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P/2007 R5 (SOHO)
Discovered byT. Lovejoy
K. Černis
B. Zhou
S. F. Hönig
Discovery dateSeptember 4, 1999
P/1999 R1, P/2003 R5, P/2007 R5, P/2011 R4
Orbital characteristics
(JD 2458720.5)[1]
Observation arc15.9 years
Number of
Aphelion4.967 AU
Perihelion0.0507 AU
(16% of Mercury's perihelion)
Semi-major axis2.509 AU
Orbital period3.97 yr
Max. orbital speed187 km/s (2023)[2]
Min. orbital speed1.9 km/s (2017-Sep-01)
Last perihelionAugust 31, 2019[1]
September 4, 2015[1]
September 7, 2011[1]
September 11, 2007[1]
Next perihelionAugust 21, 2023[2]
Earth MOID0.092 AU (13,800,000 km)
Physical characteristics
Dimensions~100-200 m
Comet total
19.00 ± 0.09
Perihelion distance
at different epochs
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]

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 was expected to return in September 2011,[6] and was recovered by B. Zhou on September 6, 2011. 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.[7]

Discovery credit goes to Terry Lovejoy (Australia, 1999), Kazimieras Černis (Lithuania, 2003), and Bo Zhou (China, 2007).

The second periodic comet discovered by SOHO is P/2003 T12 (SOHO).[8]

It was observed again in September 2019.[9] On April 11, 1947 it passed about 7.1 ± 0.22 million km (4.4 ± 0.14 million mi) from Earth.[10][11]


  1. ^ a b c d e "322P/SOHO Orbit". Minor Planet Center. Retrieved April 10, 2017.
  2. ^ 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)
  3. ^ Kinoshita, Kazuo (June 9, 2015). "322P/SOHO past, present and future orbital elements". Comet Orbit. Retrieved August 16, 2023.
  4. ^ 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.
  5. ^ Marsden, Brian (September 18, 2007), "MPEC 2007-S16 : COMET P/1999 R1 = 2003 R5 = 2007 R5 (SOHO)", Minor Planet Electronic Circular (2007-S16)
  6. ^ a b c "SOHO's new catch: its first officially periodic comet". European Space Agency. September 25, 2007. Retrieved November 19, 2007.
  7. ^ 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.
  8. ^ Karl Battams (January 30, 2012). "The tale of a very shy comet..." Sungrazing Comets @ Navy.mil. Retrieved January 30, 2012.
  9. ^ The case of the Sun-diving asteroid that thinks it's a comet Phil Plait, September 4, 2019
  10. ^ "JPL Small-Body Database Browser: 322P/SOHO" (last observation used: 2015-08-08). Jet Propulsion Laboratory. Retrieved August 16, 2023.
  11. ^ "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)

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