subterranean crater, roughly 180 km in diameter, located mostly in the Gulf of Mexico just north of the Yucatan peninsula

Cretaceous - geologic era extending from 135 to 65 million years ago

main belt - another name for asteroid belt

minor planet - another name for asteroid

protoplanetary - existing just prior to and involved in planetary formation

resonance - locations in the Solar System wherein the mean orbital motion of an asteroid is an exact integer ratio of Jupiter's mean orbital motion. For example, an asteroid at the 3:1 resonance makes three revolutions around the Sun for every one made by Jupiter.