 Composite of images of nucleus obtained by theDeep Impact impactor | |
| Discovery | |
|---|---|
| Discovered by | Wilhelm Tempel |
| Discovery date | 3 April 1867 |
| Designations | |
| |
| |
| Orbital characteristics[1][2][3][4] | |
| Epoch | 25 February 2023 (JD 2460000.5) |
| Aphelion | 4.757 AU |
| Perihelion | 1.545 AU (1.77 AU after 2024 Jupiter approach) |
| Semi-major axis | 3.151 AU |
| Eccentricity | 0.5097 |
| Orbital period | 5.59 years |
| Inclination | 10.474° |
| 68.64° | |
| Argument of periapsis | 179.54° |
| Last perihelion | 4 March 2022 2 August 2016 |
| Next perihelion | 12 February 2028[1] |
| EarthMOID | 0.52 AU |
| Physical characteristics[5][3][6] | |
| Dimensions | 7.6 km × 4.9 km (4.7 mi × 3.0 mi) |
| Mass | 7.2×1013 to 7.9×1013 kg[a] |
Meandensity | 0.62 g/cm3 |
| 40.7 hours | |
Tempel 1 (official designation:9P/Tempel) is aperiodicJupiter-family comet discovered byWilhelm Tempel in 1867. It completes an orbit of theSun every 5.6 years. Tempel 1 was the target of theDeep Impact space mission, which photographed a deliberate high-speed impact upon the comet in 2005. It was re-visited by theStardust spacecraft on 14 February 2011, and came back to perihelion in August 2016. On 26 May 2024, it made a modest approach to Jupiter at a distance of 0.55 AU (82 million km),[2][3] which lifted theperihelion distance. 9P will next come to perihelion on 12 February 2028 when it will be 1.77 AU (265 million km) from the Sun.[1]
Tempel 1 was discovered on April 3, 1867, byWilhelm Tempel, who was working atMarseille. At the time of discovery, it approachedperihelion once every 5.68 years (designations P/1867 G1 and 1867 II).[7][8] It was subsequently observed in 1873 (P/1873 G1, 1873 I, 1873a) and in 1879 (1879 III, 1879b).[9]
Photographic attempts during 1898 and 1905 failed to recover the comet, and astronomers surmised that it haddisintegrated, when in reality, its orbit had changed. Tempel 1's orbit occasionally brings it sufficiently close toJupiter to be altered, with a consequent change in the comet's orbital period.[2] 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 km (31 million mi), to 2.1 AU, rendering the comet far less visible fromEarth.[2] Perihelion did not drop below 2 AU until 1944 after a 1941 approach to Jupiter.[10]
Tempel 1 was rediscovered in 1967 (as P/1967 L1, 1966 VII) after British astronomerBrian G. Marsden performed precise calculations of the comet's orbit that took into account Jupiter'sperturbations. 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).[2] These approaches moved Tempel 1 into its presentlibration around the 1:2 resonance with Jupiter. Despite an unfavorable 1967 return,Elizabeth Roemer of the Catalina Observatory took several photographs.[2] Initial inspection revealed nothing, but in late 1968 she found a 8 June 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. At least two images are required for orbit computation, so the next return had to be awaited.[2]
Roemer and L. M. Vaughn recovered the comet on 11 January 1972, fromSteward Observatory (P/1972 A1, 1972 V, 1972a).[2] 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.[2]
Tempel 1 is not a bright comet; its brightestapparent magnitude since discovery has been 11, far below naked-eye visibility. Its nucleus measures 7.6 km × 4.9 km (4.7 mi × 3.0 mi).[3][6] Measurements taken by theHubble Space Telescope in visible light[12] and theSpitzer Space Telescope in infrared light[13] suggest a lowalbedo of only 4%. A two-day rotation rate was also determined.[14] The comet was also seen to emit x-rays due to highly charged solar wind ions removing electrons via charge exchange from gases outflowing from Tempel 1's nucleus.[11]
On 4 July 2005 at 05:52UTC (01:52 EDT), Tempel 1 was deliberately struck by one component of theNASADeep Impact probe, one day before perihelion. The impact was photographed by the other component of the probe, which recorded a bright spray from the impact site. The impact was also observed by earthbound and space telescopes, which recorded a brightening of several magnitudes.
Thecrater that formed was not visible toDeep Impact due to the cloud of dust raised by the impact, but was estimated to be between 100–250 m (330–820 ft) in diameter and 30 m (98 ft) deep.[15] Spitzer Space Telescope observations of the ejecta detected dust particles finer than human hair and discovered the presence ofsilicates,carbonates,smectite,metal sulfides (such asfool's gold),amorphous carbon andpolycyclic aromatic hydrocarbons.[16] Spitzer also detected waterice in theejecta, consistent with surface water ice detected by Deep Impact's spectrometer instrument.[17] The water ice came from 1 meter below the surface crust (the devolatized layer around the nucleus).[17]
In part, because the crater formed during theDeep Impact collision could not be imaged during the initial flyby,[15] on 3 July 2007, NASA approved the New Exploration of Tempel 1 (or NExT) mission. The low-cost mission utilized the already existingStardust spacecraft, which had studiedComet Wild 2 in 2004.Stardust was placed into a new orbit so that it approached Tempel 1. It passed at a distance of approximately 181 km (112 mi) on February 15, 2011, 04:42 UTC.[18] This was the first time that a comet was visited twice.[b]
On February 15, NASA scientists identified the crater formed byDeep Impact in images fromStardust. The crater is estimated to be 150 m (490 ft) in diameter and has a bright mound in the center likely created when material from the impact fell back into the crater.[19]Energy of impactorArchived 2016-06-23 at theWayback Machine According to NASA "The impactor delivers 19 Gigajoules (that's 4.8 tons of TNT) of kinetic energy to excavate the crater. This kinetic energy is generated by the combination of the mass of the impactor (370 kg; 816 lbs) and its velocity when it impacts (~10.2 km/s)". According to NASA, "The energy from the impact will excavate a crater approximately 100m wide and 28m deep".[20]
The geometry of the flyby allowed investigators to obtain considerably more three-dimensional information about the nucleus from stereo pairs of images than duringDeep Impact's encounter.[21] Scientists were able to quickly spot locations where an elevated flow-like formation oficy material on the comet's surface receded due tosublimation between encounters.[21]
Comets are in unstable orbits that evolve due toperturbations andoutgassing. Tempel 1 passed within 0.04 AU – or 5.9 million km (3.7 million mi) – of thedwarf planetCeres on 11 November 2011.[3] Then, as a Jupiter-family comet, it will spend years interacting with thegiant planet Jupiter, and by October 2084 perihelion will be lifted as high as 1.98 AU (296 million km).[22] Then perihelion will start dropping again and it will pass 0.0191 AU (2.86 million km; 1.78 million mi) fromMars on October 17, 2183.[3]
| Date & time of closest approach | Mars distance (AU) | Sun distance (AU) | Velocity wrt Mars (km/s) | Velocity wrt Sun (km/s) | Uncertainty region (3-sigma) | Reference |
|---|---|---|---|---|---|---|
| 2183-Oct-17 16:25 ± 2 hours | 0.0191 AU (2.86 million km; 1.78 million mi) | 1.506 AU (225.3 million km; 140.0 million mi) | 6.58 | 29.92 | ± 6620 km | Horizons |
| Numbered comets | ||
|---|---|---|
| Previous 8P/Tuttle | Tempel 1 | Next 10P/Tempel |
| International | |
|---|---|
| National | |
| Other | |
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