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 Nucleus imaged by the Deep Impact impactor | |
| Discovery | |
|---|---|
| Discovered by: | Wilhelm Tempel |
| Discovery date: | April 3, 1867 |
| Alternate designations: | 9P/1867 G1; 1867 II; 9P/1873 G1; 1873 I; 1873a 1879 III; 1879b 9P/1967 L1; 1966 VII 9P/1972 A1; 1972 V; 1972a 1978 II; 1977i 1983 XI; 1982j 1989 I; 1987e1 1994 XIX; 1993c |
| Orbital characteristics A | |
| Epoch: | March 6, 2006 |
| Aphelion distance: | 4.737 AU |
| Perihelion distance: | 1.506 AU |
| Semi-major axis: | 3.122 AU |
| Eccentricity: | 0.5175 |
| Orbital period: | 5.515 a |
| Inclination: | 10.5301° |
| Last perihelion: | July 5, 2005 |
| Next perihelion: | 2011 |
Tempel 1 (official designation: 9P/Tempel), is a periodic comet discovered by Wilhelm Tempel in 1867. It currently completes an orbit of the sun every 6.5 years. Tempel 1 was the target of the Deep Impact space mission, which photographed the deliberate high speed impact upon the comet.
Nucleus parameters
- Dimensions: 7.6×4.9 km[1][2]
- Density: 0.62 g/cm³[3]
- Mass: 7.2 × 1013 to 7.9 × 1013 kg[1][4]
- Rotation: 40.7 hours[2]
Discovery
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). However, 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 event 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. Photographic attempts during 1898 and 1905 failed to recover the comet, and astronomers surmised that it had disintegrated. (see Lost comet)
Rediscovery
Tempel 1 was re-discovered 13 orbits later, in the 1960s (as 9P/1967 L1, 1966 VII) after British astronomer Brian G. Marsden performed precise calculations of the comet's orbit, taking 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. Unfortunately, a single image does not allow an orbit computation, so the next return had to be awaited.
Roemer and L. M. Vaughn recovered the comet on January 11, 1972 from Steward Observatory (9P/1972 A1, 1972 V, 1972a). The comet became widely observed, reached a maximum brightness of magnitude 11 during May, and was last seen on July 10. Since that time the comet has been seen at every apparition, in 1978 (1978 II, 1977i), 1983 (1983 XI, 1982j), 1989 (1989 I, 1987e1), 1994 (1994 XIUX, 1993c), 2000 and 2005. Its current orbital period is 5.515 years.
Tempel 1 is not a bright comet; its maximum magnitude so far has been 11, far below naked eye visibility. Its size is believed to be 14 by 4 kilometers (8.7 by 2.5 miles), based on measurements taken by the Hubble Space Telescope in visible light and the Spitzer Space Telescope in infrared light. Combining these observations also revealed a low albedo of only 4%. A two-day rotation rate was also determined.
Deep Impact space mission
On 4 July 2005 at 05:52 UTC (01:52 EDT), Tempel 1 was deliberately targeted by one component of the NASA Deep Impact probe, one day before perihelion. The impact was photographed by the other component of the probe, recording a bright spray from the impact site. It was also observed by earthbound and space telescopes, which observed a brightening of several magnitudes after the impact.
The crater that formed was up to 200 meters in diameter and 30-50 meters deep. The probe's spectrometer instrument detected dust particles finer than human hair, and discovered the presence of silicates, carbonates, smectite, metal sulfides (like fool's gold), amorphous carbon and polycyclic aromatic hydrocarbons.
Tempel 1 will be visited again in 2011 by the Stardust spacecraft as part of its extended mission. This will be the first time that a comet will have been visited twice and is an opportunity to better observe the crater that was created by Deep Impact.
Orbit
Comets are on unstable orbits that evolve over time due to perturbations and outgassing. Tempel 1 will pass within 0.04 AU (5.9 million kilometres) of the dwarf planet Ceres on November 11, 2011.[5] Then, as a Jupiter Family Comet, it will spend years interacting with the giant planet Jupiter, finally passing within 0.02 AU (3 million kilometres) of Mars on October 17, 2183.[5]
See also
[edit] References
- ^ a b "Comet 9P/Tempel 1". The Planetary Society. http://www.planetary.org/explore/topics/asteroids_and_comets/tempel1.html. Retrieved on 2008-12-16.
- ^ a b "JPL Small-Body Database Browser: 9P/Tempel 1". 2008-10-25 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=9P. Retrieved on 2008-12-16.
- ^ D. T. Britt; G. J. Consol-magno SJ; W. J. Merline (2006). "Small Body Density and Porosity: New Data, New Insights". Lunar and Planetary Science XXXVII. http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2214.pdf. Retrieved on 2008-12-16.
- ^ Using a spherical radius of 6.25 km; volume of a sphere * a rubble pile density of 0.62 g/cm³ yields a mass (m=d*v) of 7.9E+13 kg
- ^ a b "JPL Close-Approach Data: 9P/Tempel 1". 2008-10-25 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=9P;orb=0;cov=0;log=0;cad=1#cad. Retrieved on 2009-05-06.
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