26P/Grigg–Skjellerup

Comet Grigg–Skjellerup (formally designated 26P/Grigg–Skjellerup) is a periodic comet. It was visited by the Giotto probe in July 1992.[6] The spacecraft came as close as 200 km, but could not take pictures because some instruments were damaged from its encounter with Halley's Comet.[7] The comet next comes to perihelion (closest approach to the Sun) on 25 December 2023,[2][1][4] but will be 1.8 AU from Earth and only 31 degrees from the Sun.[1]

26P/Grigg–Skjellerup
Discovery
Discovered byJohn Grigg and John Francis Skjellerup
Discovery date1902 and 1922
Designations
1808 C1; 1808 III;
1902 O1; 1902 II;
1902c; 1922 K1;
1922 I; 1922b;
1927 F1; 1927 V;
1927e; 1932 II;
1932d; 1937 III;
1937e; 1942 V;
1942d; 1947 II;
1947a; 1952 IV;
1952b; 1957 I;
1956i; 1961 IX;
1961g; 1967 I;
1966f; 1972 II;
1972b; 1977 VI;
1977b; 1982 IV;
1982a; 1987 X;
1986m; 1992 XVIII
Orbital characteristics
Epoch2023-02-25 (JD 2460000.5)
Aphelion4.947 AU
Perihelion1.0840 AU
Semi-major axis3.015 AU
Eccentricity0.6405
Orbital period5.23 yr
Max. orbital speed36.6 km/s @ perihelion[1]
Inclination22.43°
Last perihelionOctober 1, 2018[2]
July 6, 2013[3]
March 23, 2008
Next perihelion2023-Dec-25[2][1][4]
Earth MOID0.1 AU (15 million km)[5]

The comet was discovered in 1902 by John Grigg of New Zealand, and rediscovered in its next appearance in 1922 by John Francis Skjellerup, an Australian then living and working for about two decades in South Africa where he was a founder member of the Astronomical Society of Southern Africa.

In 1987, it was belatedly discovered by Ľubor Kresák that the comet had been observed in 1808 as well, by Jean-Louis Pons.

The comet has often suffered the gravitational influence of Jupiter, which has altered its orbit considerably. For instance, its perihelion distance has changed from 0.77 AU in 1725 to 0.89 AU in 1922 to 0.99 AU in 1977 and to 1.12 AU in 1999.

In 1972 the comet was discovered to produce a meteor shower, the Pi Puppids, and its current orbit makes them peak around April 23, for observers in the southern hemisphere, best seen when the comet is near perihelion.

During the comet's 1982 approach it was detected using radar by the Arecibo Observatory.[8]

Having its recent perihelion so close to Earth's orbit made it an easy target to reach for the Giotto mission (spacecraft) in 1992, whose primary mission was to Comet Halley. Giotto had a closest approach to Grigg–Skjellerup of 200 km, much closer than its approach to Comet Halley, but was unable to obtain images as its camera was destroyed during the Halley rendezvous in 1986.

The 2002 return (expected perihelion around October 8, 2002) was very unfavorable and no observations were reported.

The comet nucleus is estimated to be 2.6 kilometers in diameter.[5]

The comet is a type locality for the mineral brownleeite.[9][10]

References
  1. "Horizons Batch for 26P/Grigg-Skjellerup (90000375) on 2023-Dec-25" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on 2023-02-16. Retrieved 2023-02-11. (JPL#K234/7 Soln.date: 2022-Dec-19)
  2. "26P/Grigg-Skjellerup Orbit". Minor Planet Center. Retrieved 2014-06-16.
  3. Syuichi Nakano (2010-04-08). "26P/Grigg-Skjellerup (NK 1908)". OAA Computing and Minor Planet Sections. Retrieved 2012-02-18.
  4. Kinoshita, Kazuo (2018-07-03). "26P/Grigg-Skjellerup past, present and future orbital elements". Comet Orbit. Archived from the original on 2011-05-20. Retrieved 2023-07-24.
  5. "JPL Small-Body Database Browser: 26P/Grigg–Skjellerup" (2022-12-15 last obs). Jet Propulsion Laboratory. Retrieved 2020-09-29.
  6. "Giotto, ESA's first deep-space mission: 25 years ago". European Space Agency. March 11, 2011. Archived from the original on October 17, 2011.
  7. "Giotto's second comet encounter". European Space Agency. March 10, 2006. Archived from the original on January 19, 2012.
  8. Harmon, J.K; Campbell, D.B; Ostro, S.J; Nolan, M.C (1999). "Radar observations of comets" (PDF). Planetary and Space Science. 47 (12): 1409–1422. Bibcode:1999P&SS...47.1409H. doi:10.1016/S0032-0633(99)00068-9. Retrieved 22 November 2020.
  9. "Comet 26P/Grigg-Skjellerup, Outer Space". www.mindat.org. Archived from the original on May 20, 2017. Retrieved April 3, 2017.
  10. "NASA Finds New Type of Comet Dust Mineral". www.nasa.gov. June 12, 2008. Retrieved April 3, 2017.


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