205P/Giacobini
Lost for over a century, then rediscovered in three fragments.
205P/Giacobini is a Jupiter-family comet that orbits the Sun once every 6.68 years. It was first spotted by Michel Giacobini on September 4, 1896, who described it as faint with a coma roughly one arcminute across. The following day, other observers confirmed the sighting and estimated its brightness at magnitude 11.3, with the comet located in the constellation Serpens. It faded over time and was last seen on January 5, 1897, by William Hussey. Early calculations by Perrotin and Giacobini gave it an elliptical orbit with a period of 6.65 years and a perihelion date of October 28.80.
Soon after discovery, on September 26, Henri Perrotin noted an extremely faint companion, suggesting the comet had split. Throughout late September and early October, other observers using the Lick Observatory recorded a second condensation within the coma, and on October 10 they saw an elongated nucleus. Zdenek Sekanina later estimated that the fragment had separated from the main nucleus on April 24, 1896, indicating it was short-lived.
The comet was then lost until Koichi Itagaki and Hiroshi Kaneda rediscovered it on September 10, 2008, during a supernova patrol survey. At that time, it had an apparent magnitude of 13.5, a coma about 25 arcseconds across, and a tail roughly 2 arcminutes long. Maik Meyer initially linked it to the comet 1896V, and Nakano confirmed the connection. On September 17, a companion about 4 magnitudes fainter (nucleus B) was observed, and on September 19, another fragment more than 5 magnitudes fainter (nucleus C) was seen farther away. Sekanina estimated that nucleus B had separated in 2006, about 700 days before perihelion, while nucleus C had split off in 1998, before the comet’s previous perihelion. Neither fragment was observed during the 2015 perihelion.
During the next perihelion, starting October 15, 2021, a secondary nucleus was seen drifting away from the primary. It remains unclear whether this was a new fragmentation event or the reactivation of a previously observed fragment.
Quick Facts
- Discovery Ref
- cometography
- Discoverer
- Michel Giacobini
- Discovery Site
- Nice, France
- Discovery Date
- 4 September 1896
- Mpc Name
- D/1896 R2, P/2008 R6
- Designations
- 1896 V, 1896dICQ1
- Orbit Ref
- jpl1 · jpl2
- Epoch
- 19 February 2014 (JD 2456707.5)
- Observation Arc
- 112.05 years
- Obs
- 1,143
- Perihelion
- 1.536 AU
- Aphelion
- 5.558 AU
Facts from the source article.
Lore & Background
The comet was discovered by Michel Giacobini on 4 September 1896, who described it as faint with a coma about one arcminute across. Other observers confirmed it the next day, estimating an apparent magnitude of 11.3. The comet was last observed on 5 January 1897 by William Hussey. The first elliptical orbit, calculated by Perrotin and Giacobini, indicated an orbital period of 6.65 years and a perihelion date of October 28.80. Starting on 26 September, Henri Perrotin observed an extremely faint companion, suggesting the comet had split. Other observers recorded a second condensation in late September and early October, and an elongated nucleus on 10 October. Zdenek Sekanina estimated the fragment separated from the main nucleus on 24 April 1896, indicating a short-lived companion.
The comet was lost until Koichi Itagaki and Hiroshi Kaneda rediscovered it on 10 September 2008 during a supernova patrol survey. It then had an apparent magnitude of 13.5, a coma about 25 arcseconds across, and a tail about 2 arcminutes long. The link to the 1896 comet was made by Maik Meyer and confirmed by Nakano. A companion about 4 magnitudes fainter (nucleus B) was observed on 17 September, and another more than 5 magnitudes fainter (nucleus C) on 19 September. Sekanina estimated nucleus B separated in 2006, about 700 days before perihelion, while nucleus C separated in 1998, before the previous perihelion. The two fragments were not observed in the 2015 perihelion. During the next perihelion, a secondary nucleus was observed drifting away starting 15 October 2021; it is unclear if this is a new fragmentation event or the reactivation of a previously observed fragment.
Reader's Guide
205P/Giacobini's significance lies in its long period of being lost and its dramatic rediscovery in a fragmented state. The comet was first observed in 1896 and then vanished from view for over 111 years, until it was recovered in 2008 by Koichi Itagaki and Hiroshi Kaneda. Upon rediscovery, it was found to have split into three distinct pieces, with two fragments (nuclei B and C) observed shortly after. Zdenek Sekanina's analysis estimated that nucleus B separated in 2006 and nucleus C in 1998, suggesting fragmentation events occurred both before and after the comet's previous perihelion. The fact that the two fragments were not seen in the 2015 perihelion indicates that such fragments may be short-lived. The comet's behavior continues to be studied, as a secondary nucleus was observed drifting away in 2021, though it remains uncertain whether this is a new fragmentation or a reactivation of an older fragment. This comet thus provides a valuable case study in the fragmentation and evolution of Jupiter-family comets over multiple orbits.
Did You Know?
- It was lost for over a century until rediscovered by Koichi Itagaki on 10 September 2008.
- Upon rediscovery, the comet was found to have fragmented into three pieces.
More in Periodic Comets 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced