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,[5] but in 1946 it underwent a series of outbursts that made it as bright as 5th magnitude. It is the parent body of the Giacobinidsmeteor 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.[6]
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.[7] Earlier in the same month the comet was observed by the Pioneer Venus Orbiter.[8] 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 will next pass perihelion on 25 March 2025, and will have its closest approach to Earth 4 days before, on 21 March. It is expected to brighten to magnitude ~11.[9]
References
^S. Nakano (5 February 2012). "21P/Giacobini-Zinner (NK 2191)". OAA Computing and Minor Planet Sections. Retrieved 18 February 2012.
^C. Stelzried; L. Efron; J. Ellis (1986). Halley Comet Missions(PDF) (Report). NASA. pp. 241–242. TDA Progress Report 42-87. This article incorporates text from this source, which is in the public domain.
.png)
