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Discovered byTom Gehrels
Discovery dateSeptember 29, 1973
1973 XI; 1981 XVII; 1989 XVII
Orbital characteristics A
EpochMarch 6, 2006
Aphelion5.462 AU
Perihelion2.009 AU
Semi-major axis3.735 AU
Orbital period7.22 yr
Last perihelionJanuary 12, 2012[1]
October 27, 2004[2][3]
Next perihelion2019 April 2[4]

78P/Gehrels, also known as Gehrels 2, is a Jupiter-family periodic comet in the Solar System with a current orbital period of 7.22 years.

It was discovered by Tom Gehrels at the Lunar and Planetary Laboratory, Arizona, USA on photographic plates exposed between 29 September and 5 October 1973 at the Palomar Observatory. It had a brightness of apparent magnitude of 15. Brian G. Marsden computed the parabolic and elliptical orbits which suggested an orbital period of 8.76 years, later revising the data to give a perihelion date of 30 November 1963 and orbital period of 7.93 years.[5]

The comet's predicted next appearance in 1981 was observed by W. and A. Cochran at the McDonald Observatory, Texas on 8 June 1981. It was observed again in 1989 and in 1997, when favourable conditions meant that brightness increased to magnitude 12. It has subsequently been observed in 2004 and 2012.

Outward migration[edit]

Comet 78P/Gehrels' aphelion (furthest distance from the Sun) of 5.4AU[1] is in the zone of control of the giant planet Jupiter and the orbit of the comet is frequently perturbed by Jupiter.[6] On September 15, 2029, the comet will pass within 0.018 AU (2.7 million kilometers) of Jupiter[6] and be strongly perturbed. By the year 2200, the comet will have a centaur-like orbit with a perihelion (closest distance to the Sun) near Jupiter.[7] This outward migration from a perihelion of 2AU to a perihelion of ~5AU could cause the comet to go dormant.

The Outward Migration of 78P/Gehrels
Year (epoch) 2009[1] 2030 2200[7]
Semi-major axis 3.73 6.02 9.37
Perihelion 2.00 4.08 4.99
Aphelion 5.46 7.96 13.7
Comet 78P passing within 0.018 AU of Jupiter in 2029.[6]

See also[edit]


  1. ^ a b c "JPL Small-Body Database Browser: 78P/Gehrels 2" (2011-05-21 last obs). Retrieved 2009-05-11.
  2. ^ Seiichi Yoshida (2006-10-03). "78P/Gehrels 2". Seiichi Yoshida's Comet Catalog. Retrieved 2010-02-24.
  3. ^ Syuichi Nakano (2009-04-20). "78P/Gehrels 2 (NK 1760)". OAA Computing and Minor Planet Sections. Retrieved 2010-02-24.
  4. ^ Syuichi Nakano (2011-06-10). "78P/Gehrels 2 (NK 2102)". OAA Computing and Minor Planet Sections. Retrieved 2012-02-18.
  5. ^ Kronk, Gary W. "78P/Gehrels 2". Cometography. Retrieved 25 February 2015.
  6. ^ a b c "JPL Close-Approach Data: 78P/Gehrels 2" (2006-02-26 last obs). Retrieved 2009-05-11.
  7. ^ a b Heider. "Orbital Elements of 78P/Gehrels in 2200". Archived from the original on 2015-06-06. Retrieved 2009-05-11.

External links[edit]

Numbered comets
78P/Gehrels Next
79P/du Toit–Hartley