 Comet Grigg–Skjellerup photographed from theEuropean Southern Observatory on 29 June 1992 | |
| Discovery | |
|---|---|
| Discovered by | John Grigg John Francis Skjellerup |
| Discovery date | 23 July 1902 17 May 1922 |
| Designations | |
| |
| |
| Orbital characteristics[4][5] | |
| Epoch | 17 October 2024 (JD 2460600.5) |
| Observation arc | 216.67 years |
| Earliestprecovery date | 6 February 1808[1] |
| Number of observations | 827 |
| Aphelion | 4.947 AU |
| Perihelion | 1.084 AU |
| Semi-major axis | 3.015 AU |
| Eccentricity | 0.64056 |
| Orbital period | 5.236 years |
| Max.orbital speed | 36.6 km/s[2] |
| Inclination | 22.433° |
| 211.54° | |
| Argument of periapsis | 2.136° |
| Mean anomaly | 55.845° |
| Last perihelion | 25 December 2023 |
| Next perihelion | 18 March 2029[3] |
| TJupiter | 2.804 |
| EarthMOID | 0.085 AU |
| JupiterMOID | 0.006 AU |
| Physical characteristics | |
Mean radius | 1.3 km (0.81 mi)[6] |
| 12 hours[7] | |
| (V–R) =0.42±0.10[7] | |
| Comet total magnitude (M1) | 16.5 |
Comet Grigg–Skjellerup (formally designated26P/Grigg–Skjellerup) is aperiodic comet. It was visited by theGiotto probe in July 1992.[8] The spacecraft came as close as 200 km, but could not take pictures because some instruments were damaged from its encounter withHalley's Comet.[9] The comet last came toperihelion (closest approach to the Sun) on 25 December 2023,[5][2][10] but was 1.8 AU from Earth and only 31 degrees from the Sun.[2]
The comet was discovered in 1902 byJohn Grigg ofNew Zealand, and rediscovered in its next appearance in 1922 byJohn Francis Skjellerup, anAustralian then living and working for about two decades inSouth Africa where he was a founder member of theAstronomical Society of Southern Africa. In 1987, it was belatedly discovered byĽubor Kresák that the comet had been observed in 1808 as well, byJean-Louis Pons. Pons observed the comet on 6 and 9 February, which was insufficient to calculate an approximate orbit.[1]
In 1972 the comet was discovered to produce ameteor shower, thePi Puppids, and its current orbit makes them peak around April 23, for observers in the southern hemisphere, best seen when the comet is near perihelion.
During the comet's 1982 approach it was detected using radar by theArecibo Observatory.[11]
The apparitions of 1997 and 2002 were very unfavorable due to solar conjunctions, thus no observations were conducted at those times.[12]
The comet has often suffered the gravitational influence ofJupiter, which has altered its orbit considerably. For instance, itsperihelion distance has changed from 0.77AU in 1725 to 0.89 AU in 1922 to 0.99 AU in 1977 and to 1.12 AU in 1999.
Thecomet nucleus is estimated to be 2.6 km (1.6 mi) in diameter.[6] Light-curve analysis from theGiotto flyby in 1992 revealed that Grigg–Skjellerup is surprisingly an old comet compared to1P/Halley, suggesting that 26P is estimated to be around 89 comet-years in age.[12] Ground-based photometry of the comet reveal a non-spherical nucleus with a rotation period longer than 12 hours.[7]
The comet is atype locality for the mineralbrownleeite.[13][14]
In 1987, Grigg–Skjellerup was selected as the second comet targeted by theGiotto mission due to its perihelion in 1992 occurring very close to the Earth's orbit itself.[15]
By February 1990, the mission control at theEuropean Space Agency reactivated the spacecraft after four years of hibernation following the Halley mission, subsequently executing the first ever Earth flyby in space exploration history to reach 26P on July 1990.[16]Giotto reached Grigg–Skjellerup on 10 July 1992 at a distance of 200 km (120 mi), much closer than its approach toHalley's Comet, but was unable to obtain images as its camera was destroyed during the Halley rendezvous in 1986. Despite this, the spacecraft was able to measure the interaction of the solar wind and how it affects thecoma of this comet.[17]
Giotto was deactivated just 13 days after its flyby of Grigg–Skjellerup on 23 July 1992.
In 1972, a NASA spacecraft mission based from theExplorer 47/50 satellite calledCometary Explorer was proposed to intercept Grigg–Skjellerup at a distance of 1,000 km (620 mi) by April 1977,[18] with an option to flyby21P/Giacobini–Zinner on a potential mission extension in 1979.[19] This would serve as a precursor mission for an eventual mission to Halley in 1986,[18] however it was rejected due to budget cuts.[19]
| Numbered comets | ||
|---|---|---|
| Previous 25D/Neujmin | 26P/Grigg–Skjellerup | Next 27P/Crommelin |
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