21P/Giacobini–Zinner
{{Short description|Periodic comet with 6 year orbit}}
{{Infobox comet
| name = 21P/Giacobini–Zinner
| image = Comet 21P Giacobini-Zinner September 2018.jpg
| caption = Comet Giacobini–Zinner photographed from Moscow, Russia on 9 September 2018.
| discoverer = Michel Giacobini
Ernst Zinner
| discovery_date = 20 December 1900
23 October 1913
| mpc_name = P/1900 Y1
P/1913 U1
| designations = 1900 III; 1913 V; 1926 VI;
1933 III; 1940 I; 1946 V;
1959 VIII; 1966 I; 1972 VI;
1979 III; 1985 XIII; 1992 IX
| orbit_ref = {{r|Horizons_2025|jpldata}}
| epoch = 13 November 2017 (JD 2458070.5)
| observation_arc = 4,922 days (13.48 years)
| obs = 1,993
| perihelion = 1.013 AU/2192480km (2031 aparition)
| aphelion = 5.987 AU
| semimajor = 3.492 AU
| period = 6.549 years
| eccentricity = 0.71047
| inclination = 32.002°
| asc_node = 195.40°
| arg_peri = 172.81°
| tjup = 2.465
| Earth_moid = 0.018 AU
| Jupiter_moid = 0.248 AU
| physical_ref = {{r|jpldata}}
| dimensions = {{cvt|2.0|km|mi}}
| M1 = 13.2
| last_p = 10 September 2018{{r|Nakano_2012}}
| next_p = 25 March 2025{{r|Yoshida_2024}} 8 October 2031
}}
Comet Giacobini–Zinner (officially designated as 21P/Giacobini–Zinner) is a periodic comet in the Solar System. 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.
Physical properties
The comet nucleus is estimated to be {{cvt|2.0|km|mi}} in diameter.{{r|jpldata}} During its apparitions, Giacobini–Zinner can reach about the 7-8th magnitude,{{r|King_2018}} 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 {{convert|0.035|AU|e6km|abbr=unit}}.{{r|jpldata}}
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.{{r|Shinnaka_2020}}
Exploration
{{See also|List of minor planets and comets visited by spacecraft}}
Giacobini–Zinner was the target of the International Cometary Explorer spacecraft, which passed through its plasma tail at a distance of {{cvt|7800|km|mi}} on 11 September 1985, becoming the first comet ever visited in space exploration.{{r|Stelzried_1986}} Earlier in the same month the comet was observed by the Pioneer Venus Orbiter.{{r|Ulivi_2007}} 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
21P/Giacobini-Zinner most recently passed perihelion on 25 March 2025, making its closest approach to Earth 4 days before, on 21 March. It was expected to brighten to magnitude ~11.{{r|Van_Buitenen_2024}}
References
{{Reflist|refs=
| title= Horizons Batch for 21P/Giacobini-Zinner (90000322) on 2025-Mar-25
| url= https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%2790000322%27&START_TIME=%272025-Mar-22%27&STOP_TIME=%272025-Mar-28%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27
| publisher= JPL Horizons
| type= Perihelion occurs when rdot flips from negative to positive
| access-date= 10 April 2021 }} (JPL#K182/14 Soln.date: 2021-Mar-23)
| title= 21P/Giacobini–Zinner – JPL Small-Body Database Lookup
| url= https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=21P
| website= ssd.jpl.nasa.gov
| publisher= Jet Propulsion Laboratory
| access-date= 10 January 2016 }}
| author1= B. King
| title= Comet 21P/Giacobini-Zinner Shines in September
| url= https://www.skyandtelescope.com/observing/comet-21p-giacobini-zinner-shines-in-september/
| website= Sky & Telescope
| date= 29 August 2018
| access-date= 15 September 2018 }}
| author1= S. Nakano
| title= 21P/Giacobini-Zinner (NK 2191)
| url= http://www.oaa.gr.jp/~oaacs/nk/nk2191.htm
| publisher= OAA Computing and Minor Planet Sections
| date= 5 February 2012
| access-date= 18 February 2012 }}
| author1= Y. Shinnaka
| author2= H. Kawakita
| author3= A. Tajitsu
| title= High-resolution Optical Spectroscopic Observations of Comet 21P/Giacobini–Zinner in its 2018 Apparition
| year= 2020
| journal= Astronomical Journal
| volume= 159
| issue= 5
| pages= 203
| bibcode= 2020AJ....159..203S
| arxiv= 2004.11008
| doi= 10.3847/1538-3881/ab7d34
| doi-access= free }}
| author1= C. Stelzried
| author2= L. Efron
| author3= J. Ellis
| title= Halley Comet Missions
| url= http://ipnpr.jpl.nasa.gov/progress_report/42-87/87X.PDF
| year= 1986
| id= TDA Progress Report 42-87
| publisher= NASA
| pages= 241–242 }} {{PD-notice}}
| author1= P. Ulivi
| author2= D. M. Harland
| title= Robotic Exploration of the Solar System Part I: The Golden Age 1957–1982
| url= https://books.google.com/books?id=Fi1mCYJWBwAC&pg=PA281
| publisher= Springer
| year= 2007
| page= 281
| isbn= 978-0-387-49326-8
| issn= 2945-7475
| doi= 10.1007/978-0-387-73983-0 }}
| author1= S. Yoshida
| title= 21P/Giacobini–Zinner
| url= http://www.aerith.net/comet/catalog/0021P/index.html
| website= www.aerith.net
| access-date= 5 January 2025 }}
| author1= G. van Buitenen
| title= 21P/Giacobini–Zinner
| url= http://astro.vanbuitenen.nl/comet/21
| website= astro.vanbuitenen.nl
| access-date= 8 November 2024 }}
}}
External links
- {{JPL Small Body|id=1000032}}
- [http://cometography.com/pcomets/021p.html 21P at Kronk's Cometography]
- [http://www.cometwatch.co.uk/comet-21p/ Comet 21P – Comet Watch]
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