Non-periodic comets are comets have only passed through the Solar System once. They do not orbit around the Sun, or they may take longer than 200 years to orbit. They are on orbits that will not bring them back to the Sun for hundreds, thousands, or even millions of years – if ever. Comets not expected to return to the Solar System include C/1980 E1, C/2000 U5, C/2001 Q4 (NEAT), C/2009 R1, C/1956 R1, and C/2007 F1 (LONEOS).
The official names of non-periodic comets begin with a "C"; comets that have been lost or disappeared have names that begin with a "D".