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21P/Giacobini–Zinner

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21P/Giacobini–Zinner
Comet Giacobini–Zinner photographed from Moscow, Russia on 9 September 2018.
Discovery
Discovered byMichel Giacobini
Ernst Zinner
Discovery date20 December 1900
23 October 1913
Designations
P/1900 Y1, P/1913 U1
Pronunciation/ˌdʒækoʊˈbiːniˈzɪnər/
  • 1900 III, 1913 V, 1926 VI
  • 1933 III, 1940 I, 1946 V
  • 1959 VIII, 1966 I, 1972 VI
  • 1979 III, 1985 XIII
  • 1992 IX
Orbital characteristics[1]
Epoch26 March 2025 (JD 2460760.5)
Observation arc123.84 years[a]
Number of
observations		7,423
Aphelion5.97 AU
Perihelion1.009 AU
Semi-major axis3.49 AU
Eccentricity0.7111
Orbital period6.525 years
Inclination32.05°
195.3°
Argument of
periapsis		172.9°
Last perihelion25 March 2025[2]
Next perihelion30 August 2031[3]
TJupiter2.465
Earth MOID0.018 AU
Jupiter MOID0.248 AU
Physical characteristics[4]
Dimensions2.0 km (1.2 mi)[5]
Mean density
640±100 kg/m3[6]
7.39±0.01 hours[7]
0.044[8]
Comet total
magnitude (M1)		13.2
Perihelion distance
at different epochs[9]
EpochPerihelion
(AU)
18941.23
19000.93
19851.03
20311.07
20780.97

Comet Giacobini–Zinner (officially designated as 21P/Giacobini–Zinner) is a Jupiter-family comet with a 6.53-year orbit around the Sun. It was discovered by Michel Giacobini, who observed it in the constellation of Aquarius on 20 December 1900. It was recovered two orbits later by Ernst Zinner, while he was observing variable stars near Beta Scuti on 23 October 1913.

It will pass 0.364 AU (54.5 million km) from Jupiter on 14 February 2029,[4] then come to perihelion on 30 August 2031 at 1.07 AU from the Sun,[3] and then pass 0.554 AU (82.9 million km) from Earth on 3 September 2031.[10]

Physical properties

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The comet nucleus is estimated to be 2.0 km (1.2 mi) in diameter.[4] During its apparitions, Giacobini–Zinner can reach about the 7-8th magnitude,[11] but in 1946 it underwent a series of outbursts that made it as bright as 5th magnitude. It is the parent body of the Giacobinids meteor shower (also known as the Draconids). The comet currently has a minimum orbit intersection distance to Earth of 0.035 AU (5.2 million km).[4]

During the apparition of 2018, the optical spectra have revealed the comet is depleted in carbon-chain molecules and carbon dioxide, likely indicating its origin in relatively warm portion of the Solar System.[12]

Exploration

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Giacobini–Zinner was the target of the International Cometary Explorer spacecraft, which passed through its plasma tail at a distance of 7,800 km (4,800 mi) on 11 September 1985, becoming the first comet ever visited in space exploration.[13] Earlier in the same month the comet was observed by the Pioneer Venus Orbiter.[14] In addition, Japanese space officials considered redirecting the Sakigake interplanetary probe toward a 1998 encounter with Giacobini–Zinner, but that probe lacked the propellant for the necessary maneuvers and the project was abandoned.

2025 Perihelion

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21P/Giacobini-Zinner most recently passed perihelion on 25 March 2025. Closest Earth approach was 4 days before, on 21 March on the opposite side of the Sun at an unfavorable distance of 2.0 AU. It brightened to magnitude ~11.[15]

Notes

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  1. ↑ Observation arc from the Minor Planet Center database only covered dates from 24 December 1900 until 21 October 2024 (123.83 years). This figure includes its entire arc up to 20 December 1900.

References

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  1. ↑ "21P/Giacobini-Zinner". Minor Planet Center. Retrieved 30 October 2025.
  2. ↑ S. Yoshida. "21P/Giacobini–Zinner". www.aerith.net. Retrieved 5 January 2025.
  3. 1 2 "Horizons Batch for 21P/Giacobini-Zinner (90000323) on 2031-Aug-30" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on 26 September 2025. Retrieved 26 September 2025. (JPL#K253/3 Soln.date: 2024-Dec-05)
  4. 1 2 3 4 "21P/Giacobini–Zinner – JPL Small-Body Database Lookup". ssd.jpl.nasa.gov. Jet Propulsion Laboratory. Retrieved 10 January 2016.
  5. ↑ P. L. Lamy; I. Toth; Y. R. Fernández; H. A. Weaver (2004). "The Sizes, Shapes, Albedos, and Colors of Cometary Nuclei" (PDF). Comets II. University of Arizona Press. pp. 223–264. Bibcode:2004come.book..223L. doi:10.2307/j.ctv1v7zdq5.22. ISBN 978-0-8165-2450-1. JSTOR j.ctv1v7zdq5.22. Archived from the original (PDF) on 9 October 2022. Retrieved 17 September 2026.
  6. ↑ M. L. Paradowski (2022). "A New Indirect Method of Determining Density of Cometary Nuclei" (PDF). Acta Astronomica. 72 (2): 141–159. Bibcode:2022AcA....72..141P. doi:10.32023/0001-5237/72.2.4. ISSN 0001-5237.
  7. ↑ M. M. Knight; R. Kokotanekova; N. H. Samarasinha (2024). "Physical and Surface Properties of Comet Nuclei from Remote Observations". In K. J. Meech (ed.). Comets III. University of Arizona Press. pp. 361–404. arXiv:2304.09309. JSTOR jj.21819446.18.
  8. ↑ E. Rondón; F. Roig; D. Lazzaro; F. Fernandez (2025). "Secular light curves of periodic comets observed by SWAN/SOHO" (PDF). Monthly Notices of the Royal Astronomical Society. 538 (4): 2869–2904. Bibcode:2025MNRAS.538.2869R. doi:10.1093/mnras/staf454.
  9. ↑ Kinoshita, Kazuo (23 May 2019). "21P/Giacobini-Zinner past, present and future orbital elements". Comet Orbit. Retrieved 30 October 2025.
  10. ↑ "Earth approach on 3 September 2031". JPL Horizons. Retrieved 30 October 2025.
  11. ↑ B. King (29 August 2018). "Comet 21P/Giacobini-Zinner Shines in September". Sky & Telescope. Retrieved 15 September 2018.
  12. ↑ Y. Shinnaka; H. Kawakita; A. Tajitsu (2020). "High-resolution Optical Spectroscopic Observations of Comet 21P/Giacobini–Zinner in its 2018 Apparition". The Astronomical Journal. 159 (5): 203. arXiv:2004.11008. Bibcode:2020AJ....159..203S. doi:10.3847/1538-3881/ab7d34.
  13. ↑ C. Stelzried; L. Efron; J. Ellis (1986). Halley Comet Missions (PDF) (Report). NASA. pp. 241–242. TDA Progress Report 42-87. Public Domain This article incorporates text from this source, which is in the public domain.
  14. ↑ P. Ulivi; D. M. Harland (2007). Robotic Exploration of the Solar System Part I: The Golden Age 1957–1982. Springer. p. 281. Bibcode:2007ress.book.....U. doi:10.1007/978-0-387-73983-0. ISBN 978-0-387-49326-8. ISSN 2945-7475.
  15. ↑ G. van Buitenen. "21P/Giacobini–Zinner". astro.vanbuitenen.nl. Retrieved 8 November 2024.
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