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
EpochJanuary 1, 2013 (JD 2456293.5)
Number of
Aphelion4.978257 AU
Perihelion0.05338 AU
Semi-major axis2.5158179 AU
Orbital period3.99 yr
Max. orbital speed186 km/s (2019)
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 perihelion2023-Aug-21[2]
Earth MOID0.092 AU (13,800,000 km)
Physical characteristics
Dimensions~100-200 m
Comet total
19.00 ± 0.09

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) in August 2023.[2]

The periodicity of this comet was predicted by Sebastian Hönig, a German graduate student and prolific asteroid discoverer, in 2006.[3] 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.[4] 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.[5]

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.[5]

It was expected to return in September 2011,[5] 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.[6]

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).[7]

It was observed again in September 2019.[8]


  1. ^ a b c d "322P/SOHO Orbit". Minor Planet Center. Retrieved April 10, 2017.
  2. ^ a b "Horizons Batch for 322P/SOHO on 2023-Aug-21" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved April 29, 2023. (JPL#10/Soln.date: 2016-Oct-27)
  3. ^ Jaggard, Victoria (September 25, 2007). "Photo in the News: Sun Probe Spies New Periodic Comet". National Geographic News. National Geographic Society. Retrieved September 25, 2007.
  4. ^ Marsden, Brian (September 18, 2007), "MPEC 2007-S16 : COMET P/1999 R1 = 2003 R5 = 2007 R5 (SOHO)", Minor Planet Electronic Circular (2007-S16)
  5. ^ a b c "SOHO's new catch: its first officially periodic comet". European Space Agency. September 25, 2007. Retrieved November 19, 2007.
  6. ^ Rainer Kracht (September 7, 2011). "Recent comet discoveries 2123-2137". Yahoo Groups: SOHO Hunter. Retrieved September 11, 2011.
  7. ^ Karl Battams (January 30, 2012). "The tale of a very shy comet..." Sungrazing Comets @ Navy.mil. Retrieved January 30, 2012.
  8. ^ The case of the Sun-diving asteroid that thinks it's a comet Phil Plait, September 4, 2019