55P/Tempel–Tuttle
Halley-type comet
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Through Comet, Hubble Space Telescope and Spectrum
Observational history
In 1699, it was observed by Gottfried Kirch, however it was not recognized as a periodic comet until the discoveries by Tempel and Tuttle during the 1866 perihelion. In 1933, S. Kanda deduced that the comet of 1366 was Tempel–Tuttle, which was confirmed by Joachim Schubart in 1965. On 26 October 1366, the comet passed 0.0229 AU (3.43 million km; 2.13 million mi) from Earth. It is possible the comet was also observed in October 1234, however it is only mentioned briefly by a single Japanese source, and also a comet observed in China in January 1035 could be comet Temple–Tuttle, however unless it had undergone a major outburst, it would have been too dim to observe with the naked eye.
Comet Tempel–Tuttle was recovered by J. Schubart in images taken by Michiel John Bester on 30 June 1965 using the 10-inch telescope of Boyden Observatory, South Africa. At that time the comet had an apparent magnitude of 16. The presence of the comet was confirmed in plates obtained by Palomar Observatory on 30 June. These were the only two observations of the comet during the 1965 apparition.
The comet was recovered on 4 March 1997 by Karen Meech, Olivier Hainaut and James "Gerbs" Bauer, at the University of Hawai`i. At the time it was very faint (22.5 mag), but the recovery proved that it was returning on schedule and that its orbit was very well determined. During the 1998 apparition the comet brightened more than predicted and reached an apparent magnitude of 7.4–7.8 in late February and could be observed with binoculars. It was last observed on 5 July 1998.
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Physical characteristics
The nucleus of the comet was observed by Hubble Space Telescope during the 1998 apparition, and assuming an albedo of 0.04, its nucleus was estimated to have a mean radius of 1.8 km. Spectrometric observations of its nucleus reveal that it has a reddish color, with a B−V of 0.75±0.05 and V−R of 0.51±0.05. A jet was observed emanating from the nucleus and based on its movement the rotation period was calculated to be between 14.79±0.02 and 15.31±0.03 hours.
The spectrum of the comet revealed the presence of diatomic carbon, NH2 and [Oi]. The relative production rates indicate that the comet is depleted in diatomic carbon, with the gas-to-dust ratio also indicated it was gas rich compared with Halley's Comet. The infrared spectrum of the comet closely resembled that of a black body with a temperature of 330 K and lacked silicate emission that has been detected in other comets.
William Huggins observed the spectrum of the comet in January 1866, making it the second time spectrographic observations of a comet were obtained.
55P/Tempel–Tuttle is estimated to have a total nuclear mass of 1.2×1013 kg, with its meteoroid stream is estimated to have a mass of 5×1012 kg in total.
Orbit
Orbital calculations in 2014 suggested that Tempel–Tuttle was at one point about 5,000 years before discovery, the comet made a close encounter with Uranus, which reduced its orbital period from that of a long-period comet out to the Kuiper Belt to its present-day 33-year retrograde orbit around the Sun, however this remains unconfirmed.
The comet currently has an Earth-MOID of about 0.008 AU (1.2 million km).
Meteor shower
Tempel–Tuttle is the parent body of the Leonid meteor shower. The retrograde orbit of 55P/Tempel–Tuttle causes meteors to impact Earth at a high speed of 70 km/s. The orbit intersects that of Earth nearly exactly, hence streams of material ejected from the comet during perihelion passages do not have to spread out much over time to encounter Earth. This coincidence means that past streams from the comet at perihelion are still dense when they encounter Earth, resulting in the 33-year cycle of Leonid meteor storms. For example, the 1833 meteor storm was created by the previous 1800 perihelion passage. Between 2021–2030, Earth will often pass through the meteoroid stream left behind from the 1733 orbit.