Lost comet

Comet which was not detected during its most recent perihelion passage

A lost comet is one which was not detected during its most recent perihelion passage. This generally happens when data is insufficient to reliably calculate the comet's location or if the solar elongation is unfavorable near perihelion passage. The D/ designation is used for a periodic comet that no longer exists or is deemed to have disappeared.

This keyword could refer to multiple things. Here are some suggestions: