67P/Churyumov–Gerasimenko

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67P/Churyumov–Gerasimenko
Comet 67P on 19 September 2014 NavCam mosaic.jpg
Comet Churyumov–Gerasimenko as seen by Rosetta
Discovery
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
Designations
1969 R1, 1969 IV, 1969h, 1975 P1, 1976 VII, 1975i, 1982 VIII, 1982f, 1989 VI, 1988i[1]
Orbital characteristics[1]
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)
Eccentricity 0.64102
6.44 yr
303.71°
Inclination 7.0405°
50.147°
12.780°
Physical characteristics
Dimensions Large lobe:
4.1×3.2×1.3 km (2.5×2.0×0.8 mi)
Small lobe:
2.5×2.5×2.0 km (1.6×1.6×1.2 mi)[2]
Mass (1.0±0.1)×1013 kg[3]
Mean density
 0.4 g/cm³[2]
Estimated 1 m/s (3 ft/s)[4]
12.4043±0.0007 h[5]
North pole right ascension
 69.00°[2]
North pole declination
 64.00°[2]
Surface temp. min mean max
Kelvin 205 230
Celsius −68 −43
Fahrenheit −90 −45

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,[6] with a current orbital period of 6.45 years,[1] a rotation period of approximately 12.4 hours[5] and a maximum velocity of 135,000 km/h (38 km/s; 84,000 mph).[7] Churyumov–Gerasimenko is approximately 4.1 kilometres (2.5 mi) by 4.3 kilometres (2.7 mi) at its widest and longest dimensions.[8] It will next come to perihelion (closest approach to the Sun) on 13 August 2015.[9][10][11] 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.[12][13][14] Rosetta rendezvoused with Churyumov–Gerasimenko on 6 August 2014[15][16] and entered orbit on 10 September 2014.[17] Rosetta '​s lander, Philae, touched down on its surface on 12 November 2014, becoming the first spacecraft to land on a comet nucleus.[18][19][20]

Discovery[edit]

Churyumov–Gerasimenko was discovered in 1969 by Klim Ivanovych Churyumov of the Kiev University's Astronomical Observatory,[21] 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.[22]

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.[22]

Orbital history[edit]

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[23] moved its perihelion inward to about 1.3 AU (190,000,000 km), where it remains today.[11]

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.[5]

2015 perihelion[edit]

As of September 2014, Churyumov–Gerasimenko's nucleus had an apparent magnitude of roughly 20.[10] It next comes to perihelion on 13 August 2015.[9] From December 2014 until September 2015, it will have an elongation less than 45 degrees from the Sun.[24] 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.[24] It crosses the celestial equator on 5 May 2015 and will start to become best seen from the Northern Hemisphere.[24] Even right after perihelion when it is in the constellation of Gemini, it might only brighten to apparent magnitude 11,[9] and will require a telescope to be seen.

Rosetta mission[edit]

Main articles: Rosetta (spacecraft) and Philae (spacecraft)
See also: Timeline of Rosetta spacecraft

Churyumov–Gerasimenko is the destination of the Rosetta mission, launched in 2004, which rendezvoused with it in 2014 and was the first mission to land a space probe on a comet.

Advance work[edit]

This animation comprises 86 images acquired by the Navigation Camera on board ESA's Rosetta spacecraft as it approached Churyumov–Gerasimenko in August 2014.

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.[25]

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.[26][27] 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).[14][28][29]

Rendezvous and orbit[edit]

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.[14][30] Ground controllers rendezvoused Rosetta with Churyumov–Gerasimenko on 6 August 2014.[15][16] 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.[15][16][31]

Landing[edit]

For more details on the comet landing, see Philae mission.

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.[14][32] 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.[33] The acceleration due to gravity on the surface of Churyumov–Gerasimenko has been estimated for simulation purposes at 10−3 m/s2,[34] 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.[35][36][37] 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,[38] two hours after first contact.[39]

Science[edit]

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.[6][40][41]

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.[42]

Gallery[edit]

  • As seen by the Very Large Telescope on 11 August 2014[43]

  • As seen by Rosetta on 22 August 2014

  • As seen by Rosetta on 14 September 2014

  • As seen by Rosetta on 30 October 2014

References[edit]

  1. ^ a b c "JPL Small-Body Database Browser: 67P/Churyumov-Gerasimenko". NASA/Jet Propulsion Laboratory. 5 October 2013. Retrieved 21 January 2014. 
  2. ^ a b c d Baldwin, Emily (6 October 2014). "Measuring Comet 67P/C-G". European Space Agency. Retrieved 7 October 2014. 
  3. ^ Baldwin, Emily (21 August 2014). "Determining the mass of comet 67P/C-G". European Space Agency. Retrieved 21 August 2014. 
  4. ^ Dambeck, Thorsten (21 January 2014). "Expedition to primeval matter". Max-Planck-Gesellschaft. Retrieved 19 September 2014. 
  5. ^ a b c Mottola, S.; Lowry, S.; Snodgrass, C.; Lamy, P. L.; Toth, I. et al. (September 2014). "The rotation state of 67P/Churyumov-Gerasimenko from approach observations with the OSIRIS cameras on Rosetta". Astronomy and Astrophysics 569. L2. Bibcode:2014A&A...569L...2M. doi:10.1051/0004-6361/201424590. 
  6. ^ a b Borenstein, Seth (10 December 2014). "The mystery of where Earth's water came from deepens". Excite News. Associated Press. Retrieved 14 December 2014. 
  7. ^ "Rosetta's Frequently Asked Questions". European Space Agency. 2014. Retrieved 12 November 2014. 
  8. ^ "Bigger than you think! Comet 67P compared to cities. HD". YouTube. 12 November 2014. Retrieved 17 November 2014. 
  9. ^ a b c Yoshida, Seiichi (30 December 2010). "67P/Churyumov-Gerasimenko". Aerith.net. Retrieved 9 February 2012. 
  10. ^ a b "67P/Churyumov-Gerasimenko". Minor Planet Center. Retrieved 17 June 2014. 
  11. ^ a b Kinoshita, Kazuo (7 May 2009). "67P/Churyumov-Gerasimenko". Comet Orbit. Retrieved 25 April 2009. 
  12. ^ Krolikowska, Malgorzata (2003). "67P/Churyumov–Gerasimenko – potential target for the Rosetta mission". Acta Astronomica 53: 195–209. arXiv:astro-ph/0309130. Bibcode:2003AcA....53..195K. 
  13. ^ Agle, D. C.; Cook, Jia-Rui; Brown, Dwayne; Bauer, Markus (17 January 2014). "Rosetta: To Chase a Comet". NASA. Release 2014-015. Retrieved 18 January 2014. 
  14. ^ a b c d Chang, Kenneth (5 August 2014). "Rosetta Spacecraft Set for Unprecedented Close Study of a Comet". The New York Times. Retrieved 5 August 2014. 
  15. ^ a b c Fischer, D. (6 August 2014). "Rendezvous with a crazy world". The Planetary Society. Archived from the original on 6 August 2014. Retrieved 6 August 2014. 
  16. ^ a b c Bauer, Markus (6 August 2014). "Rosetta Arrives at Comet Destination". European Space Agency. Archived from the original on 6 August 2014. Retrieved 6 August 2014. 
  17. ^ Scuka, Daniel (10 September 2014). "Down, down we go to 29 km – or lower?". European Space Agency. Retrieved 20 September 2014. 
  18. ^ Agle, D. C.; Webster, Guy; Brown, Dwayne; Bauer, Markus (12 November 2014). "Rosetta's 'Philae' Makes Historic First Landing on a Comet". NASA. Retrieved 13 November 2014. 
  19. ^ Chang, Kenneth (12 November 2014). "European Space Agency's Spacecraft Lands on Comet's Surface". The New York Times. Retrieved 12 November 2014. 
  20. ^ "Probe makes historic comet landing". BBC News. 12 November 2014. Retrieved 12 November 2014. 
  21. ^ "Klim Ivanovich Churyumov". International Astronomical Union. Retrieved 8 August 2014. 
  22. ^ a b Kronk, Gary W.; Meyer, Maik (2010). "67P/1969 R1 (Churyumov-Gerasimenko)". Cometography: A Catalog of Comets; Volume 5: 1960-1982. Cambridge University Press. pp. 241–245. ISBN 978-0-521-87226-3. 
  23. ^ "JPL Close-Approach Data: 67P/Churyumov-Gerasimenko". NASA/Jet Propulsion Laboratory. 29 June 2010. Retrieved 9 February 2012. 
  24. ^ a b c "Elements and Ephemeris for 67P/Churyumov-Gerasimenko". Minor Planet Center. Retrieved 9 August 2014. 
  25. ^ Buckley, Michael; Villard, Ray; Christensen, Lars (5 September 2003). "Hubble Assists Rosetta Comet Mission". HubbleSite.org. 
  26. ^ Baldwin, Emily (23 June 2014). "First Detection of Water from 67P/C-G". European Space Agency. Retrieved 23 June 2014.  Sungrazer Comets at Twitter.com.
  27. ^ Agle, D. C.; Brown, Dwayne; Bauer, Markus (30 June 2014). "Rosetta's Comet Target 'Releases' Plentiful Water". NASA. Retrieved 30 June 2014. 
  28. ^ "The twofold comet: Comet 67P/Churyumov-Gerasimenko". Astronomy.com. 17 July 2014. Retrieved 18 July 2014. 
  29. ^ Temming, Maria (17 July 2014). "Rosetta's Comet has a Split Personality". Sky & Telescope. Retrieved 18 July 2014. 
  30. ^ Gannon, Megan (4 August 2014). "Comet-chasing Euro-probe could make history Wednesday". The Christian Science Monitor. Retrieved 6 August 2014. 
  31. ^ Lakdawalla, Emily (15 August 2014). "Finding my way around comet Churyumov-Gerasimenko". The Planetary Society. Archived from the original on 15 August 2014. Retrieved 15 August 2014. 
  32. ^ Chang, Kenneth (10 November 2014). "Philae Lander Nears a Cosmic Touchdown". The New York Times. Retrieved 11 November 2014. 
  33. ^ Amos, Jonathan (4 November 2014). "Rosetta comet mission: Landing site named 'Agilkia'". BBC News. Retrieved 9 November 2014. 
  34. ^ Hilchenbach, M. (2004). "Simulation of the Landing of Rosetta Philae on Comet 67P/Churyumov-Gerasimenko". SIMPACK User Meeting. 9–10 November 2004. Wartburg/Eisenach, Germany. p. 25. Retrieved 6 August 2014. 
  35. ^ Ellis, Ralph (13 November 2014). "Space probe scores a 310-million-mile bull's-eye with comet landing". CNN. Retrieved 13 November 2014. Comet 67P has a very weak gravity, so anchoring harpoons were designed to shoot into the comet to fix the spacecraft to the surface. 
  36. ^ Parnell, Brid-Aine (12 November 2014). "Bouncy bouncy: Comet probot Philae may have landed twice". The Register. Retrieved 13 November 2014. Philae's flywheel was part of its landing gear and stopped the craft from rotating while it was operational, but it was switched off once the probot indicated it had touched down. 
  37. ^ O'Neill, Ian (12 November 2014). "Rosetta's Lander Grabs Onto Comet and Lands". Discovery News. Retrieved 13 November 2014. 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. 
  38. ^ Agle, D. C.; Brown, Dwayne; Bauer, Markus (13 November 2014). "Rosetta's Comet Lander Landed Three Times". NASA. Retrieved 13 November 2014. 
  39. ^ Beatty, Kelly (12 November 2014). "Philae Lands on Its Comet – Three Times!". Sky & Telescope. Retrieved 26 November 2014. 
  40. ^ Agle, D. C.; Bauer, Markus (10 December 2014). "Rosetta Instrument Reignites Debate on Earth's Oceans". NASA. Retrieved 10 December 2014. 
  41. ^ Chang, Kenneth (10 December 2014). "Comet Data Clears Up Debate on Earth's Water". The New York Times. Retrieved 10 December 2014. 
  42. ^ Baldwin, Emily (18 November 2014). "Philae settles in dust-covered ice". European Space Agency. Retrieved 18 December 2014. 
  43. ^ "VLT Tracks Rosetta's Comet". European Southern Observatory. 8 September 2014. Retrieved 8 September 2014. 

Further reading[edit]

External links[edit]

Wikimedia Commons has media related to 67P/Churyumov-Gerasimenko.
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