Enceladus

View of trailing hemisphere in natural color
Voyager 2 view of Enceladus in 1981: Samarkand Sulci vertical grooves (lower center); Ali Baba and Aladdin craters (upper left)
Enceladus's orbit (red) – Saturn's north pole view
Possible origins of methane found in plumes
Eruptions on Enceladus look like discrete jets, but may be "curtain eruptions" instead ( video animation)
South polar view of the anti-Saturn hemisphere, with fractured areas in blue (false color)
Enceladus – tilted terminator – north is up
Enceladus – possibility of fresh ice detected (September 18, 2020)
Enceladus – Infrared map view (September 29, 2020)
View of Enceladus's Europa-like surface with the Labtayt Sulci fractures at center and the Ebony and Cufa dorsa at lower left, imaged by Cassini on February 17, 2005
Close-up of south pole terrain
Y-shaped discontinuities, imaged February 15, 2016
One possible scheme for Enceladus's cryovolcanism
A model of the interior of Enceladus: silicate core (brown); water-ice-rich mantle (white); a proposed diapir under the south pole (noted in the mantle (yellow) and core (red))
Artist's impression of a global subsurface ocean of liquid water ([[:File:PIA20013-Enceladus-SaturnMoon-ArtistConcept-20151026.jpg|updated and better scaled version]])
Enceladus – organics on ice grains (artist concept)
Chemical composition of Enceladus's plumes
Heat map of the south polar fractures, dubbed 'tiger stripes'
Enceladus (artist concept; February 24, 2020)
Artist's impression of possible hydrothermal activity on Enceladus's ocean floor
Animated 3D model of the Cassini–Huygens spacecraft
Enceladus orbiting within Saturn's E ring
Enceladus geyser tendrils - comparison of images ("a";"c") with computer simulations
Enceladus south polar region - locations of most active tendril-producing geysers
Enceladus and south polar jets (April 13, 2017).
Plumes above the limb of Enceladus feeding the E ring
A false-color Cassini image of the jets
Enceladus transiting the moon Titan
Size comparison of Earth, the Moon, and Enceladus
A size comparison of Enceladus against the British Isles.

Sixth-largest moon of Saturn .

- Enceladus

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William Herschel

German-born British astronomer and composer.

1785 portrait by Lemuel Francis Abbott
Original manuscript of Symphony No. 15 in E-flat major (1762)
Replica in the William Herschel Museum, Bath, of a telescope similar to that with which Herschel discovered Uranus
Herschel's mirror polisher, on display in the Science Museum, London
Uranus, discovered by Herschel in 1781
NGC 2683 is an unbarred spiral galaxy discovered by William Herschel on 5 February 1788
William and Caroline Herschel polishing a telescope lens (probably a mirror); 1896 lithograph
The 40-foot (12 m) telescope
A Cassini orbiter's view of Mimas, a moon of Saturn discovered by Herschel in 1789.
William Herschel's model of the Milky Way, 1785
William Herschel's coat of arms deemed a notorious example of debased heraldry: Argent, on a mount vert a representation of the 40 ft. reflecting telescope with its apparatus proper on a chief azure the astronomical symbol of Uranus irradiated or. Crest: A demi terrestrial sphere proper thereon an eagle, wings elevated or
William Herschel, portrait by James Sharples, c. 1805

Other work included an improved determination of the rotation period of Mars, the discovery that the Martian polar caps vary seasonally, the discovery of Titania and Oberon (moons of Uranus) and Enceladus and Mimas (moons of Saturn).

Moons of Saturn

Larger than the planet Mercury.

Saturn (overexposed) and the moons Iapetus, Titan, Dione, Hyperion, and Rhea viewed through a 12.5-inch telescope
Possible beginning of a new moon of Saturn imaged on 15 April 2014
Quadruple Saturn–moon transit captured by the Hubble Space Telescope
The number of moons known for each of the four outer planets up to October 2019. Saturn currently has 83 known satellites.
Shepherd moon Daphnis in the Keeler gap
Shepherd moons Atlas, Daphnis and Pan (enhanced color). They bear distinct equatorial ridges that appear to have formed from material accreted from Saturn's rings.
South pole map of tiger stripes on Enceladus
Diagram illustrating the orbits of the irregular satellites of Saturn. The inclination and semi-major axis are represented on the Y and X-axis, respectively. The eccentricity of the orbits is shown by the segments extending from the pericenter to apocenter. The satellites with positive inclinations are prograde, those with negative are retrograde. The X-axis is labeled in km. The prograde Inuit and Gallic groups and the retrograde Norse group are identified.
Orbits and positions of Saturn's irregular moons as of 1 January 2021. Prograde orbits are colored blue while retrograde orbits are colored red.
Orbital diagram of the orbital inclination and orbital distances for Saturn's rings and moon system at various scales. Notable moons, moon groups, and rings are individually labeled. Open the image for full resolution.

Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System (after Jupiter's Ganymede), with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes, Enceladus, which emits jets of gas and dust from its south-polar region, and Iapetus, with its contrasting black and white hemispheres.

Geyser

Spring characterized by an intermittent discharge of water ejected turbulently and accompanied by steam.

A cross-section of a geyser in action
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Hyperthermophiles produce some of the bright colors of Grand Prismatic Spring, Yellowstone National Park
Distribution of major geysers in the world.
The geyser Strokkur in Iceland – a tourist spot.

Water vapor jets have been observed near the south pole of Saturn's moon Enceladus, while nitrogen eruptions have been observed on Neptune's moon Triton.

Titan (moon)

Largest moon of Saturn and the second-largest natural satellite in the Solar System.

Pictured in 2012 in natural color. The thick atmosphere is orange due to a dense haze.
Christiaan Huygens discovered Titan in 1655.
Titan's orbit (highlighted in red) among the other large inner moons of Saturn. The moons outside its orbit are (from the outside to the inside) Iapetus and Hyperion; those inside are Rhea, Dione, Tethys, Enceladus, and Mimas.
True-color image of layers of haze in Titan's atmosphere
Trace organic gases in Titan's atmosphere—HNC (left) and HC3N (right).
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Methane clouds (animated; July 2014).
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False-color Cassini radar mosaic of Titan's north polar region. Blue coloring indicates low radar reflectivity, caused by hydrocarbon seas, lakes and tributary networks filled with liquid ethane, methane and dissolved . About half of the large body at lower left, Kraken Mare, is shown. Ligeia Mare is at lower right.
Mosaic of three Huygens images of channel system on Titan
Rimmed lakes of Titan (artist concept)
Near-infrared radiation from the Sun reflecting off Titan's hydrocarbon seas
Radar image of a 139 km-diameter impact crater on Titan's surface, showing a smooth floor, rugged rim, and possibly a central peak.
Ligeia Mare – SAR and clearer despeckled views.
Near-infrared image of Tortola Facula, thought to be a possible cryovolcano
False-color VIMS image of the possible cryovolcano Sotra Patera, combined with a 3D map based on radar data, showing 1000-meter-high peaks and a 1500-meter-deep crater.
Sand dunes in the Namib Desert on Earth (top), compared with dunes in Belet on Titan
Titan - three dust storms detected in 2009–2010.
Voyager 1 view of haze on Titan's limb (1980)
Cassini's Titan flyby radio signal studies (artist's concept)
The balloon proposed for the Titan Saturn System Mission (artistic rendition)
Global map of Titan – with IAU labels (August 2016).
Titan – infrared views (2004–2017)
Titan's North Pole (2014)
Titan's South Pole (2014)

The name Titan, and the names of all seven satellites of Saturn then known, came from John Herschel (son of William Herschel, discoverer of two other Saturnian moons, Mimas and Enceladus), in his 1847 publication Results of Astronomical Observations Made during the Years 1834, 5, 6, 7, 8, at the Cape of Good Hope.

Hydrothermal vent

Fissure on the seafloor from which geothermally heated water discharges.

In this phase diagram, the green dotted line illustrates the anomalous behavior of water. The dotted green line marks the melting point and the blue line the boiling point, showing how they vary with pressure; the solid green line shows the typical melting point behavior for other substances.
Deep-sea vent biogeochemical cycle diagram
Black smokers were first discovered in 1979 on the East Pacific Rise at 21° north latitude
A dense fauna (Kiwa anomurans and Vulcanolepas-like stalked barnacles) near East Scotia Ridge vents
Giant tube worms (Riftia pachyptila) cluster around vents in the Galapagos Rift
A cross-section of a typical volcanogenic massive sulfide (VMS) ore deposit as seen in the sedimentary record
Distribution of hydrothermal vents. This map was created by making use of the InterRidge ver.3.3 database.

Active hydrothermal vents are thought to exist on Jupiter's moon Europa and Saturn's moon Enceladus, and it is speculated that ancient hydrothermal vents once existed on Mars.

Cryovolcano

Type of volcano that erupts volatiles such as water, ammonia or methane into an extremely cold environment that is at or below their freezing point.

Doom Mons, one of the most reliably identified cryovolcanoes on Saturn's moon Titan
Plumes of Enceladus, feeding Saturn's E Ring, seem to arise from the "Tiger Stripes" near the south pole.

In addition, although they are not known to form volcanoes, ice geysers have been observed on Enceladus and potentially Triton.

Cassini–Huygens

The Cassini–Huygens space-research mission, commonly called Cassini, involved a collaboration among NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, including its rings and natural satellites.

Huygens' explanation for the aspects of Saturn, Systema Saturnium (1659)
Cassini-Huygens on the launch pad
Cassini-Huygens assembly
Titan's surface revealed by VIMS
Rhea in front of Saturn
Saturn's north polar hexagon
Saturn in natural-color (January 2010)
Animated 3D model of the spacecraft
Cassini UVIS instrument built by the Laboratory for Atmospheric and Space Physics at the University of Colorado.
VIMS spectra taken while looking through Titan's atmosphere towards the Sun helped understand the atmospheres of exoplanets (artist's concept; May 27, 2014).
A Cassini GPHS-RTG before installation
A glowing-hot plutonium pellet that is the power source of the probe's radioisotope thermoelectric generator
Animation of Cassini trajectory from October 15, 1997 to May 4, 2008 ·····
Animation of Cassini trajectory around Saturn from May 1, 2004 to September 15, 2017 ····
Picture of the Moon during flyby
A Jupiter flyby picture
Cassini photographed Io transiting Jupiter on January 1, 2001.
The possible formation of a new moon was captured on April 15, 2013.
Discovery photograph of moon Daphnis
Cassini arrival (left) and departure mosaics of Phoebe (2004)
Saturn reached equinox in 2008, shortly after the end of the prime mission.
Titan – infrared views (2004 – 2017)
View of Enceladus's Europa-like surface with the Labtayt Sulci fractures at center and the Ebony (left) and Cufa dorsa at lower left; imaged by Cassini on February 17, 2005
Ligeia Mare, on the left, is compared at scale to Lake Superior.
Titan - Evolving feature in Ligeia Mare (August 21, 2014).
Taken on September 10, 2007 at a distance of 62,331 km Iapetus's equatorial ridge and surface are revealed. (CL1 and CL2 filters)
Closeup of Iapetus surface, 2007
Northern hemisphere storm in 2011
The Day the Earth Smiled - Saturn with some of its moons, Earth, Venus, and Mars as visible in this Cassini montage (July 19, 2013)
2012 and 2016: hexagon color changes
2013 and 2017: hexagon color changes
Animation of Cassinis Grand Finale ·
Saturn by Cassini, 2016
Cassini-Huygens by the numbers (September 2017)
Farewell to Saturn and moons (Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus) (September 13, 2017)

The extension enabled another 155 revolutions around the planet, 54 flybys of Titan and 11 flybys of Enceladus.

Rings of Saturn

The rings of Saturn are the most extensive ring system of any planet in the Solar System.

The full set of rings, imaged as Saturn eclipsed the Sun from the vantage of the Cassini orbiter, 1.2 million km distant, on 19 July 2013 (brightness is exaggerated). Earth appears as a dot at 4 o'clock, between the G and E rings.
Voyager 2 view of Saturn casting a shadow across its rings. Four satellites, two of their shadows and ring spokes are visible.
Detail of Galileo's drawing of Saturn in a letter to Belisario Vinta (1610).
Huygens' ring theory in Systema Saturnium (1659).
Simulated appearance of Saturn as seen from Earth over the course of one Saturn year
Simulated image using color to present radio-occultation-derived particle size data. The attenuation of 0.94-, 3.6-, and 13-cm signals sent by Cassini through the rings to Earth shows abundance of particles of sizes similar to or larger than those wavelengths. Purple (B, inner A Ring) means few particles are < 5 cm (all signals similarly attenuated). Green and blue (C, outer A Ring) mean particles < 5 cm and < 1 cm, respectively, are common. White areas (B Ring) are too dense to transmit adequate signal. Other evidence shows rings A to C have a broad range of particle sizes, up to m across.
The dark Cassini Division separates the wide inner B Ring and outer A ring in this image from the HST's ACS (March 22, 2004). The less prominent C Ring is just inside the B Ring.
Cassini mosaic of Saturn's rings on August 12, 2009, a day after equinox. With the rings pointed at the Sun, illumination is by light reflected off Saturn, except on thicker or out-of-plane sections, like the F Ring.
Cassini space probe view of the unilluminated side of Saturn's rings (May 9, 2007).
A 2007 artist impression of the aggregates of icy particles that form the 'solid' portions of Saturn's rings. These elongated clumps are continually forming and dispersing. The largest particles are a few meters across.
The illuminated side of Saturn's rings with the major subdivisions labeled
A Cassini image of the faint D Ring, with the inner C Ring below
View of the outer C Ring; the Maxwell Gap with the Maxwell Ringlet on its right side are above and right of center. The Bond Gap is above a broad light band towards the upper right; the Dawes Gap is within a dark band just below the upper right corner.
The Cassini Division imaged from the Cassini spacecraft. The Huygens Gap lies at its right border; the Laplace Gap is towards the center. A number of other, narrower gaps are also present. The moon in the background is Mimas.
The central ringlet of the A Ring's Encke Gap coincides with Pan's orbit, implying its particles oscillate in horseshoe orbits.
observing the possible formative stage
Waves in the Keeler gap edges induced by the orbital motion of Daphnis (see also a stretched closeup view in the gallery).
Near Saturn's equinox, Daphnis and its waves cast shadows on the A Ring.
Propeller moonlet Santos-Dumont from lit (top) and unlit sides of rings
Location of the first four moonlets detected in the A ring.
The Roche Division (passing through image center) between the A Ring and the narrow F Ring. Atlas can be seen within it. The Encke and Keeler gaps are also visible.
The outer rings seen back-illuminated by the Sun
The Anthe Ring Arc – the bright spot is Anthe
The Phoebe ring's huge extent dwarfs the main rings. Inset: 24 µm Spitzer image of part of the ring
Saturn, behind the rings and draped with their shadows, as seen by Cassini from a distance of 725,000 km.
Cassini image mosaic of the unlit side of the outer C Ring (bottom) and inner B Ring (top) near Saturn's equinox, showing multiple views of the shadow of Mimas. The shadow is attenuated by the denser B ring. The Maxwell Gap is below center.
A spiral density wave in Saturn's inner B Ring which forms at a 2:1 orbital resonance with Janus. The wavelength decreases as the wave propagates away from the resonance, so the apparent foreshortening in the image is illusory.<ref group=n>Janus's orbital radius changes slightly each time it has a close encounter with its co-orbital moon Epimetheus. These encounters lead to periodic minor disruptions in the wave pattern.</ref>
Natural color view of the outer C Ring and B Ring.
Dark B Ring spokes in a low-phase-angle Cassini image of the rings' unlit side. Left of center, two dark gaps (the larger being the Huygens Gap) and the bright (from this viewing geometry) ringlets to their left comprise the Cassini Division.
Cassini image of the sun-lit side of the rings taken in 2009 at a phase angle of 144°, with bright B Ring spokes.
Pan's motion through the A ring's Encke Gap induces edge waves and (non-self-propagating) spiraling wakes<ref>NASA.gov</ref> ahead of and inward of it. The other more tightly wound bands are spiral density waves.
Radially stretched (4x) view of the Keeler Gap edge waves induced by Daphnis.
Prometheus (at right) and Pandora orbit just inside and outside the F Ring, but only Prometheus acts as a ring shepherd.
Prometheus near apoapsis carving a dark channel in the F Ring (with older channels to the right). A movie of the process may be viewed at the Cassini Imaging Team website<ref>{{cite web|url=http://ciclops.org/view.php?id=3806|title=Soft Collision (NASA Cassini Saturn Mission Images)|work=ciclops.org}}</ref> or YouTube.<ref>{{cite AV media|url=https://www.youtube.com/watch?v=6JdzjXlvBYE| archive-url=https://ghostarchive.org/varchive/youtube/20211107/6JdzjXlvBYE| archive-date=2021-11-07 | url-status=live|title=Prometheus collision|date=18 November 2007|work=YouTube}}{{cbignore}}</ref>
F ring dynamism, probably due to perturbing effects of small moonlets orbiting close to or through the ring's core.
Saturn's shadow truncates the backlit G Ring and its bright inner arc. A video showing the arc's orbital motion may be viewed on YouTube<ref>{{cite AV media|url=https://www.youtube.com/watch?v=jrmV07lzBsg| archive-url=https://ghostarchive.org/varchive/youtube/20211107/jrmV07lzBsg| archive-date=2021-11-07 | url-status=live|title=Saturn's G Ring|date=6 August 2007|work=YouTube}}{{cbignore}}</ref> or the Cassini Imaging Team website.<ref>{{cite web|url=http://ciclops.org/view.php?id=2273|title=Rounding the Corner (NASA Cassini Saturn Mission Images)|work=ciclops.org}}</ref>
Saturn and its A, B and C rings in visible and (inset) infrared light. In the false-color IR view, greater water ice content and larger grain size lead to blue-green color, while greater non-ice content and smaller grain size yield a reddish hue.

Like the O2, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic ions that bombard water molecules ejected by Saturn's moon Enceladus.

Saturn

Sixth planet from the Sun and the second-largest in the Solar System, after Jupiter.

Pictured in natural color approaching equinox, photographed by Cassini in July 2008; the dot in the bottom left corner is Titan
The symbol for Saturn in late Classical (4th & 5th c.) and medieval Byzantine (11th c.) manuscripts, derives from (kappa-rho).
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Composite image comparing the sizes of Saturn and Earth
Diagram of Saturn, to scale
Methane bands circle Saturn. The moon Dione hangs below the rings to the right.
A global storm girdles the planet in 2011. The storm passes around the planet, such that the storm's head (bright area) passes its tail.
Saturn and rings as viewed by the Cassini spacecraft (28 October 2016)
A montage of Saturn and its principal moons (Dione, Tethys, Mimas, Enceladus, Rhea and Titan; Iapetus not shown). This image was created from photographs taken in November 1980 by the Voyager 1 spacecraft.
Possible beginning of a new moon (white dot) of Saturn (image taken by Cassini on 15 April 2013)
Galileo Galilei observed the rings of Saturn in 1610, but was unable to determine what they were
Robert Hooke noted the shadows (a and b) cast by both the globe and the rings on each other in this drawing of Saturn in 1666.
Pioneer 11 image of Saturn
At Enceladus's south pole geysers spray water from many locations along the tiger stripes.
Amateur telescopic view of Saturn
Simulated appearance of Saturn as seen from Earth (at opposition) during an orbit of Saturn, 2001–2029
Saturn eclipses the Sun, as seen from Cassini. The rings are visible, including the F Ring.
orientation of its rings
HST Saturn portrait from 20 June 2019
Farewell to Saturn and moons (Enceladus, Epimetheus, Janus, Mimas, Pandora and Prometheus), by Cassini (21 November 2017).

This variance may be caused by geyser activity on Saturn's moon Enceladus.

Europa (moon)

Smallest of the four Galilean moons orbiting Jupiter, and the sixth-closest to the planet of all the 80 known moons of Jupiter.

Europa's trailing hemisphere in approximate natural colour. The prominent crater in the lower right is Pwyll and the darker regions are areas where Europa's primarily water ice surface has a higher mineral content. Imaged on 7 September 1996 by Galileo spacecraft.
Animation of the Laplace resonance of Io, Europa and Ganymede (conjunctions are highlighted by color changes)
Size comparison of Europa (lower left) with the Moon (top left) and Earth (right)
Approximate natural color (left) and enhanced color (right) Galileo view of leading hemisphere
Realistic-color Galileo mosaic of Europa's anti-Jovian hemisphere showing numerous lineae
Enhanced-color view showing the intricate pattern of linear fractures on Europa's surface
Two possible models of Europa
Europa - internal structure (artwork; 25 May 2021)
Closeup views of Europa obtained on 26 September 1998; images clockwise from upper left show locations from north to south as indicated at lower left.
Water plumes on Europa detected by the Galileo space probe
Photo composite of suspected water plumes on Europa
Magnetic field around Europa. The red line shows a trajectory of the Galileo spacecraft during a typical flyby (E4 or E14).
A black smoker in the Atlantic Ocean. Driven by geothermal energy, this and other types of hydrothermal vents create chemical disequilibria that can provide energy sources for life.
Europa – possible effect of radiation on biosignature chemicals

In addition, the Hubble Space Telescope detected water vapor plumes similar to those observed on Saturn's moon Enceladus, which are thought to be caused by erupting cryogeysers.