Some grazing comets come very close to the Sun. Why aren they Vulcanoids?
All known grazing comets that survive their very close perihelion passage to the Sun have an aphelion that is much farther away. Their mean distance to the Sun is greater than that of Mercury. Some comets that pass close to the Sun eject fragments that temporarily orbit. Those fragments soon vaporize and/or fall into the Sun and therefore are not permanent residents of the Vulcanoid zone.
