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Encyclopedia > Enceladus (moon)
Enceladus
Degraded craters, fractures and disrupted terrain in Cassini mosaic of the north polar region of Enceladus
Discovery
Discovered by William Herschel
Discovery date August 28, 1789[1]
Semi-major axis 237,948 km
Eccentricity 0.0047[2]
Orbital period 1.370218 days or 118386.82 seconds[3]
Inclination 0.019° (to Saturn's equator)
Satellite of Saturn
Physical characteristics
Dimensions 513.2×502.8×496.6 km[4]
Mean radius 252.1 ± 0.1 km (0.0395 Earths)[5]
Mass 1.08022 ± 0.00101×1020 kg[5] (1.8×10-5 Earths)
Mean density 1.6096 ± 0.0024 g/cm3[5]
Equatorial surface gravity 0.111 m/s2 (0.0113 g)
Escape velocity 0.239 km/s (860.4 km/h)
Rotation period synchronous
Axial tilt zero
Albedo 1.375 ± 0.008 (geometric)[6]
Surface temp.
   Kelvin[8]
min mean max
32.9 K 75 K 145 K
Apparent magnitude 11.7 [7]
Adjectives Enceladean
Atmosphere
Surface pressure trace, significant spatial variability[9][10]
Composition 91% Water vapour
4% Nitrogen
3.2% Carbon dioxide
1.7% Methane[11]

Enceladus (pronounced /ɛnˈsɛlədəs/ en-SEL-ə-dəs, or as Greek Εγκέλαδος), discovered in 1789 by William Herschel,[12] is the sixth-largest moon of Saturn.[13] Until the two Voyager spacecraft passed near it in the early 1980s, very little was known about this small moon besides the identification of water ice on its surface. The Voyagers showed that Enceladus is only 500 km in diameter and reflects almost 100% of the sunlight that strikes it. Voyager 1 found that Enceladus orbited in the densest part of Saturn's diffuse E ring, indicating a possible association between the two, while Voyager 2 revealed that despite the moon's small size, it had a wide range of terrains ranging from old, heavily cratered surfaces to young, tectonically deformed terrain, with some regions with surface ages as young as 100 million years old. For other persons named William Herschel, see William Herschel (disambiguation). ... is the 240th day of the year (241st in leap years) in the Gregorian calendar. ... Year 1789 (MDCCLXXXIX) was a common year starting on Thursday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 11-day slower Julian calendar). ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... “km” redirects here. ... (This page refers to eccitricity in astrodynamics. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... For the science fiction novella by William Shunn, see Inclination (novella). ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... For other uses, see Mass (disambiguation). ... Kg redirects here. ... For other uses, see Density (disambiguation). ... BIC pen cap, about 1 gram. ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... Acceleration is the time rate of change of velocity and/or direction, and at any point on a velocity-time graph, it is given by the slope of the tangent to the curve at that point. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... Space Shuttle Atlantis launches on mission STS-71. ... In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis relative to the background stars. ... Due to synchronous rotation of their moon, the inhabitants of the central body will never be able to see its green side. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... For other uses, see Albedo (disambiguation). ... The geometric albedo of an astronomical body is the ratio of its total brightness at zero phase angle to that of an idealised fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. ... For other uses, see Temperature (disambiguation). ... For other uses, see Kelvin (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... Atmospheric pressure is the pressure at any given point in the Earths atmosphere. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Methane is a chemical compound with the molecular formula . ... For other persons named William Herschel, see William Herschel (disambiguation). ... The Saturnian system (photographic montage) Saturn has 60 confirmed natural satellites, plus three hypothetical moons. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... Voyager Project redirects here. ... KM, Km, or km may stand for: Khmer language (ISO 639 alpha-2, km) Kilometre Kinemantra Meditation Knowledge management KM programming language KM Culture, Korean Movie Maker. ... Prism splitting light High Resolution Solar Spectrum Sunlight in the broad sense is the total spectrum of the electromagnetic radiation given off by the Sun. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... Tycho crater on Earths moon. ... Look up million in Wiktionary, the free dictionary. ...


The Cassini spacecraft of the mid- to late 2000s acquired additional data on Enceladus, answering a number of the mysteries opened by the Voyager spacecraft and starting a few new ones. Cassini performed several close flybys of Enceladus in 2005, revealing the moon's surface and environment in greater detail. In particular, the probe discovered a water-rich plume venting from the moon's south polar region. This discovery, along with the presence of escaping internal heat and very few (if any) impact craters in the south polar region, shows that Enceladus is geologically active today. Moons in the extensive satellite systems of gas giants often become trapped in orbital resonances that lead to forced libration or orbital eccentricity; proximity to the planet can then lead to tidal heating of the satellite's interior, offering a possible explanation for the activity. Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... Location of the polar regions Northern Hemisphere permafrost (permanently frozen ground) in purple. ... In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other. ... Not to be confused with Liberation. ... (This page refers to eccitricity in astrodynamics. ... Tidal acceleration is an effect of the tidal forces between an orbiting natural satellite ( a moon), and the planet (called the primary) that it orbits. ...


Enceladus is one of only three outer solar system bodies (along with Jupiter's moon Io and Neptune's moon Triton) where active eruptions have been observed. Analysis of the outgassing suggests that it originates from a body of sub-surface liquid water, which along with the unique chemistry found in the plume, has fueled speculations that Enceladus may be important in the study of astrobiology.[14] The discovery of the plume has added further weight to the argument that material released from Enceladus is the source of the E-ring. This article is about the Solar System. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... Atmospheric characteristics Surface pressure ≫100 MPa Hydrogen - H2 80% ±3. ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... The DNA structure might not be the only nucleic acid in the universe capable of supporting life[1] Astrobiology (from Greek: ἀστρο, astro, constellation; βίος, bios, life; and λόγος, logos, knowledge) is the interdisciplinary study of life in space, combining aspects of astronomy, biology and geology. ...

Contents

Name

See also: List of geological features on Enceladus

Enceladus is named after the Giant Enceladus of Greek mythology. It is also designated Saturn II or S II Enceladus. The name Enceladus – like the names of each of the first seven satellites of Saturn to be discovered– was suggested by William Herschel's son John Herschel in his 1847 publication Results of Astronomical Observations made at the Cape of Good Hope.[15] He chose these names because Saturn, known in Greek mythology as Cronus, was the leader of the Titans. The adjectival form of the name is either Enceladean or Enceladan (both are used with roughly equal frequency). This is a list of named geological features on Enceladus. ... Gigantomachia: Dionysos attacking a Gigante, Attic red-figure pelike, ca. ... Fountain of the Gigantes in the gardens of Versailles In Greek mythology, Enceladus was one of the Gigantes, the enormous children of Gaia (Earth). ... The bust of Zeus found at Otricoli (Sala Rotonda, Museo Pio-Clementino, Vatican) Greek mythology is the body of stories belonging to the Ancient Greeks concerning their gods and heroes, the nature of the world and the origins and significance of their own cult and ritual practices. ... John Herschel Sir John Frederick William Herschel (7 March 1792 – 11 May 1871) was an English mathematician and astronomer. ... Saturnus, Caravaggio, 16th c. ... Cronus is not to be confused with Chronos, the personification of time. ...


Features on Enceladus are named by the International Astronomical Union (IAU) after characters and places from the Arabian Nights.[16] Impact craters are named after characters, while other feature types, such as Fossae (long, narrow depressions), Dorsa (ridges), Planitia (plains), and Sulci (long parallel grooves), are named after places. 57 features have been officially named by the IAU; 22 features were named in 1982 based on the results of the Voyager flybys, and 35 features were approved in November 2006 based on the results of Cassini's three flybys in 2005.[17] Examples of approved names include Samarkand Sulci, Aladdin crater, Daryabar Fossa, and Sarandib Planitia. IAU redirects here. ... Queen Scheherazade tells her stories to King Shahryar. ... Tycho crater on Earths moon. ... External resources Fossae on Mars Fossae on Venus Fossae on the Moon Fossae on Enceladus Fossae on Ganymede Categories: Stub ... Dorsum (pl. ... Planitia is the Latin word for plain. ... In geography, a plain is a large area of land with relatively low relief. ... Sulcus (pl. ... 67 die and about 300,000 people are affected by floods in Ethiopias Somali Region of Ogaden after the Shabelle River bursts its banks. ... Voyager 2 and Cassini views of Samarkand Sulci Samarkand Sulci is a region of grooved terrain on the surface of Saturns moon Enceladus. ... Voyager 2 view of Aladdin crater (northern of the two large craters) Aladdin is a crater in the northern hemisphere of Saturns moon Enceladus. ... Voyager 2 view of Daryabar Fossa (southern of the two east-west set of grooves) Daryabar Fossa is an east-west trending trough on Saturns moon Enceladus. ... Cassini view of Sarandib Planitia Sarandib Planitia is a region of relatively un-cratered terrain on Saturns moon Enceladus. ...


Exploration

Figure 1: Enceladus as seen by Voyager 2, August 26, 1981
Figure 1: Enceladus as seen by Voyager 2, August 26, 1981

Enceladus was discovered by Fredrick William Herschel on August 28, 1789, during the first use of his new 1.2 m telescope, then the largest in the world.[18][19] Herschel first observed Enceladus in 1787, but in his smaller, 16.5-cm telescope, the moon was not recognized.[20] Due to Enceladus' faint apparent magnitude (+11.7m) and its proximity to much brighter Saturn and its rings, Enceladus is difficult to observe from Earth, requiring a telescope with a mirror of 15–30 cm in diameter, depending on atmospherical conditions and light pollution. Like many Saturnian satellites discovered prior to the Space Age, Enceladus was first observed during a ring crossing, when Earth is within the ring plane during Saturnian equinox. During these periods, Enceladus is easier to observe due to the reduction in glare from the rings. Download high resolution version (1004x1004, 93 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1004x1004, 93 KB) Wikipedia does not have an article with this exact name. ... For other persons named William Herschel, see William Herschel (disambiguation). ... is the 240th day of the year (241st in leap years) in the Gregorian calendar. ... Year 1789 (MDCCLXXXIX) was a common year starting on Thursday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Monday of the 11-day slower Julian calendar). ... This article is about the unit of length. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... This time exposure photo of New York City shows sky glow, one form of light pollution. ... The Space Shuttle takes off on a manned mission to space. ...


Prior to the Voyager program, the view of Enceladus improved little from the dot first observed by Herschel. Only its orbital characteristics, along with an estimation of its mass, density, and albedo, were known. Voyager Project redirects here. ... For other uses, see Mass (disambiguation). ... For other uses, see Density (disambiguation). ... For other uses, see Albedo (disambiguation). ...

Planned Cassini encounters with Enceladus[21]
Date Distance (km)
February 17, 2005 1,264
March 9, 2005 500
March 29, 2005 64,000
May 21, 2005 93,000
July 14, 2005 175
October 12, 2005 49,000
December 24, 2005 94,000
January 17, 2006 146,000
September 9, 2006 40,000
November 9, 2006 95,000
June 28, 2007 90,000
September 30, 2007 98,000
March 12, 2008 52
June 30, 2008 84,000
August 11, 2008 54
October 9, 2008 25
October 31, 2008 200
November 8, 2008 52,804
November 2, 2009 103
November 21, 2009 1,607
April 28, 2010 103
May 18, 2010 201

The two Voyager spacecraft obtained the first close-up images of Enceladus. Voyager 1 was the first to fly past Enceladus, at a distance of 202,000 km on November 12, 1980.[22] Images acquired from this distance had very poor spatial resolution, but revealed a highly reflective surface devoid of impact craters, indicating a youthful surface.[23] Voyager 1 also confirmed that Enceladus was embedded in the densest part of Saturn's diffuse E-ring. Combined with the apparent youthful appearance of the surface, Voyager scientists suggested that the E-ring consisted of particles vented from Enceladus' surface.[23] is the 48th day of the year in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 68th day of the year (69th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 88th day of the year (89th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 141st day of the year (142nd in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 285th day of the year (286th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 358th day of the year (359th in leap years) in the Gregorian calendar. ... 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Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 71st day of the year (72nd in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 181st day of the year (182nd in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 223rd day of the year (224th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 282nd day of the year (283rd in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 304th day of the year (305th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 312th day of the year (313th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... is the 306th day of the year (307th in leap years) in the Gregorian calendar. ... 2009 (MMIX) will be a common year starting on Thursday of the Gregorian calendar. ... is the 325th day of the year (326th in leap years) in the Gregorian calendar. ... 2009 (MMIX) will be a common year starting on Thursday of the Gregorian calendar. ... is the 118th day of the year (119th in leap years) in the Gregorian calendar. ... 2010 (MMX) will be a common year starting on Friday of the Gregorian calendar. ... is the 138th day of the year (139th in leap years) in the Gregorian calendar. ... 2010 (MMX) will be a common year starting on Friday of the Gregorian calendar. ... Voyager Project redirects here. ... For the album by The Verve, see Voyager 1 (album). ... is the 316th day of the year (317th in leap years) in the Gregorian calendar. ... Year 1980 (MCMLXXX) was a leap year starting on Tuesday (link displays the 1980 Gregorian calendar). ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ...


Voyager 2 passed closer to Enceladus (87,010 km) on August 26, 1981, allowing much higher resolution images of this satellite.[22] These images revealed the youthful nature of much of its surface, as seen in Figure 1.[24] They also revealed a surface with different regions with vastly different surface ages, with a heavily cratered mid- to high-northern latitude region, and a lightly cratered region closer to the equator. This geologic diversity contrasts with the ancient, heavily cratered surface of Mimas, another moon of Saturn slightly smaller than Enceladus. The geologically youthful terrains came as a great surprise to the scientific community, because no theory was then able to predict that such a small (and cold, compared to Jupiter's highly active moon Io) celestial body could bear signs of such activity. However, Voyager 2 failed to determine whether Enceladus was currently active or whether it was the source of the E-ring. Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... is the 238th day of the year (239th in leap years) in the Gregorian calendar. ... AUGUST 25 1981 US Marine Sean Vance is Born on the 25th of August {ear nav|1981}} Year 1981 (MCMLXXXI) was a common year starting on Thursday (link displays the 1981 Gregorian calendar). ... An open surface with X-, Y-, and Z-contours shown. ... Mimas (mee-mÉ™s or mye-mÉ™s, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ... For other uses, see Jupiter (disambiguation). ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ...


The answer to these and other mysteries would have to wait until the arrival of the Cassini spacecraft on July 1, 2004, when it went into orbit around Saturn. Given the results from the Voyager 2 images, Enceladus was considered a priority target by the Cassini mission planners, and several targeted flybys within 1,500 km of the surface were planned as well as numerous, "non-targeted" opportunities within 100,000 km of Enceladus. These encounters are listed at right. So far, four close flybys of Enceladus have been performed, yielding significant information concerning Enceladus' surface, as well as the discovery of water vapor and complex hydrocarbons venting from the geologically active South Polar Region. These discoveries have prompted the adjustment of Cassini's flight plan to allow closer flybys of Enceladus, including an encounter in March 2008 which took the probe to within 50 km of the moon's surface.[21] A planned extended mission for Cassini includes seven close flybys of Enceladus between July 2008 and July 2010, including two passes at only 50 km in the later half of 2008.[25] Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... is the 182nd day of the year (183rd in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... In orbital mechanics and aerospace engineering, a gravitational slingshot or gravity assist is the use of the gravity of a planet or other celestial body to alter the path and speed of a spacecraft. ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... Look up Hydrocarbon in Wiktionary, the free dictionary. ...


The discoveries Cassini has made at Enceladus have prompted several studies into follow-up missions. In 2007, NASA performed a concept study for a mission that would orbit Enceladus and would perform a detailed examination of the south polar plumes.[26] The concept was not selected for further study.[27] The European Space Agency is also recently explored plans to send a probe to Enceladus in a mission to be combined with studies of Titan.[28]


Characteristics

Orbit

Figure 2: View of Enceladus' orbit (highlighted in red) from above Saturn's north pole
Figure 2: View of Enceladus' orbit (highlighted in red) from above Saturn's north pole

Enceladus is one of the major inner satellites of Saturn. It is the fourteenth satellite when ordered by distance from Saturn, and orbits within the densest part of the E Ring, the outermost of Saturn's rings, an extremely wide but very diffuse disk of microscopic icy or dusty material, beginning at the orbit of Mimas and ending somewhere around the orbit of Rhea. Image File history File linksMetadata Download high resolution version (632x632, 119 KB)The orbit of Enceladus around Saturn, showing its position among Saturns inner moons. ... Image File history File linksMetadata Download high resolution version (632x632, 119 KB)The orbit of Enceladus around Saturn, showing its position among Saturns inner moons. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... Mimas (mee-məs or mye-məs, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ... Atmosphere none Rhea (ree-a, Greek ‘Ρέα) is the second largest moon of Saturn and was discovered in 1672 by Giovanni Domenico Cassini. ...


Enceladus orbits Saturn at a distance of 238,000 km from the planet's center and 180,000 km from its cloudtops, between the orbits of Mimas and Tethys, requiring 32.9 hours to revolve once (fast enough for its motion to be observed over a single night of observation). Enceladus is currently in a 2:1 mean motion orbital resonance with Dione, completing two orbits of Saturn for every one orbit completed by Dione. This resonance helps maintain Enceladus' orbital eccentricity (0.0047) and provides a heating source for Enceladus' geologic activity.[2] Mimas (mee-məs or mye-məs, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ... Atmosphere none Tethys (tee-thəs or teth-əs, IPA , Greek Τηθύς) is a moon of Saturn that was discovered by Giovanni Domenico Cassini in 1684. ... In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ...


Like most of the larger satellites of Saturn, Enceladus rotates synchronously with its orbital period, keeping one face pointed toward Saturn. Unlike the Earth's moon, Enceladus does not appear to librate about its spin axis (more than 1.5°). However, analysis of the shape of Enceladus suggests that at some point it was in a 1:4 forced secondary spin-orbit libration.[2] This libration, like the resonance with Dione, could have provided Enceladus with an additional heat source. Not to be confused with Liberation. ...


Interaction with E Ring

Figure 3: View of Enceladus' orbit from the side, showing Enceladus in relation to Saturn's E ring
Figure 3: View of Enceladus' orbit from the side, showing Enceladus in relation to Saturn's E ring

The E Ring is the widest and outermost ring of Saturn. It is an extremely wide but very diffuse disk of microscopic icy or dusty material, beginning at the orbit of Mimas and ending somewhere around the orbit of Rhea, though some observations suggest that it extends beyond the orbit of Titan, making it 1,000,000 km wide. However, numerous mathematical models show that such a ring is unstable, with a lifespan between 10,000 and 1,000,000 years. Therefore, particles composing it must be constantly replenished. Enceladus is orbiting inside this ring, in a place where it is narrowest but present in its highest density. Therefore, several theories suspected Enceladus to be the main source of particles for the E Ring. This hypothesis was proven by Cassini's flyby. Image File history File links Download high resolution version (2672x970, 122 KB) Description Original caption Saturns Rings (Artists Concept) This is an artists concept of Saturns rings and major icy moons. ... Image File history File links Download high resolution version (2672x970, 122 KB) Description Original caption Saturns Rings (Artists Concept) This is an artists concept of Saturns rings and major icy moons. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ... Mimas (mee-məs or mye-məs, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ... Atmosphere none Rhea (ree-a, Greek ‘Ρέα) is the second largest moon of Saturn and was discovered in 1672 by Giovanni Domenico Cassini. ...


There are actually two distinct mechanisms feeding the ring with particles.[29] The first, and probably the most important, source of particles comes from the cryovolcanic plume in the South polar region of Enceladus. While a majority of particles fall back to the surface, some of them escape Enceladus' gravity and enter orbit around Saturn, since Enceladus' escape velocity is only 866 km/h. The second mechanism comes from meteoric bombardment of Enceladus, raising dust particles from the surface. This mechanism is not unique to Enceladus, but is valid for all Saturn's moons orbiting inside the E Ring. Ganesa Macula, a dark feature on Saturns moon Titan, might be a cryovolcanic dome. ... Space Shuttle Atlantis launches on mission STS-71. ...


Size and shape

Figure 4: Enceladus (top left) transits in front of Titan, as seen from Cassini on February 5, 2006. Enceladus was 4.1 million km away, and Titan a further 1.2 million km.
Figure 4: Enceladus (top left) transits in front of Titan, as seen from Cassini on February 5, 2006. Enceladus was 4.1 million km away, and Titan a further 1.2 million km.
Figure 5: Enceladus' size compared to the United Kingdom
Figure 5: Enceladus' size compared to the United Kingdom

Enceladus is a relatively small satellite, with a mean diameter of 505 km, only one-seventh the diameter of Earth's own Moon. Its dimensions would allow the satellite to be placed inside a state such as Arizona or Colorado, or the British Isles (see picture), although as a spherical object its surface area is much greater, just over 800,000 square km, almost the same as Mozambique, or 15% larger than Texas. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Image File history File links Download high resolution version (685x649, 68 KB) Description original image caption: Saturns moon Enceladus is only 505 kilometers (314 miles) across, small enough to fit within the length of the United Kingdom, as illustrated here. ... Image File history File links Download high resolution version (685x649, 68 KB) Description original image caption: Saturns moon Enceladus is only 505 kilometers (314 miles) across, small enough to fit within the length of the United Kingdom, as illustrated here. ... This article is about Earths moon. ... Official language(s) English Spoken language(s) English 74. ... Official language(s) English Demonym Coloradan Capital Denver Largest city Denver Largest metro area Denver-Aurora Metro Area Area  Ranked 8th in the US  - Total 104,185 sq mi (269,837 km²)  - Width 280 miles (451 km)  - Length 380 miles (612 km)  - % water 0. ... This article explains the archipelago in north-western Europe. ... For other uses, see Texas (disambiguation). ...


Its mass and diameter make Enceladus the sixth most massive and largest satellite of Saturn, after Titan (5150 km), Rhea (1530 km), Iapetus (1440 km), Dione (1120 km) and Tethys (1050 km). It is also one of the smallest of Saturn's spherical satellites, since all smaller satellites except Mimas (390 km) have an irregular shape. Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ... Atmosphere none Rhea (ree-a, Greek ‘Ρέα) is the second largest moon of Saturn and was discovered in 1672 by Giovanni Domenico Cassini. ... Iapetus (eye-ap-ə-təs, IPA , Greek Ιαπετός) is the third-largest moon of Saturn, discovered by Giovanni Domenico Cassini in 1671. ... Atmosphere none Dione (dye-oe-nee, Greek Διώνη) is a moon of Saturn discovered by Giovanni Cassini in 1684. ... Atmosphere none Tethys (tee-thəs or teth-əs, IPA , Greek Τηθύς) is a moon of Saturn that was discovered by Giovanni Domenico Cassini in 1684. ... Mimas (mee-məs or mye-məs, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ...


Enceladus has a shape of a flattened ellipsoid; its dimensions, calculated from pictures taken by Cassini's ISS instrument, are of 513(a)×503(b)×497(c) km,[2] with (a) corresponding to the diameter between sub- and anti-Saturnian poles, (b) to the diameter between the leading and trailing poles, and (c) to the distance between the north and south poles. 3D rendering of an ellipsoid In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. ...


Surface

Voyager 2, in August of 1981, was the first spacecraft to observe the surface in detail. Examination of the resulting highest resolution mosaic reveals at least five different types of terrain, including several regions of cratered terrain, regions of smooth (young) terrain, and lanes of ridged terrain often bordering the smooth areas.[24] In addition, extensive linear cracks[30] and scarps were observed. Given the relative lack of craters on the smooth plains, these regions are probably less than a few hundred million years old. Accordingly, Enceladus must have been recently active with "water volcanism" or other processes that renew the surface. The fresh, clean ice that dominates its surface gives Enceladus probably the most reflective surface of any body in the solar system with a visual geometric albedo of 1.38.[6] Because it reflects so much sunlight, the mean surface temperature at noon only reaches −198 °C (somewhat colder than other Saturnian satellites).[8] Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... This article is about a decorative art. ... In geology, an escarpment is a transition zone between different physiogeographic provinces that involves an elevation differential, often involving high cliffs. ... Image of the south pole of Triton taken by Voyager 2 in 1989. ... The geometric albedo of an astronomical body is the ratio of its total brightness at zero phase angle to that of an idealised fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. ...


Observations during three flybys by Cassini on February 17, March 9, and July 14 of 2005 revealed Enceladus' surface features in much greater detail than the Voyager 2 observations. For example, the smooth plains observed by Voyager 2 resolved into relatively crater-free regions filled with numerous small ridges and scarps. In addition, numerous fractures were found within the older, cratered terrain, suggesting that the surface has been subjected to extensive deformation since the craters were formed.[31] Finally, several additional regions of young terrain were discovered in areas not well-imaged by either Voyager spacecraft, such as the bizarre terrain near the south pole.[2] is the 48th day of the year in the Gregorian calendar. ... is the 68th day of the year (69th in leap years) in the Gregorian calendar. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... This article is about the use of the term in geography and physical geology. ...

A composite image map of Enceladus' surface.
A composite image map of Enceladus' surface.

Impact craters

Figure 6: Degraded craters on Enceladus, imaged by Cassini, 17 February 2005. Hamah Sulci can be seen running from left to right along the bottom quarter of the image. Craters from Enceladus' ct2 and cp cratered units are visible above Hamah Sulci
Figure 6: Degraded craters on Enceladus, imaged by Cassini, 17 February 2005. Hamah Sulci can be seen running from left to right along the bottom quarter of the image. Craters from Enceladus' ct2 and cp cratered units are visible above Hamah Sulci

Impact cratering is a common occurrence on many solar system bodies. Much of Enceladus's surface is covered with craters at various densities and levels of degradation. From Voyager 2 observations, three different units of cratered topography were identified on the basis of their crater densities, from ct1 and ct2, both containing numerous 10–20 km-wide craters though differing in the degree of deformation, to cp consisting of lightly cratered plains.[32] This subdivision of cratered terrains on the basis of crater density (and thus surface age), suggests that Enceladus has been resurfaced in multiple stages. Download high resolution version (1024x1024, 537 KB)View of Degraded Craters north and east of Samarkand Sulci on Saturns Moon Enceladus. ... Download high resolution version (1024x1024, 537 KB)View of Degraded Craters north and east of Samarkand Sulci on Saturns Moon Enceladus. ... is the 48th day of the year in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Tycho crater on Earths moon. ... A volume of rock or ice of identifiable origin and age range that is defined by the distinctive and dominant, easily mapped and recognizable petrographic, lithologic or paleontologic features (facies) that characterize it. ...


Recent Cassini observations have provided a much closer look at the ct2 and cp cratered units. These high-resolution observations, like Figure 6, reveal that many of Enceladus' craters are heavily deformed through viscous relaxation and fracturing.[33] Viscous relaxation causes craters and other topographic features formed in water ice to deform over geologic time scales due to the effects of gravity, reducing the amount of topography over time. The rate at which this occurs is dependent on the temperature of the ice: warmer ice is easier to deform than colder, stiffer ice. Viscously relaxed craters tend to have domed floors, or are recognized as craters only by a raised, circular rim (seen at center just below the terminator in Figure 6). Dunyazad, the large crater seen in Figure 8 just left of top center, is a prime example of a viscously relaxed crater on Enceladus, with a prominent domed floor. In addition, many craters on Enceladus have been heavily modified by tectonic fractures. The 10-km-wide crater right of bottom center in Figure 8 is a prime example: thin fractures, several hundred metres to a kilometre wide, have heavily altered the crater's rim and floor. Nearly all craters on Enceladus thus far imaged by Cassini in the Ct2 unit show signs of tectonic deformation. These two deformation styles—viscous relaxation and fracturing—demonstrate that, while cratered terrains are the oldest regions on Enceladus due to their high crater retention, nearly all craters on Enceladus are in some stage of degradation. For other uses, see Fracture (disambiguation). ... For other uses, see Dome (disambiguation). ... World map with terminator (April) A composite image showing the terminator dividing night from day, running across Europe and Africa. ... Dunyazad crater (bottom center) as seen by the Cassini spacecraft on March 9, 2005 Dunyazad is a large crater on Saturns moon Enceladus first discovered by the Voyager spacecraft. ...


Tectonics

Figure 7: Enceladus' Europa-like surface near the fracture Labtayt Sulci, imaged by Cassini, 17 February 2005
Figure 7: Enceladus' Europa-like surface near the fracture Labtayt Sulci, imaged by Cassini, 17 February 2005

Voyager 2 found several types of tectonic features on Enceladus, including troughs, scarps, and belts of grooves and ridges.[24] Recent results from Cassini suggest that tectonism is the dominant deformation style on Enceladus. One of the more dramatic types of tectonic features found on Enceladus are rifts. These canyons can be up to 200 km long, 5–10 km wide, and one km deep. Figure 7 shows a typical large fracture on Enceladus cutting across older, tectonically deformed terrain. Another example can be seen running along the bottom of the frame in Figure 8. Such features appear relatively young, as they cut across other tectonic features and have sharp topographic relief with prominent outcrops along the cliff faces. Download high resolution version (2340x1580, 2356 KB)Mosaic of Four Images showing tectonic features on the surface of Saturns moon Enceladus Original caption released with image: This spectacular view is a mosaic of four high resolution images taken by the Cassini narrow angle camera on February 16, 2005 during... Download high resolution version (2340x1580, 2356 KB)Mosaic of Four Images showing tectonic features on the surface of Saturns moon Enceladus Original caption released with image: This spectacular view is a mosaic of four high resolution images taken by the Cassini narrow angle camera on February 16, 2005 during... Apparent magnitude: 5. ... Labtayt Sulci running from left to right across mosaic taken by the Cassini spacecraft on February 17, 2005 Labtayt Sulci is a system of deep fractures on Saturns moon Enceladus. ... is the 48th day of the year in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... In geology, a trough generally referrs to a depression that extends laterally over a distence, while being less steep than a trench. ... Belt can refer to the following objects: Look up belt in Wiktionary, the free dictionary. ... Groove (engineering) - a slot cut into hard material. ... This article is about the use of the term in geography and physical geology. ... Plate tectonics (from the Greek word for one who constructs, τεκτων, tekton) is a theory of geology developed to explain the phenomenon of continental drift, and is currently the theory accepted by the vast majority of scientists working in this area. ...

Figure 8: False-color view of Enceladus' surface, showing several tectonic and crater degradation styles. Taken by Cassini on 9 March 2005
Figure 8: False-color view of Enceladus' surface, showing several tectonic and crater degradation styles. Taken by Cassini on 9 March 2005

Another example of tectonism on Enceladus is grooved terrain, consisting of lanes of curvilinear grooves and ridges. These bands, first discovered by Voyager 2, often separate smooth plains from cratered regions.[24] An example of this terrain type can be seen in Figures 6 and 10 (in this case, a feature known as Samarkand Sulci). Grooved terrain such as Samarkand Sulci are reminiscent of grooved terrain on Ganymede. However, unlike those seen on Ganymede, grooved topography on Enceladus is generally much more complex. Rather than parallel sets of grooves, these lanes can often appear as bands of crudely aligned, chevron-shaped features. In other areas, these bands appear to bow upwards with fractures and ridges running the length of the feature. Cassini observations of Samarkand Sulci have revealed intriguing dark spots (125 and 750 m wide), which appear to run parallel to narrow fractures. Currently, these spots are interpreted as collapse pits within these ridged plain belts.[33] Download high resolution version (1000x1000, 441 KB)False-color view of Enceladus. ... Download high resolution version (1000x1000, 441 KB)False-color view of Enceladus. ... A false color image showing the Chesapeake Bay and the city of Baltimore. ... is the 68th day of the year (69th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Voyager 2 and Cassini views of Samarkand Sulci Samarkand Sulci is a region of grooved terrain on the surface of Saturns moon Enceladus. ... This article is about the natural satellite of Jupiter. ... This article is about the unit of length. ...

Figure 9: High-resolution mosaic of Enceladus' surface, showing several tectonic and crater degradation styles. Taken by Cassini on 9 March 2005.
Figure 9: High-resolution mosaic of Enceladus' surface, showing several tectonic and crater degradation styles. Taken by Cassini on 9 March 2005.

In addition to deep fractures and grooved lanes, Enceladus has several other types of tectonic terrain. Figure 9 shows sets of narrow fractures (still several hundred metres wide) that were first discovered by the Cassini spacecraft. Many of these fractures are found in bands cutting across cratered terrain. These fractures appear to propagate down only a few hundred metres into the crust. Many appear to have been influenced during their formation by the weakened regolith produced by impact craters, often changing the strike of the propagating fracture.[33][34] Another example of tectonic features on Enceladus are the linear grooves first found by Voyager 2 and seen at a much higher resolution by Cassini. Examples of linear grooves can be found in the lower left of the figure at top and Figure 10 (lower left), running from north to south from top center before turning to the southwest. These linear grooves can be seen cutting across other terrain types, like the groove and ridge belts. Like the deep rifts, they appear to be among the youngest features on Enceladus. However, some linear grooves appear to be softened like the craters nearby, suggesting an older age. Ridges have also been observed on Enceladus, though not nearly to the extent as those seen on Europa. Several examples can be seen in the lower left corner of Figure 7. These ridges are relatively limited in extent and are up to one km tall. One-kilometre high domes have also been observed.[33] Given the level of tectonic resurfacing found on Enceladus, it is clear that tectonism has been an important driver of geology on this small moon for much of its history. Download high resolution version (5936x4744, 3609 KB)Large mosaic of images taken by the Cassini Spacecraft of Saturns moon Enceladus Original caption released with image: The complex history of Enceladus surface is revealed in great detail in this mosaic of images taken during Cassinis closest encounter with this... Download high resolution version (5936x4744, 3609 KB)Large mosaic of images taken by the Cassini Spacecraft of Saturns moon Enceladus Original caption released with image: The complex history of Enceladus surface is revealed in great detail in this mosaic of images taken during Cassinis closest encounter with this... is the 68th day of the year (69th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Apparent magnitude: 5. ...


Smooth plains

Figure 10: Samarkand Sulci on Enceladus. Taken by Cassini on 17 February 2005. The northwest portion of Sarandib Planitia can be seen at right
Figure 10: Samarkand Sulci on Enceladus. Taken by Cassini on 17 February 2005. The northwest portion of Sarandib Planitia can be seen at right

Two units of smooth plains were also observed by Voyager 2. These plains generally have low relief and have far fewer craters than in the cratered terrains and plains, indicating a relatively young surface age.[32] In one of the smooth plain regions, Sarandib Planitia, no impact craters were visible down to the limit of resolution. Another region of smooth plains to the southwest of Sarandib, is criss-crossed by several troughs and scarps. Cassini has since viewed these smooth plains regions, like Sarandib Planitia and Diyar Planitia at much higher resolution. Cassini images show smooth plain regions to be filled with low-relief ridges and fractures. These features are currently interpreted as being caused by shear deformation.[33] The high resolution images of Sarandib Planitia have revealed a number of small impact craters, which allow for an estimate of the surface age, either 170 million years or 3.7 billion years, depending on assumed impactor population.[2][35] Download high resolution version (1024x1024, 635 KB)High Resolution image of Saturns moon Enceladus. ... Download high resolution version (1024x1024, 635 KB)High Resolution image of Saturns moon Enceladus. ... is the 48th day of the year in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Cassini view of Sarandib Planitia Sarandib Planitia is a region of relatively un-cratered terrain on Saturns moon Enceladus. ... Cassini views of Diyar Planitia Diyar Planitia is a region of relatively un-cratered terrain on Saturns moon Enceladus. ... Shear stress is a stress state where the stress is parallel or tangential to a face of the material, as opposed to normal stress when the stress is perpendicular to the face. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ...


The expanded surface coverage provided by Cassini has allowed for the identification of additional regions of smooth plains, particularly on Enceladus' leading hemisphere (the side of Enceladus that faces the direction of motion as the moon orbits Saturn). Rather than being covered in low relief ridges, this region is covered in numerous criss-crossing sets of troughs and ridges, similar to the deformation seen in the south polar region. This area is on the opposite side of the satellite from Sarandib and Diyar Planitiae, suggesting that the placement of these regions is influenced by Saturn's tides on Enceladus.[36]


South polar region

See also: Tiger Stripes (Enceladus)
Figure 11: False-color mosaic of Enceladus taken by the Cassini-Huygens probe July 14, 2005. Shows the south polar region, as demarcated by the circumpolar set of ridges and troughs in the bottom half of the mosaic
Figure 11: False-color mosaic of Enceladus taken by the Cassini-Huygens probe July 14, 2005. Shows the south polar region, as demarcated by the circumpolar set of ridges and troughs in the bottom half of the mosaic

Images taken by Cassini during the flyby on July 14, 2005 revealed a distinctive, tectonically-deformed region surrounding Enceladus' south pole. This area, reaching as far north as 60° south latitude, is covered in tectonic fractures and ridges.[2][37] The area has few sizable impact craters, suggesting that it is the youngest surface on Enceladus and on any of the mid-sized icy satellites; modeling of the cratering rate suggests that the region is less than 10–100 million years old.[2] Near the center of this terrain are four fractures bounded on either side by ridges, unofficially called "Tiger stripes". These fractures appear to be the youngest features in this region and are surrounded by mint-green-colored (in false color, UV-Green-near IR images), coarse-grained water ice, seen elsewhere on the surface within outcrops and fracture walls.[37] Here the "blue" ice is on a flat surface, indicating that the region is young enough not to have been coated by fine-grained water ice from E ring. Results from the Visual and Infrared Spectrometer (VIMS) instrument suggest that the green-colored material surrounding the tiger stripes is chemically distinct from the rest of the surface of Enceladus. VIMS detected crystalline water ice in the stripes, suggesting that they are quite young (likely less than 1,000 years old) or the surface ice has been thermally altered in the recent past.[38] VIMS also detected simple organic compounds in the tiger stripes, chemistry not found anywhere else on the satellite thus far.[39] Cassini view of Enceladus south pole and the tiger stripes Tiger Stripes consist of four, sub-parallel, linear depressions in the south polar region of Saturns moon Enceladus. ... Image File history File links Download high resolution version (3237x3812, 1243 KB) // Summary Large mosaic of images taken by the Cassini Spacecraft of Saturns moon Enceladus Original caption: A masterpiece of deep time and wrenching gravity, the tortured surface of Enceladus and its fascinating ongoing geologic activity tell the... Image File history File links Download high resolution version (3237x3812, 1243 KB) // Summary Large mosaic of images taken by the Cassini Spacecraft of Saturns moon Enceladus Original caption: A masterpiece of deep time and wrenching gravity, the tortured surface of Enceladus and its fascinating ongoing geologic activity tell the... A false color image showing the Chesapeake Bay and the city of Baltimore. ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... Cassini view of Enceladus south pole and the tiger stripes Tiger Stripes consist of four, sub-parallel, linear depressions in the south polar region of Saturns moon Enceladus. ... The full set of rings, photographed as Saturn eclipsed the sun from the vantage of the Cassini spacecraft on September 15, 2006 (brightness has been exaggerated in this image). ...


One of these areas of "blue" ice in the south polar region was observed at very high resolution during the July 14 flyby, revealing an area of extreme tectonic deformation and blocky terrain, with some areas covered in boulders 10–100 m across.[40] is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... This article is about the unit of length. ...


The boundary of the South Polar Region is marked by a pattern of parallel, Y- and V-shaped ridges and valleys. The shape, orientation, and location of these features indicate that they are caused by changes in the overall shape of Enceladus. Currently, there are two theories for what could cause such a shift in shape. First, the orbit of Enceladus may have migrated inward (from the article: "the lack of any plausible mechanism for increased flattening"), leading to an increase in Enceladus' rotation rate. Such a shift would have led to a flattening of Enceladus' rotation axis.[2] Another theory suggests that a rising mass of warm, low density material in Enceladus' interior led to a shift in the position of the current south polar terrain from Enceladus' southern mid-latitudes to its south pole.[36] Consequently, the ellipsoid shape of Enceladus would have adjusted to match the new orientation. One consequence of the axial flattening theory is that both polar regions should have similar tectonic deformation histories.[2] However, the north polar region is densely cratered, and has a much older surface age than the south pole.[32] Thickness variations in Enceladus' lithosphere is one explanation for this discrepancy. Variations in lithospheric thickness are supported by the correlation between the Y-shaped discontinuities and the V-shaped cusps along the south polar terrain margin and the relative surface age of the adjacent non-south polar terrain regions. The Y-shaped discontinuities, and the north-south trending tension fractures into which they lead, are correlated with younger terrain with presumably thinner lithospheres. The V-shaped cusps are adjacent to older, more heavily cratered terrains.[2] 2006 is a common year starting on Sunday of the Gregorian calendar. ... The tectonic plates of the lithosphere on Earth. ...


Cryovolcanism

Figure 12: Plumes above the limb of Enceladus feeding the E ring. These appear to emanate from the "tiger stripes" near the south pole. (View from Cassini spacecraft)
Figure 12: Plumes above the limb of Enceladus feeding the E ring. These appear to emanate from the "tiger stripes" near the south pole. (View from Cassini spacecraft)

Following the Voyager encounters with Enceladus in the early 1980s, scientists postulated that the moon may be geologically active based on its young, reflective surface and location near the core of the E ring.[24] Based on the connection between Enceladus and the E ring, it was thought that Enceladus was the source of material from the E ring, perhaps through venting of water vapor from Enceladus' interior. However, the Voyagers failed to provide conclusive evidence that Enceladus is active today. Image File history File links Download high resolution version (1019x863, 99 KB) Summary Original Caption Released with Image Recent Cassini images of Saturns moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. ... Image File history File links Download high resolution version (1019x863, 99 KB) Summary Original Caption Released with Image Recent Cassini images of Saturns moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. ...


Thanks to data from a number of instruments on the Cassini spacecraft in 2005, cryovolcanism, where water and other volatiles are the materials erupted instead of silicate rock, has been discovered on Enceladus. The first Cassini sighting of a plume of icy particles above Enceladus' south pole came from the Imaging Science Subsystem (ISS) images taken in January and February 2005,[2] though the possibility of the plume being a camera artifact stalled an official announcement. Data from the magnetometer instrument during the February 17, 2005 encounter provided a hint that the feature might be real when it found evidence for an atmosphere at Enceladus. The magnetometer observed an increase in the power of ion cyclotron waves near Enceladus. These waves are produced by the interaction of ionized particles and magnetic fields, and the frequency of the waves can be used to identify the composition, in this case ionized water vapor.[9] During the next two encounters, the magnetometer team determined that gases in Enceladus's atmosphere are concentrated over the south polar region, with atmospheric density away from the pole being much lower.[9] The Ultraviolet Imaging Spectrograph (UVIS) confirmed this result by observing two stellar occultations during the February 17 and July 14 encounters. Unlike the magnetometer, UVIS failed to detect an atmosphere above Enceladus during the February encounter when it looked for evidence for an atmosphere over the equatorial region, but did detect water vapor during an occultation over the south polar region during the July encounter.[10] Image of the south pole of Triton taken by Voyager 2 in 1989. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... is the 48th day of the year in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... An electrostatic ion cyclotron wave is a longitudinal oscillation of the ions (and electrons) in a magnetized plasma, propagating nearly (but not exactly) perpendicular to the magnetic field. ... This article is about the electrically charged particle. ... Water vapor or water vapour (see spelling differences), also aqueous vapor, is the gas phase of water. ... A magnetometer is a scientific instrument used to measure the strength and/or direction of the magnetic field in the vicinity of the instrument. ... For other uses, see Ultraviolet (disambiguation). ... In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation. ... is the 48th day of the year in the Gregorian calendar. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ...


Fortuitously, Cassini flew through this gas cloud during the July 14 encounter, allowing instruments like the Ion and Neutral Mass Spectrometer (INMS) and the Cosmic Dust Analyser (CDA) to directly sample the plume. INMS measured the composition of the gas cloud, detecting mostly water vapor, as well as minor components like molecular nitrogen, methane, and carbon dioxide.[11] CDA "detected a large increase in the number of particles near Enceladus," confirming the satellite as the primary source for the E ring.[29] Analysis of the CDA and INMS data suggest that the gas cloud Cassini flew through during the July encounter, and was observed from a distance by the magnetometer and UVIS, was actually a water-rich cryovolcanic plume, originating from vents near the south pole.[41] is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Mass spectrometry (previously called mass spectroscopy (deprecated) or informally, mass-spec and MS) is an analytical technique that measures the mass-to-charge ratio of ions. ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Methane is a chemical compound with the molecular formula . ... Carbon dioxide (chemical formula: ) is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...

Figure 13: Heat map (within white box) of the thermally active field of fractures, measured at wavelengths between 12 and 16 microns, superimposed on a visual-light image. One of the four fractures (right) was only partially imaged.
Figure 13: Heat map (within white box) of the thermally active field of fractures, measured at wavelengths between 12 and 16 microns, superimposed on a visual-light image. One of the four fractures (right) was only partially imaged.

Visual confirmation of venting came in November 2005, when ISS imaged fountain-like jets of icy particles rising from the moon's south polar region.[2] (As stated above, the plume was imaged before, in January and February 2005, but additional studies of the camera's response at high phase angles, when the sun is almost behind Enceladus, and comparison with equivalent high phase images taken of other Saturnian satellites, were required before the plume could be confirmed.[42]) The images taken in November 2005 showed the plume's fine structure, revealing numerous jets (perhaps due to numerous distinct vents) within a larger, faint component extending out nearly 500 km from the surface, thus making Enceladus the fourth body in the solar system to have confirmed volcanic activity, along with Earth, Neptune's Triton, and Jupiter's Io.[41] Cassini's UVIS later observed gas jets coinciding with the dust jets seen by ISS during a non-targeted encounter with Enceladus in October 2007. Plume of the Space Shuttle Atlantis after launch. ... This article is about Earth as a planet. ... Triton (trye-tÉ™n, IPA: , Greek Τρίτων), or Neptune I, is the planet Neptunes largest moon. ... Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... October 2007 is the tenth month of that year. ...


Additional observations were acquired during a flyby on March 12, 2008. Data on this flyby revealed additional chemicals in the plume, including simple and complex hydrocarbons such as propane, ethane, and acetylene.[43] This finding further raises the potential for life beneath the surface of Enceladus.[44] The composition of Enceladus's plume as measured by the INMS instrument on Cassini is similar to that seen at most comets.[43] is the 71st day of the year (72nd in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ... This article is about a chemical compound. ... Acetylene (systematic name: ethyne) is a hydrocarbon belonging to the group of alkynes. ...

Figure 14: One possible scheme for Enceladus's cryovolcanism.
Figure 14: One possible scheme for Enceladus's cryovolcanism.

The combined analysis of imaging, mass spectrometry, and magnetospheric data suggests that the observed south polar plume emanates from pressurized sub-surface chambers, similar to geysers on Earth.[2] Because no ammonia was found in the vented material by INMS or UVIS, which could act as an anti-freeze, such a heated, pressurized chamber would consist of nearly pure liquid water with a temperature of at least 270 K, as illustrated in Figure 14. Pure water would require more energy to melt, either from tidal or radiogenic sources, than an ammonia-water mixture. Another possible method for generating a plume is sublimation of warm surface ice. During the July 14, 2005 flyby, the Composite Infrared Spectrometer (CIRS) found a warm region near the South Pole. Temperatures found in this region range from 85–90 K, to small areas with temperatures as high as 157 K, much too warm to be explained by solar heating, indicating that parts of the south polar region are heated from the interior of Enceladus.[8] Ice at these temperatures is warm enough to sublimate at a much faster rate than the background surface, thus generating a plume. This hypothesis is attractive since the sub-surface layer heating the surface water ice could be an ammonia-water slurry at temperatures as low as 170 K, and thus not as much energy is required to produce the plume activity. However, the abundance of particles in the south polar plume favors the "cold geyser" model, as opposed to an ice sublimation model.[2] Image File history File links Size of this preview: 800 × 600 pixelsFull resolution (960 × 720 pixel, file size: 70 KB, MIME type: image/png) I converted the original, high-quality TIFF released by NASA to PNG, using GIMP, to replace Image:PIA07799. ... Image File history File links Size of this preview: 800 × 600 pixelsFull resolution (960 × 720 pixel, file size: 70 KB, MIME type: image/png) I converted the original, high-quality TIFF released by NASA to PNG, using GIMP, to replace Image:PIA07799. ... Strokkur geyser, Iceland A geyser is a type of hot spring that erupts periodically, ejecting a column of hot water and steam into the air. ... For other uses, see Ammonia (disambiguation). ... Sublimation of an element or substance is a conversion between the solid and the gas phases with no intermediate liquid stage. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ...


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 active, tiger stripe fractures.[45] This hypothesis would not require the amount of heat needed to melt water ice as required by the "Cold Geyser" model, and would explain the lack of ammonia. A clathrate or clathrate compound is a chemical substance consisting of a Greek klethra, meaning bars (in the sense of a lattice). ...


Internal structure

Figure 15: Model of the interior of Enceladus based on recent Cassini findings. The inner, silicate core is represented in brown, while the outer, water-ice-rich mantle is represented in white. The yellow and red colors in the mantle and core respectively represent a proposed diapir under the south pole.
Figure 15: Model of the interior of Enceladus based on recent Cassini findings. The inner, silicate core is represented in brown, while the outer, water-ice-rich mantle is represented in white. The yellow and red colors in the mantle and core respectively represent a proposed diapir under the south pole.[36]

Prior to the Cassini mission, relatively little was known about the interior of Enceladus. However, results from recent flybys of Enceladus by the Cassini spacecraft have provided much needed information for models of Enceladus's interior. These include a better determination of the mass and tri-axial ellipsoid shape, high-resolution observations of the surface, and new insights on Enceladus's geochemistry. Image File history File links Size of this preview: 480 × 600 pixelsFull resolution (1536 × 1920 pixel, file size: 288 KB, MIME type: image/jpeg) Orginal JPL relase: Original Caption Released with Image: This graphic illustrates the interior of Saturns moon Enceladus. ... Image File history File links Size of this preview: 480 × 600 pixelsFull resolution (1536 × 1920 pixel, file size: 288 KB, MIME type: image/jpeg) Orginal JPL relase: Original Caption Released with Image: This graphic illustrates the interior of Saturns moon Enceladus. ... A lava lamp illustrates the basic principle of diapirism. ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ... The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earths chemical components in time and space, and their interaction with...


Mass estimates from the Voyager program missions suggested that Enceladus was composed almost entirely of water ice.[24] However, based on the effects of Enceladus's gravity on Cassini, its mass was determined to be much higher than previously thought, yielding a density of 1.61 g/cm³.[2] This density is higher than Saturn's other mid-sized icy satellites, indicating that Enceladus contains a greater percentage of silicates and iron. With additional material besides water ice, Enceladus's interior may have experienced comparatively more heating from the decay of radioactive elements. Voyager Project redirects here. ... Gravity is a force of attraction that acts between bodies that have mass. ... BIC pen cap, about 1 gram. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ...


Castillo et al. 2005 suggested that Iapetus, and the other icy satellites of Saturn, formed relatively quickly after the formation of the Saturnian sub-nebula, and thus were rich in short-lived radionuclides.[46] These radionuclides, like aluminium-26 and iron-60, have short half-lives and would produce interior heating relatively quickly. Without the short-lived variety, Enceladus's complement of long-lived radionuclides would not have been enough to prevent rapid freezing of the interior, even with Enceladus' comparatively high rock-mass fraction, given Enceladus' small size.[47] Given Enceladus's relatively high rock-mass fraction, the proposed enhancement in 26Al and 60Fe would result in a differentiated body, with an icy mantle and a rocky core.[48] Subsequent radioactive and tidal heating would raise the temperature of the core to 1000 K, enough to melt the inner mantle. However, for Enceladus to still be active, part of the core must have melted too, forming magma chambers that would flex under the strain of Saturn's tides. Tidal heating, such as from the resonance with Dione or from libration, would then have sustained these hot spots in the core until the present, and would power the current geological activity.[49] Iapetus (eye-ap-É™-tÉ™s, IPA , Greek Ιαπετός) is the third-largest moon of Saturn, discovered by Giovanni Domenico Cassini in 1671. ... Aluminum redirects here. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... In cosmogony, planetary differentiation is a process by which the denser portions of a planet will sink to the center; while less dense materials rise to the surface. ... The planetary core consists of the innermost layer(s) of a planet. ... This article is about tides in the Earths oceans. ... Earth cutaway from core to exosphere. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ...


In addition to its mass and modeled geochemistry, researchers have also examined Enceladus's shape to test whether the satellite is differentiated or not. Porco et al. 2006 used limb measurements to determine that Enceladus's shape, assuming it is in hydrostatic equilibrium, is consistent with an undifferentiated interior, in contradiction to the geological and geochemical evidence.[2] However, the current shape also supports the possibility that Enceladus is not in hydrostatic equilibrium, and may have rotated faster at some point in the recent past (with a differentiated interior).[48] The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport the Earths chemical components in time and space, and their interaction with... Hydrostatic equilibrium occurs when compression due to gravity is balanced by a pressure gradient which creates a pressure gradient force in the opposite direction. ...


Sky from Enceladus

See also: Extraterrestrial skies
Figure 16: An artist's view of Enceladus' sky.
Figure 16: An artist's view of Enceladus' sky.

Seen from Enceladus, Saturn would have a visible diameter of almost 30°, sixty times more than the Moon visible from Earth [50]. Moreover, since Enceladus rotates synchronously with its orbital period and therefore keeps one face pointed toward Saturn, the planet never moves in Enceladus' sky (albeit with slight variations coming from the orbit's eccentricity), and cannot be seen from the far side of the satellite. The sky of a world refers to the view of the heavens from its surface. ... Image File history File links Saturn_seen_from_Enceladus_(artist_concept). ... Image File history File links Saturn_seen_from_Enceladus_(artist_concept). ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ...


Saturn's rings would be seen from an angle of only 0.019°, and would appear as a very narrow, bright line crossing the disk of Saturn, but their shadow on Saturn's disk would be clearly distinguishable. Like our own Moon from Earth, Saturn itself would show regular phases, cycling from "new" to "full" in about 16 hours. From Enceladus, the Sun would have a diameter of only 3.5 minutes of arc, nine times smaller than that of the Moon as seen from Earth. Moon phase redirects here. ...


An observer located on Enceladus could also observe Mimas (the biggest satellite located inside Enceladus' orbit) transit in front of Saturn every 72 hours on average. Its apparent size would be at most 26 minutes of arc, about the same size as the Moon seen from Earth. Pallene and Methone would appear nearly star-like. Tethys would reach a maximum apparent size just above one degree of arc, about twice the Moon as seen from the Earth, but is visible only from Enceladus' anti-Saturnian side when it is at closest approach. Mimas (mee-məs or mye-məs, IPA: , Greek Μίμᾱς, rarely Μίμανς) is a moon of Saturn that was discovered in 1789 by William Herschel. ... Discovery image of Pallene Pallene (pa-lee-nee, Greek Παλλήνη) is a natural satellite of Saturn. ... Discovery image of Methone Methone (me-thoe-nee, Greek Μεθωνη) is a natural satellite of Saturn. ... Atmosphere none Tethys (tee-thəs or teth-əs, IPA , Greek Τηθύς) is a moon of Saturn that was discovered by Giovanni Domenico Cassini in 1684. ...


Enceladus in popular culture

See Saturn's moons in fiction.

Saturn and its moons Several of Saturns natural satellites of have figured prominently in works of science fiction. ...

Notes and references

  1. ^ Imago Mundi - La Découverte des satellites de Saturne (in French)
  2. ^ a b c d e f g h i j k l m n o p q Porco, C. C.; et al. (2006); Cassini Observes the Active South Pole of Enceladus, Science, Vol. 311, No. 5766, pp. 1393–1401
  3. ^ NASA Celestia Solar System Definition File. Retrieved March 22, 2006.
  4. ^ Thomas, P. C.; Veverka, J.; Helfenstein, P.; Porco, C.; Burns, J.; Denk, T.; Turtle, E. P.; Jacobson, R. A. (March 13–17 2006). "Shapes of the Saturnian Icy Satellites". 37th Annual Lunar and Planetary Science Conference. 
  5. ^ a b c Jacobson, R. A.; Antreasian, P. G.; Bordi, J. J.; Criddle, K. E.; et al. (December 2006). "The Gravity Field of the Saturnian System from Satellite Observations and Spacecraft Tracking Data". The Astronomical Journal 132: 2520–2526. 
  6. ^ a b Verbiscer, A.; French, R.; Showalter, M.; and Helfenstein, P.; Enceladus: Cosmic Graffiti Artist Caught in the Act, Science, Vol. 315, No. 5813 (February 9, 2007), p. 815 (supporting online material, table S1)
  7. ^ Classic Satellites of the Solar System. Observatorio ARVAL. Retrieved on 2007-09-28.
  8. ^ a b c Spencer, J. R.; et al.; (2006); Cassini Encounters Enceladus: Background and the Discovery of a South Polar Hot Spot, Science, Vol. 311, No. 5766, pp. 1401–1405
  9. ^ a b c Dougherty, M. K.; et al.; (2006); Identification of a Dynamic Atmosphere at Enceladus with the Cassini Magnetometer, Science, Vol. 311, No. 5766, pp. 1406–1409
  10. ^ a b Hansen, C. J.; et al.; (2006); Enceladus' Water Vapor Plume, Science, Vol. 311, No. 5766, pp. 1422–1425
  11. ^ a b Waite, J. H.; et al.; (2006); Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure, Science, Vol. 311, No. 5766, pp. 1419–1422
  12. ^ Herschel, W.; Account of the Discovery of a Sixth and Seventh Satellite of the Planet Saturn; With Remarks on the Construction of Its Ring, Its Atmosphere, Its Rotation on an Axis, and Its Spheroidical Figure, Philosophical Transactions of the Royal Society of London, Vol. 80 (1790), pp. 1–20
  13. ^ Planetary Body Names and Discoverers. Retrieved March 22, 2006.
  14. ^ Cassini Images of Enceladus Suggest Geysers Erupt Liquid Water at the Moon’s South Pole. Retrieved March 22, 2006.
  15. ^ As reported by William Lassell, Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 3, pp. 42–43 1848 January 14)
  16. ^ Blue, J.; (2006) Categories for Naming Planetary Features. Accessed November 16, 2006.
  17. ^ Blue, J.; (2006); New Names for Enceladus, 13 November 2006. Accessed November 16, 2006.
  18. ^ Herschel, W. (1795) Description of a Forty-feet Reflecting Telescope, Philosophical Transactions of the Royal Society of London, Vol. 85, pp. 347–409 (reported by M. Arago (1871), Herschel, Annual Report of the Board of Regents of the Smithsonian Institution, pp. 198–223)
  19. ^ Frommert, H.; and Kronberg, C.; William Herschel (1738–1822). Accessed May 29, 2006
  20. ^ Soylent Communications, William Herschel. Accessed May 29, 2006
  21. ^ a b Planetary Society, Cassini's Tour of the Saturn System. Retrieved March 31, 2006.
  22. ^ a b Voyager Mission Description. Accessed May 29, 2006
  23. ^ a b Terrile, R. J.; and Cook, A. F.; (1981); Enceladus: Evolution and Possible Relationship to Saturn's E-Ring. 12th Annual Lunar and Planetary Science Conference, Abstract 428
  24. ^ a b c d e f Rothery, David A. (1999). Satellites of the Outer Planets: Worlds in their own right. Oxford University Press. ISBN 0-19-512555-X. 
  25. ^ Moomaw, B.; Tour de Saturn Set For Extended Play, Spacedaily.com, February 5, 2007. Accessed February 5, 2007.
  26. ^ [1]. Accessed March 2, 2008.
  27. ^ [2]. Accessed March 2, 2008
  28. ^ [3]. Accessed March 2, 2008
  29. ^ a b Spahn, F.; et al.; (2006); Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring, Science, Vol. 311, No. 5766, pp. 1416–1418
  30. ^ NASA. "Cracks on Enceladus Open and Close under Saturn's Pull", May 16, 2007. 
  31. ^ Rathbun, J. A.; et al.; (2005); Enceladus' global geology as seen by Cassini ISS, Eos Trans. AGU, Vol. 82, No. 52 (Fall Meeting Supplement), abstract P32A-03
  32. ^ a b c Smith, B. A., et al.; (1982); A New Look at the Saturn System - The Voyager 2 Images, Science, Vol. 215, pp. 504–537
  33. ^ a b c d e Turtle, E. P.; et al.; Enceladus, Curiouser and Curiouser: Observations by Cassini's Imaging Science Subsystem, Cassini CHARM Teleconference, 28 April 2005
  34. ^ Barnash, A. N.; et al.; (2006); Interactions Between Impact Craters and Tectonic Fractures on Enceladus, Bulletin of the American Astronomical Society, Vol. 38, No. 3, presentation no. 24.06
  35. ^ Without samples to provide absolute age determinations, crater counting is currently the only method for determining surface age on most planetary surfaces. Unfortunately, there is currently disagreement in the scientific community regarding the flux of impactors in the outer solar system. These competing models can significantly alter the age estimate even with the same crater counts. For the sake of completeness, both age estimates from Porco et al. 2006 are provided.
  36. ^ a b c Nimmo, F.; and Pappalardo, R. T.; (2006); Diapir-induced reorientation of Saturn's moon Enceladus, Nature, Vol. 441, pp. 614–616
  37. ^ a b Enceladus in False Color. Retrieved March 22, 2006.
  38. ^ Cassini Finds Enceladus Tiger Stripes are Really Cubs, 30 August 2005. Retrieved May 29, 2006.
  39. ^ Brown, R. H.; et al.; (2006); Composition and Physical Properties of Enceladus' Surface, Science, Vol. 311, No. 5766, pp. 1425–1428
  40. ^ Boulder-Strewn Surface. Retrieved March 22, 2006.
  41. ^ a b NASA's Cassini Images Reveal Spectacular Evidence of an Active Moon, 6 December 2005. Retrieved March 22, 2006.
  42. ^ Spray Above Enceladus. Retrieved March 22, 2005
  43. ^ a b Cassini Tastes Organic Material at Saturn's Geyser Moon, 26 March 2008. Retrieved March 26, 2008.
  44. ^ A Perspective on Life on Enceladus: A World of Possibilities, 26 March 2008. Retrieved March 26, 2008.
  45. ^ Kieffer, Susan W.; Lu, Xinli; Bethke, Craig M.; Spencer, John R.; Marshak, Stephen; and Navrotsky, Alexandra (2006). "A Clathrate Reservoir Hypothesis for Enceladus' South Polar Plume". Science 314 (5806): 1764–1766. doi:10.1126/science.1133519. 
  46. ^ Castillo, J. C.; et al.; (2005); {{subst:sup|26}}Al in the Saturnian System - New Interior Models for the Saturnian satellites, Eos Transactions AGU, Vol. 82, No. 52 (Fall Meeting Supplement), abstract P32A-01
  47. ^ Castillo, J. C.; et al.; (2006); A New Understanding of the Internal Evolution of Saturnian Icy Satellites from Cassini Observations, 37th Annual Lunar and Planetary Science Conference, Abstract 2200
  48. ^ a b Schubert, G.; et al.; (2007); Enceladus: Present Internal Structure and Differentiation by Early and Long Term Radiogenic Heating, Icarus, in press
  49. ^ Matson, D. L.; et al.; (2006); Enceladus' Interior and Geysers - Possibility for Hydrothermal Geometry and N{{subst:sub|2}} Production, 37th Annual Lunar and Planetary Science Conference, abstract 2219
  50. ^ The angular diameter of Saturn from Enceladus in radians is calculated by dividing the diameter of Saturn (from the Saturn article) by the semimajor axis of Enceladus' orbit. To convert this to [[degree (angle)|]]s, multiply by 180/pi. (More accurately, the angular diameter is twice the arcsine of the radius of Saturn divided by the distance; this reduces to the previously-given expression as long as the radius is small compared to the distance, which is true for the case of Saturn and Enceladus.) The same calculation technique can be used to calculate the size of other objects in the sky seen from Enceladus.

  Results from FactBites:
 
Saturn's Moon Enceladus (4914 words)
It is postulated that Enceladus is heated by a tidal mechanism similar to Jupiter's moon Io.
Enceladus is one of the coldest places in the Saturn system because its extremely bright surface reflects 80 percent of the sunlight that hits it, so only 20 percent is available to heat the surface.
The relatively dense accumulation of impact craters implies that this terrain is among the oldest on the moon's surface.
Enceladus (moon) - Wikipedia, the free encyclopedia (5708 words)
Enceladus was discovered by Fredrick William Herschel on August 28, 1789, during the first use of his new 1.2-meter telescope, then the largest in the world.
Enceladus orbits Saturn at a distance of 238,000 km from the planet's center and 180,000 km from its surface, between the orbits of Mimas and Tethys, requiring 32.9 hours to revolve once (fast enough for its motion to be observed over a single night of observation).
Moreover, since Enceladus rotates synchronously with its orbital period and therefore keeps one face pointed toward Saturn, the planet never moves in Enceladus' sky (albeit with slight variations coming from the orbit's eccentricity), and cannot be seen from the far side of the satellite.
  More results at FactBites »

 
 

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