322P/SOHO

322P/SOHO 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.^[8] At perihelion, it is six times closer to the Sun than the planet Mercury.

322P/SOHO

Discovery
Discovered by	SOHO Terry Lovejoy Kazimieras Černis Bo Zhou Sebastian F. Hönig
Discovery date	4 September 1999
Designations
MPC designation	P/1999 R1 P/2003 R5 P/2007 R5 P/2011 R4
Alternative designations	SOHO-85[1] SOHO-661
Orbital characteristics[2][3]
Epoch	15 September 2015 (JD 2457280.5)
Observation arc	15.93 years
Earliest precovery date	27 November 254?[4]
Number of observations	319
Aphelion	4.979 AU
Perihelion	0.0507 AU
Semi-major axis	2.516 AU
Eccentricity	0.97869
Orbital period	3.992 years
Max. orbital speed	187 km/s (2023)[5]
Min. orbital speed	1.9 km/s (2017)
Inclination	12.583°
Longitude of ascending node	359.48°
Argument of periapsis	49.098°
Mean anomaly	2.700°
Last perihelion	21 August 2023[5]
TJupiter	2.347
Earth MOID	0.092 AU
Jupiter MOID	1.044 AU
Physical characteristics[6][7]
Dimensions	~150–320 m (490–1,050 ft)
Mean density	~1.00 g/cm3
Synodic rotation period	2.8±0.3 hours
Geometric albedo	0.09–0.42
Spectral type	(V–R) = 0.41±0.04 (R–I) = 0.24±0.09
Comet total magnitude (M1)	19.0

Observational history

The comet was first spotted by Terry Lovejoy after analyzing SOHO imagery on 4 September 1999.

After Kazimieras Černis spotted another SOHO comet in 2003, Sebastian F. Hönig, later determined that both P/1999 R1 and P/2003 R5 might be the same object, where he predicted its return in 2007.^[9][10] His calculations were later proven correct when it was successfully recovered by Bo Zhou as P/2007 R5 after analyzing SOHO images on 10 September 2007.^[11] It became one of the first comets that SOHO has discovered that is confirmed to be periodic.

Bo Zhou recovered the comet once again on September 6, 2011.^[6] It was observed again in September 2019.^[12]

Possible connection with the Great Comet of 254 AD

It has been suggested that 322P/SOHO is associated with a comet observed in November–December 254 AD and is mentioned in East Asian sources to have an extremely long tail.^[4][13] If the association is correct, it is possible that the comet split in 254 AD, 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.^[13]

Physical characteristics

322P/SOHO is either an extinct comet or an active asteroid.^[14] Light-curve and infrared observations by Spitzer in 2016 suggest that its nucleus is probably only 150–320 m (490–1,050 ft) in diameter, with a rotation period lasting 2.8±0.3 hours.^[7]

Orbit

Perihelion distance at different epochs[15]
Perihelion date	Perihelion (AU)
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

322P/SOHO is a member of the Kracht sungrazer family of comets.^[1] On April 11, 1947 it passed about 7.1 ± 0.22 million km (4.4 ± 0.14 million mi) from Earth.^[2][16]

Exploration

On 2 September 2019, NASA's Parker Solar Probe incidentally passed the tail of 322P/SOHO at a distance of 0.012 AU (1.8 million km), making direct measurements of the comet as it interacts with the solar wind.^[17]

See also

• List of minor planets and comets visited by spacecraft