67P/Churyumov–Gerasimenko

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67P/Churyumov–Gerasimenko
Comet 67P on 19 September 2014 NavCam mosaic.jpg
Greyscale photograph of Comet Churyumov–Gerasimenko taken by the Rosetta spacecraft
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:[2]
4.1×3.3×1.8 km (2.5×2.1×1.1 mi)
Small lobe:[2]
2.6×2.3×1.8 km (1.6×1.4×1.1 mi)
Volume 21.4 km3 (5.1 cu mi)[2]
Mass (1.0±0.1)×1013 kg[3]
Mean density
0.47 g/cm3 (0.017 lb/cu in)[2]
est. 1 m/s (3 ft/s)[4]
12.4043±0.0007 h[5]
52°[2]
North pole right ascension
69.3°[2]
North pole declination
64.1°[2]
Albedo 0.06[2]
Surface temp. min mean max
Kelvin 180 230
Celsius −93 −43
Fahrenheit −135 −45

67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C-G, and written in Cyrillic as комета 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 4.3 by 4.1 km (2.7 by 2.5 mi) at its longest and widest dimensions.[8] It was first observed on photographic plates in 1969 by Soviet astronomers Klim Ivanovych Churyumov and Svetlana Ivanovna Gerasimenko, after whom it is named. It came to perihelion (closest approach to the Sun) on 13 August 2015.[9][10][11][12]

Churyumov–Gerasimenko was the destination of the European Space Agency's Rosetta mission, launched on 2 March 2004.[13][14][15] Rosetta rendezvoused with Churyumov–Gerasimenko on 6 August 2014[16][17] and entered orbit on 10 September 2014.[18] Rosetta‍‍ '​‍s lander, Philae, touched down on its surface on 12 November 2014, becoming the first spacecraft to land on a comet nucleus.[19][20][21]

Discovery[edit]

Churyumov–Gerasimenko was discovered in 1969 by Klim Ivanovych Churyumov of the Kiev University's Astronomical Observatory,[22] 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.[23]

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.[23]

Shape[edit]

The two-lobe shape of the comet is the result of the collision of two objects. The "terraces", layers of the interior of the comet that have been exposed by the partial stripping of outer layers during its existence, are oriented in different directions in the two lobes, indicating that two objects collided to form Churyumov–Gerasimenko.[24][25]

Surface[edit]

There are 19 distinct regions on Churyumov–Gerasimenko. Each region is named after an Egyptian deity.[26]

Region Terrain Named after
Ma'at Dust covered Ma'at
Ash Dust covered Ash
Babi Dust covered Babi
Seth Pitted and brittle material Set
Hatmehit Large-scale depression Hatmehit
Nut Large-scale depression Nut
Aten Large-scale depression Aten
Hapi Smooth Hapi
Imhotep Smooth Imhotep
Anubis Smooth Anubis
Maftet Rock-like Maftet
Bastet Rock-like Bastet
Serqet Rock-like Serqet
Hathor Rock-like Hathor
Anuket Rock-like Anuket
Khepry Rock-like Khepry
Aker Rock-like Aker
Atum Rock-like Atum
Apis Rock-like Apis

Gates[edit]

Features known as "Gates", twin prominences on the surface so named for their appearance,[clarification needed] have received names by the Rosetta Science Working Team. They are named after deceased members of the Rosetta team.[27]

Name Named after
C. Alexander Gate Claudia Alexander
A. Coradini Gate Angioletta Coradini

Orbit and rotation[edit]

In February 1959, a close encounter with Jupiter[28] moved Churyumov–Gerasimenko's perihelion inward to about 1.3 AU (190,000,000 km), where it remains today.[12] Before that, its perihelion distance was approximately 2.7 AU (400,000,000 km).

Before Churyumov–Gerasimenko's perihelion passage in 2009, its rotational period was 12.76 hours. During this perihelion passage, it decreased to 12.4 hours, which likely happened due to sublimation-induced torque.[5]

2015 perihelion[edit]

As of September 2014, Churyumov–Gerasimenko's nucleus had an apparent magnitude of roughly 20.[11] It came to perihelion on 13 August 2015.[9][10] From December 2014 until September 2015, it has an elongation less than 45 degrees from the Sun.[29] On 10 February 2015, it went through solar conjunction when it was 5 degrees from the Sun and was 3.3 AU (490,000,000 km) from Earth.[29] It crossed the celestial equator on 5 May 2015 and became easiest to see from the Northern Hemisphere.[29] Even right after perihelion when it was in the constellation of Gemini, it only brightened to about apparent magnitude 12, and required a telescope to be seen.[10] As of August 2015, the comet has a total magnitude of about 12.[11]

Exploration[edit]

This animation consists of 86 images acquired by Rosetta‍‍ '​‍s NavCam as it approached 67P in August 2014.

Churyumov–Gerasimenko was 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]

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.[30]

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.[citation needed]

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.[31][32] 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).[15][33][34]

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.[15][35] Ground controllers rendezvoused Rosetta with Churyumov–Gerasimenko on 6 August 2014.[16][17] 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.[16][17][36]

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.[15][37] 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.[38] The acceleration due to gravity on the surface of Churyumov–Gerasimenko has been estimated for simulation purposes at 103 m/s2,[39] 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.[40][41][42] During 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,[43] two hours after first contact.[44]

Contact with Philae was lost on 15 November 2014 due to dropping battery power. The European Space Operations Centre reestablished communications on 14 June 2015 and reported a healthy spacecraft.[45][dated info]

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][46][47] On 22 January 2015, NASA reported that, between June and August 2014, the comet released increasing amounts of water vapor, up to tenfold as much.[48] On 23 January 2015, the journal Science published a special issue of scientific studies related to the comet.[49]

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.[50]

The nucleus of Churyumov–Gerasimenko was found to have no magnetic field of its own after measurements were taken during Philae‍‍ '​‍s descent and landing by its ROMAP instrument and Rosetta‍‍ '​‍s RPC-MAG instrument. This suggests that magnetism may not have played a role in the early formation of the Solar System, as had previously been hypothesized.[51][52]

On 2 June 2015, NASA reported that the ALICE spectrograph on Rosetta determined that electrons (within 1 km (0.62 mi) above the comet nucleus) produced from photoionization of water molecules by solar radiation, and not photons from the Sun as thought earlier, are responsible for the degradation of water and carbon dioxide molecules released from the comet nucleus into its coma.[53][54]

On 2 July 2015, scientists reported that active pits, related to sinkhole collapses and possibly associated with outbursts, have been found on the comet by Rosetta.[55][56]

On 5 July 2015, astrobiologists Chandra Wickramasinghe and Max Wallis claimed that some of the physical features detected on the comet's surface by Rosetta and Philae, such as its organic-rich crust, could be explained by the presence of extraterrestrial microorganisms.[57][58] Rosetta program scientists dismissed the claim as "pure speculation".[59] Carbon-rich compounds are common in the Solar System. Neither Rosetta nor Philae is equipped to search for direct evidence of viable organisms.[57]

On 30 July 2015, scientists reported that upon Philae‍‍ '​‍s first touchdown on the comet's surface, measurements by the COSAC and Ptolemy instruments revealed sixteen organic compounds, four of which were seen for the first time on a comet, including acetamide, acetone, methyl isocyanate and propionaldehyde.[60][61][62]

On 11 August 2015, scientists released images of a comet outburst that occurred on 29 July 2015.[63]

Gallery[edit]

See also[edit]

References[edit]

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  2. ^ a b c d e f g h "Comet vital statistics". European Space Agency. 22 January 2015. Retrieved 24 January 2015. 
  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 "Comet where spacecraft landed makes closest approach to sun". AP News. 13 August 2015. Retrieved 14 August 2015. 
  10. ^ a b c Yoshida, Seiichi (30 December 2010). "67P/Churyumov-Gerasimenko". Aerith.net. Retrieved 9 February 2012. 
  11. ^ a b c "67P/Churyumov-Gerasimenko". Minor Planet Center. Retrieved 17 June 2014. 
  12. ^ a b Kinoshita, Kazuo (7 May 2009). "67P/Churyumov-Gerasimenko". Comet Orbit. Retrieved 25 April 2009. 
  13. ^ 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. 
  14. ^ 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. 
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  16. ^ 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. 
  17. ^ 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. 
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  35. ^ Gannon, Megan (4 August 2014). "Comet-chasing Euro-probe could make history Wednesday". The Christian Science Monitor. Retrieved 6 August 2014. 
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  55. ^ Vincent, Jean-Baptiste; et al. (2 July 2015). "Large heterogeneities in comet 67P as revealed by active pits from sinkhole collapse". Nature 523: 63–66. Bibcode:2015Natur.523...63V. doi:10.1038/nature14564. 
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  62. ^ Bibring, J.-P.; Taylor, M.G.G.T.; Alexander, C.; Auster, U.; Biele, J.; Finzi, A. Ercoli; Goesmann, F.; Klingehoefer, G.; Kofman, W.; Mottola, S.; Seidenstiker, K.J.; Spohn, T.; Wright, I. (31 July 2015). "Philae's First Days on the Comet - Introduction to Special Issue". Science (journal) 349 (6247): 493. Bibcode:2015Sci...349..493B. doi:10.1126/science.aac5116. Retrieved 30 July 2015. 
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  64. ^ "VLT Tracks Rosetta's Comet". European Southern Observatory. 8 September 2014. Retrieved 8 September 2014. 

Further reading[edit]

External links[edit]

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