| Discovery | |
|---|---|
| Discovered by | T. Lovejoy K. Černis B. Zhou S. F. Hönig |
| Discovery date | September 4, 1999 |
| Designations | |
| P/1999 R1, P/2003 R5, P/2007 R5, P/2011 R4 | |
| Orbital characteristics | |
| Epoch | 2019-08-25 (JD 2458720.5)[1] |
| 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)[2] |
| Min. orbital speed | 1.9 km/s (2017-Sep-01) |
| Inclination | 11.46° |
| Last perihelion | August 31, 2019[1] September 4, 2015[1] September 7, 2011[1] September 11, 2007[1] |
| Next perihelion | August 21, 2023[2] |
| 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 distance at different epochs[3] | |||||||
| 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 | ||||||
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]
