- History Discovery Naming
- Orbit and rotation Source of the E ring
- Geology Surface features Impact craters Tectonic features Smooth plains South polar region Internal structure Subsurface water ocean South polar plumes Possible heat sources Tidal heating Radioactive heating Chemistry
- Shape and size
- Origin Mimas–Enceladus paradox Proto-Enceladus hypothesis Date of formation
- Potential habitability Hydrothermal vents
- Exploration Voyager missions Cassini Proposed mission concepts
- See also
- Notes
- References
- Further reading
- External links
| name = Enceladus
| pronounced = {{IPAc-en|ɛ|n|ˈ|s|ɛ|l|ə|d|ə|s}}
| alt_names = Saturn II[1]
| adjectives = Enceladean, Enceladan
| image = PIA17202 - Approaching Enceladus.jpg
| image_size = 280
| caption = View of trailing hemisphere in natural color
| note = yes
| discoverer = William Herschel
| discovered = August 28, 1789[4]
| semimajor = {{val|237948|u=km}}[5]
| eccentricity = {{val|0.0047}}[5][7]
| period = {{val|1.370218|u=days}}[5]
| inclination = 0.009° (to Saturn's equator)[5]
| satellite_of = Saturn
| dimensions = 513.2 × 502.8 × 496.6 km[5][11]
| mean_radius = {{val|252.1|0.2|u=km}}[5][11] ({{val|0.0395}} Earths, {{val|0.1451}} Moons)
| mass = {{val|1.08022|0.00101|e=20|u=kg}}[5][15] (1.8{{e|-5}} Earths)
| density = {{val|1.609|0.005|u=g/cm3}}[5][11]
| surface_grav = {{Gr|0.108|252.1|3}} m/s2 ({{val|0.0113}} g)
| moment_of_inertia_factor = ~0.335[2] (estimate)
| escape_velocity = {{V2|0.108|252.1|3}} km/s (860.4 km/h)[5]
| rotation = Synchronous
| axial_tilt = 0
| albedo = {{val|1.375|0.008}} (geometric at 550 nm)[20] or {{val|0.81|0.04}} (Bond)[21]
| magnitude = 11.7[22]
| temp_name1 = Kelvin[3]
| min_temp_1 = 32.9 K
| mean_temp_1 = 75 K
| max_temp_1 = 145 K
| temp_name2 = Celsius
| min_temp_2 = −240 °C
| mean_temp_2 = −198 °C
| max_temp_2 = −128 °C
| atmosphere = Trace (water vapor)
| surface_pressure = Trace, significant spatial variability[4][5]
| atmosphere_composition = 91% water vapor
4% nitrogen
3.2% carbon dioxide
1.7% methane[6]
}}
Enceladus ({{IPAc-en|ɛ|n|ˈ|s|ɛ|l|ə|d|ə|s}}; {{respell|en|SEL|ə-dəs}})[7] is the sixth-largest moon of Saturn. It is about {{convert|500|km|sp=us}} in diameter,[8] 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 {{convert|-198|°C|0|abbr=on}}, 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.
Enceladus was discovered on August 28, 1789, by William Herschel,[9][10][31] but little was known about it until the two Voyager spacecraft, Voyager 1 and Voyager 2, passed nearby in the early 1980s.[32] In 2005, the Cassini spacecraft started multiple close flybys of Enceladus, revealing its surface and environment in greater detail. In particular, Cassini discovered water-rich plumes venting from the south polar region.[11] Cryovolcanoes near the south pole shoot geyser-like jets of water vapor, molecular hydrogen, other volatiles, and solid material, including sodium chloride crystals and ice particles, into space, totaling about {{convert|200|kg|lb|abbr=on}} per second.[5][12][13] Over 100 geysers have been identified.[14] Some of the water vapor falls back as "snow"; the rest escapes, and supplies most of the material making up Saturn's E ring.[15][16] According to NASA scientists, the plumes are similar in composition to comets.[17] In 2014, NASA reported that Cassini found evidence for a large south polar subsurface ocean of liquid water with a thickness of around {{convert|10|km|0|abbr=on}}.[41][42][43]
These geyser observations, along with the finding of escaping internal heat and very few (if any) impact craters in the south polar region, show that Enceladus is currently geologically active. Like many other satellites in the extensive systems of the giant planets, Enceladus is trapped in an orbital resonance. Its resonance with Dione excites its orbital eccentricity, which is damped by tidal forces, tidally heating its interior and driving the geological activity.[18]
On 27 June 2018, scientists reported the detection of complex macromolecular organics on Enceladus' jet plumes, as sampled by the Cassini orbiter.[45][46]
History
Discovery
Enceladus was discovered by William Herschel on August 28, 1789, during the first use of his new {{convert|1.2|m|in|abbr=on}} 40-foot telescope, then the largest in the world, at Observatory House in Slough, England.[19][20] Its faint apparent magnitude (HV = +11.7) and its proximity to the much brighter Saturn and Saturn's rings make Enceladus difficult to observe from Earth with smaller telescopes. Like many satellites of Saturn discovered prior to the Space Age, Enceladus was first observed during a Saturnian equinox, when Earth is within the ring plane. At such times, the reduction in glare from the rings makes the moons easier to observe.[1] Prior to the Voyager missions the view of Enceladus improved little from the dot first observed by Herschel. Only its orbital characteristics were known, with estimations of its mass, density and albedo.
Naming
Enceladus is named after the giant Enceladus of Greek mythology.[9] The name, 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.[21] He chose these names because Saturn, known in Greek mythology as Cronus, was the leader of the Titans.
Features on Enceladus are named by the International Astronomical Union (IAU) after characters and places from Burton's translation of The Book of One Thousand and One Nights.[22] Impact craters are named after characters, whereas other feature types, such as fossae (long, narrow depressions), dorsa (ridges), planitiae (plains), sulci (long parallel grooves), and rupes (cliffs) are named after places. The IAU has officially named 85 features on Enceladus, most recently Samaria Rupes, formerly called Samaria Fossa.[23][24]
Orbit and rotation
Enceladus is one of the major inner satellites of Saturn along with Dione, Tethys, and Mimas. It orbits at 238,000 km from Saturn's center and 180,000 km from its cloud tops, between the orbits of Mimas and Tethys. It orbits Saturn every 32.9 hours, 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 around Saturn for every one orbit completed by Dione. This resonance maintains Enceladus's orbital eccentricity (0.0047), which is known as a forced eccentricity. This non-zero eccentricity results in tidal deformation of Enceladus. The dissipated heat resulting from this deformation is the main heating source for Enceladus's geologic activity.[7] Enceladus orbits within the densest part of Saturn's E ring, the outermost of its major rings, and is the main source of the ring's material composition.[25]
Like most of Saturn's larger satellites, Enceladus rotates synchronously with its orbital period, keeping one face pointed toward Saturn. Unlike Earth's Moon, Enceladus does not appear to librate more than 1.5° about its spin axis. However, analysis of the shape of Enceladus suggests that at some point it was in a 1:4 forced secondary spin–orbit libration.[7] This libration could have provided Enceladus with an additional heat source.[18]
[26][27]Source of the E ring
Plumes from Enceladus, which are similar in composition to comets,[17] have been shown to be the source of the material in Saturn's E ring.[15] 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 distributed between the orbits of Mimas and Titan.[28]
Mathematical models show that the E ring is unstable, with a lifespan between 10,000 and 1,000,000 years; therefore, particles composing it must be constantly replenished.[29] Enceladus is orbiting inside the ring, at its narrowest but highest density point. In the 1980s some suspected that Enceladus is the main source of particles for the ring.[30][31][32][33] This hypothesis was confirmed by Cassini's first two close flybys in 2005.[34][35]
{{clear}}|image = Saturn's Rings PIA03550.jpg
|image-width = 700
|width = 700
|height = 200
|float = none
|annotations =
|caption =
Geology
Surface features
{{see also|List of geological features on Enceladus}}Voyager 2 was the first spacecraft to observe Enceladus's surface in detail, in August 1981. Examination of the resulting highest-resolution imagery revealed 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.[71] In addition, extensive linear cracks[36] 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.[37] The fresh, clean ice that dominates its surface gives Enceladus the most reflective surface of any body in the Solar System, with a visual geometric albedo of 1.38[20] and bolometric Bond albedo of {{val|0.81|0.04}}.[21] Because it reflects so much sunlight, its surface only reaches a mean noon temperature of {{convert|−198|°C|0|abbr=on}}, somewhat colder than other Saturnian satellites.[3]Observations during three flybys by Cassini on February 17, March 9, and July 14, 2005, revealed Enceladus' surface features in much greater detail than the Voyager 2 observations. The smooth plains, which Voyager 2 had observed, resolved into relatively crater-free regions filled with numerous small ridges and scarps. Numerous fractures were found within the older, cratered terrain, suggesting that the surface has been subjected to extensive deformation since the craters were formed.[38] Some areas contain no craters, indicating major resurfacing events in the geologically recent past. There are fissures, plains, corrugated terrain and other crustal deformations. 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.[7] All of this indicates that Enceladus's interior may be liquid today, even though it should have been frozen long ago.[37]
{{clear}}|image = PIA08409 North Polar Region of Enceladus.jpg
|image-width = 600
|width = 600
|height = 300
|float = none
|annotations =
|caption =
|image = Color map of Enceladus PIA18435 Nov. 2014 full size.jpg
|image-width = 600
|width = 600
|height = 305
|float = none
|annotations =
|caption =
|image = Color polar maps of Enceladus PIA18435 Nov. 2014 full size.jpg
|image-width = 600
|width = 600
|height = 295
|float = none
|annotations =
|caption =
northern and southern hemispheres of Enceladus
|image = PIA18435-SaturnMoon-Enceladus-20141104-fig2.jpg
|image-width = 600
|width = 600
|height = 300
|float = none
|annotations =
|caption =
trailing and leading hemispheres of Enceladus
Impact craters
Impact cratering is a common occurrence on many Solar System bodies. Much of Enceladus' surface is covered with craters at various densities and levels of degradation.[39] This subdivision of cratered terrains on the basis of crater density (and thus surface age) suggests that Enceladus has been resurfaced in multiple stages.[37]Cassini observations provided a much closer look at the crater distribution and size, showing that many of Enceladus' craters are heavily degraded through viscous relaxation and fracturing.[40] Viscous relaxation allows gravity, over geologic time scales, to deform craters and other topographic features formed in water ice, 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. Dunyazad crater is a prime example of a viscously relaxed crater on Enceladus, with a prominent domed floor.[41]Tectonic features
Voyager 2 found several types of tectonic features on Enceladus, including troughs, scarps, and belts of grooves and ridges.[71] Results from Cassini suggest that tectonics is the dominant mode of deformation on Enceladus, including rifts, one of the more dramatic types of tectonic features that were noted. These canyons can be up to 200 km long, 5–10 km wide, and 1 km deep. Such features are geologically young, because they cut across other tectonic features and have sharp topographic relief with prominent outcrops along the cliff faces.[42]Evidence of tectonics on Enceladus is also derived from grooved terrain, consisting of lanes of curvilinear grooves and ridges. These bands, first discovered by Voyager 2, often separate smooth plains from cratered regions.[71] Grooved terrains such as the Samarkand Sulci are reminiscent of grooved terrain on Ganymede. However, unlike those seen on Ganymede, grooved topography on Enceladus is generally more complex. Rather than parallel sets of grooves, these lanes often appear as bands of crudely aligned, chevron-shaped features. In other areas, these bands bow upwards with fractures and ridges running the length of the feature. Cassini observations of the Samarkand Sulci have revealed dark spots (125 and 750 m wide) located parallel to the narrow fractures. Currently, these spots are interpreted as collapse pits within these ridged plain belts.[40]
In addition to deep fractures and grooved lanes, Enceladus has several other types of tectonic terrain. Many of these fractures are found in bands cutting across cratered terrain. These fractures probably propagate down only a few hundred meters into the crust. Many have probably been influenced during their formation by the weakened regolith produced by impact craters, often changing the strike of the propagating fracture.[40][43] 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. These linear grooves can be seen cutting across other terrain types, like the groove and ridge belts. Like the deep rifts, they are among the youngest features on Enceladus. However, some linear grooves have been softened like the craters nearby, suggesting that they are older. Ridges have also been observed on Enceladus, though not nearly to the extent as those seen on Europa. These ridges are relatively limited in extent and are up to one kilometer tall. One-kilometer high domes have also been observed.[40] Given the level of resurfacing found on Enceladus, it is clear that tectonic movement has been an important driver of geology for much of its history.[42]
Smooth plains
Two regions of smooth plains were observed by Voyager 2. They generally have low relief and have far fewer craters than in the cratered terrains, indicating a relatively young surface age.[39] 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 these regions filled with low-relief ridges and fractures, probably caused by shear deformation.[40] The high-resolution images of Sarandib Planitia 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.[7]
The expanded surface coverage provided by Cassini has allowed for the identification of additional regions of smooth plains, particularly on Enceladus's leading hemisphere (the side of Enceladus that faces the direction of motion as it 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 Enceladus from Sarandib and Diyar Planitiae, suggesting that the placement of these regions is influenced by Saturn's tides on Enceladus.[44]
South polar region
{{See also|Tiger stripes (Enceladus)}}Images taken by Cassini during the flyby on July 14, 2005, revealed a distinctive, tectonically deformed region surrounding Enceladus's south pole. This area, reaching as far north as 60° south latitude, is covered in tectonic fractures and ridges.[7][45] 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 some regions of the south polar terrain are possibly as young as 500,000 years or less.[7] Near the center of this terrain are four fractures bounded by ridges, unofficially called "tiger stripes". They 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.[45] 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 the 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.[46] VIMS also detected simple organic (carbon-containing) compounds in the tiger stripes, chemistry not found anywhere else on Enceladus thus far.[47] And in 27 June 2018, scientists reported the detection of complex macromolecular organics on Enceladus' jet plumes, as sampled by the Cassini orbiter.[48][49]
One of these areas of "blue" ice in the south polar region was observed at high resolution during the July 14, 2005 flyby, revealing an area of extreme tectonic deformation and blocky terrain, with some areas covered in boulders 10–100 m across.[50]
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 suggest they are caused by changes in the overall shape of Enceladus. As of 2006 there were two theories for what could cause such a shift in shape: the orbit of Enceladus may have migrated inward, leading to an increase in Enceladus's rotation rate. Such a shift would lead to a more oblate shape;[7] or a rising mass of warm, low-density material in Enceladus's interior may have led to a shift in the position of the current south polar terrain from Enceladus's southern mid-latitudes to its south pole.[44] Consequently, the moon's ellipsoid shape would have adjusted to match the new orientation. One problem of the polar flattening hypothesis is that both polar regions should have similar tectonic deformation histories.[7] However, the north polar region is densely cratered, and has a much older surface age than the south pole.[39] Thickness variations in Enceladus's 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.[7]
Internal structure
Before the Cassini mission, little was known about the interior of Enceladus. However, flybys by Cassini provided information for models of Enceladus's interior, including a better determination of the mass and shape, high-resolution observations of the surface, and new insights on the interior.[51][52]
Mass estimates from the Voyager program missions suggested that Enceladus was composed almost entirely of water ice.[71] 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.[7] This density is higher than Saturn's other mid-sized icy satellites, indicating that Enceladus contains a greater percentage of silicates and iron.
Castillo et al. (2005) suggested that Iapetus and the other icy satellites of Saturn formed relatively quickly after the formation of the Saturnian subnebula, and thus were rich in short-lived radionuclides.[53][54] 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's comparatively high rock–mass fraction, given its small size.[55] 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.[56][54] Subsequent radioactive and tidal heating would raise the temperature of the core to 1,000 K, enough to melt the inner mantle. However, for Enceladus to still be active, part of the core must have also melted, 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 and would power the current geological activity.[27][57]
In addition to its mass and modeled geochemistry, researchers have also examined Enceladus's shape to determine if it is differentiated. Porco et al. (2006) used limb measurements to determine that its shape, assuming hydrostatic equilibrium, is consistent with an undifferentiated interior, in contradiction to the geological and geochemical evidence.[7] 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).[56] Gravity measurements by Cassini show that the density of the core is low, indicating that the core contains water in addition to silicates.[125]
Subsurface water ocean
Evidence of liquid water on Enceladus began to accumulate in 2005, when scientists observed plumes containing water vapor spewing from its south polar surface,[7][59] with jets moving 250 kg of water vapor every second[59] at up to {{convert|2189|km/h|mph|abbr=on}} into space.[60] Soon after, in 2006 it was determined that Enceladus's plumes are the source of Saturn's E Ring.[7][34] The sources of salty particles are uniformly distributed along the tiger stripes, whereas sources of "fresh" particles are closely related to the high-speed gas jets. The "salty" particles are heavier and mostly fall back to the surface, whereas the fast "fresh" particles escape to the E ring, explaining its salt-poor composition of 0.5–2% of sodium salts by mass.[61] The plumes' "salty" composition indicates that the source is a salty subsurface ocean.[62] Cassini also found traces of simple organic compounds in some dust grains,[61][63] as well as organics such as benzene ({{chem|C|6|H|6}}),[64] and complex macromolecular organics as large as 200 atomic mass units,[48] and at least 15 carbon atoms in size.[65]
Gravimetric data from Cassinis December 2010 flybys showed that Enceladus likely has a liquid water ocean beneath its frozen surface, but at the time it was thought the subsurface ocean was limited to the south pole.[66][67][68][69] The top of the ocean probably lies beneath a {{convert|30|to|40|km|mi|sp=us}} thick ice shelf. The ocean may be {{convert|10|km|mi|sp=us}} deep at the south pole.[66][70]
Measurements of Enceladus's "wobble" as it orbits Saturn—called libration—suggests that the entire icy crust is detached from the rocky core and therefore that a global ocean is present beneath the surface.[71] The amount of libration (0.120° ± 0.014°) implies that this global ocean is about 26 to 31 kilometers (16-19 mi) deep.[72][73][74][75] For comparison, Earth's ocean has an average depth of 3.7 kilometers.[74]
A model suggests that Enceladus's salty ocean (-Na, -Cl, -CO3) has an alkaline pH of 11 to 12.[76][77] The high pH is interpreted to be a consequence of serpentinization of chondritic rock that leads to the generation of H2, a geochemical source of energy that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in Enceladus's plumes.[76][78]
South polar plumes
{{See also|Cryovolcano}}Following Voyager's encounters with Enceladus in the early 1980s, scientists postulated that it may be geologically active based on its young, reflective surface and location near the core of the E ring.[71] Based on the connection between Enceladus and the E ring, scientists suspected that Enceladus was the source of material in the E ring, perhaps through venting of water vapor.[30][31] Readings from Cassini's 2005 passage suggested that cryovolcanism, where water and other volatiles are the materials erupted instead of silicate rock, had been discovered on Enceladus. The first Cassini sighting of a plume of icy particles above Enceladus's south pole came from the Imaging Science Subsystem (ISS) images taken in January and February 2005,[7] though the possibility of a camera artifact delayed 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 a planetary atmosphere. 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 waves' frequency can be used to identify their composition, in this case ionized water vapor.[4] During the two following 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.[4] 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 over the equatorial region, but did detect water vapor during an occultation over the south polar region during the July encounter.[5]
Fortuitously, Cassini flew through this gas cloud during the July 14 encounter, allowing instruments such as the ion and neutral mass spectrometer (INMS) and the cosmic dust analyzer (CDA) to directly sample the plume. INMS measured the composition of the gas cloud, detecting mostly water vapor, as well as traces of molecular nitrogen, methane, and carbon dioxide.[6] The CDA "detected a large increase in the number of particles near Enceladus", confirming Enceladus as the primary source for the E ring.[34] Analysis of the CDA and INMS data suggest that the gas cloud Cassini flew through during the July encounter, and observed from a distance with its magnetometer and UVIS, was actually a water-rich cryovolcanic plume, originating from vents near the south pole.[79]
Visual confirmation of venting came in November 2005, when ISS imaged geyser-like jets of icy particles rising from Enceladus's south polar region.[7][16] (Although the plume was imaged before, in January and February 2005, additional studies of the camera's response at high phase angles, when the Sun is almost behind Enceladus, and comparison with equivalent high-phase-angle images taken of other Saturnian satellites, were required before this could be confirmed.[80]) The November 2005 images showed the plume's fine structure, revealing numerous jets (perhaps issuing from numerous distinct vents) within a larger, faint component extending out nearly 500 km from the surface.[79] The particles have a bulk velocity of 1.25 ±0.1 km/s,[81] and a maximum velocity of 3.40 km/s.[82] 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.
Observations during a flyby on March 12, 2008, revealed additional chemicals in the plume, including trace amounts of simple hydrocarbons such as methane, propane, acetylene and formaldehyde.[83][84] The plumes' composition, as measured by the INMS, is similar to that seen at most comets.[84]
In 2015, the Cassini probe made a close fly-by of Enceladus' south pole, flying within 48.3 km (30 mi) of the surface, and through a plume. Its mass spectrometer detected molecular hydrogen which was in "thermodynamic disequilibrium" with the other components.[85]
The combined analysis of imaging, mass spectrometry, and magnetospheric data suggests that the observed south polar plume emanates from pressurized subsurface chambers, similar to Earth's geysers.[7] The mechanism that drives and sustains the eruptions is thought to be tidal heating.[86] The intensity of the eruption of the south polar jets varies significantly as a function of the position of Enceladus in its orbit. The plumes are about four times brighter when Enceladus is at apoapsis (the point in its orbit most distant from Saturn) than when it is at periapsis.[87][88][89] This is consistent with geophysical calculations which predict the south polar fissures are under compression near periapsis, pushing them shut, and under tension near apoapsis, pulling them open.[90]
Much of the plume activity consists of broad curtain-like eruptions. Optical illusions from a combination of viewing direction and local fracture geometry previously made the plumes look like discrete jets.[91][92][93]
The extent to which cryovolcanism really occurs is a subject of some debate, as water, being denser than ice by about 8%, has difficulty erupting under normal circumstances. At Enceladus, it appears that cryovolcanism occurs because water-filled cracks are periodically exposed to vacuum, the cracks being opened and closed by tidal stresses.[94][95][96]
Possible heat sources
During the flyby of July 14, 2005, the Composite Infrared Spectrometer (CIRS) found a warm region near the south pole. Temperatures in this region ranged from 85–90 K, with small areas showing as high as {{convert|157|K|°C|abbr=on}}, much too warm to be explained by solar heating, indicating that parts of the south polar region are heated from the interior of Enceladus.[3] The presence of a subsurface ocean under the south polar region is now accepted,[97] but it cannot explain the source of the heat, with an estimated heat flux of 200 mW/m2, which is about 10 times higher than that from radiogenic heating alone.[98]
Several explanations for the observed elevated temperatures and the resulting plumes have been proposed, including venting from a subsurface reservoir of liquid water, sublimation of ice,[99] decompression and dissociation of clathrates, and shear heating,[100] but a complete explanation of all the heat sources causing the observed thermal power output of Enceladus has not yet been settled.
Heating in Enceladus has occurred through various mechanisms ever since its formation. Radioactive decay in its core may have initially heated it,[101] giving it a warm core and a subsurface ocean, which is now kept above freezing through an unidentified mechanism. Geophysical models indicate that tidal heating is a main heat source, perhaps aided by radioactive decay and some heat-producing chemical reactions.[102][103][104][105] A 2007 study predicted the internal heat of Enceladus, if generated by tidal forces, could be no greater than 1.1 gigawatts,[200] but data from Cassini's infrared spectrometer of the south polar terrain over 16 months, indicate that the internal heat generated power is about 4.7 gigawatts,[106] and suggest that it is in thermal equilibrium.[3][46][107]
The observed power output of 4.7 gigawatts is challenging to explain from tidal heating alone, so the main source of heat remains a mystery.[7][102] Most scientists think the observed heat flux of Enceladus is not enough to maintain the subsurface ocean, and therefore any subsurface ocean must be a remnant of a period of higher eccentricity and tidal heating, or the heat is produced through another mechanism.[108][208]
Tidal heating
Tidal heating occurs through the tidal friction processes: orbital and rotational energy are dissipated as heat in the crust of an object. In addition, to the extent that tides produce heat along fractures, libration may affect the magnitude and distribution of such tidal shear heating.[27] Tidal dissipation of Enceladus's ice crust is significant because Enceladus has a subsurface ocean. A computer simulation that used data from Cassini was published in November 2017, and it indicates that friction heat from the sliding rock fragments within the permeable and fragmented core of Enceladus could keep its underground ocean warm for up to billions of years.[109][110][111] It is thought that if Enceladus had a more eccentric orbit in the past, the enhanced tidal forces could be sufficient to maintain a subsurface ocean, such that a periodic enhancement in eccentricity could maintain a subsurface ocean that periodically changes in size.[112] A more recent analysis claimed that "a model of the tiger stripes as tidally flexed slots that puncture the ice shell can simultaneously explain the persistence of the eruptions through the tidal cycle, the phase lag, and the total power output of the tiger stripe terrain, while suggesting that eruptions are maintained over geological timescales."[86] Previous models suggest that resonant perturbations of Dione could provide the necessary periodic eccentricity changes to maintain the subsurface ocean of Enceladus, if the ocean contains a substantial amount of ammonia.[7] The surface of Enceladus indicates that the entire moon has experienced periods of enhanced heat flux in the past.[113]Radioactive heating
The "hot start" model of heating suggests Enceladus began as ice and rock that contained rapidly decaying short-lived radioactive isotopes of aluminium, iron and manganese. Enormous amounts of heat were then produced as these isotopes decayed for about 7 million years, resulting in the consolidation of rocky material at the core surrounded by a shell of ice. Although the heat from radioactivity would decrease over time, the combination of radioactivity and tidal forces from Saturn's gravitational tug could prevent the subsurface ocean from freezing.[101] The present-day radiogenic heating rate is 3.2{{E-sp|15}} ergs/s (or 0.32 gigawatts), assuming Enceladus has a composition of ice, iron and silicate materials.[7] Heating from long-lived radioactive isotopes uranium-238, uranium-235, thorium-232 and potassium-40 inside Enceladus would add 0.3 gigawatts to the observed heat flux.[102] The presence of Enceladus's regionally thick subsurface ocean suggests a heat flux ~10 times higher than that from radiogenic heating in the silicate core.[81]
Chemistry
Because no ammonia was initially found in the vented material by INMS or UVIS, which could act as an antifreeze, it was thought such a heated, pressurized chamber would consist of nearly pure liquid water with a temperature of at least {{convert|270|K|°C|abbr=on}}, because pure water requires more energy to melt.
In July 2009 it was announced that traces of ammonia had been found in the plumes during flybys in July and October 2008.[114][115] Reducing the freezing point of water with ammonia would also allow for outgassing and higher gas pressure,[116] and less heat required to power the water plumes.[117] The subsurface layer heating the surface water ice could be an ammonia–water slurry at temperatures as low as {{convert|170|K|°C|abbr=on}}, and thus less energy is required to produce the plume activity.
However, the observed 4.7 gigawatts heat flux is enough to power the cryovolcanism without the presence of ammonia.[106][117]
Shape and size
Enceladus is a relatively small satellite composed of ice and rock.[118] It is a scalene ellipsoid in shape; its diameters, calculated from images taken by Cassini's ISS (Imaging Science Subsystem) instrument, are {{nowrap|513 km}} between the sub- and anti-Saturnian poles, {{nowrap|503 km}} between the leading and trailing hemispheres, and {{nowrap|497 km}} between the north and south poles.[7] Enceladus is only one-seventh the diameter of Earth's Moon. It ranks sixth in both mass and size among the satellites of Saturn, after Titan ({{nowrap|5,150 km}}), Rhea ({{nowrap|1,530 km}}), Iapetus ({{nowrap|1,440 km}}), Dione ({{nowrap|1,120 km}}) and Tethys ({{nowrap|1,050 km}}).[119][120]
Origin
Mimas–Enceladus paradox
Mimas, the innermost of the round moons of Saturn and directly interior to Enceladus, is a geologically dead body, even though it should experience stronger tidal forces than Enceladus. This apparent paradox can be explained in part by temperature-dependent properties of water ice (the main constituent of the interiors of Mimas and Enceladus). The tidal heating per unit mass is given by the formula
, where ρ is the (mass) density of the satellite, n is its mean orbital motion, r is the satellite's radius, e is the orbital eccentricity of the satellite, μ is the shear modulus and Q is the dimensionless dissipation factor. For a same-temperature approximation, the expected value of qtid for Mimas is about 40 times that of Enceladus. However, the material parameters μ and Q are temperature dependent. At high temperatures (close to the melting point), μ and Q are low, so tidal heating is high. Modeling suggests that for Enceladus, both a 'basic' low-energy thermal state with little internal temperature gradient, and an 'excited' high-energy thermal state with a significant temperature gradient, and consequent convection (endogenic geologic activity), once established, would be stable. For Mimas, only a low-energy state is expected to be stable, despite its being closer to Saturn. So the model predicts a low-internal-temperature state for Mimas (values of μ and Q are high) but a possible higher-temperature state for Enceladus (values of μ and Q are low).[121] Additional historical information is needed to explain how Enceladus first entered the high-energy state (e.g. more radiogenic heating or a more eccentric orbit in the past).[122]The significantly higher density of Enceladus relative to Mimas (1.61 vs. 1.15 g/cm3), implying a larger content of rock and more radiogenic heating in its early history, has also been cited as an important factor in resolving the Mimas paradox.[123]
It has been suggested that for an icy satellite the size of Mimas or Enceladus to enter an 'excited state' of tidal heating and convection, it would need to enter an orbital resonance before it lost too much of its primordial internal heat. Because Mimas, being smaller, would cool more rapidly than Enceladus, its window of opportunity for initiating orbital resonance-driven convection would have been considerably shorter.[234]
Proto-Enceladus hypothesis
Enceladus is losing mass at a rate of 200 kg/second. If mass loss at this rate continued for 4.5 Gyr, the satellite would have lost approximately 30% of its initial mass. A similar value is obtained by assuming that the initial densities of Enceladus and Mimas were equal.[124] It suggests that tectonics in the south polar region is probably mainly related to subsidence and associated subduction caused by the process of mass loss.[124]
Date of formation
In 2016, a study of how the orbits of Saturn's moons should have changed due to tidal effects suggested that all of Saturn's satellites inward of Titan, including Enceladus (whose geologic activity was used to derive the strength of tidal effects on Saturn's satellites), may have formed as little as 100 million years ago.[125]
Potential habitability
Enceladus ejects plumes of salt water that are laced with grains of silica-rich sand,[126] nitrogen (in ammonia),[239] and organic molecules, including trace amounts of simple hydrocarbons such as methane ({{chem|C|H|4}}), propane ({{chem|C|3|H|8}}), acetylene ({{chem|C|2|H|2}}) and formaldehyde ({{chem|C|H|2|O}}), which are carbon-bearing molecules.[83][84][127] This indicates that hydrothermal activity—an energy source—may be at work in Enceladus's subsurface ocean.[126][128] In addition, models indicate the large rocky core is porous, allowing water to flow through it to pick up heat.[129][130][131] Molecular hydrogen ({{chem|H|2}}), a geochemical source of energy that can be metabolized by methanogen microbes to provide energy for life, could be present if, as models suggest, Enceladus's salty ocean has an alkaline pH from serpentinization of chondritic rock.[76][77][78]
The presence of an internal global salty ocean with an aquatic environment supported by global ocean circulation patterns,[129] with an energy source and complex organic compounds[48] in contact with Enceladus's rocky core,[67][68][132] may advance the study of astrobiology and the study of potentially habitable environments for microbial extraterrestrial life.[66][69][70][133][134][135] The presence of a wide range of organic compounds and ammonia indicates their source may be similar to the water/rock reactions known to occur on Earth and that are known to support life.[136] Therefore, several robotic missions have been proposed to further explore Enceladus and assess its habitability; some of the proposed missions are: Journey to Enceladus and Titan (JET), Enceladus Explorer (En-Ex), Enceladus Life Finder (ELF), Life Investigation For Enceladus (LIFE), and Enceladus Life Signatures and Habitability (ELSAH).
Hydrothermal vents
On April 13, 2017, NASA announced the discovery of possible hydrothermal activity on Enceladus' sub-surface ocean floor. In 2015, the Cassini probe made a close fly-by of Enceladus' south pole, flying within 48.3 km (30 mi) of the surface, as well as through a plume in the process. A mass spectrometer on the craft detected molecular hydrogen (H2) from the plume, and after months of analysis, the conclusion was made that the hydrogen was most likely the result of hydrothermal activity beneath the surface.[137] It has been speculated that such activity could be a potential oasis of habitability.[138][139][140]
The presence of ample hydrogen in Enceladus's ocean means that microbes – if any exist there – could use it to obtain energy by combining the hydrogen with carbon dioxide dissolved in the water. The chemical reaction is known as "methanogenesis" because it produces methane as a byproduct, and is at the root of the tree of life on Earth, the birthplace of all life that is known to exist.[141][142]
Exploration
Voyager missions
{{Main|Voyager program}}The two Voyager spacecraft made 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.[143] Images acquired from this distance had very poor spatial resolution, but revealed a highly reflective surface devoid of impact craters, indicating a youthful surface.[144] 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's surface.[144]
Voyager 2 passed closer to Enceladus (87,010 km) on August 26, 1981, allowing higher-resolution images to be obtained.[143] These images showed a young surface.[145] 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.
Cassini
{{Main|Cassini–Huygens}}{{multiple image|center|caption_align=center|header_align=center|align=center|header=Enceladus – Close Flyby (October 28, 2015)[146]|width= |direction=horizontal|image1=PIA17203-SaturnMoon-Enceladus-BeforeFlyby-20151028.jpg
|width1=200
|caption1=
|image2=PIA17204-SaturnMoon-Enceladus-UpClose-20151028.jpg
|width2=200
|caption2=
|image3=PIA17202-SaturnMoon-Enceladus-FlybyPlumes-20151028.jpg
|width3=200
|caption3=
|image4=PIA17205-SaturnMoon-Enceladus-AfterFlyby-20151028.jpg
|width4=220
|caption4=
}}{{multiple image|center|caption_align=center|header_align=center|align=center|header=Enceladus – Final Flyby (December 19, 2015)[147]|width= |direction=horizontal
|image1=PIA18347-SaturnMoon-Enceladus-CassiniHuygens-20150818.jpg
|width1=220
|caption1=
|image2=PIA17211-SaturnMoon-Enceladus-CloseFlyby-20151219.jpg
|width2=200
|caption2=
|image3=PIA17209-SaturnMoon-Enceladus-CloseFlyby-20151219.jpg
|width3=200
|caption3=
|image4=PIA20017-SaturnMoonEnceladus-DarkSpots-20151219.jpg
|width4=200
|caption4=Dark spots
|image5=PIA17210-SaturnMoon-Enceladus-CloseFlyby-20151219.jpg
|width5=200
|caption5=
}}
| Date | Distance (km) |
|---|---|
| February 17, 2005 | 1,264 |
| March 9, 2005 | 500 |
| July 14, 2005 | 175 |
| December 24, 2005 | 94,000 |
| March 12, 2008 | 48 |
| August 11, 2008 | 54 |
| October 9, 2008 | 25 |
| October 31, 2008 | 200 |
| November 2, 2009 | 103 |
| November 21, 2009 | 1,607 |
| April 28, 2010 | 103 |
| May 18, 2010 | 201 |
| August 13, 2010 | 2,554 |
| November 30, 2010 | 48 |
| December 21, 2010 | 50 |
| October 1, 2011 | 99 |
| October 19, 2011 | 1,231 |
| November 6, 2011 | 496 |
| March 27, 2012 | 74 |
| April 14, 2012 | 74 |
| May 2, 2012 | 74 |
| October 14, 2015 | 1,839 |
| October 28, 2015 | 49 |
| December 19, 2015 | 4,999 |
The answers to many remaining mysteries of Enceladus had to wait until the arrival of the Cassini spacecraft on July 1, 2004, when it entered 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. The flybys have yielded significant information concerning Enceladus's surface, as well as the discovery of water vapor with traces of simple hydrocarbons venting from the geologically active south polar region. These discoveries prompted the adjustment of Cassini's flight plan to allow closer flybys of Enceladus, including an encounter in March 2008 that took it to within 48 km of the surface.[149] Cassini's extended mission included seven close flybys of Enceladus between July 2008 and July 2010, including two passes at only 50 km in the later half of 2008.[150] Cassini performed a flyby on October 28, 2015, passing as close as {{convert|49|km|abbr=on}} and through a plume.[151] Confirmation of molecular hydrogen ({{chem|H|2|}}) would be an independent line of evidence that hydrothermal activity is taking place in the Enceladus seafloor, increasing its habitability.[78]
Cassini has provided strong evidence that Enceladus has an ocean with an energy source, nutrients and organic molecules, making Enceladus one of the best places for the study of potentially habitable environments for extraterrestrial life.[281][152] By contrast, the water thought to be on Jupiter's moon Europa is located under a much thicker layer of ice.[153]Proposed mission concepts
The discoveries Cassini made at Enceladus have prompted studies into follow-up mission concepts, including a probe flyby (Journey to Enceladus and Titan or JET) to analyze plume contents in-situ,[154][155] a lander by the German Aerospace Center to study the habitability potential of its subsurface ocean (Enceladus Explorer),[156][157][158] and two astrobiology-oriented mission concepts (the Enceladus Life Finder[159][160] and Life Investigation For Enceladus (LIFE)).[161][162][163][164]
The European Space Agency (ESA) was assessing concepts in 2008 to send a probe to Enceladus in a mission to be combined with studies of Titan: Titan Saturn System Mission (TSSM).[165] TSSM was a joint NASA/ESA flagship-class proposal for exploration of Saturn's moons, with a focus on Enceladus, and it was competing against the Europa Jupiter System Mission (EJSM) proposal for funding. In February 2009, it was announced that NASA/ESA had given the EJSM mission priority ahead of TSSM,[166] although TSSM will continue to be studied and evaluated.
In November 2017, Russian billionaire Yuri Milner expressed interest in funding a "low-cost, privately funded mission to Enceladus which can be launched relatively soon."[167][168] In September 2018, NASA and the Breakthrough Initiatives, founded by Milner, signed a cooperation agreement for the mission's initial concept phase.[169] The spacecraft would be low-cost, low mass, and would be launched at high speed on an affordable rocket. The spacecraft would be directed to perform a single flyby through Enceladus plumes in order to sample and analyze its content for biosignatures.[170][171] NASA will be providing scientific and technical expertise through various reviews, from March 2019 to December 2019.[172]
| Year proposed | Proponent | Project name | References |
|---|---|---|---|
| 2006 | GSFC NASA Academy | EAGLE study | [173] |
| 2006 | NASA | 'Titan and Enceladus $1B Mission Feasibility' Study | [174][175] |
| 2007 | NASA | 'Enceladus Flagship' study | [175] |
| 2007 | ESA | Titan and Enceladus Mission (TandEM) | [165] |
| 2007 | NASA JPL | Enceladus RMA Study | [176] |
| 2008 | NASA/ESA | TandEM became Titan Saturn System Mission (TSSM) | [165] |
| 2010 | PSDS Decadal Survey | Encedalus Orbiter | [177] |
| 2010 | NASA JPL | Journey to Enceladus and Titan (JET) | [178] |
| 2012 | DLR | Enceladus Explorer (EnEx) lander, employing the IceMole | [179] |
| 2012 | NASA JPL | Life Investigation For Enceladus (LIFE) | [163][180][181] |
| 2015 | NASA JPL | Enceladus Life Finder (ELF) | [182] |
| 2017 | ESA/NASA | Explorer of Enceladus and Titan (E2T) | [183] |
| 2017 | NASA | Enceladus Life Signatures and Habitability (ELSAH) | [184][185] |
| 2017 | Breakthrough Initiatives | Breakthrough Enceladus flyby study | [167] |
See also
{{Portal|Solar System}}- Enceladus in fiction
- List of geological features on Enceladus
- List of natural satellites
Notes
2. ^{{cite journal|last1= Iess|first1= L.|last2= Stevenson|first2=D. J.|last3= Parisi|first3= M.|last4= Hemingway|first4= D.|last5= Jacobson|first5=R. A.|last6= Lunine|first6=J. I.|last7= Nimmo|first7= F.|last8= Armstrong|first8=J. W.|last9= Asmar|first9=S. W.|last10= Ducci|first10= M.|last11= Tortora|first11= P.|title=The Gravity Field and Interior Structure of Enceladus |journal= Science|volume= 344|issue= 6179|year= 2014|pages= 78–80|doi= 10.1126/science.1250551|pmid=24700854|bibcode= 2014Sci...344...78I}}
3. ^1 2 3 {{cite journal|doi=10.1126/science.1121661|title=Cassini Encounters Enceladus: Background and the Discovery of a South Polar Hot Spot|date=2006|journal=Science|volume=311|pages=1401–5|pmid=16527965|issue=5766|bibcode=2006Sci...311.1401S|last=Spencer|first=J. R.|last2=Pearl|first2=J. C.|display-authors=etal}}
4. ^1 2 {{cite journal|doi=10.1126/science.1120985|title=Identification of a Dynamic Atmosphere at Enceladus with the Cassini Magnetometer|date=2006|journal=Science|volume=311|pages=1406–9|pmid=16527966|issue=5766|bibcode=2006Sci...311.1406D|last=Dougherty|first=M. K.|last2=Khurana|first2=K. K.|display-authors=etal}}
5. ^1 2 {{cite journal|doi=10.1126/science.1121254|title=Enceladus' Water Vapor Plume|date=2006|journal=Science|volume=311|pages=1422–5|pmid=16527971|issue=5766|bibcode=2006Sci...311.1422H|last=Hansen|first=Candice J.|last2=Esposito|first2=L.|display-authors=etal}}
6. ^1 {{cite journal|doi=10.1126/science.1121290|title=Cassini Ion and Neutral Mass Spectrometer: Enceladus Plume Composition and Structure|date=2006|journal=Science|volume=311|pages=1419–22|pmid=16527970|issue=5766|bibcode=2006Sci...311.1419W|last1=Waite|first1=J. H.|last2=Combi|first2=M. R.|display-authors=etal}}
7. ^* [https://www.ahdictionary.com/word/search.html?q=Enceladus "Enceladus" in the American Heritage Dictionary (2018)]* [https://www.merriam-webster.com/dictionary/Enceladus "Enceladus" in Merriam–Webster (2018)]* [https://en.oxforddictionaries.com/definition/Enceladus "Enceladus" in Oxford (2018)]
8. ^1 2 3 4 5 6 7 8 9 {{cite web|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Enceladus&Display=Facts|title=Solar System Exploration – Enceladus: Facts & Figures|publisher=NASA|date=August 12, 2013|accessdate=April 26, 2014|archiveurl=https://web.archive.org/web/20131016093801/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Enceladus&Display=Facts|archivedate=October 16, 2013 }}
9. ^1 2 {{cite web|url=http://planetarynames.wr.usgs.gov/append7.html|title=Planetary Body Names and Discoverers|work=Gazetteer of Planetary Nomenclature|publisher=USGS Astrogeology Science Center|accessdate=January 12, 2015}}
10. ^{{cite journal|last=Herschel|first=W.|title=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 Spheroidal Figure|url=http://rstl.royalsocietypublishing.org/content/80.toc|journal=Philosophical Transactions of the Royal Society of London|volume=80|date=January 1, 1790|doi=10.1098/rstl.1790.0004|pages=1–20}}
11. ^{{cite news|last=Chang|first=Kenneth|title=Suddenly, It Seems, Water Is Everywhere in Solar System|url=https://www.nytimes.com/2015/03/13/science/space/suddenly-it-seems-water-is-everywhere-in-solar-system.html|date=March 12, 2015|work=The New York Times|accessdate=March 13, 2015}}
12. ^1 {{cite web|url=http://www.cosmosmagazine.com/features/secret-life-saturns-moon-enceladus/|title=Secret life of Saturn's moon: Enceladus|work=Cosmos Magazine|last=Lovett|first=Richard A.|date=September 4, 2012|accessdate=August 29, 2013}}
13. ^{{Cite journal|last1=Spencer|first1=J. R.|last2=Nimmo|first2=F.|doi=10.1146/annurev-earth-050212-124025|title=Enceladus: An Active Ice World in the Saturn System|journal=Annual Review of Earth and Planetary Sciences|volume=41|pages=693–717|date=May 2013|bibcode=2013AREPS..41..693S}}
14. ^{{cite web|display-authors=etal|last=Dyches|first=Preston|last2=Brown|first2=Dwayne|title=Cassini Spacecraft Reveals 101 Geysers and More on Icy Saturn Moon|url=http://www.jpl.nasa.gov/news/news.php?release=2014-246&2|date=July 28, 2014|publisher=NASA|accessdate=July 29, 2014}}
15. ^1 {{cite news|url=http://www.nasa.gov/jpl/cassini/icy-tendrils-reaching-into-saturn-ring-traced-to-their-source/|title=Icy Tendrils Reaching into Saturn Ring Traced to Their Source|work=NASA News|date=April 14, 2015|accessdate=April 15, 2015}}
16. ^1 {{cite web|url= https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA08321|title=Ghostly Fingers of Enceladus|work=NASA/JPL/Space Science Institute|publisher=NASA|date=September 19, 2006|accessdate=April 26, 2014|archive-url=https://web.archive.org/web/20140427010559/http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2276#|archive-date=April 27, 2014|dead-url= no|df=mdy-all}}
17. ^1 {{cite web|last=Battersby|first=Stephen|title=Saturn's moon Enceladus surprisingly comet-like|url=https://www.newscientist.com/article/dn13541-saturns-moon-enceladus-surprisingly-cometlike.html|date=March 26, 2008|work=New Scientist|accessdate=April 16, 2015}}
18. ^1 {{cite journal|last=Efroimsky|first=M.|title=Tidal viscosity of Enceladus|journal=Icarus|volume=300|date=January 1, 2018|doi=10.1016/j.icarus.2017.09.013|pages=223–226|arxiv=1706.09000|bibcode=2018Icar..300..223E}}
19. ^1 {{cite journal|last=Herschel|first=W.|date=1795|url=http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1795RSPT...85..347H&db_key=AST&link_type=ABSTRACT&high=45eb6e10af23195|title=Description of a Forty-feet Reflecting Telescope|journal=Philosophical Transactions of the Royal Society of London|volume=85|pages=347–409|bibcode=1795RSPT...85..347H|doi=10.1098/rstl.1795.0021}} (reported by {{cite web|first=M.|last=Arago|date=1871|url=http://laplaza.org/~tom/People/Herschel.htm|title=Herschel|work=Annual Report of the Board of Regents of the Smithsonian Institution|pages=198–223|deadurl=yes|archiveurl=https://web.archive.org/web/20160113070818/http://laplaza.org/~tom/People/Herschel.htm|archivedate=January 13, 2016|df=mdy-all}})
20. ^{{cite web|last=Frommert|first=H.|last2=Kronberg|first2=C.|url=http://messier.seds.org/xtra/Bios/wherschel.html|title=William Herschel (1738–1822)|accessdate=March 11, 2015}}
21. ^As reported by {{cite journal|authorlink=William Lassell|last=Lassell|first=William|url=http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000042.000.html|title=Names|journal=Monthly Notices of the Royal Astronomical Society|volume=8|issue=3|pages=42–3|date=January 14, 1848|bibcode=1848MNRAS...8...42L|doi=10.1093/mnras/8.3.42}}
22. ^{{cite web|url=http://planetarynames.wr.usgs.gov/append6.html|title=Categories for Naming Features on Planets and Satellites|work=Gazetteer of Planetary Nomenclature|publisher=USGS Astrogeology Science Center|accessdate=January 12, 2015}}
23. ^{{cite web|url=http://planetarynames.wr.usgs.gov/SearchResults?target=ENCELADUS|title=Nomenclature Search Results: Enceladus|work=Gazetteer of Planetary Nomenclature|publisher=USGS Astrogeology Science Center|accessdate=January 13, 2015}}
24. ^{{GPN|15329|Samaria Rupes}}
25. ^{{cite journal|last=Hillier|first=J. K.|last2=Green|first2=S. F.|title=The composition of Saturn's E ring|journal=Monthly Notices of the Royal Astronomical Society|volume=377|issue=4|pages=1588–96|date=June 2007|bibcode=2007MNRAS.377.1588H|doi=10.1111/j.1365-2966.2007.11710.x|display-authors=etal}}
26. ^{{cite journal|last=Efroimsky|first=M.|title=Dissipation in a tidally perturbed body librating in longitude|journal=Icarus|volume=306|date=May 15, 2018|doi=10.1016/j.icarus.2017.10.020|pages=328–354|arxiv=1706.08999|bibcode=2018Icar..306..328E}}
27. ^1 2 {{cite journal|title=Implications of Spin-orbit Librations on Enceladus|last=Hurford|first=Terry|last2=Bruce|first2=B.|journal=American Astronomical Society, DPS Meeting #40, #8.06|pages=8.06|accessdate=|bibcode=2008DPS....40.0806H|year=2008}}
28. ^{{cite journal|display-authors=etal|last1=Hedman|first1=M. M.|last2=Burns|first2=J. A.|date=2012|title=The three-dimensional structure of Saturn's E ring|journal=Icarus|volume=217|issue=1|pages=322–338|doi=10.1016/j.icarus.2011.11.006|arxiv=1111.2568|bibcode=2012Icar..217..322H}}
29. ^{{cite web|url=https://www.researchgate.net/publication/251317042|title=Cassini visits Enceladus: New light on a bright world|last=Vittorio|first=Salvatore A.|work=Cambridge Scientific Abstracts (CSA)|publisher=CSA|date=July 2006|accessdate=April 27, 2014}}
30. ^1 {{cite journal|title=Saturn's E ring: I. CCD observations of March 1980|journal=Icarus|date=July 1981|last=Baum|first=W. A.|last2=Kreidl|first2=T.|volume=47|issue=1|pages=84–96|doi=10.1016/0019-1035(81)90093-2|accessdate=|bibcode=1981Icar...47...84B}}
31. ^1 {{cite journal|first=P. K.|last=Haff|first2=A.|last2=Eviatar|display-authors=etal|title=Ring and plasma: Enigmae of Enceladus|journal=Icarus|date=1983|volume=56|issue=3|pages=426–438|bibcode=1983Icar...56..426H|doi=10.1016/0019-1035(83)90164-1}}
32. ^{{cite journal|first=Kevin D.|last=Pang|first2=Charles C.|last2=Voge|display-authors=etal|title=The E ring of Saturn and satellite Enceladus|journal=Journal of Geophysical Research|date=1984|volume=89|page=9459|doi=10.1029/JB089iB11p09459|bibcode=1984JGR....89.9459P}}
33. ^{{cite book|title=Solar System Update|publisher=Springer Science|location=Berlin Heidelberg|first=Philippe|last=Blondel|first2=John|last2=Mason|date=August 23, 2006|pages=241–3|url=https://www.springer.com/us/book/9783540260561|isbn=978-3-540-37683-5|doi=10.1007/3-540-37683-6}}
34. ^1 2 {{cite journal|title=Cassini Dust Measurements at Enceladus and Implications for the Origin of the E ring|journal=Science|volume=311|issue=5766|pages=1416–18 |date=2006|doi=10.1126/science.1121375|pmid=16527969|bibcode=2006Sci...311.1416S|last=Spahn|first=F.|last2=Schmidt|first2=J.|display-authors=etal|citeseerx=10.1.1.466.6748}}
35. ^{{cite news|last=Cain|first=Fraser|url=http://www.universetoday.com/12710/enceladus-is-supplying-ice-to-saturns-a-ring/|title=Enceladus is Supplying Ice to Saturn's A-Ring|work=NASA|publisher=Universe Today|date=February 5, 2008|accessdate=April 26, 2014}}
36. ^{{cite news|publisher=NASA|title=Cracks on Enceladus Open and Close under Saturn's Pull|url=http://www.nasa.gov/mission_pages/cassini/media/enceladus_cracks.html|date=May 16, 2007|first=Bill|last=Steigerwald}}
37. ^1 2 {{cite web|url=http://saturn.jpl.nasa.gov/science/moons/enceladus/|title=Satun Moons – Enceladus|work=Cassini Solstice Mission Team|publisher=JPL/NASA|accessdate=April 26, 2014}}
38. ^{{cite journal|last=Rathbun|first=J. A.|last2=Turtle|first2=E. P.|display-authors=etal|date=2005|title=Enceladus' global geology as seen by Cassini ISS|journal=Eos Trans. AGU|volume=82|issue=52 (Fall Meeting Supplement), abstract P32A–03|pages=P32A–03|bibcode=2005AGUFM.P32A..03R }}
39. ^1 2 {{cite journal|doi=10.1126/science.215.4532.504|title=A New Look at the Saturn System: The Voyager 2 Images|date=1982|journal=Science|volume=215|pages=504–37|pmid=17771273|issue=4532|bibcode=1982Sci...215..504S|last=Smith|first=B. A.|last2=Soderblom |first2=L.|display-authors=etal}}
40. ^1 2 3 4 {{cite web|last=Turtle |first=E. P. |display-authors=etal |url=http://saturn.jpl.nasa.gov/multimedia/products/pdfs/CHARM_Turtle_050426.pdf |archiveurl=https://www.webcitation.org/5nDebNFQ5?url=http://saturn.jpl.nasa.gov/multimedia/products/pdfs/CHARM_Turtle_050426.pdf |archivedate=February 1, 2010 |title=Enceladus, Curiouser and Curiouser: Observations by Cassini's Imaging Science Subsystem |work=Cassini CHARM Teleconference |publisher=JPL/NASA |date=April 28, 2005 |deadurl=yes |df=mdy }}
41. ^{{cite web|title=Shahrazad (Se-4)|work=PIA12783: The Enceladus Atlas|publisher=NASA/Cassini Imaging Team|url=http://photojournal.jpl.nasa.gov/figures/PIA12783_full_5.jpg|accessdate=February 4, 2012}}
42. ^1 {{cite conference|display-authors=etal|last=Helfenstein|first=P.|last2=Thomas|first2=P. C.|title=Patterns of fracture and tectonic convergence near the south pole of Enceladus|url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2182.pdf|format=PDF|conference=Lunar and Planetary Science XXXVII (2006)}}
43. ^{{cite conference|last=Barnash|first=A. N.|display-authors=etal|date=2006|bibcode=2006DPS....38.2406B|title=Interactions Between Impact Craters and Tectonic Fractures on Enceladus|work=Bulletin of the American Astronomical Society|volume=38|issue=3, presentation no. 24.06|page=522}}
44. ^1 2 {{cite journal|last=Nimmo|first=F.|last2=Pappalardo|first2=R. T.|date=2006|title=Diapir-induced reorientation of Saturn's moon Enceladus|journal=Nature|volume=441|issue=7093|pages=614–16|doi=10.1038/nature04821|pmid=16738654|bibcode=2006Natur.441..614N}}
45. ^1 {{cite web|url=http://ciclops.org/view.php?id=1223|title=Enceladus in False Color|publisher=Cassini Imaging|date=July 26, 2005|accessdate=March 22, 2006}}
46. ^1 {{cite web|url=http://www.nasa.gov/mission_pages/cassini/media/cassini-083005.html|title=Cassini Finds Enceladus Tiger Stripes Are Really Cubs|work=NASA.gov|publisher=NASA|date=August 30, 2005|accessdate=April 3, 2014}}
47. ^{{cite journal|date=2006|title=Composition and Physical Properties of Enceladus' Surface|journal=Science|volume=311|issue=5766|pages=1425–28|doi=10.1126/science.1121031|pmid=16527972|bibcode=2006Sci...311.1425B|last=Brown|first=R. H.|last2=Clark |first2=R. N.|displayauthors=etal}}
48. ^1 2 3 {{cite journal |author=Postberg, Frank |display-authors=etal |title=Macromolecular organic compounds from the depths of Enceladus |date=27 June 2018 |journal=Nature |volume=558 |issue=7711 |pages=564–568 |doi=10.1038/s41586-018-0246-4 |pmid=29950623 |pmc=6027964 }}
49. ^1 {{cite web |last1=McCartney |first1=Gretchen |last2=Brown |first2=Dwayne |last3=Wendel |first3=JoAnna |last4=Bauer |first4=Markus |title=Complex Organics Bubble up from Enceladus |url=https://www.jpl.nasa.gov/news/news.php?feature=7174 |date=27 June 2018 |work=NASA |accessdate=27 June 2018 }}
50. ^{{cite web|url=http://ciclops.org/view.php?id=1250|title=Boulder-Strewn Surface|publisher=Cassini Imaging|date=July 26, 2005|accessdate=March 26, 2006}}
51. ^{{cite web|url=http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens/Icy_moon_Enceladus_has_underground_sea|title=Icy moon Enceladus has underground sea|publisher=ESA|date=April 3, 2014|accessdate=April 30, 2014}}
52. ^{{cite conference|display-authors=etal|last=Tajeddine|first=R.|last2=Lainey|first2=V.|date=October 2012|title=Mimas and Enceladus: Formation and interior structure from astrometric reduction of Cassini images|bibcode=2012DPS....4411203T|conference=American Astronomical Society, DPS meeting #44, #112.03}}
53. ^{{Cite journal|last=Castillo|first=J. C.|last2=Matson |first2=D. L.|display-authors=etal|date=2005|title=26Al in the Saturnian System – New Interior Models for the Saturnian satellites|journal=Eos Trans. AGU|volume=82|issue=52 (Fall Meeting Supplement), abstract P32A–01|pages=P32A–01|bibcode=2005AGUFM.P32A..01C}}
54. ^1 {{cite journal|last1=Bhatia|first1= G.K.|last2=Sahijpal|first2= S.|title=Thermal evolution of trans-Neptunian objects, icy satellites, and minor icy planets in the early solar system |journal=Meteoritics & Planetary Science |doi=10.1111/maps.12952|volume=52|issue= 12|year=2017|pages=2470–2490|bibcode=2017M&PS...52.2470B}}
55. ^{{cite conference|last=Castillo|first=J. C.|last2=Matson|first2=D. L.|display-authors=etal|date=2006|url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2200.pdf|format=PDF|title=A New Understanding of the Internal Evolution of Saturnian Icy Satellites from Cassini Observations|conference=37th Annual Lunar and Planetary Science Conference, Abstract 2200}}
56. ^1 {{cite journal|doi=10.1016/j.icarus.2006.12.012|title=Enceladus: Present internal structure and differentiation by early and long-term radiogenic heating|date=2007|last=Schubert|first=G.|last2=Anderson|first2=J.|display-authors=etal|journal=Icarus|volume=188|issue=2|pages=345–55|bibcode=2007Icar..188..345S}}
57. ^{{cite web|last=Matson|first=D. L.|display-authors=etal|date=2006|url=http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2219.pdf|title=Enceladus' Interior and Geysers – Possibility for Hydrothermal Geometry and N2 Production|work=37th Annual Lunar and Planetary Science Conference, abstract|page=2219}}
58. ^{{cite journal|last1=Hsu|first1=Hsiang-Wen|last2=Postberg|first2=Frank|display-authors=etal|title=Ongoing hydrothermal activities within Enceladus|journal=Nature|date=March 11, 2015|volume=519|issue=7542|pages=207–10|doi=10.1038/nature14262|bibcode=2015Natur.519..207H|pmid=25762281}}
59. ^1 {{cite web|url=http://www.esa.int/Our_Activities/Space_Science/Herschel/Enceladus_rains_water_onto_Saturn|title=Enceladus rains water onto Saturn|publisher=European Space Agency|date=2011|accessdate=January 14, 2015}}
60. ^{{cite news|agency=The Associated Press|title=Astronomers find hints of water on Saturn moon|url=http://www.news9.com/story/9422981/astronomers-find-hints-of-water-on-saturn-moon?redirected=true|work=News9.com|date=November 27, 2008|accessdate=September 15, 2011}}
61. ^1 {{Cite journal|last1=Postberg|first1=F.|last2=Schmidt|first2=J.|display-authors=etal|title=A salt-water reservoir as the source of a compositionally stratified plume on Enceladus|doi=10.1038/nature10175|journal=Nature|volume=474|issue=7353|pages=620–2|year=2011|pmid=21697830|bibcode=2011Natur.474..620P }}
62. ^{{cite web|url=http://www.space.com/scienceastronomy/090624-enceladus-ocean.html|title=Ocean Hidden Inside Saturn's Moon|publisher=Space.com|date=June 24, 2009|accessdate=January 14, 2015}}
63. ^{{cite web|url=http://www.esa.int/esaSC/SEMSZ2037PG_index_0.html|title=Cassini samples the icy spray of Enceladus' water plumes|publisher=ESA|date=2011}}
64. ^{{cite journal |title=Neutral Gas Composition of Enceladus' Plume – Model Parameter Insights from Cassini-INMS |journal=Lunar and Planetary Science XLVIII |date=24 March 2017 |last=Magee |first=B. A. |last2=Waite |first2=J. H. |url=https://www.hou.usra.edu/meetings/lpsc2017/pdf/2974.pdf |accessdate=2017-09-16 }}
65. ^[https://www.space.com/41005-saturn-moon-enceladus-complex-organic-molecules.html? Saturn Moon Enceladus Is First Alien 'Water World' with Complex Organics]. Charles. Q. Choi, Space. 27 June 2018.
66. ^1 2 3 4 {{cite web|last=Platt|first=Jane|last2=Bell|first2=Brian|title=NASA Space Assets Detect Ocean inside Saturn Moon|url=http://www.jpl.nasa.gov/news/news.php?release=2014-103|work=NASA|date=April 3, 2014|accessdate=April 3, 2014}}
67. ^1 2 {{Cite journal|doi=10.1038/nature.2014.14985|title=Icy Enceladus hides a watery ocean|url=http://www.nature.com/news/icy-enceladus-hides-a-watery-ocean-1.14985|journal=Nature|date=April 3, 2014|last1=Witze|first1=A.}}
68. ^1 2 3 {{cite journal|last=Iess|first=L.|last2=Stevenson|first2=D. J.|display-authors=etal|title=The Gravity Field and Interior Structure of Enceladus|journal=Science|volume=344|number=6179|pages=78–80|doi=10.1126/science.1250551|date=April 4, 2014|bibcode=2014Sci...344...78I|pmid=24700854}}
69. ^1 {{cite news|last=Amos|first=Jonathan|url=https://www.bbc.com/news/science-environment-26872184|title=Saturn's Enceladus moon hides 'great lake' of water|work=BBC News|date=April 3, 2014|accessdate=April 7, 2014}}
70. ^1 {{cite web|last=Sample|first=Ian|title=Ocean discovered on Enceladus may be best place to look for alien life|url=https://www.theguardian.com/science/2014/apr/03/ocean-enceladus-alien-life-water-saturn-moon|publisher=The Guardian|date=April 3, 2014|accessdate=April 3, 2014}}
71. ^{{cite web|title=Cassini finds global ocean in Saturn's moon Enceladus|url=http://www.astronomy.com/news/2015/09/cassini-finds-global-ocean-in-saturns-moon-enceladus|publisher=Astronomy|accessdate=September 15, 2015}}
72. ^{{Cite journal|title=Enceladus's measured physical libration requires a global subsurface ocean|journal=Icarus|doi=10.1016/j.icarus.2015.08.037|first=P. C.|last=Thomas|first2=R.|last2=Tajeddine|display-authors=etal|arxiv=1509.07555|bibcode=2016Icar..264...37T|volume=264|pages=37–47|year=2016}}
73. ^{{cite web|title=Cassini Finds Global Ocean in Saturn's Moon Enceladus|url=http://www.nasa.gov/press-release/cassini-finds-global-ocean-in-saturns-moon-enceladus|accessdate=September 17, 2015}}
74. ^1 {{cite web|title=Cassini Confirms a Global Ocean on Saturn's Moon Enceladus|url=http://blogs.scientificamerican.com/observations/cassini-confirms-a-global-ocean-on-saturn-s-moon-enceladus/|accessdate=September 17, 2015|first=Lee|last=Billings}}
75. ^{{cite web|title=Under Saturnian moon's icy crust lies a 'global' ocean {{!}} Cornell Chronicle|url=http://www.news.cornell.edu/stories/2015/09/under-saturnian-moons-icy-crust-lies-global-ocean|work=Cornell University|accessdate=September 17, 2015}}
76. ^1 2 {{cite journal|title=The pH of Enceladus' ocean|journal=Geochimica et Cosmochimica Acta|date=April 16, 2015|last=R. Glein|first=Christopher|last2=Baross|first2=John A.|display-authors=etal|doi=10.1016/j.gca.2015.04.017|arxiv=1502.01946|bibcode=2015GeCoA.162..202G|volume=162|pages=202–19}}
77. ^1 {{cite conference|last=Glein|first=C. R.|last2=Baross|first2=J. A.|display-authors=etal|title=The chemistry of Enceladus' ocean from a convergence of Cassini data and theoretical geochemistry|url=http://www.hou.usra.edu/meetings/lpsc2015/pdf/1685.pdf|format=PDF|conference=46th Lunar and Planetary Science Conference 2015|date=March 26, 2015}}
78. ^1 2 {{cite news|last=Wall|first=Mike|url=http://www.space.com/29334-enceladus-ocean-energy-source-life.html|title=Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life|work=Space.com|date=May 7, 2015|accessdate=May 8, 2015}}
79. ^1 {{cite web| url=http://www.jpl.nasa.gov/news/news.php?release=2005-171 |title=NASA's Cassini Images Reveal Spectacular Evidence of an Active Moon| publisher=JPL/NASA| date=December 5, 2005| accessdate=May 4, 2016}}
80. ^{{cite web|url=http://ciclops.org/view.php?id=1652|title=Spray Above Enceladus|publisher=Cassini Imaging|accessdate=March 22, 2005}}
81. ^1 {{cite conference |last=Perry |first= M. E. |last2= Teolis |first2=B. D. |last3=Grimes |first3=J. |display-authors=etal |title=Direct Measurement of the Velocity of the Enceladus Vapor Plumes |url=http://www.hou.usra.edu/meetings/lpsc2016/pdf/2846.pdf |format=PDF |conference=47th Lunar and Planetary Science Conference |place=The Woodlands, Texas |date=March 21, 2016 |page=2846 }}
82. ^{{cite journal |title=Enceladus Plume Structure and Time Variability: Comparison of Cassini Observations |journal=Astrobiology |date=September 5, 2017 |last1=Teolis |first1=Ben D. |last2=Perry |first2=Mark E. |last3=Hansen |first3=Candice J. |last4=Waite |first4=J. Hunter |last5=Porco |first5=Carolyn C. |last6=Spencer |first6=John R. |last7=Howett |first7=Carly J.A. |volume=17 |issue=9 |pages=926–940 |doi=10.1089/ast.2017.1647 |pmid=28872900 |pmc=5610430 |bibcode=2017AsBio..17..926T }}
83. ^1 {{cite news|last=Mosher|first=Dave|url=http://www.space.com/5179-seeds-life-saturn.html|title=Seeds of Life Found Near Saturn|work=Space.com|date=March 26, 2014|accessdate=April 9, 2014}}
84. ^1 2 {{cite web|url=http://www.nasa.gov/mission_pages/cassini/media/cassini-20080326.html|title=Cassini Tastes Organic Material at Saturn's Geyser Moon|publisher=NASA|date=March 26, 2008|accessdate=March 26, 2008}}
85. ^{{Cite news|url=http://www.ndtv.com/world-news/nasa-finds-ingredients-for-life-spewing-out-of-saturns-icy-moon-enceladus-1681326|title=NASA Finds Ingredients For Life Spewing Out Of Saturn's Icy Moon Enceladus|work=NDTV.com|access-date=2017-04-14}}
86. ^1 {{cite journal |title=Sustained eruptions on Enceladus explained by turbulent dissipation in tiger stripes |journal=Proceedings of the National Academy of Sciences of the United States of America |date=January 29, 2016 |last=Kite |first=Edwin S. |last2=Rubin |first2=Allan M. |volume=113 |issue=15 |doi=10.1073/pnas.1520507113 |pages=3972–3975 |pmid=27035954 |pmc=4839467|arxiv = 1606.00026 |bibcode = 2016PNAS..113.3972K }}
87. ^{{cite web| last=Spotts|first=P.| title=What's going on inside Saturn moon? Geysers offer intriguing new clue| work=The Christian Science Monitor|url=http://www.csmonitor.com/Science/2013/0731/What-s-going-on-inside-Saturn-moon-Geysers-offer-intriguing-new-clue| date=July 31, 2013|accessdate=August 3, 2013}}
88. ^{{cite web| last=Lakdawalla|first=E.| title=Enceladus huffs and puffs: plumes vary with orbital longitude| work=Planetary Society blogs| publisher=The Planetary Society| url=http://www.planetary.org/blogs/emily-lakdawalla/2013/12111647-enceladus-huffs-and-puffs.html| date=March 11, 2013| accessdate=January 26, 2014}}
89. ^{{cite journal| last=Spencer| first=J.| title=Solar system: Saturn's tides control Enceladus' plume| journal=Nature| date=July 31, 2013| issn=0028-0836| doi=10.1038/nature12462| bibcode=2013Natur.500..155S|volume=500| issue=7461| pages=155–6| pmid=23903653}}
90. ^{{cite journal| last=Hedman|first=M. M.| last2=Gosmeyer| first2=C. M.| display-authors=etal| title=An observed correlation between plume activity and tidal stresses on Enceladus| journal=Nature| issn=0028-0836|doi=10.1038/nature12371| bibcode=2013Natur.500..182H| volume=500|issue=7461| pages=182–4| pmid=23903658|date=July 31, 2013}}
91. ^{{Cite journal| title=Curtain eruptions from Enceladus' south-polar terrain| journal=Nature| date=May 7, 2015| issn=0028-0836| pages=57–60| volume=521| issue=7550| doi=10.1038/nature14368| first=Joseph N.| last=Spitale| first2=Terry A.| last2=Hurford|display-authors=etal|bibcode=2015Natur.521...57S| pmid=25951283}}
92. ^{{cite web|title='Jets' on Saturn Moon Enceladus May Actually Be Giant Walls of Vapor and Ice| url=http://www.space.com/29330-saturn-moon-enceladus-geysers-curtains.html| accessdate=May 8, 2015| publisher=Space.com|date=May 6, 2015|author=Charles Q. Choi}}
93. ^{{Cite news| title=Long 'curtains' of material may be shooting off Saturn's moon Enceladus| url=http://www.latimes.com/science/sciencenow/la-sci-sn-enceladus-jets-curtains-20150506-story.html| newspaper=Los Angeles Times|access-date=May 8, 2015|issn=0458-3035}}
94. ^{{cite journal |title=Ocean worlds in the outer solar system |journal=Journal of Geophysical Research |date=8 August 2016 |last=Nimmo |first=F. |last2=Pappalardo |first2=R. T. |doi=10.1002/2016JE005081 |url=https://websites.pmc.ucsc.edu/~fnimmo/website/ocean_worlds_new.pdf |accessdate=2017-10-01 |bibcode=2016JGRE..121.1378N |volume=121 |issue=8 |pages=1378–1399}}
95. ^Hurford et al., 2007
96. ^Hedman et al., 2013
97. ^{{cite journal|title=The effect of an asymmetric core on convection in Enceladus' ice shell: Implications for south polar tectonics and heat flux |journal=Geophysical Research Letters| display-authors=etal| last=Showman| first=Adam P.| last2=Han| first2=Lijie| bibcode=2013GeoRL..40.5610S| date=November 2013| volume=40 |issue=21 |pages=5610–14 |doi= 10.1002/2013GL057149}}
98. ^{{cite conference |last=Kamata |first=S. |last2=Nimmo |first2=F. |title=INTERIOR THERMAL STATE OF ENCELADUS INFERRED FROM THE VISCOELASTIC STATE OF ITS ICY SHELL |url=http://www.hou.usra.edu/meetings/lpsc2016/pdf/1097.pdf |format=PDF |conference=47th Lunar and Planetary Science Conference |publisher=Lunar and Planetary Institute |date=March 21, 2016 }}
99. ^{{cite journal|title=Enceladus Near-Fissure Surface Temperatures|journal=American Astronomical Society|volume=45|pages=416.01|date=2013|last=Howell|first=Robert R.|last2=Goguen |first2=J. D.|display-authors=etal|bibcode=2013DPS....4541601H}}
100. ^{{cite conference|last=Abramov|first=O.|last2=Spencer|first2=J. R.|title=New Models of Endogenic Heat from Enceladus' South Polar Fractures|url=http://www.hou.usra.edu/meetings/lpsc2014/eposter/2878.pdf|format=PDF|conference=45th Lunar and Planetary Science Conference 2014|publisher=LPSC|date=March 17–21, 2014}}
101. ^1 {{cite web|url=http://www.astrobio.net/pressrelease/2269/a-hot-start-on-enceladus|title=A Hot Start on Enceladus|publisher=Astrobio.net|accessdate=March 21, 2010|date=March 14, 2007}}
102. ^1 2 {{cite news|url=http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20110307.html|title=Cassini Finds Enceladus is a Powerhouse|publisher=NASA|date=March 7, 2011|accessdate=April 7, 2014}}
103. ^{{cite journal|title=Non-steady state tidal heating of Enceladus|journal=Icarus|volume=235|pages=75–85|date=March 14, 2014|last=Shoji|first=D.|last2=Hussmann |first2=H.|display-authors=etal|doi=10.1016/j.icarus.2014.03.006|bibcode=2014Icar..235...75S}}
104. ^{{cite journal|title=Enceladus: An Active Ice World in the Saturn System|journal=Annual Review of Earth and Planetary Sciences|date=May 2013|last=Spencer|first=John R.|last2=Nimmo|first2=Francis|volume=41|pages=693–717|doi=10.1146/annurev-earth-050212-124025|bibcode=2013AREPS..41..693S}}
105. ^{{cite journal|title=Impact of tidal heating on the onset of convection in Enceladus's ice shell|journal=Icarus|date=September–October 2013|last=Běhounková|first=Marie|last2=Tobie |first2=Gabriel|display-authors=etal|volume=226|issue=1|pages=898–904|doi=10.1016/j.icarus.2013.06.033|bibcode=2013Icar..226..898B}}
106. ^1 2 {{cite conference|last=Spencer|first=J. R.|title=Enceladus Heat Flow from High Spatial Resolution Thermal Emission Observations|url=http://meetingorganizer.copernicus.org/EPSC2013/EPSC2013-840-1.pdf|format=PDF|conference=European Planetary Science Congress 2013|publisher=EPSC Abstracts|date=2013}}
107. ^{{cite journal|last=Spitale|first=J. N.|last2=Porco|first2=Carolyn C.|title=Association of the jets of Enceladus with the warmest regions on its south-polar fractures|journal=Nature|date=2007|volume=449|issue=7163|pages=695–7|doi=10.1038/nature06217|pmid=17928854|bibcode=2007Natur.449..695S}}
108. ^{{cite journal|last=Meyer|first=J.|last2=Wisdom|first2=Jack|title=Tidal heating in Enceladus|journal=Icarus|date=2007|volume=188|issue=2|pages=535–9|doi=10.1016/j.icarus.2007.03.001|bibcode=2007Icar..188..535M|citeseerx=10.1.1.142.9123}}
109. ^[https://www.space.com/38679-saturn-moon-enceladus-warm-churning-insides.html Saturn Moon Enceladus' Churning Insides May Keep Its Ocean Warm]. Charles Q. Choi, Space 6 November 2017.
110. ^[https://phys.org/news/2017-11-ocean-moon-enceladus-billions-years.html Heating ocean moon Enceladus for billions of years]. PhysOrg. 6 November 2017.
111. ^"Powering prolonged hydrothermal activity inside Enceladus". Gaël Choblet et al. Nature Astronomy (2017). {{doi|10.1038/s41550-017-0289-8}}
112. ^1 {{cite journal|last=Roberts|first=J. H.|last2=Nimmo|first2=Francis|title=Tidal heating and the long-term stability of a subsurface ocean on Enceladus|journal=Icarus|date=2008|volume=194|issue=2|pages=675–689|doi=10.1016/j.icarus.2007.11.010|bibcode=2008Icar..194..675R}}
113. ^{{cite journal|last=Bland|first=M. T.|last2=Singer |first2=Kelsi N.|display-authors=etal|title=Enceladus' extreme heat flux as revealed by its relaxed craters|journal=Geophysical Research Letters|date=2012|volume=39|issue=17|pages=n/a|doi=10.1029/2012GL052736|bibcode=2012GeoRL..3917204B}}
114. ^{{cite web|author=JPL|url=http://www.jpl.nasa.gov/news/features.cfm?feature=2238|title=Saturnian Moon Shows Evidence of Ammonia|publisher=NASA|date=July 22, 2009|accessdate=March 21, 2010}}
115. ^{{cite journal|last=Waite Jr.|first=J. H.|last2=Lewis|first2=W. S.|title=Liquid water on Enceladus from observations of ammonia and 40 Ar in the plume|date=July 23, 2009|journal=Nature|volume=460|issue=7254|pages=487–490|doi=10.1038/nature08153|display-authors=etal|bibcode=2009Natur.460..487W }}
116. ^{{cite journal|last=Fortes|first=A. D.|date=2007|url=http://discovery.ucl.ac.uk/84452/|title=Metasomatic clathrate xenoliths as a possible source for the south polar plumes of Enceladus|journal=Icarus|volume=191|issue=2|pages=743–8|doi=10.1016/j.icarus.2007.06.013|bibcode=2007Icar..191..743F}}
117. ^1 {{cite journal|title=Ammonia clathrate hydrates as new solid phases for Titan, Enceladus, and other planetary systems|journal=Proceedings of the National Academy of Sciences of the USA|date=September 11, 2012|last=Shin|first=Kyuchul|last2=Kumar|first2=Rajnish|display-authors=etal|volume=109|issue=37|pages=14785–90|doi=10.1073/pnas.1205820109|pmid=22908239|bibcode=2012PNAS..10914785S|pmc=3443173}}
118. ^{{cite web|url=http://www.jpl.nasa.gov/news/news.php?release=2007-025|title=A Hot Start Might Explain Geysers on Enceladus|publisher=NASA/Jet Propulsion Laboratory|date=March 12, 2007|accessdate=January 12, 2015}}
119. ^{{cite web|url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturniansatfact.html|title=Saturnian Satellite Fact Sheet|publisher=NASA|accessdate=July 15, 2016|date=October 13, 2015}}
120. ^{{cite journal|display-authors=etal|last=Thomas|first=P. C.|last2=Burns|first2=J. A.|title=Shapes of the saturnian icy satellites and their significance|journal=Icarus|volume=190|pages=573–584|date=2007|doi=10.1016/j.icarus.2007.03.012 |bibcode=2007Icar..190..573T|issue=2}}
121. ^{{cite journal|last=Czechowski|first=Leszek|date=2006|title=Parameterized model of convection driven by tidal and radiogenic heating|journal=Advances in Space Research|volume=38|pages=788–93|doi=10.1016/j.asr.2005.12.013|bibcode=2006AdSpR..38..788C|issue=4}}
122. ^{{cite journal|title=Strong tidal dissipation in Saturn and constraints on Enceladus' thermal state from astrometry|journal=The Astrophysical Journal|date=May 22, 2012|last=Lainey|first=Valery|last2=Karatekin|first2=Ozgur|display-authors=etal|volume=752|issue=1|page=14|doi=10.1088/0004-637X/752/1/14|url=http://iopscience.iop.org/0004-637X/752/1/14/article|accessdate=April 28, 2014|arxiv=1204.0895|bibcode=2012ApJ...752...14L}}
123. ^{{cite journal|last=Cowen|first=Ron|title=The Whole Enceladus: A new place to search for life in the outer solar system|journal=Science News|volume=169|issue=15|pages=282–284|date=April 15, 2006|url=http://www.phschool.com/science/science_news/articles/whole_enceladus.html|accessdate=April 8, 2014|doi=10.2307/4019332|jstor=4019332}}
124. ^1 2 {{Cite journal|doi=10.1016/j.pss.2014.09.010|title=Some remarks on the early evolution of Enceladus|journal=Planetary and Space Science|volume=104|pages=185–99|date=December 2014|last=Czechowski|first=L.|bibcode=2014P&SS..104..185C}}
125. ^{{cite web|url=http://www.astronomy.com/news/2016/03/moons-of-saturn-may-be-younger-than-the-dinosaurs|title=Moons of Saturn may be younger than the dinosaurs|publisher=}}
126. ^1 {{cite journal |title=Planetary science: Enceladus' hot springs |journal=Nature |date=March 12, 2015 |last=Tobie |first=Gabriel |volume=519 |issue=7542 |doi=10.1038/519162a|bibcode = 2015Natur.519..162T |pmid=25762276 |pages=162–3}}
127. ^{{cite web | url=http://www.space.com/29334-enceladus-ocean-energy-source-life.html | title=Ocean on Saturn Moon Enceladus May Have Potential Energy Source to Support Life | publisher=Space.com | date=May 7, 2015 | accessdate=August 15, 2015 | author=Wall, Mike}}
128. ^{{cite web | url=http://news.discovery.com/space/alien-life-exoplanets/potentially-life-giving-hydrothermal-activity-revealed-on-enceladus-150312.htm | title=Enceladus Has Potentially Life-Giving Hydrothermal Activity | publisher=Discovery News | date=March 12, 2015 | accessdate=August 15, 2015 | author=O' Neill, Ian}}
129. ^1 {{cite news |last=Spotts |first=Peter |url=http://www.csmonitor.com/Science/2015/0916/Proposed-NASA-mission-to-Saturn-moon-If-there-s-life-we-ll-find-it |title=Proposed NASA mission to Saturn moon: If there's life, we'll find it |work=The Christian Science Monitor |date=September 16, 2015 |accessdate=September 27, 2015 }}
130. ^{{cite conference |last=Taubner |first=R.-S. |last2=Leitner |first2=J. J. |last3=Firneis |first3=M. G. |last4=Hitzenberger |first4=R. |title=Including Cassini’s Gravity Measurements from the Flybys E9, E12, E19 into Interior Structure Models of Enceladus |url=http://meetingorganizer.copernicus.org/EPSC2014/EPSC2014-676.pdf |format=PDF |conference=European Planetary Science Congress 2014 |publisher=EPSC Abstracts |date=September 7, 2014 }}
131. ^Czechowski (2014). Enceladus: a cradle of life of the Solar System? Geophysical Research Abstracts Vol. 16, EGU2014-9492-1
132. ^{{cite web |url=http://www.nasa.gov/mission_pages/cassini/media/enceladus-f20080326.html |title=A Perspective on Life on Enceladus: A World of Possibilities |website= |publisher=NASA |date=March 26, 2008 |accessdate=September 15, 2011 }}
133. ^{{cite web|last1=McKie|first1=Robin|title=Enceladus: home of alien lifeforms?|url=https://www.theguardian.com/science/2012/jul/29/alien-life-enceladus-saturn-moon|publisher=The Guardian|accessdate=August 16, 2015|date=July 29, 2012}}
134. ^{{cite web | url=http://blogs.discovermagazine.com/crux/2015/03/12/enceladus-oceans-life/ | title=Warm Oceans on Saturn's Moon Enceladus Could Harbor Life | publisher=Discover Magazine | date=March 12, 2015 | accessdate=August 15, 2015 | author=Coates, Andrew}}
135. ^Habitability of Enceladus: Planetary Conditions for Life. (PDF) Christopher D. Parkinson, Mao-Chang Liang,Yuk L. Yung, and Joseph L. Kirschivnk. Origins of Life and Evolution of Biospheres April 10, 2008. {{DOI|10.1007/s11084-008-9135-4}}
136. ^{{cite web| url=https://nai.nasa.gov/media/medialibrary/2015/10/NASA_Astrobiology_Strategy_2015_151008.pdf| title=NASA Astrobiology Strategy| year=2015| work=NASA| access-date=September 26, 2017| archive-url=https://web.archive.org/web/20161222190306/https://nai.nasa.gov/media/medialibrary/2015/10/NASA_Astrobiology_Strategy_2015_151008.pdf| archive-date=December 22, 2016| dead-url=yes| df=mdy-all}}
137. ^{{cite journal|pmid=28408597|year=2017|author1=Waite|first1=J. H|title=Cassini finds molecular hydrogen in the Enceladus plume: Evidence for hydrothermal processes|journal=Science|volume=356|issue=6334|pages=155–159|last2=Glein|first2=C. R|last3=Perryman|first3=R. S|last4=Teolis|first4=B. D|last5=Magee|first5=B. A|last6=Miller|first6=G|last7=Grimes|first7=J|last8=Perry|first8=M. E|last9=Miller|first9=K. E|last10=Bouquet|first10=A|last11=Lunine|first11=J. I|last12=Brockwell|first12=T|last13=Bolton|first13=S. J|doi=10.1126/science.aai8703|bibcode=2017Sci...356..155W}}
138. ^{{cite news |last=Chang |first=Kenneth |title=Conditions for Life Detected on Saturn Moon Enceladus |url=https://www.nytimes.com/2017/04/13/science/saturn-cassini-moon-enceladus.html |date=April 13, 2017 |work=The New York Times |accessdate=April 13, 2017 }}
139. ^{{Cite news|url=https://www.pbs.org/newshour/rundown/nasa-ocean-saturn-moon-may-possess-life-sustaining-hydrothermal-vents/|title=NASA: Ocean on Saturn moon may possess life-sustaining hydrothermal vents|work=PBS NewsHour|access-date=2017-04-13|language=en-US}}
140. ^{{Cite web|url=https://www.theverge.com/2017/4/13/15270854/nasa-enceladus-ocean-hydrothermal-vents-alien-life-conditions-cassini-saturn|title=NASA finds more evidence that the ocean on Enceladus could support alien life|date=2017-04-13|website=The Verge|access-date=2017-04-13}}
141. ^{{Cite news|url=https://www.nasa.gov/press-release/nasa-missions-provide-new-insights-into-ocean-worlds-in-our-solar-system|title=NASA Missions Provide New Insights into 'Ocean Worlds'|last=Northon|first=Karen|date=2017-04-13|work=NASA|access-date=2017-04-13|language=en}}
142. ^{{cite news|last1=Kaplan|first1=Sarah|title=NASA finds ingredients for life spewing out of Saturn’s icy moon Enceladus|url=https://www.washingtonpost.com/news/speaking-of-science/wp/2017/04/13/nasa-finds-ingredients-for-life-spewing-out-of-saturns-moon/|accessdate=May 3, 2017|agency=NASA|publisher=Washington Post|date=April 13, 2017}}
143. ^1 {{cite web |url=http://pds-rings.seti.org/voyager/mission/ |title=Voyager Mission Description |publisher=SETI |date=February 19, 1997 |accessdate=May 29, 2006 }}
144. ^1 {{cite web |last=Terrile |first=R. J. |last2=Cook |first2=A. F. |date=1981 |url=http://articles.adsabs.harvard.edu//full/seri/LPICo/0428//0000010.000.html |title=Enceladus: Evolution and Possible Relationship to Saturn's E-ring |work=12th Annual Lunar and Planetary Science Conference, Abstract |page=428 |publisher= }}
145. ^1 2 3 4 5 {{cite book |last=Rothery |first=David A. |title=Satellites of the Outer Planets: Worlds in their own right |publisher=Oxford University Press |date=1999 |isbn=978-0-19-512555-9 }}
146. ^{{cite web |last1=Dyches |first1=Preston |last2=Brown |first2=Dwayne |last3=Cantillo |first3=Laurie |title=Saturn's Geyser Moon Shines in Close Flyby Views |url=http://www.jpl.nasa.gov/news/news.php?feature=4759 |date=October 30, 2015 |work=NASA |accessdate=October 31, 2015 }}
147. ^{{cite web |last=Dyches |first=Preston |title=Cassini Completes Final Close Enceladus Flyby |url=http://www.jpl.nasa.gov/news/news.php?feature=4803 |date=December 21, 2015 |work=NASA |accessdate=December 22, 2015 }}
148. ^{{cite web |url=http://saturn.jpl.nasa.gov/science/moons/enceladus/index.cfm?pageListID=1 |publisher=Cassini Solstice Mission, NASA JPL |title=Enceladus |accessdate=January 14, 2015 }}
149. ^{{cite web |url=http://www.planetary.org/explore/space-topics/space-missions/cassinis-tour.html |title=Cassini's Tour of the Saturn System |publisher=Planetary Society |date= |accessdate=March 11, 2015}}
150. ^{{cite web |last=Moomaw |first=B. |url=http://www.spacedaily.com/reports/Tour_de_Saturn_Set_For_Extended_Play_999.html |title=Tour de Saturn Set For Extended Play |work=Spacedaily |date=February 5, 2007 |accessdate=February 5, 2007 }}
151. ^{{cite web| url=http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20151028/| title=Deepest-Ever Dive Through Enceladus Plume Completed| publisher=Jet Propulsion Laboratory| accessdate=October 29, 2015| date=October 28, 2015}}
152. ^{{cite web |url=http://ciclops.org/view.php?id=1881 |title=Cassini Images of Enceladus Suggest Geysers Erupt Liquid Water at the Moon's South Pole |website= |publisher=Cassini Imaging |date= |accessdate=March 22, 2006 }}
153. ^{{cite web |url=https://www.nasa.gov/jpl/signs-of-europa-plumes-remain-elusive-in-search-of-cassini-data |title=Signs of Europa Plumes Remain Elusive in Search of Cassini Data |publisher=NASA |date=December 17, 2014 |accessdate=January 12, 2015}}
154. ^{{cite conference |last=Sotin |first=C. |last2=Altwegg |first2=K. |display-authors=etal |title=JET: Journey to Enceladus and Titan |url=http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1326.pdf |format=PDF |conference=42nd Lunar and Planetary Science Conference |publisher=Lunar and Planetary Institute |date=2011 }}
155. ^{{cite web |url=http://futureplanets.blogspot.com/search?q=jet+enceladus+titan |title=Cost Capped Titan-Enceladus Proposal |work=Future Planetary Exploration |date=March 21, 2011 |accessdate=April 9, 2014 }}
156. ^{{cite journal |title=A lander mission to probe subglacial water on Saturn's moon Enceladus for life |journal=Acta Astronautica |date=February 2015 |last=Konstantinidis |first=Konstantinos |last2=Flores Martinez |first2=Claudio L. |last3=Dachwald |first3=Bernd |last4=Ohndorf |first4=Andreas |last5=Dykta |first5=Paul |volume=106| pages=63–89 |doi=10.1016/j.actaastro.2014.09.012 |url=https://www.researchgate.net/publication/268748795 |accessdate=April 11, 2015 |bibcode = 2015AcAau.106...63K }}
157. ^{{cite news |last=Anderson |first=Paul Scott |url=http://www.universetoday.com/93879/exciting-new-enceladus-explorer-mission-proposed-to-search-for-life/ |title=Exciting New 'Enceladus Explorer' Mission Proposed to Search for Life |work=Universe Today |date=February 29, 2012 | accessdate=April 9, 2014 }}
158. ^{{cite web |url=http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10081/151_read-2751/#gallery/4874 |title=Searching for life in the depths of Enceladus |publisher=German Aerospace Center (DLR) |date=February 22, 2012 |accessdate=April 9, 2014 }}
159. ^{{cite conference |last=Lunine |first=J. I. |last2=Waite |first2=J. H. |last3=Postberg |first3=F. |last4=Spilker |first4=L. |title=Enceladus Life Finder: The Search for Life in a Habitable Moon| url=http://www.hou.usra.edu/meetings/lpsc2015/pdf/1525.pdf |format=PDF |conference=46th Lunar and Planetary Science Conference (2015) |publisher= Lunar and Planetary Institute |place=Houston, Texas. |year=2015 }}
160. ^{{cite news |last=Clark |first=Stephen |url=http://spaceflightnow.com/2015/04/06/diverse-destinations-considered-for-new-interplanetary-probe/ |title=Diverse destinations considered for new interplanetary probe |work=Space Flight Now |date=April 6, 2015 |accessdate=April 7, 2015 }}
161. ^1 {{cite journal |title=Follow the Plume: The Habitability of Enceladus |journal=Astrobiology |date=April 15, 2014|display-authors=2|last=McKay |first=Christopher P. |last2=Anbar |first2=Ariel D. |last3=Porco |first3=Carolyn |last4=Tsou |first4=Peter |volume=14 |issue=4 |pages=352–355 |bibcode = 2014AsBio..14..352M |doi = 10.1089/ast.2014.1158 |pmid=24684187 }}
162. ^1 {{cite conference |last=Tsou |first=P. |last2=Brownlee |first2=D. E. |last3=McKay |first3=C. P. |last4=Anbar |first4=A. |display-authors=2 |title=Low Cost Enceladus Sample Return Mission Concept |url=http://lcpm10.caltech.edu/pdf/session-5/10_LIFE_LCPM_FINAL.pdf |format=PDF |conference=Low Cost Planetary Missions Conference (LCPM) # 10 |date=June 18–20, 2013 |access-date=April 9, 2014 |archive-url=https://web.archive.org/web/20140408060245/http://lcpm10.caltech.edu/pdf/session-5/10_LIFE_LCPM_FINAL.pdf |archive-date=April 8, 2014 |dead-url=yes |df=mdy-all }}
163. ^1 {{cite news |last=Wall |first=Mike |url=http://www.space.com/18792-enceladus-sample-return-mission.html |title=Saturn Moon Enceladus Eyed for Sample-Return Mission |work=Space.com |date= December 6, 2012 |accessdate=April 10, 2015 }}
164. ^{{cite journal |title=LIFE: Life Investigation For Enceladus A Sample Return Mission Concept in Search for Evidence of Life. |journal=Astrobiology |date=August 2012 |last=Tsou |first=Peter |last2=Brownlee |first2=D. E. |first3=Christopher |last3=McKay |last4=Anbar |first4=A. D. |last5= Yano |first5=H. |volume=12 |issue=8 |pages=730–742 |doi=10.1089/ast.2011.0813 |pmid=22970863|bibcode = 2012AsBio..12..730T }}
165. ^1 2 {{cite web |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=42337 |title=TandEM (Titan and Enceladus Mission) Workshop |website= |publisher=European Space Agency |date=February 7, 2008 |accessdate=March 2, 2008 }}
166. ^{{cite news |last=Rincon |first=Paul |url=http://news.bbc.co.uk/1/hi/sci/tech/7897585.stm |work=Science & Environment |title=Jupiter in space agencies' sights |publisher=BBC News |date=February 18, 2009 |accessdate=March 13, 2009 }}
167. ^1 {{Cite news|url=https://www.newscientist.com/article/mg23631533-900-private-mission-may-get-us-back-to-enceladus-sooner-than-nasa/ |title=Private mission may get us back to Enceladus sooner than NASA|work=New Scientist|access-date=2017-12-31|language=en-US}}
168. ^{{Cite news |url=https://firenewsfeed.com/lifestyle/720408| title='Looking for a smoking gun': Russian billionaire to fund alien-hunting mission to Saturn moon|access-date=2017-12-31| language=ru| archive-url=https://web.archive.org/web/20171231103746/https://firenewsfeed.com/lifestyle/720408|archive-date=December 31, 2017 |dead-url=yes| df=mdy-all}}
169. ^{{Cite news|url=https://spacenews.com/nasa-to-support-initial-studies-of-privately-funded-enceladus-mission/|title=NASA to support initial studies of privately funded Enceladus mission - SpaceNews.com|date=2018-11-09|work=SpaceNews.com|access-date=2018-11-10|language=en-US}}
170. ^[https://spacenews.com/nasa-to-support-initial-studies-of-privately-funded-enceladus-mission/ NASA to support initial studies of privately funded Enceladus mission]. Jeff Foust, 9 November 2018.
171. ^[https://www.nbcnews.com/mach/science/billionaire-aims-jump-start-search-alien-life-rewrite-rules-space-ncna949311 Billionaire aims to jump-start search for alien life and rewrite rules of space exploration]. Corey S. Powell NBC News. 19 December 2018.
172. ^A different trajectory for funding space science missions. Jeff Foust, Space Review. 12 November 2018.
173. ^[https://www.lpi.usra.edu/opag/meetings/nov2006/presentations/eagle.pdf EAGLE study]. (PDF) Mission to Enceladus - Overview. November 2006.
174. ^[https://www.lpi.usra.edu/opag/TitanEnceladusBillionDollarBox.pdf Titan and Enceladus $1B Mission Feasibility Study]. (PDF) NASA. 2006.
175. ^1 Enceladus Mission Options. Future Planetary Exploration. June 20, 2011.
176. ^{{cite book |last=Adler |first=M. |last2=Moeller |first2=R. C. |last3=Borden |first3=C. S. |last4=Smythe |first4=W. D. |last5=Shotwell |first5=R. F. |last6=Cole |first6=B. F. |last7=Spilker |first7=T. R. |last8=Strange |first8=N. J. |last9=Petropoulos |first9=A. E. |last10=Chattopadhyay |first10=D. |last11=Ervin |first11=J. |last12=Deems |first12=E. |last13=Tsou |first13=P. |last14=Spencer |first14=J. |displayauthors=2 |title=Rapid Mission Architecture (RMA) study of possible missions to Saturn's moon Enceladus |work=Aerospace Conference |publisher=IEEE |date=March 5–12, 2011 |doi=10.1109/AERO.2011.5747289 |issn=1095-323X |isbn=978-1-4244-7350-2 }}
177. ^{{cite web|last1=Spencer|first1=John|title=Planetary Science Decadal Survey Enceladus Orbiter |url=http://sites.nationalacademies.org/cs/groups/ssbsite/documents/webpage/ssb_059320.pdf|publisher=NASA|accessdate=23 June 2016|date=May 2010}}
178. ^{{cite news |last=Kane |first=Van |title=Discovery Missions for an Icy Moon with Active Plumes |url=http://www.planetary.org/blogs/guest-blogs/van-kane/20140402-discovery-missions-for-an-icy-moon-with-plumes.html |work=The Planetary Society |date=April 3, 2014 |accessdate=April 9, 2015 }}
179. ^{{cite news |last=Brabaw |first=Kasandra |url=http://www.space.com/28930-icemole-drills-glacier-saturn-moon-enceladus.html?cid=514630_20150408_43377416&adbid=10152745517721466&adbpl=fb&adbpr=17610706465 |title=IceMole Drill Built to Explore Saturn's Icy Moon Enceladus Passes Glacier Test |work=Space.com |date=April 7, 2015 |accessdate=April 9, 2015 }}
180. ^{{cite journal |title=LIFE – Enceladus Plume Sample Return via Discovery |journal=45th Lunar and Planetary Science Conference |year=2014 |last=Tsou |first=Peter |last2=Anbar |first2=Ariel |last3=Atwegg |first3=Kathrin |last4=Porco |first4=Carolyn |last5=Baross |first5=John |last6=McKay |first6=Christopher |url=http://www.hou.usra.edu/meetings/lpsc2014/pdf/2192.pdf |accessdate=April 10, 2015 }}
181. ^{{cite web|url=http://discoveringenceladus.com/downloads/LIFE%20-%20Life%20Investigation%20For%20Enceladus%20-%20A%20Sample%20Return%20Mission%20Concept%20in%20Search%20for%20Evidence%20of%20Life.doc |format=.doc |title=LIFE: Life Investigation For Enceladus – A Sample Return Mission Concept in Search for Evidence of Life. |last=Tsou |first=Peter |work=Jet Propulsion Laboratory |date=2013 |accessdate=April 10, 2015 |deadurl=yes |archiveurl=https://web.archive.org/web/20150901121008/http://discoveringenceladus.com/downloads/LIFE%20-%20Life%20Investigation%20For%20Enceladus%20-%20A%20Sample%20Return%20Mission%20Concept%20in%20Search%20for%20Evidence%20of%20Life.doc |archivedate=September 1, 2015 |df=mdy }}
182. ^Enceladus Life Finder 2015, PDF.
183. ^{{cite journal |title=Explorer of Enceladus and Titan (E2T): Investigating the habitability and evolution of ocean worlds in the Saturn system |journal=American Astronomical Society |year=2017|url=https://e2tmission.wordpress.com/ |last=Mitri, Giuseppe; Postberg, Frank; Soderblom, Jason M.; Tobie, Gabriel; Tortora, Paolo; Wurz, Peter; Barnes, Jason W.; Coustenis, Athena; Ferri, Francesca; Hayes, Alexander; Hayne, Paul O.; Hillier, Jon; Kempf, Sascha; Lebreton, Jean-Pierre; Lorenz, Ralph; Orosei, Roberto; Petropoulos, Anastassios; Yen, Chen-wan; Reh, Kim R.; Schmidt, Jürgen; Sims, Jon; Sotin, Christophe; Srama, Ralf |accessdate=2017-09-16 }}
184. ^{{cite news |url=http://futureplanets.blogspot.com/2017/08/proposed-new-frontiers-missions.html |title=Proposed New Frontiers Missions |work=Future Planetary Exploration |date=4 August 2017 |accessdate=2017-09-20 }}
185. ^{{cite news |last=McIntyre |first=Ocean |url=http://www.spaceflightinsider.com/missions/solar-system/cassini-legend-legacy-one-nasa-prolific-missions/ |title=Cassini: The legend and legacy of one of NASA’s most prolific missions |work=Spaceflight Insider |date=17 September 2017 |accessdate=2017-09-20 }}
186. ^1 2 {{cite journal |title =Thermal inertia and bolometric Bond albedo values for Mimas, Enceladus, Tethys, Dione, Rhea and Iapetus as derived from Cassini/CIRS measurements |last1=Howett |first1=C. J. A. |last2=Spencer |first2=J. R. |last3=Pearl |first3=J. |last4=Segura |first4=M. |date =2010 |journal=Icarus |volume =206 |issue =2 |pages =573–593 |doi =10.1016/j.icarus.2009.07.016 |bibcode=2010Icar..206..573H}}
187. ^1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 {{cite journal| doi = 10.1126/science.1123013| last1 = Porco| first1 = C. C.| authorlink1 = Carolyn Porco| last2 = Helfenstein| first2 = P.| last3 = Thomas| first3 = P. C.| last4 = Ingersoll| first4 = A. P.| last5 = Wisdom| first5 = J.| last6 = West| first6 = R.| last7 = Neukum| first7 = G.| last8 = Denk| first8 = T.| last9 = Wagner| first9 = R.| date = March 10, 2006| title = Cassini Observes the Active South Pole of Enceladus| journal = Science| volume = 311| issue = 5766| pages = 1393–1401| pmid = 16527964| pmc = | bibcode = 2006Sci...311.1393P| ref = {{sfnRef|Porco, Helfenstein et al. 2006}}}}
188. ^1 2 3 {{cite book| doi = 10.1007/978-1-4020-9217-6_24| last1 = Roatsch| first1 = T.| last2 = Jaumann| first2 = R.| last3 = Stephan| first3 = K.| last4 = Thomas| first4 = P. C.| year = 2009| chapter = Cartographic Mapping of the Icy Satellites Using ISS and VIMS Data| title = Saturn from Cassini-Huygens| pages = 763–781| isbn = 978-1-4020-9216-9| pmid = | pmc = | ref = {{sfnRef|Roatsch Jaumann et al.|2009}}}}
189. ^1 {{cite journal| doi=10.1086/508812| last1=Jacobson | first1=R. A.| last2=Antreasian | first2=P. G.| last3=Bordi | first3=J. J.| last4=Criddle | first4=K. E.| last5=Ionasescu | first5=R.| last6=Jones | first6=J. B.| last7=Mackenzie | first7=R. A.| last8=Meek | first8=M. C.| last9=Parcher | first9=D.| first10=F. J. | last10=Pelletier| first11=W. M. | last11=Owen, Jr.| first12=D. C. | last12=Roth| first13=I. M. | last13=Roundhill| first14=J. R. | last14=Stauch| date=December 2006| title=The Gravity Field of the Saturnian System from Satellite Observations and Spacecraft Tracking Data| journal=The Astronomical Journal| volume=132 | issue=6 | pages=2520–2526| url=http://iopscience.iop.org/1538-3881/132/6/2520/fulltext| bibcode=2006AJ....132.2520J| ref={{sfnRef|Jacobson Antreasian et al.|2006}}}}
190. ^1 2 {{cite journal| doi = 10.1126/science.1134681| last1 = Verbiscer| first1 = A.| last2 = French| first2 = R.| last3 = Showalter| first3 = M.| last4 = Helfenstein| first4 = P.| title = Enceladus: Cosmic Graffiti Artist Caught in the Act| journal = Science| volume = 315| issue = 5813| page = 815| date = February 9, 2007| pmid = 17289992| bibcode = 2007Sci...315..815V| ref = {{sfnRef|Verbiscer French et al.|2007}}}} (supporting online material, table S1)
191. ^1 {{cite web |author=Observatorio ARVAL |title=Classic Satellites of the Solar System |publisher=Observatorio ARVAL |date=April 15, 2007 |url=http://www.oarval.org/ClasSaten.htm |ref={{sfnRef|Observatorio ARVAL}} |accessdate=December 17, 2011 |archive-url=https://www.webcitation.org/61Cvx6xRx?url=http://www.oarval.org/ClasSaten.htm |archive-date=August 25, 2011 |dead-url=yes |df=mdy-all }}
192. ^1 {{citation | author=Taubner R. S. | author2=Leitner J. J. | author3=Firneis M. G. | author4=Hitzenberg, R. |title=Including Cassini gravity measurements from the flyby E9, E12, E19 into interior structure models of Enceladus. Presented at EPSC 2014-676 | journal=European Planetary Science Congress 2014 | volume=9 | pages=EPSC2014–676 |date=April 2014 |bibcode=2014EPSC....9..676T }}
}}
References
{{reflist| colwidth=30em
| refs=[186][187][188][189][190][191][192]
}}
Further reading
- {{Cite book |author=Ralph Lorenz |title=NASA/ESA/ASI Cassini-Huygens: 1997 onwards (Cassini orbiter, Huygens probe and future exploration concepts) (Owners' Workshop Manual)|publisher=Haynes Manuals, UK |year=2018 |isbn=978-1785211119}}
External links
{{Spoken Wikipedia|Enceladus (moon).ogg|October 24, 2011}}{{Sister project links|Enceladus}}- [https://web.archive.org/web/20070801204600/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Enceladus Enceladus Profile] at NASA's Solar System Exploration site
- Calvin Hamilton's Enceladus page
- The Planetary Society: Enceladus blogs
- CHARM: Cassini–Huygens Analysis and Results from the Mission page, contains presentations on Enceladus results
- Paul Schenk's 3D images and flyover videos of Enceladus and other outer solar system satellites
- Habitability of Enceladus: Planetary Conditions for Life
- Images
- Cassini images of Enceladus
- Images of Enceladus at JPL's Planetary Photojournal
- Movie of [https://web.archive.org/web/20100601171634/http://sos.noaa.gov/videos/Enceladus.mov Enceladus's rotation] from the National Oceanic and Atmospheric Administration
- Enceladus global and polar basemaps (December 2011) from Cassini images
- Enceladus atlas (May 2010) from Cassini images
- Enceladus nomenclature and Enceladus map with feature names from the USGS planetary nomenclature page
- [https://www.google.com/maps/space/enceladus/@-57.2040629,172.8918819,8043544m/data=!3m1!1e3 Google Enceladus 3D], interactive map of the moon
- [https://www.flickr.com/photos/kevinmgill/albums/72157676485084546 Image album] by Kevin M. Gill
- Richard Brocklesby (priest)
- Richard Brodie
- Richard Brodie (cricketer)
- Richard Brodie (disambiguation)
- Richard Brodie (footballer)
- Richard Broke
- Richard Bromfield
- Richard Bromley
- Richard Brompton
- Richard Bromsgrove
- Richard Bronaugh Barnitz
- Richard Bronson
- Richard Brook
- Richard Brook (bishop)
- Richard Brooke
- Richard Brooke (antiquary)
- Richard Brooke (disambiguation)
- Richard Brookes
- Richard Brookes (disambiguation)
- Richard Brooks (captain)
- Richard Brooks (Captain)
- Richard Brooks (disambiguation)
- Richard Brooks (footballer)
- Richard Brookshaw
- Richard Brooks (sailor)