Tempel 1
 Composite of images of nucleus obtained by the Deep Impact impactor |
|
| Discovery | |
|---|---|
| Discovered by | Wilhelm Tempel |
| Discovery date | April 3, 1867 |
| Orbital characteristics A | |
| Epoch | July 31, 2016 |
| Aphelion | 4.748 AU |
| Perihelion | 1.542 AU |
| Semi-major axis | 3.145 AU |
| Eccentricity | 0.5096 |
| Orbital period | 5.58 years (2,038 days) |
| Inclination | 10.474° |
| Dimensions | 7.6 km × 4.9 km (4.7 mi × 3.0 mi) |
| Last perihelion | August 2, 2016 |
| Next perihelion | March 4, 2022 |
Tempel 1 (official designation: 9P/Tempel) is a periodic Jupiter-family comet discovered by Wilhelm Tempel in 1867. It completes an orbit of the Sun every 5.5 years. Tempel 1 was the target of the Deep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by the Stardust spacecraft on February 14, 2011 and came back to perihelion in August 2016.
Tempel 1 was discovered on April 3, 1867, by Wilhelm Tempel, an astronomer working in Marseille. At the time of discovery, it approached perihelion once every 5.68 years (designations 9P/1867 G1 and 1867 II). It was subsequently observed in 1873 (9P/1873 G1, 1873 I, 1873a) and in 1879 (1879 III, 1879b).
Photographic attempts during 1898 and 1905 failed to recover the comet, and astronomers surmised that it had disintegrated. In fact, its orbit had changed. Tempel 1's orbit occasionally brings it sufficiently close to Jupiter to be altered, with a consequent change in the comet's orbital period. This occurred in 1881 (closest approach to Jupiter of 0.55 AU), lengthening the orbital period to 6.5 years. Perihelion also changed, increasing by 50 million kilometres, rendering the comet far less visible from Earth.
Tempel 1 was rediscovered 13 orbits later in 1967 (as 9P/1967 L1, 1966 VII), after British astronomer Brian G. Marsden performed precise calculations of the comet's orbit that took into account Jupiter's perturbations. Marsden found that further close approaches to Jupiter in 1941 (0.41 AU) and 1953 (0.77 AU) had decreased both the perihelion distance and the orbital period to values smaller than when the comet was initially discovered (5.84 and 5.55 years, respectively). These approaches moved Tempel 1 into its present libration around the 1:2 resonance with Jupiter. Despite an unfavorable 1967 return, Elizabeth Roemer of the Catalina Observatory took several photographs. Initial inspection revealed nothing, but in late 1968 she found a June 8, 1967 exposure (Tempel 1 had passed perihelion in January) that held the image of an 18th magnitude diffuse object very close to where Marsden had predicted the comet to be. A single image does not allow an orbit computation, so the next return had to be awaited.
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