21P/Giacobini–Zinner
First comet visited by a spacecraft; parent of the Draconid meteor shower.
21P/Giacobini–Zinner is a Jupiter-family comet with an orbital period of 6.53 years. It was discovered by Michel Giacobini in 1900 and recovered by Ernst Zinner in 1913. The comet is notable as the parent body of the Giacobinids (Draconids) meteor shower and as the first comet ever visited by a spacecraft, when the International Cometary Explorer passed through its plasma tail in 1985.
Quick Facts
- Pronounced
- dZ · ae · k · ou · ' · b · i: · n · i · ' · z · I · n · @r
- 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
- mpc
- Epoch
- 26 March 2025 (JD 2460760.5)
- Observation Arc
- 4,922 days (13.48 years)
- Obs
- 7,387
- Perihelion
- 1.009 AU
- Aphelion
- 5.97 AU
- Semimajor
- 3.49 AU
Facts from the source article.
Lore & Background
Michel Giacobini first observed the comet in the constellation of Aquarius on 20 December 1900. It was recovered two orbits later by Ernst Zinner on 23 October 1913 while he was observing variable stars near Beta Scuti. The comet nucleus is estimated to be 2.0 km in diameter. During its apparitions it typically reaches magnitude 7–8, but in 1946 a series of outbursts made it as bright as 5th magnitude. The comet is the parent body of the Giacobinids (Draconids) meteor shower. Its minimum orbit intersection distance to Earth is 0.035 AU. Optical spectra from the 2018 apparition showed the comet is depleted in carbon-chain molecules and carbon dioxide, suggesting an origin in a relatively warm portion of the Solar System.
Reader's Guide
Giacobini–Zinner holds a unique place in space exploration as the target of the International Cometary Explorer (ICE) spacecraft, which passed through its plasma tail at a distance of 7,800 km on 11 September 1985, becoming the first comet ever visited. Earlier that month, the comet was also observed by the Pioneer Venus Orbiter. Japanese space officials considered redirecting the Sakigake probe toward a 1998 encounter, but the probe lacked propellant for the necessary maneuvers and the project was abandoned. The comet will pass 0.364 AU from Jupiter on 14 February 2029, reach perihelion at 1.07 AU on 30 August 2031, and pass 0.554 AU from Earth on 3 September 2031. Its most recent perihelion was on 25 March 2025, with closest Earth approach on 21 March 2025 at an unfavorable distance of 2.0 AU, brightening to about magnitude 11. As the source of the Draconid meteor shower, it continues to be of interest to both professional and amateur astronomers.
More in Named Comets, Part 5 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced