21P/Giacobini–Zinner

Physical properties

The comet nucleus is estimated to be 2.0 km in diameter. During its apparitions, Giacobini–Zinner can reach about the 7-8th magnitude, 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.

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.

Exploration

Giacobini–Zinner was the target of the International Cometary Explorer spacecraft, which passed through its plasma tail at a distance of 7800 km on 11 September 1985, becoming the first comet ever visited in space exploration. Earlier in the same month the comet was observed by the Pioneer Venus Orbiter. 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. 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.

References

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