21P/Giacobini-Zinner
21P/Giacobini–Zinner is a Jupiter-family comet that returns about every 6.5 years, and the parent of the Draconid meteors. On 11 September 1985 NASA's International Cometary Explorer flew through its tail about 7,800 km behind the nucleus — the first spacecraft to fly past a comet.
Key facts
Science
Physical
- Nucleus
- ≈ 2 km across — estimated (Lamy et al. 2004); never imaged
- Composition
- Its nucleus has never been imaged: the International Cometary Explorer carried no camera. It crossed the tail about 7,800 km antisunward of the nucleus, coming in from the south and leaving to the north at about 21 km/s, and measured the plasma and magnetic field there (Bame et al. 1986; Ogilvie et al. 1986). The nucleus is estimated at about 2 km across (Lamy et al. 2004) and is drawn as a plain sphere of that size. Its mass has not been measured.
Orbital
- Semi-major axis
- 3.49 AU
- From catalogued orbital elements (MPC)
- Eccentricity
- 0.7112
- From catalogued orbital elements (MPC)
- Inclination
- 32.08 °
- From catalogued orbital elements (MPC)
- Orbital period
- 6.52 years
- From catalogued orbital elements (MPC)
- Perihelion
- 1.01 AU
- Computed from the orbital elements
- Aphelion
- 5.97 AU
- Computed from the orbital elements
- Mean orbital velocity
- 15.9 km/s
- Computed from the orbital elements
Activity
- Perihelion distance
- 1.01 AU
- Becomes active within
- 5 AU of the Sun
Radiation & temperature
- Insolation
- 0.0821 S⊕ · 8% of the sunlight Earth receives
- Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
Discovery & history
- Discovered
- December 20, 1900
- By
- Michel Giacobini (Nice) and Ernst Zinner (Bamberg)
- Name
- Named after its two discoverers, the French astronomer Michel Giacobini, who found it in 1900, and the German astronomer Ernst Zinner, who found it again in 1913.
Michel Giacobini found it at Nice Observatory on 20 December 1900, and Ernst Zinner found it again at Bamberg on 23 October 1913, while observing variable stars. On 11 September 1985 ISEE-3, renamed the International Cometary Explorer, crossed its tail about 7,800 km behind the nucleus at about 21 km/s, measuring its plasma and magnetic field. It carried no camera, so the nucleus was never seen.
The first spacecraft to fly past a comet: it crossed the tail about 7,800 km behind the nucleus (7,796 km in JPL's post-encounter trajectory) at about 21 km/s, measuring its plasma and magnetic field. It carried no camera.
Images
Images from open archives · credit shown per image