List of periodic comets
Periodic comets are comets with orbital periods of less than 200 years or that have been observed during more than a single perihelion passage. "Periodic comet" is also sometimes used to mean any comet with a periodic orbit, even if greater than 200 years.
Periodic comets receive a permanent number prefix usually after the second perihelion passage, which is why there are a number of unnumbered periodic comets, such as. Comets that are not observed after a number of perihelion passages, or presumed to be destroyed, are given the D designation, and likewise comets given a periodic number and subsequently lost are given D instead of P, such as 3D/Biela or 5D/Brorsen.
In nearly all cases, comets are named after their discoverers, but in a few cases such as 2P/Encke and 27P/Crommelin they were named for a person who calculated their orbits. The long-term orbits of comets can be difficult to calculate due to errors in the known trajectory that can accumulate from perturbations from the planets. Even so, quite a few comets were lost because their orbits are also affected by non-gravitational effects such as the release of gas and other material that forms the comet's coma and tail. Unlike a long-period comet, the next perihelion passage of a numbered periodic comet can be predicted with a high degree of accuracy.
Periodic comets sometimes bear the same name repeatedly ; the IAU system distinguishes between them either through the number prefix or by the full designation. In the literature, an informal numbering system is applied to periodic comets, thus 181P and 192P are known as Comet Shoemaker–Levy 6 and Comet Shoemaker–Levy 1, respectively. Non-periodic Shoemaker–Levy comets are interleaved in this sequence: C/1991 B1 between 2 and 3, C/1991 T2 between 5 and 6, C/1993 K1 and C/1994 E2 after Shoemaker–Levy 9.
In comet nomenclature, the letter before the "/" is either "C", "P", "D", "X", "I" for an interstellar object, or "A" for an object that was either mistakenly identified as a comet, but is actually a minor planet, or for an object on a hyperbolic orbit that does not show cometary activity. Some lists retain the "C" prefix for comets of periods larger than about 30 years until their return is confirmed.
List of unnumbered Jupiter-family comets
While Jupiter-family comets are officially defined by 2 < TJupiter < 3, they can also be loosely defined as any comet with a period of less than 20 years, a relatively low inclination, and an orbit coinciding loosely with that of Jupiter. These comets are often patchily observed, as orbital interactions with the planet often cause comets' orbits to become perturbed, causing them to not be found at the expected position in the sky and subsequently lost. Additionally, their low cometary albedos and frequent proximity to the Sun compared to Oort Cloud comets cause them to much more quickly become depleted of volatiles, making them comparatively dimmer than comets with longer orbital periods.List of unnumbered Chiron-type comets
| Comet designation | Name/ discoverer | Period | e | a | q | i | Abs. mag. | Nucleus radii | Last observed perihelion | Next perihelion | Ref |
| P/2005 S2 | Skiff | 22.5 | 0.1967 | 7.965 | 6.398 | 3.14 | 7.9 | 2.0 km | 2006/06/30 | 2029 | |
| P/2005 T3 | Read | 20.6 | 0.1738 | 7.507 | 6.202 | 6.26 | 9.2 | 2006/01/12 | 2026 | ||
| C/2011 P2 | PanSTARRS | 30.5 | 0.3698 | 9.756 | 6.148 | 8.99 | 6.7 | 2010/09/13 | 2041 | ||
| P/2011 S1 | Gibbs | 25.4 | 0.2032 | 8.652 | 6.894 | 2.68 | 7.1 | 4.0 km | 2014/08/24 | 2040 | |
| C/2013 C2 | Tenagra | 64.3 | 0.4313 | 16.06 | 9.131 | 21.34 | 6.6 | 2015/08/29 | 2079 | ||
| C/2013 P4 | PanSTARRS | 56.8 | 0.5961 | 14.77 | 5.967 | 4.26 | 6.9 | 2014/08/12 | 2071 | ||
| [C/2014 OG392|] | PanSTARRS | 42.5 | 0.1819 | 12.19 | 9.969 | 9.04 | 11.5 | 10.0 km | 2021/12/01 | 2064 | |
| P/2015 M2 | PanSTARRS 45 | 19.33 | 0.17896 | 7.2017 | 5.9128 | 3.9741 | 8.2 | 2015/08/31 | 2024/12/29 | ||
| C/2015 T5 | Sheppard–Tholen | 148 | 0.6661 | 27.97 | 9.338 | 11.05 | 7.7 | 2016/01/24 | 2164 | ||
| C/2016 Q4 | Kowalski | 68.9 | 0.5783 | 16.8 | 7.084 | 7.26 | 12.1 | 2018/01/28 | 2068 | ||
| P/2020 B4 | Sheppard | 22.5 | 0.1925 | 7.974 | 6.439 | 11.60 | 7.6 | 2021/11/25 | 2044 | ||
| [P/2020 MK4|] | PanSTARRS 137 | 15.25 | 0.0205 | 6.150 | 6.023 | 6.691 | 7.6 | 1.1 km | 2015/06/15 | 2030 | |
| PanSTARRS | 41.1 | 0.3277 | 11.9 | 8.001 | 19.94 | 8.8 | 4.7 km | 2028/11/30 | 2069 | ||
| C/2024 C2 | PanSTARRS | 65 | 0.4440 | 16.17 | 8.991 | 27.28 | 6.2 | 2025/03/10 | 2090 | ||
| P/2025 D2 | PanSTARRS | 26.6 | 0.1780 | 8.917 | 7.329 | 5.33 | 8.1 | 2028/11/06 | 2054 |