Comet Churyumov–Gerasimenko as seen by Rosetta
|Discovered by||Klim Ivanovych Churyumov
Svetlana Ivanovna Gerasimenko
|Discovery site||Alma-Ata, Kazakh SSR, Soviet Union
Kiev, Ukrainian SSR, Soviet Union
|Discovery date||20 September 1969|
|1969 R1, 1969 IV, 1969h, 1975 P1, 1976 VII, 1975i, 1982 VIII, 1982f, 1989 VI, 1988i|
|Epoch 10 August 2014 (JD 2456879.5)|
|Aphelion||5.6829 AU (850,150,000 km)|
|Perihelion||1.2432 AU (185,980,000 km)|
|3.4630 AU (518,060,000 km)|
4.1×3.2×1.3 km (2.5×2.0×0.8 mi)
2.5×2.5×2.0 km (1.6×1.6×1.2 mi)
|Estimated 1 m/s (3 ft/s)|
North pole right ascension
North pole declination
67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C-G, and written in Cyrillic as Чурюмова-Герасименко) is a comet, originally from the Kuiper belt, with a current orbital period of 6.45 years, a rotation period of approximately 12.4 hours and a maximum velocity of 135,000 km/h (38 km/s; 84,000 mph). Churyumov–Gerasimenko is approximately 4.1 kilometres (2.5 mi) by 4.3 kilometres (2.7 mi) at its widest and longest dimensions. It will next come to perihelion (closest approach to the Sun) on 13 August 2015. Like most comets, it is named after its discoverers, Soviet astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko. They first observed it on photographic plates in 1969.
Churyumov–Gerasimenko is the destination of the European Space Agency's Rosetta mission, launched on 2 March 2004. Rosetta rendezvoused with Churyumov–Gerasimenko on 6 August 2014 and entered orbit on 10 September 2014. Rosetta 's lander, Philae, touched down on its surface on 12 November 2014, becoming the first spacecraft to land on a comet nucleus.
Churyumov–Gerasimenko was discovered in 1969 by Klim Ivanovych Churyumov of the Kiev University's Astronomical Observatory, who examined a photograph that had been exposed for Comet Comas Solà by Svetlana Ivanovna Gerasimenko on 11 September 1969 at the Alma-Ata Astrophysical Institute, near Alma-Ata (now Almaty), the then-capital city of Kazakh Soviet Socialist Republic, Soviet Union. Churyumov found a cometary object near the edge of the plate, but assumed that this was Comet Comas Solà.
After returning to his home institute in Kiev, Churyumov examined all the photographic plates more closely. On 22 October, about a month after the photograph was taken, he discovered that the object could not be Comas Solà, because it was about 1.8 degrees off the expected position. Further scrutiny produced a faint image of Comas Solà at its expected position on the plate, thus proving that the other object was a different comet.
Comets are regularly nudged from one orbit to another when they encounter Jupiter in close proximity and undergo a perturbation. Before 1959, Churyumov–Gerasimenko's perihelion distance was about 2.7 AU (400,000,000 km). In February 1959, a close encounter with Jupiter moved its perihelion inward to about 1.3 AU (190,000,000 km), where it remains today.
After Churyumov–Gerasimenko's 2009 perihelion, observers found that its rotational period had decreased from 12.76 hours to 12.4 hours. It is believed this change resulted due to sublimation-induced torque.
As of September 2014[update], Churyumov–Gerasimenko's nucleus had an apparent magnitude of roughly 20. It next comes to perihelion on 13 August 2015. From December 2014 until September 2015, it will have an elongation less than 45 degrees from the Sun. On 10 February 2015, it will come to solar conjunction when it will appear 5 degrees from the Sun and be 3.3 AU (490,000,000 km) from Earth. It crosses the celestial equator on 5 May 2015 and will start to become best seen from the Northern Hemisphere. Even right after perihelion when it is in the constellation of Gemini, it might only brighten to apparent magnitude 11, and will require a telescope to be seen.
As preparation for the Rosetta mission, Hubble Space Telescope pictures taken on 12 March 2003 were closely analysed. An overall 3D model was constructed and computer-generated images were created.
On 25 April 2012, the most detailed observations until that time were taken with the 2-metre Faulkes Telescope by N. Howes, G. Sostero and E. Guido while it was at its aphelion.
On 6 June 2014, water vapor was detected being released at a rate of roughly 1 L/s (0.26 USgal/s) when Rosetta was 360,000 km (220,000 mi) from Churyumov–Gerasimenko and 3.9 AU (580,000,000 km) from the Sun. On 14 July 2014, images taken by Rosetta showed that its nucleus is irregular in shape with two distinct lobes. One explanation is that it is a contact binary formed by low-speed accretion between two comets, but it may instead have resulted from asymmetric erosion due to ice sublimating from its surface to leave behind its lobed shape. The size of the nucleus is estimated to be 3.5×4 km (2.2×2.5 mi).
Rendezvous and orbit
Beginning in May 2014, Rosetta 's velocity was reduced by 780 m/s (2,800 km/h; 1,700 mph) with a series of thruster firings. Ground controllers rendezvoused Rosetta with Churyumov–Gerasimenko on 6 August 2014. This was done by reducing Rosetta 's relative velocity to 1 m/s (4 km/h; 2 mph). Rosetta entered orbit on 10 September, at about 30 km (19 mi) from the nucleus.
Descent of a small lander occurred on 12 November 2014. Philae is a 100 kg (220 lb) robotic probe that set down on the surface with landing gear. The landing site has been christened Agilkia in honour of Agilkia Island, where the temples of Philae Island were relocated after the construction of the Aswan Dam flooded the island. The acceleration due to gravity on the surface of Churyumov–Gerasimenko has been estimated for simulation purposes at 10−3 m/s2, or about one ten-thousandth of that on Earth.
Due to its low relative mass, landing on the comet involved certain technical considerations to keep Philae anchored. The probe contains an array of mechanisms designed to manage Churyumov–Gerasimenko's low gravity, including a cold gas thruster, harpoons, landing-leg-mounted ice screws, and a flywheel to keep it oriented during its descent. In the event, the thruster and the harpoons failed to operate, and the ice screws did not gain a grip. The lander bounced twice and only came to rest when it made contact with the surface for the third time, two hours after first contact.
On 10 December 2014, scientists reported that the composition of water vapor from Churyumov–Gerasimenko, as determined by the Rosetta spacecraft, is substantially different from that found on Earth. The ratio of deuterium to hydrogen in the water from the comet was determined to be three times that found for terrestrial water. This makes it unlikely that water found on Earth came from comets such as Churyumov–Gerasimenko.
Measurements carried out before Philae 's batteries failed indicate that the dust layer could be as much as 20 cm (7.9 in) thick. Beneath that is hard ice, or a mixture of ice and dust. Porosity appears to increase toward the center of the comet.
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Comet 67P has a very weak gravity, so anchoring harpoons were designed to shoot into the comet to fix the spacecraft to the surface.
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As there was a real risk of the lander bouncing off the comet, harpoons, landing leg ice screws and thrusters needed to work in concert to ensure Philae stayed in place.
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|Wikimedia Commons has media related to 67P/Churyumov-Gerasimenko.|
- 67P/Churyumov–Gerasimenko at Cometography.com
- 67P/Churyumov–Gerasimenko at the Wayback Machine (archived 11 November 2007) by the Instituto de Astrofísica de Canarias
- 67P/Churyumov–Gerasimenko pronunciation guide by the European Space Agency
- "Rosetta's Target: Comet 67P/Churyumov–Gerasimenko" by the European Space Agency
- "Mission to Land on a Comet" by NASA
- Churyumov–Gerasimenko image gallery by the European Space Agency
- ESA's Rosetta image gallery at Flickr.com
- Churyumov–Gerasimenko size comparison by the European Space Agency
- Rosetta: landing on a comet by the European Space Agency
|Periodic comets (by number)|