Supercomet

The “planetesimals” of the Chamberlin and Moulton hypothesis would (if we ascribe their origin to the constant formation of atoms in solar space by the various unions of electrons, protons and neutrons, instead of the one-time tidal disruption of the sun) supply the materials upon with a long-interval supercomet could feed and develop into a planetoid or, with increasing growth, into a planet.

Source: wiktionary

In Napier's Scenario, major impacts occur in the dying days of the supercomet when most of its ice has gone, at which point the rest of it disintegrates into "cometary asteroids".

Source: wiktionary

Low to one side, partly eclipsed by the curve of Earth's dark side, stretched the awesome spectacle of Athena's braided tail streaming in the solar wind as the supercomet fell toward the Sun.

Source: wiktionary