12P/Pons–Brooks

12P/Pons–Brooks is a periodic comet with an orbital period of 71 years. Comets with an orbital period of 20–200 years are referred to as Halley-type comets. It is one of the brightest known periodic comets, reaching an absolute visual magnitude of about 5 in its approach to perihelion. Comet Pons-Brooks was conclusively discovered at Marseilles Observatory in July 1812 by Jean-Louis Pons, and on its next appearance in 1883 by William Robert Brooks. There are ancient records of comets that are suspected of having been apparitions of 12P/Pons–Brooks.

The last perihelion passage was 21 April 2024, with closest approach to Earth being 1.55 AU on 2 June 2024. The comet is expected to brighten to about apparent magnitude 4.5. The comet nucleus is estimated to be around 30 km in diameter, assuming it was not producing too much dust and gas during the 2020 photometric measurements.

12P/Pons–Brooks is hypothesized to be the parent body of the weak December $1$ Draconids meteor shower that is active from about 29 November to 13 December.

Before 1812
Comet 12P/Pons–Brooks has been identified as a comet observed in 1385 and in 1457. The 1385 apparition was very favourable and the comet was recorded by the Chinese in Ming Shilu and was also mentioned in some European sources. A comet observed by Paolo dal Pozzo Toscanelli in January 1457 and mentioned in Chinese sources is also identified as comet 12P/Pons-Brooks. In both apparitions the comet had magnitude 3 or brighter, not accounting for possible outbursts. It is possible that it was also a comet recorded in Chinese sources in September 245 CE.

So-Yeon Park & Jong-Chul Chae (2007) suggested that comet 12P/Pons–Brooks was also the comets recorded in Asian sources in 1313 and 1668. However, Meyer et al. argue that in the 1313 apparition, the comet would have been difficult to observe, being dim and close to the Sun, while the suggested position in Gemini contradicts the calculated location of comet Pons-Brooks in Aries. The March 1668 comet described by Koreans is probably the bright sungrazing comet observed by Europeans, whose orbit is no way compatible with that of comet 12P/Pons–Brooks.

1812 discovery
Comet 12P/Pons–Brooks was discovered on 12 July 1812, by Jean-Louis Pons. Independently, this comet was later found by Vincent Wisniewski on 1 August, and Alexis Bouvard on 2 August the same year. The comet was spotted with the naked eye on 13 August and by the end of the month a tail measuring 2 degrees in length was reported. Shortly after its initial discovery it was found to have an orbital period of about 70 years with an error of about 5 years. Johann Franz Encke determined a definitive orbit with a period of 70.68 years. This orbit was used to generate an ephemeris for the 1883–1884 return.

1884
On 2 September 1883 a (faint) comet was accidentally discovered by William Robert Brooks and later identified with the comet of 1812. An outburst was observed on 21–23 September 1883, as the comet brightened from magnitude 10–11 to 8–8.5, and its appearance changed from diffuse to star-like. The comet became visible with naked eye in 20 November and brightened up to magnitude 3. The comet was reported to experience outbursts on 1 January and 19 January. This year it traveled from Scheat and Markab in western Pegasus, 13 January 1884; southward (through Pisces) to reach perihelion below Iota and Beta Ceti (~RA 0h, dec. -10°) around 24 January. It was last seen in June 1884.

1954
The comet was recovered on 20 June 1953 when it was 4.5 AU from the Sun. The comet outburst from magnitude 18 to magnitude 13 on 1 July 1953. Another outburst occurred in March 1954, the fourth observed in that apparition. On 23 April the comet was estimated magnitude 6.4, and its tail was half a degree long. Pons–Brooks came to perihelion on 22 May 1954 when it was 1.7 AU from Earth. After perihelion it became better visible from the south hemisphere. It was last observed on 4 September 1954 when it was 1.9 AU from the Sun. On 10 December 1954, the meteor stream of comet Pons–Brooks passed about 0.12 AU from Earth, resulting in potential meteors impacting Earth's atmosphere at relative velocity 45 km/s.

2024 passage
On 10 June 2020 Pons–Brooks was recovered at apparent magnitude 23 by the Lowell Discovery Telescope when the comet was beyond the orbit of Saturn at 11.9 AU from the Sun, with the uncertainty in the comet's heliocentric distance being roughly ± 10 000 km at the time. The comet underwent an outburst from magnitude 16–17 to magnitude 11–12 (brightening by ~100×) on 20 July 2023 when it was 3.9 AU from the Sun. The outburst resulted in the comet having a horseshoe shaped coma. It was probably created by the release of about 10 billion kilograms of dust and ice into space. The coma had expanded to a diameter of 600,000 kilometers by 5 August, having an expansion rate of 220 m/s. Although initially spherical, the coma became asymmetrical due to the effects of radiation pressure on the dust. The comet outburst again on 5 October 2023 from magnitude 15 to magnitude 11 (brightening by ~40×). Two more outbursts were recorded on 1 November and 14 November, with the comet brightening to apparent magnitude 9.3 after the later. Outbursts were also observed on 14 December and 18 January 2024.

By mid February the comet had brightened to magnitude 7.5 and had developed an ion tail about two degrees long that featured jets and filaments. A minor outburst took place on 29 February, with the comet brightening by 0.9 magnitudes. By 7 March the comet had brightened to magnitude 5.5 and was located about 10 degrees from the Andromeda Galaxy. In the following days the comet was reported to be visible by naked eye and featured a tail about 5 degrees long. Another outburst occurred on April 3, with the comet brightening to a magnitude of about 3.8. There was a solar eclipse on 8 April 2024 with the comet 25 degrees from the Sun. The perihelion passage was on 21 April 2024 at 0.781 AU from the Sun with a velocity with respect to the Sun of 47.1 km/s. The closest approach to Earth will be later on 2 June 2024 when it will be 1.55 AU from Earth. Near perihelion passage the comet was expected to brighten to about magnitude 4.5 (around 400× brighter than the July 2023 outburst). In early June Earth crossed the comet's orbital plane, resulting to an anti-tail becoming visible.

Orbit
Libration is locked at a 6:1 resonance with Jupiter. The Tisserand invariant with respect to Jupiter (J) is 0.60. Aphelion (furthest point from the Sun) is just beyond the orbit of Neptune at 33.6 AU.

With a steep orbital inclination of 74.2° this comet does not spend a lot of time near the ecliptic. The Jet Propulsion Laboratory's (JPL) website shows that between the years 1900 and 2200, that the comet was and will be most significantly perturbed by Saturn on July 29, 1957. At that point it passed within 1.6AU of the giant planet's influence; even this approach had negligible effect. The comet's orbit appears to be stable between 1740 and 2167, with no strong perturbations by any of the planets.

Before the 2020 recovery, while the last observation was in 1954, Kinoshita calculated that the comet would come to a future perihelion passage (closest approach to the Sun) on 10 August 2095. Accounting for observations in 2020–2023, the nominal time of perihelion passage is now calculated to be 15 August 2095.

Kirkwood in 1884 noticed that Pons-Brooks shares elements with De Vico's comet of 1846. He suggested that the latter had calved off Pons-Brooks some centuries prior. Later he identified the two comets' capture into their elliptical orbits (or their parent body's capture) with their shared aphelion close to Neptune 991 CE.

Other comets with a similar orbital period include 13P/Olbers, 23P/Brorsen-Metcalf, and 1P/Halley.

Meteor showers
12P/Pons-Brooks is hypothesized to be the parent body of the weak December $1$ Draconids meteor shower (#336) that is active from about 29 November to 13 December and generates less than 2 meteors/hour. This is the most abundant of the meteor showers predicted to be related to the comet. One more nighttime meteor shower has been tentatively associated with 12P/Pons-Brooks, the northern June Aquilids, although most probably isn't the parent body. Comet Pons-Brooks could also be the source of a meteor shower on Venus, along with periodic comets 122P/de Vico and 27P/Crommelin.