153P/Ikeya–Zhang
Longest orbital period of any numbered periodic comet.
Comet Ikeya–Zhang, also known as 153P/Ikeya–Zhang, is a long-period comet that was spotted separately by an astronomer in Japan and another in China during 2002. Among all numbered periodic comets, it holds the record for the longest orbital period—366.51 years. The comet was last seen in October 2002, at which point it was roughly 3.3 AU (490 million km) away from the Sun.
Quick Facts
- Discoverer
- Kaoru Ikeya / Zhang Daqing
- Discovery Date
- 1 February 2002
- Orbit Ref
- jpldata
- Epoch
- 8 May 2002 (JD 2452402.5)
- Observation Arc
- 341–1,125 years
- Obs
- 1,893
- Perihelion
- 0.507 AU
- Aphelion
- 101.73 AU
- Semimajor
- 51.119 AU
- Period
- 365.49 years
- Max Speed
- 59 km/s / (2002-03-18)
- Eccentricity
- 0.99008
Facts from the source article.
Lore & Background
On 1 February 2002, Chinese astronomer Zhang Daqing from Kaifeng discovered a new comet in the constellation Cetus and reported it to the IAU. He found that Japanese astronomer Kaoru Ikeya had discovered it earlier, as the time of sunset is earlier than China. According to tradition, since they discovered the new comet independently, it was named after both of them. The comet was initially designated as C/2002 C1 (Ikeya–Zhang).
The comet was observed in 1661, 341 years earlier, by Polish astronomer Johannes Hevelius. A bright comet had also been recorded by Chinese astronomers in 1661. Further research by Ichiro Hasegawa and Shuichi Nakano concluded that historical comets recorded in AD 877 and 1273 were likely previous apparitions of Ikeya–Zhang as well. The permanent designation '153P' was given to the comet.
Its orbital speed around the Sun varies from 59 km/s at perihelion to 0.29 km/s at aphelion. During March–April 2002, protons from the comet tail may have been detected by the Cassini–Huygens spacecraft. This data suggested the comet tail had a length greater than 7.5 AU (1.12 billion km), making it the longest yet detected.
Reader's Guide
Comet Ikeya–Zhang is notable primarily for its extreme orbital period of 366.51 years, the longest known among all numbered periodic comets. Its discovery in 2002 by two independent observers from Japan and China, with Zhang Daqing reporting it after Kaoru Ikeya, follows the tradition of naming comets after co-discoverers. The comet's historical significance is underscored by its identification with earlier apparitions: it was observed in 1661 by Johannes Hevelius and recorded by Chinese astronomers that same year, and further research linked it to comets seen in AD 877 and 1273. This long observational record makes it one of the few comets with documented returns spanning over a millennium. The comet's tail, possibly detected by the Cassini–Huygens spacecraft in 2002, was inferred to be longer than 7.5 AU, the longest tail ever detected. Its next perihelion is expected between 2362 and 2363, a distant future event that underscores the comet's slow, asymmetric outgassing and multi-century orbit. The comet's legacy lies in its unique combination of ancient historical records and modern scientific observation, providing a rare link between past and present cometary science.
Did You Know?
- Comet Ikeya–Zhang has the longest orbital period (366.51 years) of any numbered periodic comet.
- It was discovered independently by Zhang Daqing of China and Kaoru Ikeya of Japan on 1 February 2002.
Frequently Asked Questions
Who is 153P/Ikeya–Zhang?
153P/Ikeya–Zhang is a long-period periodic comet first observed in early 2002 by astronomers working independently in Japan and China. It holds the 153rd number in the official sequence of recognized periodic comets.
What makes 153P/Ikeya–Zhang's orbit unique?
This comet carries the record for the longest orbital period among all numbered periodic comets, requiring roughly 366.51 years to complete a single circuit of the Sun.
Who discovered 153P/Ikeya–Zhang?
Zhang Daqing in China and Kaoru Ikeya in Japan independently spotted the comet on 1 February 2002, which is why it bears both their surnames in its designation.
How bright did 153P/Ikeya–Zhang get at closest approach?
The comet reached perihelion on 18 March 2002 and shone at an apparent magnitude of 2.9, bright enough to be visible to the unaided eye under dark skies.
When will 153P/Ikeya–Zhang come back?
Given its approximately 367-year orbital period, the next perihelion passage is not expected until the late 24th century, so it will be gone for many generations.
More in Named Comets, Part 3 1-24
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