 Sketch of the comet on 23 August 1862 by G. J. Chambers | |
| Discovery | |
|---|---|
| Discovered by | Lewis Swift Horace Parnell Tuttle |
| Discovery date | 16–19 July 1862 |
| Designations | |
| P/1737 N1; P/1862 O1 P/1992 S2 | |
| 1737 II; 1862 III; 1992 XXVIII | |
| Orbital characteristics[1][2][3] | |
| Epoch | 4 December 1995 (JD 2448960.5) |
| Observation arc | 257 years |
| Earliestprecovery date | 69 BC |
| Number of observations | 652 |
| Aphelion | 51.225 AU |
| Perihelion | 0.9595 AU |
| Semi-major axis | 26.092 AU |
| Eccentricity | 0.9632 |
| Orbital period | 133.28 years |
| Max.orbital speed | 42.6 km/s (26.5 mi/s)[a] |
| Min.orbital speed | 0.8 km/s (0.50 mi/s) (2059-Dec-12) |
| Inclination | 113.45° |
| 139.44° | |
| Argument of periapsis | 153.00° |
| Last perihelion | 12 December 1992 |
| Next perihelion | 12 July 2126 |
| TJupiter | –0.280 |
| EarthMOID | 0.0009 AU (130,000 km; 84,000 mi) |
| Physical characteristics[4] | |
| Dimensions | 26 km (16 mi) |
| Comet total magnitude (M1) | 4.5 |
| Comet nuclear magnitude (M2) | 8.5 |
| Orbital period at different passages[3] | |||||||
| Perihelion date | Orbital period (years) | ||||||
|---|---|---|---|---|---|---|---|
| 2392-09-16 | 132.7 | ||||||
| 2261-08-10 | 134.6 | ||||||
| 2126-07-12 | 136.2 | ||||||
| 1992-12-12 | 135.0 | ||||||
| 1862-08-23 | 131.7 | ||||||
| 1737-06-15 | 127.8 | ||||||
| 1610-02-06 | 130.5 | ||||||
| 1479-10-18 | 133.4 | ||||||
| 1348-05-02 | 135.0 | ||||||
Comet Swift–Tuttle (formally designated109P/Swift–Tuttle) is a largeperiodiccomet with a 1995 (osculating)orbital period of 133 years that is in a 1:11orbital resonance withJupiter. It fits the classical definition of aHalley-type comet, which has anorbital period between 20 and 200 years.[4] The comet was independently discovered byLewis Swift on 16 July 1862 and byHorace Parnell Tuttle on 19 July 1862.
Itsnucleus is 26 km (16 mi) in diameter.[4] Swift–Tuttle is the parent body of thePerseidmeteor shower, perhaps the best known shower and among the most reliable in performance.[5]
The comet made a return appearance in 1992, when it was rediscovered by Japaneseastronomer Tsuruhiko Kiuchi and became visible with binoculars.[6] It was last observed in April 1995 when it was 8.6 AU (1.3 billion km) from the Sun.[1] In 2126, it will be a bright naked-eye comet reaching anapparent magnitude of about 0.7.[3]
| Older passages[3] | |||||||
| CE/BCE | Date | ||||||
|---|---|---|---|---|---|---|---|
| 188 CE | 188-07-10 | ||||||
| 69 BCE | –68-08-27 | ||||||
| 322 BCE | –321-09-27 | ||||||
Chinese records indicate that, in 188, the comet reachedapparent magnitude 0.1.[3] Observation was also recorded in 69BCE, and it was probably visible to the naked eye in 322 BCE.[7]
In the discovery year of 1862, the comet was as bright asPolaris.[8]
After the 1862 observations, it was incorrectly theorized that the comet would return between 1979 and 1983. However, it had been suggested in 1902 that this was the same comet as that observed byIgnatius Kegler on 3 July 1737[9] and on this basisBrian Marsden calculated correctly that it would return in 1992.[7]
The comet's perihelion is just under that ofEarth, while its aphelion is just over that ofPluto. An unusual aspect of its orbit is that it was recently captured into a 1:11orbital resonance withJupiter; it completes one orbit for every 11 of Jupiter.[7] It was the first comet in aretrograde orbit to be found in a resonance.[7] In principle this would mean that itsproper long-term average period would be 130.48 years, as itlibrates about the resonance. Over the short term, betweenepochs 1737 and 2126 the orbital period varies between 128 and 136 years.[1] However, it only entered this resonance about 1000 years ago, and will probably exit the resonance in several thousand years.[7]
The comet is on anorbit that makes repeated close approaches to theEarth–Moon system,[7] and has an Earth-MOID (Minimum orbit intersection distance) of 0.0009 AU (130,000 km; 84,000 mi).<[4] Upon its September 1992 rediscovery, the comet's date ofperihelion passage was off from the 1973 prediction by 17 days.[10] It was then noticed that if its next perihelion passage (July 2126) was also off by another 15 days (July 26), the comet could impact the Earth or the Moon on 14 August 2126 (IAUC 5636: 1992t).[11]
Given the size of the nucleus of Swift–Tuttle, this was of some concern. This prompted amateur astronomer and writerGary W. Kronk to search for previous apparitions of this comet. He found the comet was most likely observed by the Chinese at least twice, first in 69 BCE and later in 188 CE;[12] these two sightings were quickly confirmed by Brian Marsden and added to the list of perihelion passages at theMinor Planet Center.[1] Around 25 July 188 CE the comet passed about 0.129 AU (19.3 million km) from Earth.[3]
This information and subsequent observations have led to recalculation of its orbit, which indicates the comet's orbit is sufficiently stable that there is absolutely no threat over the next two thousand years.[10] It is now known that the comet will pass 0.153 AU (22.9 million km; 14.2 million mi) from Earth on August 5, 2126.[4][b] and within 0.147 AU (22.0 million km; 13.7 million mi) from Earth on August 24, 2261.[3]
A close encounter with Earth is predicted for the comet's return to the inner Solar System in the year 3044, with the closest approach estimated to be 0.011 AU (1.0 million mi; 1.6 million km).[13] Another close encounter is predicted for the year 4479, around Sept. 15; the close approach is estimated to be less than 0.05AU, with a probability of impact of 1 in a million.[7] Subsequent to 4479, the orbital evolution of the comet is more difficult to predict; the probability of Earth impact per orbit is estimated as 2×10−8 (0.000002%).[7]
Comet Swift–Tuttle is by far the largestnear-Earth object (Apollo orAten asteroid orshort-period comet) to cross Earth's orbit and make repeated close approaches to Earth.[4] With a relative velocity of 60 km/s,[14][15] an Earth impact would have an estimated energy of ~27 times that of theCretaceous–Paleogene impactor.[c] The comet has been described as "the single most dangerous object known to humanity".[15] In 1996, the long-term possibility of Comet Swift–Tuttle impacting Earth was compared to433 Eros and about 3000 other kilometer-sized objects of concern.[16]
| Date & time of closest approach | Earth distance (AU) | Sun distance (AU) | Velocity wrt Earth (km/s) | Velocity wrt Sun (km/s) | Uncertainty region (3-sigma) | Reference |
|---|---|---|---|---|---|---|
| 2126-08-05 15:50 | 0.15337 AU (22.944 million km; 14.257 million mi; 59.69 LD) | 1.04 AU (156 million km; 97 million mi; 400 LD) | 58.3 | 40.8 | ± 11000 km | Horizons |
| Numbered comets | ||
|---|---|---|
| Previous 108P/Ciffreo | Comet Swift–Tuttle | Next 110P/Hartley |
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