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P/2007 R5 (SOHO)
Discovery
Discovered by	T. Lovejoy; K. Černis; B. Zhou; S. F. Hönig
Discovery date	September 4, 1999
Designations
Alternative designations	P/1999 R1, P/2003 R5, P/2007 R5, P/2011 R4
Orbital characteristics
Epoch	2019-08-25; (JD 2458720.5)
Observation arc	15.9 years
Number of; observations	318
Aphelion	4.967 AU
Perihelion	0.0507 AU; (16% of Mercury's perihelion)
Semi-major axis	2.509 AU
Eccentricity	0.9798
Orbital period	3.97 yr
Max. orbital speed	187 km/s (2023)
Min. orbital speed	1.9 km/s (2017-Sep-01)
Inclination	11.46°
Last perihelion	August 31, 2019; September 4, 2015; September 7, 2011; September 11, 2007
Next perihelion	August 21, 2023
TJupiter	2.347
Earth MOID	0.092 AU (13,800,000 km)
Physical characteristics
Dimensions	~100-200 m
Comet total; magnitude (M1)	19.00 ± 0.09

Perihelion date	Perihelion (AU)
Perihelion distance at different epochs^[3]
1955-04-18	0.0651
1983-08-08	0.0597
1999-09-05	0.0563
2015-09-04	0.0535
2019-08-31	0.0506
2023-08-21	0.0501
2027-08-11	0.0505
2031-08-01	0.0479
2047-05-23	0.0451

Comet 322P/SOHO, also designated P/1999 R1, P/2003 R5, P/2007 R5, and P/2011 R4, is the first periodic comet to be discovered using the automated telescopes of the SOHO (SOlar and Heliospheric Observatory) spacecraft, and second to be given a numbered designation, after 321P/SOHO. JPL Horizons next predicts 322P to come to perihelion (closest approach to the Sun) on 21 August 2023 at around apparent magnitude 6 and only 3 degrees from the Sun.^[2] At perihelion it is six times closer to the Sun than the planet Mercury is at perihelion.

The periodicity of this comet was predicted by Sebastian Hönig, a German graduate student and prolific asteroid discoverer, in 2006.^[4] The announcement of the new periodic comet was made after the predicted return was confirmed by SOHO and observer Bo Zhou on 10 September 2007.^[5] Out of approximately 1,350 SOHO-observed sungrazer comets, this is the first to be verified as a short-period comet; most sungrazers are long-period comets on near-parabolic orbits that do not repeat for thousands of years, if at all.

As it passed to within 7.9 million kilometres of the Sun, around 0.05 AU, it brightened by a factor of around a million. This is common behavior for a comet.^[6] It was expected to return in September 2011,^[6] and was recovered by B. Zhou on September 6, 2011. Discovery credit goes to Terry Lovejoy (Australia, 1999), Kazimieras Černis (Lithuania, 2003), and Bo Zhou (China, 2007). It was observed again in September 2019.^[7]

P/2007 R5 is probably an extinct comet. Extinct comets are those that have expelled most of their volatile ice and have little left to form a tail or coma. They are theorized to be common objects amongst the celestial bodies orbiting close to the Sun. P/2007 R5 (SOHO) is probably only 100–200 meters in diameter.^[6] It has a 2.8 hour light curve period suggesting its rotation. It is uncertain whether to classify it as a dead comet or asteroid.^[8]

It has been suggest than 322P/SOHO is associated with a comet observed in 254 CE and is mentioned in east-asian sources to have an extremely long tail. If the association is correct, it is possible that the comet split in 254 CE, resulting in intense cometary activity, but activity decreased afterwards as the comet lost most of its volatiles, and no longer displays a tail or a prominent coma. Current activity is fueled by sodium sublimation.^[9]

On April 11, 1947 it passed about 7.1 ± 0.22 million km (4.4 ± 0.14 million mi) from Earth.^[10]^[11]

The second periodic comet discovered by SOHO is P/2003 T12 (SOHO).^[12]

References

^ ^a ^b ^c ^d ^e "322P/SOHO Orbit". Minor Planet Center. Retrieved April 10, 2017.
^ ^a ^b ^c "Horizons Batch for 322P/SOHO on 2023-Aug-21" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on June 24, 2023. Retrieved August 12, 2023. (JPL#10/Soln.date: 2016-Oct-27)
^ Kinoshita, Kazuo (June 9, 2015). "322P/SOHO past, present and future orbital elements". Comet Orbit. Retrieved August 16, 2023.
^ Jaggard, Victoria (September 25, 2007). "Photo in the News: Sun Probe Spies New Periodic Comet". National Geographic News. National Geographic Society. Archived from the original on October 11, 2007. Retrieved September 25, 2007.
^ Marsden, Brian (September 18, 2007), "MPEC 2007-S16 : COMET P/1999 R1 = 2003 R5 = 2007 R5 (SOHO)", Minor Planet Electronic Circular (2007-S16)
^ ^a ^b ^c "SOHO's new catch: its first officially periodic comet". European Space Agency. September 25, 2007. Retrieved November 19, 2007.
^ The case of the Sun-diving asteroid that thinks it's a comet Phil Plait, September 4, 2019
^ Rainer Kracht (September 7, 2011). "Recent comet discoveries 2123-2137". Yahoo Groups: SOHO Hunter. Archived from the original on January 5, 2013. Retrieved September 11, 2011.
^ Cui, Jianhua; Li, Geng; Zhao, Yongheng (March 2025). "322P/SOHO: The counterpart of a historical comet in 254 CE?". Icarus. 429: 116382. doi:10.1016/j.icarus.2024.116382.
^ "JPL Small-Body Database Browser: 322P/SOHO" (last observation used: 2015-08-08). Jet Propulsion Laboratory. Retrieved August 16, 2023.
^ "Horizons Batch for 1947-Apr-11 Earth approach uncertainty". JPL Horizons. Retrieved August 16, 2023. RNG_3sigma = uncertainty range in km. (JPL#10/Soln.date: 2016-Oct-27)
^ Karl Battams (January 30, 2012). "The tale of a very shy comet..." Sungrazing Comets @ Navy.mil. Retrieved January 30, 2012.