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Tiger stripes (Enceladus)

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For other uses, seeTiger stripes.
Cassiniview of Enceladus's south pole. The tiger stripes, from lower left to upper right, are the Damascus, Baghdad, Cairo, Alexandria and Camphor sulci.

Thetiger stripesofEnceladusconsist of four sub-parallel, linear depressions in the south polar region of theSaturnianmoon.[1][2]First observed on May 20, 2005, by theCassinispacecraft'sImaging Science Sub-system (ISS) camera (though seen obliquely during an early flyby), the features are most notable in lower resolution images by their brightness contrast from the surrounding terrain.[3]Higher resolution observations were obtained by Cassini's various instruments during a close flyby of Enceladus on July 14, 2005. These observations revealed the tiger stripes to be low ridges with a central fracture.[2]Observations from the Composite Infrared Spectrometer (CIRS) instrument showed the tiger stripes to have elevated surface temperatures, indicative of present-daycryovolcanismon Enceladus centered on the tiger stripes.[4]

Names[edit]

The name tiger stripes is an unofficial term given to these four features based on their distinctive albedo. Enceladeansulci(subparallel furrows and ridges), likeSamarkand SulciandHarran Sulci,have been named after cities or countries referred to inThe Arabian Nights.Accordingly, in November 2006, the tiger stripes were assigned the official names Alexandria Sulcus, Cairo Sulcus, Baghdad Sulcus and Damascus Sulcus (Camphor Sulcus is a smaller feature that branches off Alexandria Sulcus).[5]Baghdad and Damascus sulci are the most active, while Alexandria Sulcus is the least active.

Appearance and geology[edit]

Composite map of the southern hemisphere of Enceladus (2007)

Images from the ISS camera onboardCassinirevealed the 4 tiger stripes to be a series of sub-parallel, linear depressions flanked on each side by low ridges.[2]On average, each tiger stripe depression is 130kilometerslong, 2 kilometers wide, and 500metersdeep. The flanking ridges are, on average, 100 meters tall and 2–4 kilometers wide. Given their appearance and their geologic setting within a heavily tectonically deformed region, the tiger stripes are likely to be tectonic fractures.[2]However, their correlation with internal heat and a large, water vapor plume suggests that tiger stripes might be the result of fissures in Enceladus'lithosphere.The stripes are spaced approximately 35 kilometers apart. The ends of each tiger stripe differ in appearance between the anti-Saturnian and sub-Saturnian hemisphere. On the anti-Saturnian hemisphere, the stripes terminate in hook-shaped bends, while the sub-Saturnian tips bifurcate dendritically.[2]

Virtually noimpact cratershave been found on or near the tiger stripes, suggesting a very young surface age. Surface age estimates based on crater counting yielded an age of 4–100 million years assuming a lunar-like cratering flux and 0.5-1 million years assuming a constant cratering flux.[2]

Composition[edit]

Another aspect that distinguishes the tiger stripes from the rest of the surface of Enceladus are their unusual composition. Nearly the entire surface of Enceladus is covered in a blanket of fine-grained water ice. The ridges that surround the tiger stripes are often covered in coarse-grained, crystalline water ice.[2][6]This material appears dark in the Cassini camera's IR3 filter (central wavelength 930nanometers), giving the tiger stripes a dark appearance in clear-filter images and a blue-green appearance in false-color, near-ultraviolet, green, near-infrared images. The Visual and Infrared Mapping Spectrometer (VIMS) instrument also detected trappedcarbon dioxideice and simple organics within the tiger stripes.[6]Simple organic material has not been detected anywhere else on the surface of Enceladus.

The detection of crystalline water ice along the tiger stripes also provides an age constraint. Crystalline water ice gradually loses its crystal structure after being cooled and subjected to the Saturnian magnetospheric environment. Such a transformation into finer-grained, amorphous water ice is thought to take a few decades to a thousand years.[7]

Cryovolcanism[edit]

See also:Cryovolcano
Enceladus - South Pole - Geyser basin (August 10, 2014).[8]
Enceladus - South Pole - Geysers spray water from many locations along the "tiger stripes".

Observations byCassiniduring the July 14, 2005 flyby revealed a cryovolcanically active region on Enceladus centered on the tiger stripe region. The CIRS instrument revealed the entire tiger stripe region (south of 70° South latitude) to be warmer than expected if the region were heated solely from sunlight.[4]Higher resolution observations revealed that the hottest material near Enceladus' south pole is located within the tiger stripe fractures. Color temperatures between 113 and 157kelvinshave been obtained from the CIRS data, significantly warmer than the expected 68 kelvins for this region of Enceladus.

Data from the ISS, Ion and Neutral Mass Spectrometer (INMS), Cosmic Dust Analyser (CDA) and CIRS instruments show that a plume of water vapor and ice,methane,carbon dioxide,andnitrogenemanates from a series of jets located within the tiger stripes.[9][10]The amount of material within the plume suggests that the plume is generated from a near-surface body of liquid water.[2]Over 100 geysers have been identified on Enceladus.[8]

Alternatively, Kiefferet al.(2006) suggest that Enceladus'geysersoriginate fromclathratehydrates, where carbon dioxide, methane, and nitrogen are released when exposed to the vacuum of space by the fractures.[11]

Enceladus - Cryovolcanism
  • One possible scheme for Enceladus's cryovolcanism
    One possible scheme for Enceladus's cryovolcanism
  • Possible origins of methane found in plumes through its subsurface ocean
    Possible origins of methane found in plumes through its subsurface ocean
  • Chemical composition of the plumes of Enceladus
    Chemical composition of the plumes of Enceladus

Relation to E-Ring of Saturn[edit]

Plumes from the moon Enceladus, which seems similar in chemical makeup to comets,[12]have been shown to be the source of the material in the E Ring.[13]TheE Ringis the widest and outermost ring of Saturn (except for the tenuousPhoebe ring). It is an extremely wide but diffuse disk of microscopic icy or dusty material. The E ring is distributed between the orbits ofMimasandTitan.[14]

Numerous mathematical models show that this ring is unstable, with a lifespan between 10,000 and 1,000,000 years, therefore, particles composing it must be constantly replenished.[15]Enceladus is orbiting inside this ring, in a place where it is narrowest but present in its highest density, raising suspicion since the 1980s that Enceladus is the main source of particles for the E ring.[16][17][18][19]This hypothesis was confirmed byCassini'sfirst two close flybys in 2005.[20][21]

View of Enceladus's orbit from the side, showing Enceladus in relation to Saturn's E ring
  • Enceladus orbiting within Saturn's E ring
    Enceladus orbiting within Saturn's E ring
  • Enceladus geyser tendrils - comparison of images ("a";"c") with computer simulations
    Enceladus geyser tendrils - comparison of images ( "a"; "c" ) with computer simulations
  • Enceladus south polar region - locations of most active tendril-producing geysers
    Enceladus south polar region - locations of most active tendril-producing geysers
Eruptions on Enceladus may seem to be "discrete" jets, but may be "curtain" eruptions instead
(video animation)

References[edit]

  1. ^Drake, Nadia(9 December 2019)."How an Icy Moon of Saturn Got Its Stripes - Scientists have developed an explanation for one of the most striking features of Enceladus, an ocean world that has the right ingredients for life".The New York Times.Retrieved11 December2019.
  2. ^abcdefgh Porco, C. C.;Helfenstein, P.; Thomas, P. C.; Ingersoll, A. P.; Wisdom, J.; West, R.; Neukum, G.; Denk, T.; Wagner, R. (10 March 2006). "Cassini Observes the Active South Pole of Enceladus".Science.311(5766): 1393–1401.Bibcode:2006Sci...311.1393P.doi:10.1126/science.1123013.PMID16527964.S2CID6976648.
  3. ^J. Perry (23 May 2005)."New Enceladus Raw Images".Retrieved22 March2006.
  4. ^abSpencer, J. R.; Pearl, J. C.; Segura, M.; Flasar, F. M.; Mamoutkine, A.; Romani, P.; Buratti, B. J.; Hendrix, A. R.; Spilker, L. J.; Lopes, R. M. C. (2006)."Cassini Encounters Enceladus: Background and the Discovery of a South Polar Hot Spot".Science.311(5766): 1401–1405.Bibcode:2006Sci...311.1401S.doi:10.1126/science.1121661.PMID16527965.S2CID44788825.
  5. ^"New Names Approved for Use on Enceladus".SaturnToday.Com.SpaceRef Interactive Inc. 2006-11-17.Retrieved2008-09-20.{{cite web}}:External link in|work=(help)
  6. ^abR. H. Brownet al.,Science3111425 (2006).
  7. ^Cassini Finds Enceladus Tiger Stripes are Really CubsArchived2008-10-18 at theWayback Machine.Retrieved March 22, 2006.
  8. ^abDyches, Preston; Brown, Dwayne; et al. (July 28, 2014)."Cassini Spacecraft Reveals 101 Geysers and More on Icy Saturn Moon".NASA.RetrievedJuly 29,2014.
  9. ^NASA's Cassini Images Reveal Spectacular Evidence of an Active MoonArchived2011-10-29 at theWayback Machine.6 December 2005. Retrieved March 22, 2006.
  10. ^"Jet Spots in Tiger Stripes".CICLOPS web site.NASA/JPL/GSFC/SwRI/SSI. 2008-03-26. Archived fromthe originalon 2011-07-25.Retrieved2009-08-30.{{cite web}}:External link in|work=(help)
  11. ^Kieffer, Susan W.; Xinli Lu; et al. (2006). "A Clathrate Reservoir Hypothesis for Enceladus' South Polar Plume".Science.314(5806): 1764–1766.Bibcode:2006Sci...314.1764K.doi:10.1126/science.1133519.PMID17170301.S2CID41743663.
  12. ^Battersby, Stephen (26 March 2008)."Saturn's moon Enceladus surprisingly comet-like".New Scientist.Retrieved16 April2015.
  13. ^"Icy Tendrils Reaching into Saturn Ring Traced to Their Source".NASA News.14 April 2015. Archived fromthe originalon 2015-04-16.Retrieved2015-04-15.
  14. ^Hedman, M. M.; Burns, J. A.; et al. (2012). "The three-dimensional structure of Saturn's E ring".Icarus.217(1): 322–338.arXiv:1111.2568.Bibcode:2012Icar..217..322H.doi:10.1016/j.icarus.2011.11.006.S2CID1432112.
  15. ^Vittorio, Salvatore A. (July 2006)."Cassini visits Enceladus: New light on a bright world".Cambridge Scientific Abstracts (CSA).CSA. Archived fromthe originalon 2014-04-28.Retrieved2014-04-27.
  16. ^Baum, W. A.; Kreidl, T. (July 1981). "Saturn's E ring: I. CCD observations of March 1980".Icarus.47(1): 84–96.Bibcode:1981Icar...47...84B.doi:10.1016/0019-1035(81)90093-2.
  17. ^Haff, P. K.; Eviatar, A.; et al. (1983). Haff, P. K.; Eviatar, A.; Siscoe, G. L. (eds.). "Ring and plasma: Enigmae of Enceladus".Icarus.56(3): 426–438.Bibcode:1983Icar...56..426H.doi:10.1016/0019-1035(83)90164-1.
  18. ^Pang, Kevin D.; Voge, Charles C.; et al. (1984). "The E ring of Saturn and satellite Enceladus".Journal of Geophysical Research.89:9459–9470.Bibcode:1984JGR....89.9459P.doi:10.1029/JB089iB11p09459.
  19. ^Blondel, Philippe; Mason, John (August 23, 2006).Solar System Update.Springer Science. pp. 241–243.
  20. ^Spahn, F.; Schmidt, J; et al. (2006). "Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring".Science.311(5766): 1416–1418.Bibcode:2006Sci...311.1416S.CiteSeerX10.1.1.466.6748.doi:10.1126/science.1121375.PMID16527969.S2CID33554377.
  21. ^Cain, Fraser (5 February 2008)."Enceladus is Supplying Ice to Saturn's A-Ring".NASA.Universe Today.Retrieved2014-04-26.

External links[edit]

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