78P/Gehrels

78P/Gehrels
Comet Gehrels 2 photographed from the Zwicky Transient Facility on 27 January 2019
Discovery[1]
Discovered byTom Gehrels
Discovery sitePalomar Observatory, Arizona, USA
Discovery date29 September 1973
Designations
P/1973 S1, P/1981 L1
  • 1973 XI, 1981 XVII
  • 1989 XVII
  • 1973n, 1981f, 1989n
Orbital characteristics[4][5]
Epoch21 November 2025 (JD 2461000.5)
Observation arc52.247 years
Number of
observations		8,640
Aphelion5.461 AU
Perihelion2.005 AU
Semi-major axis3.733 AU
Eccentricity0.46299
Orbital period7.212 years
Inclination6.257°
210.49°
Argument of
periapsis		192.78°
Mean anomaly330.47°
Last perihelion2 April 2019[2][3]
Next perihelion25 June 2026
TJupiter2.887
Earth MOID1.022 AU
Jupiter MOID0.024 AU
Physical characteristics[4]
Mean radius
4.21 km (2.62 mi)[6]
  • (B–V) = 0.88±0.02[7]
  • (V–R) = 0.27±0.02[7]
Comet total
magnitude (M1)		9.1
Comet nuclear
magnitude (M2)		12.5

78P/Gehrels, also known as Gehrels 2, is a Jupiter-family comet with a current orbital period of 7.22 years. It is the second periodic comet discovered by American astronomer, Tom Gehrels.

Observational history

It was discovered by Tom Gehrels on photographic plates exposed between 29 September and 5 October 1973 at the Palomar Observatory.[1] 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.[8]

The comet's predicted next appearance was observed by W. and A. Cochran at the McDonald Observatory, Texas on 8 June 1981.[9][10] It was observed again in 1989[11] and in 1997, when favourable conditions meant that brightness increased to magnitude 12.[8] It has subsequently been observed on every apparition since,[2] with the first polarimetric observations of the comet were conducted at the Girawali Observatory in 2012.[12]

Physical characteristics

Initial CCD observations of 78P/Gehrels in 2003 indicated that it has a small nucleus of only around 1.54 km (0.96 mi).[13] Photometry obtained from the Isaac Newton Telescope in 2006 revealed it has an effective radius of about 4.21 km (2.62 mi) instead, however this might represent its upper limit.[6] The maximum dust production rate during its 2019 apparition was measured at Afρ = 1028.1±13.3 cm, making it one of the most active Jupiter-family comets ever known.[7][14]

Orbit

The dynamical history of this comet indicated that it had resided within the planetary region of the Solar System for about a million years, but its migration to the inner Solar System is only relatively recent,[7] with its first encounter with Jupiter occurred only about 500 years ago.[15] Comet 78P/Gehrels' aphelion at a distance of 5.4 AU (810 million km) from the Sun meant that its orbit is frequently perturbed by Jupiter.[4] On 15 September 2029, the comet will pass within 0.018 AU (2.7 million km) of Jupiter and be strongly perturbed.[4] By the year 2200, the comet will have a centaur-like orbit with a perihelion (closest distance to the Sun) near Jupiter.[16] This outward migration from a perihelion of 2.01 AU (301 million km) to 5.057 AU (756.5 million km) could cause the comet to go dormant.

The Outward Migration of 78P/Gehrels
Year (epoch) 2009[4] 2030 2200[16]
Semi-major axis 3.73 6.02 9.37
Perihelion 2.00 4.08 4.99
Aphelion 5.46 7.96 13.7

References

  1. ^ a b T. Gehrels; R. Adams; C. Vesely; et al. (31 October 1973). B. G. Marsden (ed.). "Comet Gehrels (1973n)". IAU Circular. 2589 (1). Bibcode:1973IAUC.2589....1G.
  2. ^ a b S. Yoshida (3 October 2006). "78P/Gehrels 2". www.aerith.net. Retrieved 24 February 2010.
  3. ^ S. Nakano (10 June 2011). "78P/Gehrels 2 (NK 2102)". OAA Computing and Minor Planet Sections. Retrieved 18 February 2012.
  4. ^ a b c d e f "78P/Gehrels 2 – JPL Small-Body Database Lookup". ssd.jpl.nasa.gov. Jet Propulsion Laboratory. Retrieved 11 May 2009.
  5. ^ "78P/Gehrels Orbit". Minor Planet Center. Retrieved 29 June 2020.
  6. ^ a b C. S. Snodgrass; S. C. Lowry; A. Fitzsimmons (2007). "Optical observations of 23 distant Jupiter Family Comets, including 36P/Whipple at multiple phase angles" (PDF). Monthly Notices of the Royal Astronomical Society. 385 (2): 737–756. arXiv:0712.4204. Bibcode:2008MNRAS.385..737S. doi:10.1111/j.1365-2966.2008.12900.x. S2CID 55536237.
  7. ^ a b c d R. Xu; J. Shi; Y. Ma; et al. (2024). "Activity Analysis on 68P/Klemola and 78P/Gehrels 2 in 2018–2020 Perihelion Passage". The Astronomical Journal. 167 (3): 111–124. Bibcode:2024AJ....167..111X. doi:10.3847/1538-3881/ad1ff2.
  8. ^ a b G. W. Kronk. "78P/Gehrels 2". Cometography.com. Retrieved 25 February 2015.
  9. ^ A. Cochran (12 June 1981). B. G. Marsden (ed.). "Periodic Comet Gehrels 2 (1981f)". IAU Circular. 3612 (1). Bibcode:1981IAUC.3612....1C.
  10. ^ A. Cochran; W. Cochran (8 July 1981). D. W. Green (ed.). "Periodic Comet Gehrels 2 (1981f)". IAU Circular. 3615 (4). Bibcode:1981IAUC.3615....4C.
  11. ^ J. Gibson (3 July 1989). D. W. Green (ed.). "Periodic Comet Gehrels 2 (1989n)". IAU Circular. 4800 (1). Bibcode:1989IAUC.4800....1G.
  12. ^ S. R. Choudhury; E. Hadamcik; A. K. Sen (2012). "A study of comet 78P/Gehrels by imaging polarimetry". Journal of Quantitative Spectroscopy and Radiative Transfer. 146: 444–451. Bibcode:2014JQSRT.146..444R. doi:10.1016/j.jqsrt.2014.02.010.
  13. ^ S. C. Lowry; P. R. Weissman (2003). "CCD observations of distant comets from Palomar and Steward Observatories". Icarus. 164 (2): 492–503. Bibcode:2003Icar..164..492L. doi:10.1016/S0019-1035(03)00129-5.
  14. ^ E. M. Epifani; P. Palumbo (2011). "The dust coma environment of the short period comets 32P/Comas Solá, 56P/Slaughter-Burnham, and 78P/Gehrels 2 from ground-based observations" (PDF). Astronomy & Astrophysics. 525: 62–76. Bibcode:2011A&A...525A..62M. doi:10.1051/0004-6361/201014989.
  15. ^ F. J. Pozuelos; F. Moreno; F. Aceituno; et al. (2014). "Dust environment and dynamical history of a sample of short-period comets" (PDF). Astronomy & Astrophysics. 568: 3–16. arXiv:1406.6220. Bibcode:2014A&A...568A...3P. doi:10.1051/0004-6361/201423762.
  16. ^ a b "Barycentric Osculating Orbital Elements for Comet 78P/Gehrels 2 in epoch 1800 and 2200". JPL Horizons On-Line Ephemeris System. Jet Propulsion Laboratory. Retrieved 11 May 2009. (Solution using the Solar System's barycenter (Sun+Jupiter). Select Ephemeris Type:Elements and Center:@0) }}


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