Comet Giacobini–Zinner (officially designated 21P/Giacobini–Zinner) is a

periodic comet Periodic comets (also known as short-period comets) are comets with orbital periods of less than 200 years or that have been observed during more than a single perihelion passage (e.g. 153P/Ikeya–Zhang). "Periodic comet" is also sometimes us ...

in the Solar System. It was discovered by

Michel Giacobini Michel Giacobini (1873–1938) was a French astronomer. He discovered a number of comets, including 21P/Giacobini-Zinner (parent body of the Giacobinids meteor shower), 41P/Tuttle-Giacobini-Kresak, and 205P/Giacobini. The latter he had disc ...

, who observed it in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

Aquarius Aquarius may refer to: Astrology * Aquarius (astrology), an astrological sign * Age of Aquarius, a time period in the cycle of astrological ages Astronomy * Aquarius (constellation) * Aquarius in Chinese astronomy Arts and entertainment ...

on December 20, 1900. It was recovered two orbits later by

Ernst Zinner Ernst Zinner (2 February 1886 in Goldberg, Silesia – 30 August 1970) was a German astronomer and noted historian of astronomy. After studies in Munich and Jena he obtained his PhD in 1907 at the University of Jena, followed by stays at ...

, while he was observing

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

s near Beta Scuti on October 23, 1913. The

comet nucleus The nucleus is the solid, central part of a comet, once termed a ''dirty snowball'' or an ''icy dirtball''. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublime and produce an atmosphere ...

is estimated to be 2.0 kilometers in diameter. During its apparitions, Giacobini–Zinner can reach about the 7-8th

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

, 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 The October Draconids, in the past also unofficially known as the Giacobinids, are a meteor shower whose parent body is the periodic comet 21P/Giacobini-Zinner. They are named after the constellation Draco, where they seemingly come from. Almost ...

meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extr ...

(also known as the Draconids). The comet currently has a

minimum orbit intersection distance Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits o ...

to Earth of . Giacobini–Zinner was the target of the

International Cometary Explorer The International Cometary Explorer (ICE) spacecraft (designed and launched as the International Sun-Earth Explorer-3 (ISEE-3) satellite), was launched 12 August 1978, into a heliocentric orbit. It was one of three spacecraft, along with the mo ...

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 The Pioneer Venus Orbiter, also known as Pioneer Venus 1 or Pioneer 12, was a mission to Venus conducted by the United States as part of the Pioneer Venus project. Launched in May 1978 atop an Atlas-Centaur rocket, the spacecraft was inserted into ...

In addition,

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...

ese space officials considered redirecting the

Sakigake , known before launch as MS-T5, was Japan's first interplanetary spacecraft, and the first deep space probe to be launched by any country other than the USA or the Soviet Union. It aimed to demonstrate the performance of the new launch vehi ...

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 Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

, likely indicating its origin in relatively warm portion of the Solar system.

References

External links

Orbital simulation
from JPL (Java)
Horizons Ephemeris

– Seiichi Yoshida @ aerith.net

Comet 21P - Comet Watch
{{DEFAULTSORT:Giacobini-Zinner, P021 Comets visited by spacecraft Periodic comets 0021 021P Meteor shower progenitors Comets in 2012 Comets in 2018 19001220