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.

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[2][4]

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.[5] It has subsequently been observed in 2004 when it reached magnitude 10, 2012, and 2018.[2]


Outward migrationEdit

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 alsoEdit


  1. ^ a b c "JPL Small-Body Database Browser: 78P/Gehrels 2" (2011-05-21 last obs). Retrieved 2009-05-11.
  2. ^ a b c 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. ^ a b 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 linksEdit

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