Tiger stripes (Enceladus)

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Cassini view of Enceladus's south pole. The tiger stripes, from lower left to upper right, are the Damascus, Baghdad, Cairo, Alexandria and Camphor sulci. Enceladus Tiger Stripes Up Close PIA06247.jpg
Cassini view of Enceladus's south pole. The tiger stripes, from lower left to upper right, are the Damascus, Baghdad, Cairo, Alexandria and Camphor sulci.

The tiger stripes of Enceladus consist of four sub-parallel, linear depressions in the south polar region of the Saturnian moon. [1] [2] First observed on May 20, 2005 by the Cassini spacecraft's Imaging 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-day cryovolcanism on Enceladus centered on the tiger stripes. [4]

Contents

Names

The name tiger stripes is an unofficial term given to these four features based on their distinctive albedo. Enceladean sulci (subparallel furrows and ridges), like Samarkand Sulci and Harran Sulci, have been named after cities or countries referred to in The 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

Composite map of the southern hemisphere of Enceladus (2007) Enceladus south pole SE15.png
Composite map of the southern hemisphere of Enceladus (2007)

Images from the ISS camera onboard Cassini revealed 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 130 kilometers long, 2 kilometers wide, and 500 meters deep. 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 no impact craters have 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

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 930 nanometers), 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 trapped carbon dioxide ice 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

Enceladus - South Pole - Geyser basin (August 10, 2014). PIA17183-Enceladus-SouthPole-Cassini-20100810.jpg
Enceladus - South Pole - Geyser basin (August 10, 2014).
Enceladus - South Pole - Geysers spray water from many locations along the "tiger stripes". Enceladus geysers June 2009.jpg
Enceladus - South Pole - Geysers spray water from many locations along the "tiger stripes".

Observations by Cassini during 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 113–157 kelvins have 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, and nitrogen emanates 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, Kieffer et al. (2006) suggest that Enceladus' geysers originate from clathrate hydrates, where carbon dioxide, methane, and nitrogen are released when exposed to the vacuum of space by the fractures. [11]

Relation to E-Ring of Saturn

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] The E Ring is the widest and outermost ring of Saturn (except for the tenuous Phoebe ring). It is an extremely wide but diffuse disk of microscopic icy or dusty material. The E ring is distributed between the orbits of Mimas and Titan. [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 by Cassini's first two close flybys in 2005. [20] [21]

Saturn's Rings PIA03550.jpg
Saturn's Rings PIA03550.jpg
View of Enceladus's orbit from the side, showing Enceladus in relation to Saturn's E ring
Eruptions on Enceladus may seem to be "discrete" jets, but may be "curtain" eruptions instead
(video animation) PIA19061-SaturnMoonEnceladus-CurtainNotDiscrete-Eruptions-20150506.jpg
Eruptions on Enceladus may seem to be "discrete" jets, but may be "curtain" eruptions instead
(video animation)

Related Research Articles

Saturn Sixth planet from the Sun in the Solar System

Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius about nine times that of Earth. It has only one-eighth the average density of Earth; however, with its larger volume, Saturn is over 95 times more massive. Saturn is named after the Roman god of wealth and agriculture; its astronomical symbol (♄) represents the god's sickle.

Rhea (moon) Moon of Saturn

Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. It is the second smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium, after dwarf planet Ceres. It was discovered in 1672 by Giovanni Domenico Cassini.

Helene (moon) moon of Saturn

Helene ( HEL-ə-nee; Greek: Ἑλένη) is a moon of Saturn. It was discovered by Pierre Laques and Jean Lecacheux in 1980 from ground-based observations at Pic du Midi Observatory, and was designated S/1980 S 6. In 1988 it was officially named after Helen of Troy, who was the granddaughter of Cronus (Saturn) in Greek mythology. Helene is also designated Saturn XII (12), which it was given in 1982, and Dione B, because it is co-orbital with Dione and located in its leading Lagrangian point (L4). It is one of four known trojan moons.

Tethys (moon) moon of Saturn

Tethys is a mid-sized moon of Saturn about 1,060 km (660 mi) across. It was discovered by G. D. Cassini in 1684 and is named after the titan Tethys of Greek mythology.

Iapetus (moon) moon of Saturn

Iapetus, or occasionally Japetus, is the third-largest natural satellite of Saturn, eleventh-largest in the Solar System, and the largest body in the Solar System known not to be in hydrostatic equilibrium. Discoveries by the Cassini mission in 2007 revealed several unusual features, such as a massive equatorial ridge running three-quarters of the way around the moon.

Epimetheus (moon) moon of Saturn

Epimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus.

Pandora (moon) moon of Saturn

Pandora is an inner satellite of Saturn. It was discovered in 1980 from photos taken by the Voyager 1 probe, and was provisionally designated S/1980 S 26. In late 1985 it was officially named after Pandora from Greek mythology. It is also designated as Saturn XVII.

Calypso (moon) moon of Saturn

Calypso is a moon of Saturn. It was discovered in 1980, from ground-based observations, by Dan Pascu, P. Kenneth Seidelmann, William A. Baum, and Douglas G. Currie, and was provisionally designated S/1980 S 25. Several other apparitions of it were recorded in the following months: S/1980 S 29, S/1980 S 30, S/1980 S 32, and S/1981 S 2. In 1983 it was officially named after Calypso of Greek mythology. It is also designated as Saturn XIV or Tethys C.

Dione (moon) moon of Saturn

Dione is a moon of Saturn. It was discovered by Italian astronomer Giovanni Domenico Cassini in 1684. It is named after the Titaness Dione of Greek mythology. It is also designated Saturn IV.

Enceladus natural satellite orbiting Saturn

Enceladus is the sixth-largest moon of Saturn. It is about 500 kilometers (310 mi) in diameter, about a tenth of that of Saturn's largest moon, Titan. Enceladus is mostly covered by fresh, clean ice, making it one of the most reflective bodies of the Solar System. Consequently, its surface temperature at noon only reaches −198 °C (−324 °F), far colder than a light-absorbing body would be. Despite its small size, Enceladus has a wide range of surface features, ranging from old, heavily cratered regions to young, tectonically deformed terrains.

Moons of Saturn The natural satellites of the planet Saturn

The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to enormous Titan, which is larger than the planet Mercury. Saturn has 82 moons with confirmed orbits that are not embedded in its rings – of which only 13 have diameters greater than 50 kilometers – as well as dense rings that contain millions of embedded moonlets and innumerable smaller ring particles. Seven Saturnian moons are large enough to have collapsed into a relaxed, ellipsoidal shape, though only one or two of those, Titan and possibly Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes, Enceladus, which emits jets of gas and dust from its south-polar region, and Iapetus, with its contrasting black and white hemispheres.

Methone (moon) moon of Saturn

Methone is a very small natural satellite of Saturn orbiting between the orbits of Mimas and Enceladus. It was discovered in 2004, and in 2012 was imaged more closely by the Cassini orbiter probe.

Rings of Saturn Planar assemblage of icy particles orbiting Saturn

The rings of Saturn are the most extensive ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit about Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. There is still no consensus as to their mechanism of formation. Although theoretical models indicated that the rings were likely to have formed early in the Solar System's history, new data from Cassini suggest they formed relatively late.

Cryovolcano A type of volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock

A cryovolcano is a type of volcano that erupts volatiles such as water, ammonia or methane, instead of molten rock. Collectively referred to as cryomagma, cryolava or ice-volcanic melt, these substances are usually liquids and can form plumes, but can also be in vapour form. After eruption, cryomagma is expected to condense to a solid form when exposed to the very low surrounding temperature. Cryovolcanoes may potentially form on icy moons and other objects with abundant water past the Solar System's snow line. A number of features have been identified as possible cryovolcanoes on Pluto, Titan and Ceres. In addition, although they are not known to form volcanoes, ice geysers have been observed on Enceladus and potentially Triton.

Magnetosphere of Saturn

The magnetosphere of Saturn is the cavity created in the flow of the solar wind by the planet's internally generated magnetic field. Discovered in 1979 by the Pioneer 11 spacecraft, Saturn's magnetosphere is the second largest of any planet in the Solar System after Jupiter. The magnetopause, the boundary between Saturn's magnetosphere and the solar wind, is located at a distance of about 20 Saturn radii from the planet's center, while its magnetotail stretches hundreds of Saturn radii behind it.

Labtayt Sulci sulci on Enceladus

Labtayt Sulci is a system of deep fractures on Saturn's moon Enceladus. Labtayt Sulci was first seen in low-resolution Voyager 1 images, but was observed in much more detail by the Cassini spacecraft during its February 2005 flyby of Enceladus. It is centered at 28.0° South Latitude, 284.0° West Longitude and is approximately 162 kilometers long, 4 kilometers wide, and 1 kilometer deep. The association between a cusp along the South Polar terrain boundary and Labtayt suggests that the fracture was forced open by thrust faulting where the fracture intersects with Cashmere Sulci.

Exploration of Saturn exploration in space

The exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The Cassini–Huygens spacecraft, launched in 1997, was in orbit from 2004 to 2017.

Aegaeon (moon) moon of Saturn

Aegaeon, also Saturn LIII, is a natural satellite of Saturn. It is thought to be similarly smooth as Methone. It orbits between Janus and Mimas within Saturn's G Ring.

Journey to Enceladus and Titan (JET) is an astrobiology mission concept to assess the habitability potential of Enceladus and Titan, moons of Saturn.

THEO is a feasibility study for a New Frontiers class orbiter mission to Enceladus that would directly sample its south pole water plumes in order to study its internal habitability and to search for biosignatures. Specifically, it would take advantage of the direct sampling opportunities of a subsurface ocean.

References

  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 . Retrieved 11 December 2019.
  2. 1 2 3 4 5 6 7 8 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. PMID   16527964.
  3. J. Perry (23 May 2005). "New Enceladus Raw Images" . Retrieved 22 March 2006.
  4. 1 2 Spencer, 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.
  5. "New Names Approved for Use on Enceladus". SaturnToday.Com . SpaceRef Interactive Inc. 2006-11-17. Retrieved 2008-09-20.External link in |work= (help)
  6. 1 2 R. H. Brown et al., Science311 1425 (2006).
  7. Cassini Finds Enceladus Tiger Stripes are Really Cubs Archived 2008-10-18 at the Wayback Machine . Retrieved March 22, 2006.
  8. 1 2 Dyches, Preston; Brown, Dwayne; et al. (July 28, 2014). "Cassini Spacecraft Reveals 101 Geysers and More on Icy Saturn Moon". NASA . Retrieved July 29, 2014.
  9. NASA's Cassini Images Reveal Spectacular Evidence of an Active Moon. 6 December 2005. Retrieved March 22, 2006.
  10. "Jet Spots in Tiger Stripes". CICLOPS web site . NASA/JPL/GSFC/SwRI/SSI. 2008-03-26. Retrieved 2009-08-30.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. PMID   17170301.
  12. Battersby, Stephen (26 March 2008). "Saturn's moon Enceladus surprisingly comet-like". New Scientist . Retrieved 16 April 2015.
  13. "Icy Tendrils Reaching into Saturn Ring Traced to Their Source". NASA News. 14 April 2015. Retrieved 2015-04-15.
  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.
  15. Vittorio, Salvatore A. (July 2006). "Cassini visits Enceladus: New light on a bright world". Cambridge Scientific Abstracts (CSA). CSA. Retrieved 2014-04-27.
  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. 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. CiteSeerX   10.1.1.466.6748 . doi:10.1126/science.1121375. PMID   16527969.
  21. Cain, Fraser (5 February 2008). "Enceladus is Supplying Ice to Saturn's A-Ring". NASA. Universe Today. Retrieved 2014-04-26.