The comet nucleus is estimated to be 2.0 kilometers in diameter.[1] 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 (5,200,000 km; 3,300,000 mi).[1]
Giacobini–Zinner was the target of the International Cometary Explorer spacecraft, which passed through its plasma tail on September 11, 1985. Earlier in the same month the comet was observed by the Pioneer Venus Orbiter.[6] 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.
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.[7]
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.[8]
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