Dione->The notices described below are including both the original passages scheduled for the mission along with the passages which were performed during the first (2008-2010) and the second (2010-2017) extensions of the Cassini mission. Data collected during the extensions however mostly are added to any of the extant notices, except any passage of exception
Cassini had an original, official timetable about Saturn's moons, which was to perform imaging passages at Enceladus (four of them), and at Phoebe, Hyperion, Dione, Rhea, Epimetheus, Mimas, and Iapetus (one passage each) only. This timetable was accomodated to allow imaging passages of opportunity at other moons
You will note that some of the notices below may contain pictures which have not been taken during the flyby but which were released at the Cassini site at other moments
About Particle-Coated Surfaces at Moon of Saturn
Views in enhanced colors by late 2014 have shown that they are differences in color and brightness between
the two hemispheres of Tethys, Dione and Rhea. The dark reddish colors on the
moons' trailing hemispheres are due to alteration by charged particles and
radiation in Saturn's magnetosphere. Except for Mimas and Iapetus, the blander
leading hemispheres of these moon are all coated with icy dust from Saturn’s
E-ring, formed from tiny particles erupting from the south pole of Enceladus.
Enceladus itself displays a variety of colorful features. Some of the gas and
dust being vented into space from large fractures near the moon's south pole
returns to the surface and paints Enceladus with a fresh coating
62 Saturn's moons still feature many mysteries. They might be 4 billions years, or 100 million old and they did not form at the same time and rearranged somehow, or are captured objects, which determined their composition also. The presence of subterranean oceans is ill-explained
(notices by alphabetical order)
| Dione (2 Passages) Enceladus (4 Passages) Hyperion, Sep. 26, 2005 Iapetus (2 passages) | Mimas, Aug. 2, 2005 Phoebe, Jun. 11th, 2004 Rhea, Nov. 26, 2005 Tethys, Sep. 24, 2005 |
Cassini succesfully performed it first imaging passage at Dione, Dec. 14th. The craft was to fly at a distance of 50,600 miles (81,400 km) from the moon. The craft obtained the most detailed pictures ever of the moon. The bright, large, rays seen at Dione have been found bright, tectonics-related ice cliffs, forming braided canyons. "This is one of the most surprising results so far. It just wasn't what we expected," Dr. Carolyn Porco, Cassini imaging team leader, Space Science Institute, Boulder, Colo. said. From these first views, it seems that tectonics at Dione might be related to large impact craters. On the other hand, Dione is appearing like heavily cratered which is the mark of an old surface as some views taken earlier are showing three large, aligned, impact craters. The moon might also display a transient atmosphere. Further studies, on the other hand, hinted to that some kind of geological activity, or even ice volcanism likely occurs at Dione and makes that the moon is dilapidating icy, ionized particles into Saturn's magnetic field's plasma. Dione thus is encircled on its orbit with a cloud of methane and water ice. Dione, with Phoebe, Iapetus, Hyperion and Epimetheus, and also Saturn's F-ring likely sharing a common, comet-originating dark material. Of the five big icy moons of Saturn, Dione and Rhea are considered close relatives like already hinted too by the Voyager missions, which is probably coming from their nearness to each other in orbit. Rhea however does not sport a ring. Both are darker than the others as geological differences exist however, with while parts of Dione are heavily cratered like Rhea, there are other areas covered by relatively smooth plains which have been resurfaced at some point in Dione's past, an event that seems to be missing from Rhea. Sinuous canyons at Dione carve interconnected paths across the moon's icy landscape. Subtle variations in brightness hint at differences in composition, as well as the size and shape of grains in Dione’s regolith. Dione's density suggests that about a third of the moon is made up of a dense core (probably silicate rock) accounting for one third of the satellite, with the remainder of its material being water ice. At Dione's average temperature of -304 degrees Fahrenheit (-186 degrees Celsius), ice is so hard it behaves like rock. Dione is more heavily cratered on the trailing hemisphere as that unusual pattern suggests Dione suffered an impact which turned the moon 180 degrees
 | Dione seen from 746,000 miles (1.2 million km) on Oct 27, 2004. picture courtesy NASA/JPL/Space Science Institute |
 | Sequence about Dione (from left to right: Dione seen against the disk of Saturn; detailed view of Dione's rays (1); detailed view of Dione's rays (2); Dione cratered surface). picture site 'Amateur Astronomy' with pictures NASA/JPL/Space Science Institute |
 | Global mosaic view of Dione. The wispy, white trails have been surprisingly discovered to be bright, tectonics-related, ice cliffs rather than thick ice deposits. Such bright fractures are interestingly taking their origin in a in a region, the terrain of which is significantly darker than the rest of the moon. 'Wisps' are relatively young fractures found on the trailing hemisphere of Dione. picture courtesy NASA/JPL/Space Science Institute |
 | In this additional view taken Nov. 1, 2004, a line of three large impact craters is well seen near the terminator. This is another feature of Dione. picture courtesy NASA/JPL/Space Science Institute |
 | This other view of Dione, taken on Nov. 2 , 2004 is adding to a comprehensive understanding of the topography of Dione. Apart its bright rays, Dione seems to be characterized by large impact features. picture courtesy NASA/JPL/Space Science Institute |
 | Another view of Dione, taken on Dec. 14 , 2004 is showing other impact features at Dione. picture courtesy NASA/JPL/Space Science Institute |
 | Seen here (right) on an enhanced picture of Cassini is the large 109-mile (175 km) wide crater Aeneas. Its tall, 2-miles (3.2 km) high central peak is as high as the crater's walls. A part of Dione bright streaks is seen on the limb, at the upper right. picture site 'Amateur Astronomy' based on a picture courtesy NASA/JPL/Space Science Institute |
 | Crater Penelope, right (this view was not taken during the flyby). picture courtesy NASA/JPL/Space Science Institute |
 | This view, taken Aug. 1 from 167,000 mi (269,000 km), is showing how fractures in the southern polar region of Dione are softened, pointing to a different age. The region is also notably brighter. The X-shaped rayed feature near the center may be a rayed crater or a tectonic feature. It's named Cassandra. picture courtesy NASA/JPL/Space Science Institute |
Oct. 11, 2005
Cassini flew by Dione for the second time, on Oct. 11, 2005 from a distance of 310 miles (500 km). Dione is greyish in color, like most of Saturn's moons, as evidenced by one of the pictures taken, where the moon is seen against the backdrop of Saturn. It's heavily cratered like its sibblings in the Saturnian system as cracked features are dominating a whole side of the body, crosscutting everything. They are thought by scientists to be the older version of the tectonic fractures seen at Enceladus.
Dione was likely active in the past and could still be active now, like a weaker copycat Enceladus, alike with other solar system bodies which have a subsurface ocean (Titan, Europa) and among the
most geologically active worlds in our solar system. A faint particle stream coming from the moon has been observed and images showed
evidence for a possible liquid or slushy layer under its rock-hard ice crust. Other Cassini images have also revealed ancient, inactive fractures at Dione
similar to those seen at Enceladus that currently spray water ice and organic
particles. Dione gets heated up by being stretched and squeezed as it gets closer to and
farther from Saturn in its orbit and a icy crust that can slide around
independently of the moon's core. Thus the gravitational pulls of Saturn get
exaggerated and create 10 times more heat. Enceladus might have turned more active because maybe the larger fraction of rock in the core of Enceladus
provided more radioactive heating from heavy elements. Another striking feature at Dione are dense, fine and parallel fractures. Larger, irregular bright ones are interrupting the previous. Dione is featuring landslides too, revealing cleaner ice, with the dark materials accumulated downslope. Although Dione is orbiting within the E-ring, this ring which is nurtured by Enceladus' activity, the moon has not been seen with an atmosphere as the possible interaction of the ring's particles with Dione's surface will be investigated. Scientists are seeing Dione like an older Enceladus. Features' names on Dione are chosen by the International Astronomical Union (IAU) from the Virgil's Aeneid, this Roman version of the Odysseus. Following this passage, further pictures of the Moon showed that Dione leading hemisphere (the one with a large crater impact) is smoother than the trailing one (the one with the streaks), as the trailing hemisphere is dark, and the leading one bright as dark material of unknown origin is extant too at the moon. By 2012, the Cassini mission confirmed the
presence of a very tenuous atmosphere -or exosphere- at Dione, one of a thin neutral, with oxygen ions are quite sparse – one
for every 0.67 cubic inches of space or about 2,550 per cubic foot (90,000 per cubic meter). At the moon' surface that equals 300 miles (480 km) of altitude at Earth. Dione, with Saturn's rings and Rhea thus is a source of oxygen ion in the Saturnian system and molecular oxygen is actually common. Dione's oxygen appears to derive from either solar photons or energetic
particles from space bombarding the moon's water ice surface and liberating
oxygen molecules. Geological processes could also explain. A dark coating on the trailing hemisphere of Dione is thought to be due to radiation from Saturn’s magnetosphere, causing organic elements in the moon’s surface to become darker and redder as the leading hemisphere has been painted with icy dust from Saturn’s E-ring, itself fed by tiny particles ejected from nearby Enceladus. Dione's fractured surface certainly points to a more geologically active past, with also a underground ocean around a rocky core
 | Dione in color, seen on the background of Saturn and the ring. picture courtesy NASA/JPL/Space Science Institute |
 | Comprehensive view of Dione. picture courtesy NASA/JPL/Space Science Institute |
 | Receding limb of Dione, Cassini departing. picture courtesy NASA/JPL/Space Science Institute |
 | Striking: densely packed parallel grooves are seen in the inside of a crater, interrupted by larger, irregular fractures. Landslides are seen too. picture courtesy NASA/JPL/Space Science Institute |
 | False color composites have been applied unto a general view of Dione. This makes appear areas with possible different surface characteristics. picture courtesy NASA/JPL/Space Science Institute |
 | Real color view: craters and multiple generations of young, bright fractures slicing the terrain. picture courtesy NASA/JPL/Space Science Institute |
 | Linear grooves and subtle streaks. Picture taken Dec. 24, 2005. picture courtesy NASA/JPL/Space Science Institute |
 | This fine view of tectonic faults and craters is showing that the moon has had some kind of geologic activity. View taken on Dec. 24, 2005. picture courtesy NASA/JPL/Space Science Institute |
 | Detailed view of faults and craters. View dated December 24th, 2005. picture courtesy NASA/JPL/Space Science Institute |
Views taken after the imaging passage:
 | Another view of Dione. picture courtesy NASA/JPL/Space Science Institute |
 | Craters density gradation at Dione, with more craters on the right, sub-Saturn hemisphere, than on the left, anti-Saturn one, side. picture courtesy NASA/JPL/Space Science Institute |
 | Dione's trailing and leading hemispheres differ also by their luminosity, the trailing hemisphere being dark (to the left of the picture), and the leading one bright (to the right). picture courtesy NASA/JPL/Space Science Institute |
 | Wispy terrain of Dione is well seen here like a fractured region in this image of 2010. The wispy markings are actually exposures of bright ice along the steep walls of long scarps, or lines of cliffs, that indicate tectonic activity. Such systems of braided canyons are featuring bright walls . picture courtesy NASA/JPL/Space Science Institute |
 | The last passage at Dione by Cassini yielded that close-up view by the summer of 2015. picture site 'Amateur Astronomy' based upon a picture courtesy NASA |
 | A crater duo at Dione is seen superimposed on older, linear features. Fossae are believed to be tectonic features, formed when the area between tectonic faults drops down into trough-like structures. picture site 'Amateur Astronomy' based upon a picture courtesy NASA |
Feb. 17, 2005
Mar. 9, 2005
Jul. 14, 2005
Aug. 11, 2008
Feb. 17, 2005
Cassini successfully performed its first imaging passage of Enceladus at a distance of 730 miles (1,180 km). This flyby is the closest ever for this moon. Enceladus is of the same kind than Jupiter's Europa and Ganymede, that is that its surface is ice and, from these new pictures, it appears that ice tectonics and volcanism are active too at Enceladus. The Saturn's moon however is appearing much more with a snow-covered look compared to Jupiter's Europa which is much more icy-like. Enceladus has the most reflective surface of the solar system. Enceladus has a considerably higher reflectivity compared to other Saturn's moons with a similar composition, because it endures a constant
rain of ice grains from its south polar jets, yielding a more fresh, bright surface. As clean, fresh surfaces are left exposed in space,
they slowly gather dust and radiation damage and darken in a process known as
'space weathering.' A contrast, generally, exists at Enceladus between its older and newer
terrain as the latter had no time yet to accumulate craters. The most intriguing feature found at the moon are series of small, dark spots which, in many places, seem to be aligned in chains, parallel to narrow fractures, as the composition of the ice of Enceladus has been found pure water ice! Ammonia or carbon dioxide were expected. On March 12, 2008, Cassini further performed as low-pass flying over Enceladus to gather data from the plumes of the moon's geysers, which are rising to thousands of miles high. The probe just passed at 30 miles (50 km) over the surface. The passage also permitted to better detail the north polar region of Enceladus and see how it is much older and pitted with craters of various sizes, and at different stages of disruption and alteration by tectonic activity, and probably past heating from below. Craters further are sliced by small parallel cracks. The passage, at last, allowed, unexpectedly, to find that the material ejected through Enceladus' vents is similar to that of comets! The regions of the geysers, further, have been found with temperatures of at least minus 135°F (minus 93°C), about 200°F (93°C) warmer than the moon's other regions. Materials found in the plumes were volatile gases, water vapor, carbon dioxide and carbon monoxide, as well as organic materials. Enceladus was eventually found by 2015 featuring a subsurface ocean likely providing for south pole jet of vapor, icy particles and organic molecules. Underneath is to be found a large, rocky core
 | The entire globe of Enceladus. picture courtesy NASA/JPL |
 | A stunnigly detailed view of Enceladus's leading, or western, hemisphere. Near the South Pole, the more recently formed terrain transition to older terrains to the north. Lanes, on the hemisphere, enclose quasi-polygonal provinces of fractured, grooved, and striated plains of widely varying geological age. Heavily cratered terrain in the upper right of the image is the oldest. Less cratered terrain in the lower right is less old. Terrain on the left side of the image is younger, but that at the bottom is the youngest, most recently formed region. The image has been taken in visible light on a flyby performed on Nov. 21, 2009. picture courtesy NASA/JPL/Space Science Institute |
 | Mosaic view of Enceladus' south hemisphere. Linear grooves are crisscrossing the surface. picture courtesy NASA/JPL/Space Science Institute |
 | Enceladus is a world divided with North displaying copious amounts of craters as South with geological activity -- the plume above the south pole included -- resurfacing the satellite, with wrinkles. picture courtesy NASA/JPL-Caltech/Space Science Institute |
 | Relief features and impact craters. picture courtesy NASA/JPL/Space Science Institute |
 | Curious dark spots aligned in chains parallel to narrow fractures. These spots are 400-2,500 ft (125-750 m) wide. Area is 43 x 52 mi (70 x 84 km). picture courtesy NASA/JPL/Space Science Institute |
 | This false color view is showing how some linear features are slightly different in color than some others. It is unclear whether such variations are due to varying composition, varying ice crystal sizes and if they might be evidence for contamination of the ice. picture courtesy NASA/JPL/Space Science Institute |
 | Closest view of Enceladus by Cassini on Dec. 14, 2004. The moon is 417,600 mi (672,000 km) away. picture courtesy NASA/JPL/Space Science Institute |
->Cassini, as it's studying Saturn's ring has further confirmed the existence of a dust-icy cloud about Enceladus. The mystery of its origin are deepening as this might be an atmosphere, or particles coming from Saturn's E ring. In the first of the cases, it's the tidal interactions between Enceladus and Mimas which would have caused internal heating and water volcanism at Enceladus. The existence of the cloud of particles compared to the weak gravity of Enceladus needs a replenishment source however. To get more data, the Cassini team has decided to lower the next July 14th, 2005 flyby at Enceladus from 620 mi (1,000 km) to a stunning 109 mi only (175 km)!
->The Action of Enceladus on its Environment
Enceladus' impact on the Saturn's system seems more important than thought as the icy particles released by the moon's geysers are nurturing the E-ring, infiltrating into the planet's magnetic field, creating a donut-shape zone around Saturn, and, like lastly found, having the A-ring outer edge snatching the material in the donut. This is due to that the particles trapped into the powerful magnetif field of Saturn are bouncing back and forth to the poles of it, crossing the A-ring on the way. This leads to that the A-ring too is fed by the material from Enceladus. Those discoveries lead to think that the ring system at Saturn is in turn having a role compared to the magnetic environment of the planet, likely trapping part of the particles themselves trapped into the magnetic field. 150,000 miles (240,000 km) from Saturn, further, a cloud of water-related molecules is found too, likely migrating somewhat inwards to be absorbed by the A-ring. Water expelled from
the moon Enceladus forms a giant torus of water vapour around
Saturn and is the
source of the water in Saturn’s upper atmosphere. The torus is more than 373,000 miles (600,000 kilometers) across and
about 37,000 miles (60,000 kilometers) thick. Though most of the water in the torus is lost to space, water molecules, as far as they are concerned are reaching Saturn's atmosphere like broken down into separate atoms of hydrogen and
oxygen. When water lies in the torus, a dissociating processes first turn those into hydrogen and hydroxide, and
then the hydroxide dissociates into hydrogen and atomic oxygen. That oxygen self is
dispersed through the Saturn system. Astronomers calculated that Enceladus, every second, is ejecting
about 440 pounds (200 kilograms) of water vapor. Enceladus orbits the planet at a distance of about four Saturn radii, replenishing the torus with its jets of water. Saturn's atmosphere is known to contain traces of gaseous water in its deeper layers. A particular enigma has been the presence of water in its upper atmosphere. As most of the water from Enceladus is lost into space, freezes on the rings or perhaps falls onto Saturn’s other moons, the small fraction that does fall into the planet is sufficient to explain the water observed in its upper atmosphere. It is also responsible for the production of additional oxygen-bearing compounds, such as carbon dioxide. Ultimately, water in Saturn's upper atmosphere is transported to lower levels, where it will condense but the amounts are so tiny that the resulting clouds are not observable. Saturn and its moon Enceladus on the other hand are electrically linked as magnetic field lines arc from Saturn’s north polar region to south polar region. Enceladus resides in the arc of a set of the field lines which also causes feeding charged particles into the Saturn atmosphere to a glowing patch of ultraviolet light on the planet. Interaction between Enceladus and Saturn makes that the latter responds by launching signals in the form of plasma waves, through the circuit of magnetic field lines connecting it to Enceladus, a response to that Enceladus is emitting plumes of water vapor that become ionized and fill the environment around Saturn. Geysers give birth to long, sinuous, tendril-like structures seen in the vicinity of Enceladus. Tendrils reach into Saturn's E ring in which Enceladus orbits extending tens of thousands of miles (or
kilometers) away from the moon. The gravitational pull of Saturn changes the amount of particles spraying from the south pole of Enceladus at different points in its orbit, with the jets more active when the moon farthest away from its planet. A cycle of activity in these jets, generally, may be periodically lofting extra particles into space, causing
the overall plume to brighten dramatically as gas and water in the plume do not play a important role into pushing the dust into space
Enceladus is an icy and snowy world, maybe akin to Miranda, one of the moons of Uranus, as it seems to have an atmosphere on the other hand, that's what Cassini saw during its second imaging passage at the Saturnian moon! This second passage was made at an altitude of 310 mi (500 km) only. Enceladus is a world of ice vastnesses, grooves, slabs, and fractured terrain, with craters. As far as its atmosphere is concerned, it was noticed by Cassini by measuring Saturn's magnetosphere. The latter was found perturbed at the level of Enceladus, hinting to a possible extended, thin atmosphere. As the gravity at Enceladus is too weak to retain such an envelope, it has to be constantly replenished. This might be the fact of volcanism, geysers or gases coming from the surface or the interior. Should such an activity be confirmed, Enceladus might become, along with Io of Jupiter, and Triton of Neptune, the third moon with an active surface. It was known already since the Voyagers that some geological activity at Enceladus -whatever it might be- seemed responsible for Saturn's icy E ring. It might that the same activity be responsible for the permanent deposit of fresh snow at the surface of Enceladus. The complex web of interaction
between Saturn and Encealdus also holds a glowing
patch of ultraviolet light emissions near Saturn's north pole that marks the
presence of a magnetic circuit linking Saturn to its moon. The patch occurs at the end of the connecting magnetic field lines. The process is the same than the one creating Saturnian auroras as energetic
electrons dive into the planet's atmosphere. The auroral occurrence originates from a beam of energetic protons near Enceladus aligned
with the magnetic field and field-aligned electron beams as currents travel from the moon to the top of Saturn's
atmosphere. The massive, ionized plasma at Enceladus is produced by Enceladus interactions with the magnetic bubble around Saturn. The footprint appears to flicker hinting to that the rate at which Enceladus is spewing particles may vary. The footprint however is very small, compared to a aurora, as measured about 750 miles (1,200 kilometers) by less than 250 miles (400 kilometers) or comparable to the size of California and very feeble in luminosity. It is
located by about 65 degrees north latitude or slightly below the auroral oval. As the magnetic lines linking Enceladus to Saturn is also reaching to the southern pole, no footprint have been observed there yet
 | This fine natural color view of Enceladus is showing the snowy surface. Rugged ridge crests near upper left are ranging in height from 164 to 328 ft (50-100 m). Craters (few on this picture) and ridged and grooved region seem to be characterized by large grain ice. picture courtesy NASA/JPL/Space Science Institute |
 | The crater at the image's top is 13-mile wide (21 km) as the prominent, complex fracture in the bottom extends over 53 miles (85 km). The narrow, parallel grooves seen in abundance, are slicing the surface into parallel slabs of ice 1,600 ft (500 m) each in thickness. picture courtesy NASA/JPL/Space Science Institute |
 | The crater bottom is 12-mile wide (20 km). Fractures and faults are ranging from as narrow as a few hundred yards (meters) up to 3 miles (5 km). See the large portion of fractured terrain at picture's upper right. picture courtesy NASA/JPL/Space Science Institute |
 | Fractures 330 to 1,300 feet wide (100-400 m) are well visible on this picture. Such features are due to tectonic stress. picture courtesy NASA/JPL/Space Science Institute |
 | Further fractures of the surface are "slicing" craters. The one near the upper right is 6-mile-wide (10 km). picture courtesy NASA/JPL/Space Science Institute |
 | Band in enhanced colors are seen on Saturn's moon as they are mostly due to Enceladus spray and the E ring. As the moon is covered by the fallback of its own particles, Tethys, Dione and Rhea are concerned on their leading or Mimas on the trailing (because it orbits inside Enceladus orbit). At Tethys, Dione and Rhea with darker, rust-colored reddish hues paint the entire trailing hemisphere from circulating Saturn magnetosphere's plasma. Tiny, iron-rich "nanoparticles" may also be involved. Mimas and Tethys also sport a dark, bluish band which might be irradiated by high-energy electrons that drift in a direction opposite to the flow of Saturnian plasma. On Rhea, a unique chain of bluish splotches appears where fresh, bluish ice has been exposed on older crater rims maybe due to the crash of orbiting material, perhaps a ring in the not too distant past. Inktomi Crateris, a impact crater which exhausted fresh material, is believed to be the youngest feature on Rhea. picture courtesy NASA/JPL/SSI/LPI |
 | That picture is showing how Enceladus and Saturn link through magnetic lines. The box, right, is showing a cross-section of the magnetic field lines as the white square, links, is showing where the magnetic footprint is reaching close to Saturn's north pole and aurora. picture courtesy site 'Amateur Astronomy' based upon a picture NASA/JPL/JHUAPL/University of Colorado/Central Arizona College/SSI |
 |
Enceladus is a world divided. To the north, the terrain is covered in impact
craters, much like other icy moons. But to the south, the record of impact
cratering is much more sparse, and instead the land is covered in fractures,
ropy or hummocky terrain and long, linear features. Further studies just brought the evidence of what was expected! Enceladus is really an active body with icy volcanism and hot spots replenishing a huge cloud over the moon's south pole. The activity at Enceladus is likely due to tidal energy as the cloud might come from a localized source comparable to a geothermal hot spot. The fractures at the southern region of the moon are contributing too. Enceladus, on the other hand is really at the origin of the E ring as micrometeoroids blast particles off, forming a further icy dust cloud. A part of the particles are escaping, forming the bulk of the E ring. The south pole, generally, has been found warmer (-307°F with small areas near the faults at -261°F, -153°C/-128°C) than the equator (-316°F, -158°C)
Most recent data are showing that the tidal fractures seen around Enceladus' south pole are very recent -something like between 10 and 1,000 years old, likely the sources for the moon's south atmosphere. picture: Enceladus cloud-shaped atmosphere, picture NASA/JPL
An Overview of the Question of the Geothermy at Enceladus and the Moon's Potential for Life Get more details about the geothermal activity at Enceladus and that the moon might be another world in the solar system prone to life. go to the overview!
| Elements of the Enceladus' atmosphere | |
|---|---|
| Compound | Percent |
| water vapor | 65 |
| molecular hydrogen | 20 |
| carbon dioxide, molecular nitrogen, carbon monoxide | remaining 15 |
This third flyby was the closest to the moon, with a mere 109 mi (175 km) from the surface.
The most important target was to look at the southern, geologically-young, polar region to search for evidence of geologically recent tectonic or volcanic activity. The findings are matching what was expected. Cassini pictures are revealing areas almost entirely free of impact craters, with house-sized ice boulders. The global emerging image of Enceladus is that this moon has endured multiple geological episodes, compared to the other moons of Saturn, which, most, are highly cratered and have a much more tormented terrain. Enceladus, as far as it is concerned has much more light relief features, likely due to tectonics-linked resurfacing. It seems, on the other hand, that a Y-shaped tectonic fault is isolating the south polar terrains from the older surrounding ones, at about 60° south latitude. Such a fault would moreover be an hint to that the rotation of Enceladus evolved over time, this having provided the energy for the geological activity. The youth of the south polar regions of the moon is further evidenced by the coarse-grained ice cover and ice fractures seen there. Tectonics, faults, and boulders at Enceladus' south pole! The south polar region of Enceladus was found by 2017 warmer than expected just a few feet below the surface, hinting to that Enceladus' ocean of liquid water might be only a couple of miles beneath -- which is closer than previously thought -- That status have been found over three dormant fractures. That might suggest the moon might have experienced several episodes of activity, in different places on its surface and agrees with a 2016 study finding that Enceladus' icy crust had a average depth of 11 to 14 miles (18 to 22 kilometers), with a thickness of less than 3 miles (5 kilometers) at the south pole
 | This enhanced-color view (infrared, green, ultraviolet; image re-worked by this site) is showing at the lower right the faults-ridden terrain at the moon's south pole. The "petal-shaped" aspect of a series of fault is hinting to a variation of Enceladus' rotation. picture courtesy NASA/JPL/Space Science Institute |
 | The terrain at Enceladus' south pole as seen from 129 mi (208 km) with a resolution of 121 ft (37 m) per pixel is showing a tormented, and faulted terrain. The insert is showing a most detailed view of a part of the terrain, with ice boulders. This view is seen in its larger size on the following picture. picture courtesy NASA/JPL/Space Science Institute |
 | This most detailed view is a detailed view of the center of the previous picture. Ice boulders, the origin of which is enigmatic, are seen, with a size between 33 and 330 ft (10 and 100 m)!. picture courtesy NASA/JPL/Space Science Institute |
 | On this picture dated Dec. 24, 2005, a transition is well seen between the wrinkled and the cratered terrain at Enceladus. picture courtesy NASA/JPL/Space Science Institute |
 | At its flyby at Enceladus on Oct. 14, 2015, by 1,142 miles (1,839km) of altitude, Cassini took that stunning image of the moon's north pole. The northern regions are crisscrossed by a spidery network of gossamer-thin cracks that slice through the craters as such thin cracks are ubiquitous on Enceladus. picture site 'Amateur Astronomy' sur la base d'une image NASA/JPL-Caltech/Space Science Institute |
 | NASA's Cassini spacecraft spied this tight trio of craters as it approached Saturn's icy moon Enceladus for a close flyby on Oct. 14, 2015. picture site 'Amateur Astronomy' sur la base d'une image NASA/JPL-Caltech/Space Science Institute |
Aug. 11, 2008
During its flyby at Enceladus on August 11th, 2008 (this passage was not scheduled as the one of March 12th, 2008 doesn't have a rubric there), Cassini focused upon the source of the moon's particles jets, and especially the 'tiger stripe' fractures near the southern pole, also called 'sulci'. The sulci are about 980 ft (300 meters) deep, with sharp walls and the outer flanks of some coated with fine material as they are spewing jets of water vapor and organic particles hundreds of miles, out into space. Finely fractured surface, littered with blocks of ice tens of yeards (tens of meters) in size and larger surround the fractures. The mechanism of jets is that warm water vapor rises from the underground to the surface through narrow channels. The water may condense and seal off an active vent. New jets then are appearing elsewhere along the sulci! The ice and particles jets emanating from Enceladus pole are spewing even trace organics into the surrounding space! Correlation the spraying of jets of water vapor with the way Saturn's gravity stretches and stresses the
fissures have been proved in March 2012 with scientists showing that the greatest stresses pulling apart the tiger stripes,
occurred right after Enceladus made its closest approach to Saturn in its orbit. Saturn's gravitational pull could also deform the
fissure by making one side move relative to the other side. That kind of
deformation seemed to occur even when Enceladus is very far away from Saturn. The reverse might also be true. Such flexion enough might well be enabled by a global, or local subterranean ocean on Enceladus. A enormous amount of heat is also yielded by Saturn's
tides in the area. The high speed of Cassini during the flyby (40,000 miles per hour -64,000 km/h) necessitated a special technique called 'skeet shooting' at the effect to cancel out the large relative speed of the mission relative to Enceladus. The technique consisted into pointing the craft far ahead of Enceladus, have it spin as a whole in the direction of the apparent path of the moon, to have the craft's motion matching Enceladus one
 | Baghdad and Cairo Sulcus as seen during the Aug. 11, 2008 flyby. Features at Enceladus are named from characters and places from 'The Arabian Nights'. Images range in resolution from 33 to 79 feet (10 to 24 meters) per pixel. picture courtesy NASA/JPL/Space Science Institute |
 | This picture, which was taken during a following passage, on Nov. 21, 2009, is showing another region littered with ice boulders, showing that the feature seems frequent at Enceladus. picture courtesy NASA/JPL/Space Science Institute |
 | A perspective view of Baghdad Sulcus, a linear, active structure at the south pole of Enceladus, with views ranging in resolution from 40 to 100 feet (12 to 30 meters) at the best, to 165 to 260 feet (50 to 80 meters) either side. Each main trough is 1.2-mile (2 km)-across and 910 to 1,150 ft (280 to 360 meters)-deep. Relief has been exaggerated by a factor of 10 to enhance clarity. picture courtesy NASA/JPL/Space Science Institute/Universities Space Research Association/Lunar & Planetary Institute |
 | A mass spectrum that shows the chemical constituents sampled in Enceladus' plume by Cassini's Ion and Neutral Mass Spectrometer during its fly-through of the plume on Mar. 12, 2008. picture courtesy NASA/JPL/SwRI |
 | Gravity measurements in April 2014 suggest that Enceladus possesses a ice outer shell and a low density, rocky core with a regional water ocean sandwiched in between at high southern latitudes. picture courtesy NASA/JPL-Caltech |
 | Enceladus' jets are venting into space from the moon's subterranean global ocean. picture site 'Amateur Astronomy' based upon a picture courtesy NASA |
 | Enceladus drifts before Saturn's rings as its plumes of water ice is seen at the moon's south pole. The bright speck to the right of Enceladus is a bright star in the field. picture site 'Amateur Astronomy' based upon a picture courtesy NASA/JPL-Caltech/Space Science Institute |
 | The Cassini spacecraft performed its final close flyby of Enceladus, on Dec. 19, 2015. It captured that view (left) of the nearly parallel furrows and ridges of the feature named Samarkand Sulci as it also peered out over the moon's northern territory (right), capturing this view of two different terrain types. A region of older terrain covered in craters that have been modified by geological processes is seen at right, while at left is a province of relatively craterless, and presumably more youthful, wrinkled terrain (pictures colorized by us). picture site 'Amateur Astronomy' based upon pictures courtesy NASA/JPL-Caltech/Space Science Institute |
 | The last flyby at Enceladus also allowed to those small dark spots on that image. Those are evidently large, relatively dark protrusions of solid bedrock ice and ice blocks scattered on and around the prominent ridge that runs across the scene from North to South (from top center toward lower left). The ice blocks range in size from dozens to hundreds of feet (tens to hundreds of meters). The light used to that picture is covering a wider spectrum region than the human eye. Exposures of these kinds of ices are also found on the walls of cracks and troughs in this scene and elsewhere on Enceladus. The prominent trending ridge might be tilted, triangular outcroppings of rock, or flatirons like seen at Earth but more shallow. Sublimation or downslope movement are a factor of erosion as there is no wind at Enceladus. This terrain is on Enceladus' Saturn-facing side, a few degrees South of the equator, and North is up. picture site 'Amateur Astronomy' based upon a picture courtesy NASA |
 | The north polar area of Enceladus (313 miles or 504 kilometers across) seen on that view of 2016 is heavily cratered, as opposed to south polar region which shows signs of a intense geologic activity focused around the long fractures known as 'tiger stripes' that spray gas and tiny particles from the moon. based upon a picture courtesy NASA |
->the dark material at Hyperion explained! It's of the same kind than the one found at Iapetus! check more!
Cassini flew by Hyperion on September 26th, 2005 by a distance of 310 miles (500 km). Hyperion, despite the fact it's one of Saturn major moons, is a rubble-pile moon with an irregular shape just like the ring-linked minor moons. Many craters at this moon have a dark floor. Such a dark material seems to be only tens of yards (tens of meters) thick. Evidence of landslides have been seen too. In natural color, Hyperion has a reddish color. Hydrocarbons found on Hyperion lead to think that life building blocks are much more usual than thought in the Universe. Dark material might get deeper into the surface due to a process called 'thermal erosion' as Sun' heat allow the material deeper. Hyperion, with Phoebe, Iapetus, and Epimetheus, and also Saturn's F-ring and Dione likely sharing a common, comet-originating dark material. Evidence of static charge have been found at Hyperion, beaming electrons in the nearby space. Hyperion is the largest of Saturn’s irregular moons and might be the remnant of a violent collision that shattered a larger object into pieces. Cassini scientists attribute Hyperion's peculiar, sponge-like appearance and numerous cratersto the fact that it has an unusually low density for such a large object indicating that Hyperion is quite porous, with a weak surface gravity. These characteristics mean impactors tend to compress the surface, rather than excavating it, and most material that is blown off the surface never returns. Hyperion's (168 miles or 270 kilometers across) spin axis has a chaotic orientation in time, meaning that it is essentially impossible to predict how the moon will be spinning in the future
 | This might be the natural color of Hyperion. Various hues might hint to various materials (picture modified by the site 'Amateur Astronomy' from a false-color picture Cassini). picture courtesy NASA/JPL/Space Science Institute, modified site 'Amateur Astronomy' |
 | Cassini took this shot of Hyperion's limb as getting distant from the moon. picture courtesy NASA/JPL/Space Science Institute |
 | Dark-floored craters and landslide materials are seen here in this detailed view. picture courtesy NASA/JPL/Space Science Institute |
 | Cassini returned images from its final close approach to Hyperion on May 31, 2015, with many craters displaying dark material on their floors. The pictures were taken at a distance of about 21,000 miles (34,000 kilometers). picture courtesy NASA |
 | A more detailed view than the previous taken at the same distance of about 21,000 miles (34,000 kilometers). picture courtesy NASA |
Pictures dating from before the flyby:
 | Non spherical Hyperion seen from 1.4 million miles (2.2 million km), Oct 20, 2004. picture courtesy NASA/JPL/Space Science Institute |
| Hyperion seen from 2.2 million miles (3.5 million km), Dec. 10, 2004. Hyperion is the largest irregularly-shaped moon in the solar system. It's 165 miles (266 km) across. picture courtesy NASA/JPL/Space Science Institute |
 | Hyperion seen in October 2004 and February 2005 from distances ranging 800,000-990,000 mi (1.3-1.6 million km). The best September 2005 passage altitude at Hyperion has been lowered from 615 to 310 mi (990-500 km). picture courtesy NASA/JPL/Space Science Institute |
 | Hyperion seen on Feb. 23, 2005 from 1 million miles (1.6 million km) away. picture courtesy NASA/JPL/Space Science Institute |
 | Another view from 824,000 mi (1.3 million km)). picture courtesy NASA/JPL/Space Science Institute |
The Dark Material Explained at Iapetus, Phoebe and Hyperion: Hydrocarbon Turned Interstellar Dust-Like Substance!
As astronomers knew for long that such material originates in the original proto-planetary disk and that, from sampling the asteroids, they range in color from neutral gray to deep red, they never could match the spectrum of it to known Earth's material until in the late 1970's when they were able to make in a laboratory, an organic substance they named 'tholin'. Tholin is an hydrocarbon. Thus the red substance of most asteroids and the three moons of Saturn is such an organic, hydrocarbon substance. A darkening and dehydrogenation of organic molecules by the space environment of the moons and the other objects however had mostly turned the material into a substance similar to the interstellar dust grains. Such processes likely account for the variety of colors found on asteroids and Kuiper Belt objects!
A Tenuous Ring Discovered at the Orbit of Phoebe Likely Involved Too!
A immense, tenuous ring discovered at the orbit of Phoebe by the Spitzer Space Telescope in October 2009 likely is contributing too to the darkening of a part of Iapetus! The ice and dust of that ring is likely generated starting at Phoebe!
Dec. 31, 2004
Sep. 10, 2007
Additional Pictures
Cassini successfully imaged Iapetus, the two-sided moon of Saturn, on December 31st, 2004. JPL received confirmation that the probe glided at Iapetus at a distance of 76,700 miles (123,400 km). Imaging focused primarily on the dark terrain of Iapetus, in an area known as Cassini Regio. The pictures obtained are at the same time the most detailed ever of the moon with a planned resolution of 1.5 km per pixel and better to 8 km per pixel for Voyager 2 in August 1981. Three main centers of interest appeared from the flyby. Large impact basins, old and younger ones, are seen. Younger ones have steep slopes of about 9-mile (15 km) high. An immense, tall, narrow ridge, is lying along the moon's equator, reaching 8-mile (13 km) high, 12-mile (20 km) wide, and extending at least over an entire hemisphere . No such a feature is seen elsewhere in the solar system. It may either be a mountain range that was pushed up through tectonics, or a line of fault from which icy material erupted and accumulated. At last, the aspect of the moon's dark/bright dichotomy was further investigated. Due to the coating aspect of the dark material and to streaks of it extending South-North, the dark region is a young geological event at Iapetus, and a light one -that is it did not eradicate the previous terrain, as its explanation might be constrained to either some material coming from an impact event at an other moon of Saturn, to plume-style eruptions to which the tall equatorial ridge might be related, or to an impact event. Another hint provided by this passage is that north-facing scarps or craters' slopes are bright as south-facing dark. This might mean that the dark material process -this bodes well with the streaks- might imply a South-North motion. It's the leading atmosphere of Iapetus (the one in the direction of the moon's orbit) which is dark and the trailing one which is bright. Temperatures measured at Iapetus are -226°F (-107°C) at noon, at the equator in the dark regions -probably the warmest place in the Saturn system, and -280°F (-136°C) at the bright regions. On the other hand the dark region's thermal inertia is weak -which means the material there is bad at storing heat. The heat quickly dissipates at night, hinting to some fluffy material which may originate from the pulverizing effect of billions of years of meteorite impacts, or from the darkening process too. The nut-like shape of Iapetus is due to that, at its beginnings, the moon was rotating more swiftly (about in 5 hour instead of 80 days now) and was warmer than today, hence acquiring an oblong shape. That shape collapsed into Iapetus' mountain range, when Iapetus colded
Iapetus, like Phoebe, Hyperion, Epimemtheus, Dione and Saturn's F-ring likely sharing a common, comet-originating dark material
 | This map of Iapetus is showing the imaging area of Cassini during its passage at Iapetus Dec. 31, 2004. Yellow circles are the two large circular features seen on the pictures as red ones are other ones seen on various images. The relative sizes may be non accurate. picture 'Amateur Astronomy', map NASA/JPL/Space Science Institute |
 | This composite is showing a global, colorized (by the site 'Amateur Astronomy') view of Iapetus during Cassini approach (left) and three views showing (from left to right), a part of the largest 375-mile (600 km) wide impact basin, the boundary zone between the bright (top) and dark (bottom) region, an an overall view of the dark region. picture 'Amateur Astronomy' based on pictures courtesy NASA/JPL |
 | Global mosaic centered on Cassini Region (equator/90°W), that is the leading hemisphere of the moon. The dark region albedo is of the order of 4 percent, the bright's of 60 percent. The equatorial ridge is well documented. The largest 375-mile (600 km) impact basin is seen right as a smaller, eroded one is seen just at the picture's center. picture courtesy NASA/JPL/Space Science Institute |
 | This truecolor view is useful to discriminate between shadows (black) and dark terrain (brownish). The dark streaks, pointing northeast are well seen, typically a few kilometers wide and sometimes tens of kilometers long.. picture courtesy NASA/JPL/Space Science Institute |
 | The larger circular, caldeira-like feature is impressive with its steep, tall slopes which may reach 9-mile (15 km) high. On the other hand it gives a detailed view of the dark terrain. Slopes are about. picture courtesy NASA/JPL |
 | A landslide inside the 375-mile (600 km) impact basin. Scarp is 9-mile (15 km) high as the distance to which the landslide slipped is indicative of that the surface icy material at Iapetus is very fine-grained, being able to flow extended distances. picture courtesy NASA/JPL/Space Science Institute |
 | This view in the infrared is showing an upper, ice-rich, blue region and a lower, dark brown, organic materil related region, as the yellow region is a mixture of ice and organics. Such a gradation might hint to the outer moons debris origin of Iapetus dark material. picture courtesy NASA/JPL/University of Arizona |
 | Surface composition at Iapetus. Rightmost picture is a composite where minerals are red, carbon dioxide green and water/water ice blue. B&w pictures are, from left to right: minerals, carbon dioxide, water/water ice. picture courtesy NASA/JPL/GSFC |
->More About Iapetus' Surface
Cassini completed a second flyby at Iapetus on Sept. 10, 2007, with the craft flying at 1,000 miles (1,640 kilometers) above the surface of the moon. The passage helped to better characterize the nature of the dark-bright terrain differentation which is seen at Iapetus. It seems like the dark material originally originated at dust coming from moons orbiting at a much greater distance from Saturn, and in an opposite direction, hitting Iapetus head-on, and causing the forward-facing side of Iapetus to darken. Then, a thermal process triggers, with a darken surface absorbing more sunlight and warm up, leading to that the water ice at the surface evaporates. That vapor then condenses, possibly at the moon's poles then too at areas at lower latitudes on the side of the moon opposite to Iapetus motion on its orbit. Both albedos on those opposite sides keep differentiating, as the dark material keeps getting darker and the bright one brighter. Scientists now think that the dark layer on Iapetus is barely one foot thick, as bright, cleaner ice is found below. The terrain, on the other hand, in the boundary region, has the isolated bright patches mainly found on slopes facing toward the bright trailing hemisphere or toward the south pole. The same polarity is found within the bright terrain, where the dark material can be seen at the bottom of craters and on equator-facing slopes
 | Amazing dark patches on the background of a bright terrain, at Iapetus. picture courtesy NASA/JPL/Space Science Institute |
 | We 'lightened' that picture, as it spectacularly shows the dark coating at Iapetus, in the transition regions. picture courtesy NASA/JPL/Space Science Institute |
Here are to follow any additional picture of interest about Iapetus, mostly from the additional passages performed by Cassini!
 | Iapetus' leading hemisphere (left), and trailing one (right). In one model of the explanation of the difference between both hemisphers, dark, reddish dust coming in from space and preferentially deposited on the leading side forms a small, but crucial thermal difference between the leading and trailing hemispheres, sufficient to allow the thermal effect to evaporate the water ice on the leading side completely, but only marginally on the trailing side. picture courtesy NASA/JPL/Space Science Institute |
 | Close-up view of the equatorial ridge at Iapetus as viewed during the close flyby performed by Cassini in September 2007. picture courtesy NASA/JPL/Space Science Institute |
Mimas Aug. 2nd, 2004
Mimas has been dubbed the "Death Star" due to it looking like the famed movie's spacecraft. That came to the moon through the spectacular 87-mile (140-km) wide, landslide-filled Herschel crater which further features a peak nearly as tall as Mount Everest on Earth. During its Aug. 2, 2005 flyby (at an altitude of 38,800 mi -62,700 km), Cassini saw how the moon had been battered with numerous impacts. A thoroughful study of Mimas will surely allow astronomers to a precise idea about the population of impactors which cruised in the Saturnian system and where they came from. The impactor which created Herschel, on the other hand, was another major contributor to the moon's features. Long (some stretching for more than 63 mi -100km) grooves on the opposite side of Mimas and already seen by the Voyager missions might be related to it, as a region of presumably different composition or texture is lying just West of the crater. Grooves might be too the indication that there might have been once an internal activity at Mimas. Mimas, at last, is slightly out of round. A unexplained difference of a dozen of degrees K has been found at Mimas by a study in 2010, concerning the daytime temperatures of a same face. The difference further is neatly delineated. The explanation found until now is that the colder part is due to some surface materials which have a greater thermal conductivity letting the energy into the subsurface instead of warming the surface itself. The reason why such a neat, linear border exists between both areas remains unclear. The impactor which created the Herschel Crater at Mimas is a main contributor to relief features of the moon as Mimas' wobbles hint to several possible models for its interior, like a oblong core a fossil of a early liquid core, or a ocean (Mimas might feature either a subsurface ocean lying at 15-20 miles (25-30 kilometers) beneath the surface, or a core shaped like a football ball). There is a strong connection between Mimas and Saturn's rings, though. Gravity links them together and shapes the way they both move. The gravitational pull of Mimas creates waves in Saturn's rings as Mimas' gravity also helps create the Cassini Division
 | General view of Mimas. The moon is battered with craters. picture courtesy NASA/JPL/Space Science Institute |  | In a view of Mimas taken during another flyby, the closest-ever of the moon, on Feb. 13, 2010, by 5,900 miles (9,500 km) only. This view looks toward the area between the region that leads on Mimas' orbit and the region of the moon facing away from Saturn. The view is in visible light, North is up as the resolution is of 790 ft (240 meters) per pixel! The slopes of the Herschel Crater appear to be pitched around 24 degrees as the walls are about 3 miles (5 km) high, and parts of the floor are approximately 6 miles (10 km) deep . picture courtesy NASA/JPL/Space Science Institute |
 | Detailed view of the 87-mile (140-km) wide Herschell crater, the distinctive feature of Mimas. It's an usual impact crater with a central peak. picture courtesy NASA/JPL/Space Science Institute |
 | A most detailed view of the landscape at Mimas. Grooves are visible. picture courtesy NASA/JPL/Space Science Institute |
 | Another general view of Mimas. picture courtesy NASA/JPL/Space Science Institute |
Views taken prior to the imaging passage:
 | A view of Mimas with chasms and craters, as seen by Cassini on Dec. 14, 2004 from 560,000 miles (902,000 km) away. picture courtesy NASA/JPL/Space Science Institute |
 | The impactor which formed the distinctive 80-mile (130 km) wide Herschel crater likely nearly destroyed the moon (view in the ultraviolet and a polarizing filter, from 132,000 miles (213,000 miles)). picture courtesy NASA/JPL/Space Science Institute |
Views taken after the imaging passage:
 | Mimas seen in the ultraviolet on March 21St, 2006. The surface is heavily battered with craters as the moon is interestingly seen against Saturn's hazy limb. picture courtesy NASA/JPL/Space Science Institute |
 | Mimas surface, in the afternoon, few after Sun has been at the zenith of the area shown on the image, is strangely and sharply divided. The warm part has typical temperatures near 92 Kelvin (minus 294 Fahrenheit), while typical temperatures on the cold part are about 77 Kelvin (minus 320 Fahrenheit). The cold part is probably colder because surface materials there have a greater thermal conductivity, so the sun's energy soaks into the subsurface instead of warming the surface itself. But why conductivity should vary so dramatically across the surface of Mimas is a mystery. It's not yet known whether Herschel is responsible in some way for the larger region of cold temperatures that surrounds it. This study was realized en April 2010. picture courtesy NASA/JPL/GSFC/SWRI/Space Science Institute |
Phoebe, Jun. 11th, 2004
->the dark material at Phoebe explained! It's of the same kind than the one found at Iapetus! check more!
 |
| When one looks at Phoebe, one sees an object 4.5 billion years old! picture NASA/JPL/Space Science Institute |
->Phoebe, like Iapetus, Hyperion and Epimetheus, and also Saturn's F-ring and Dione likely sharing a common, comet-originating dark material
En route to Saturn, Cassini-Huygens grazed Phoebe by 1,240 miles (2,000 km) only on June, 11th 2004. Voyager missions had only seen this moon from much afar. The emerging picture is that Phoebe really is a planetesimal dating back to the earliest days of the solar system. It's why Phoebe had been chosen as a science target. As gas giants cores formed from such bodies, gravitational interactions pushed away much of them to more distant orbits where they joined a native population, forming the Kuiper Belt. Phoebe staid behind and became a Saturn's moon
Phoebe is a mixture of ice, rock and carbon dioxide, similar to Pluto or Neptune's moon Triton. Solid hydrocarbons similar to those found in primitive meteorites and similarities to materials seen at comets are part of the result too. Phoebe is one the darkest known bodies in the solar system. Temperatures at moon's surface are varying between -257/-324° F as its density is about half that of Mars at 100 lbs/ft3 (pure ice is approximately at 58). A large day/night temperature contrast is indicating the Phoebe's surface is covered in loose dust or ice particles which store little heat thus cooling rapidly at night
Topography at Phoebe has been provided with provisional names by the International Astronomical Union (IAU). These names refer to the story of the Argonauts, these Greek heroes who journeyed in quest of the golden fleece
 | Phoebe seen by Cassini June 4th-7th (distances, left to right, are ranging from 2.6 million miles (4.1 million km) to 1.5 million miles (2.5 million km)). picture courtesy NASA/JPL/Space Science Institute |
 | Phoebe seen by Cassini June 10th (distances, left: 594,000 miles (956,000 km), right: 409,000 miles (658,000 km)). picture courtesy NASA/JPL/Space Science Institute |
 | Phoebe closing, left: 88,918 miles (143,068 km), right: 48,130 miles (77,441 km) . picture courtesy NASA/JPL/Space Science Institute |
 | Phoebe seen from 20,200 miles (32,500 km). picture courtesy NASA/JPL/Space Science Institute |
 | Crater above center is showing a layered structure all along under the rim (Phoebe was at 8,314 miles (13,377 km)). picture courtesy NASA/JPL/Space Science Institute |
 | A 8-mile wide crater (13 km) with a debris-covered floor. Boulders are ranging from 160 to 990 ft (50-300 m). picture courtesy NASA/JPL/Space Science Institute |
 | Landscape at Phoebe. Crater left is about 28 miles in diameter (45 km). Slopes right are about 12-mile (20 km) tall. A fine view. picture courtesy NASA/JPL/Space Science Institute |
 | Mosaic general picture of Phoebe. North is up. This picture showing the entirety of the moon is a mosaic of six pictures taken at close range by Cassini. picture courtesy NASA/JPL/Space Science Institute |
 | Digitally rendered model of Phoebe based on Cassini pictures. Heights are illustrated by the color (from blue, low, to red, high). Large depression which may be seen on some of the pictures above is visible in blue on longitude 180 and 270 W. Heights' range at Phoebe are 10 miles (16 km). picture courtesy NASA/JPL/Space Science Institute |
 | Spectrography at Phoebe. Dark and bright areas are delineated in the infrared view. Carbon dioxide and ferreous iron are linked to dark areas as water-ice to bright ones. picture courtesy NASA/JPL/University of Arizona |
 | This ultraviolet imaging spectrograph picture indicates water frost in a wall which is visible on the visible light picture left. picture courtesy NASA/JPL/University of Colorado |
Cassini successfully imaged Rhea, Saturn's second largest moon, on November 26th, 2005. Rhea is about one quarter rock mixed with three quarters ice. The moon is cratered, with powdery, ice regolith at the surface as billions of
years of impacts have sculpted Rhea's surface into the form we see today. Its ancient surface is one of the most heavily cratered of all of Saturn's moons. Subtle albedo variations across the disk of Rhea hint at past geologic activity. The Cassini craft flew by the moon by 310 miles (500 km), as it more recently saw that some bright streaks may be seen at Rhea too. Data are beginning to build up about Saturn's moons. The different geological histories hinted at by Cassini images, for icy moons of about the same age, is remaining an object of study for scientists. The number of impact craters is hinting to Rhea's great age, as the whispy, bright lines to a past tectonic activity. Some grabens, or a block of ground lower than its surroundings and bordered by cliffs on either
side have also been observed on Rhea
A ring composed of particles and dust exists at Rhea, making this moon the first to be discovered with such a feature, as until now it had been seen at planets only. It might about the remainings of a collision with an asteroid or comet. Rhea's albedo overall is quite high. By 2010, Cassini has further detected a very tenuous
atmosphere known as an exosphere, infused with oxygen and carbon dioxide around Rhea. Such a phenomenon is due to Saturn's magnetic field rotating over with energetic particles ejected from the ring by ultraviolet light and trapped in coming to hit the moon’s
water-ice surface, with chemical reactions releasing oxygen as the source of carbon dioxide is less certain. Such exospheres might be common throughout the solar system or instrumental into life presence. Icy material sprayed by the moon Enceladus hits Rhea head-on and leaves a coral-colored tint. Darker, rust-colored reddish hues paint the trailing hemisphere as they are thought to be caused by tiny particle strikes from circulating plasma, a gas-like state of matter so hot that atoms split into an ion and an electron, in Saturn's magnetic environment. Tiny, iron-rich 'nanoparticles' may also be involved. A distinct hue along Rhea's equator has led astronomers to hypothetize that that could have been exposed by the crash of orbiting material -perhaps a ring- to the surface of Rhea in the not too distant past
 | Although overexposed, this view is showing a comprehensive view of Rhea. Giant Tirawa impact basin is seen to the upper right of center. picture courtesy NASA/JPL/Space Science Institute |
 | Large, 30 mile (50 km)-wide crater at Rhea. picture courtesy NASA/JPL/Space Science Institute |
 | Large, 56 mile (90-km)-wide, degraded crater at Rhea. The surface is made of icy regolith. picture courtesy NASA/JPL/Space Science Institute |
 | Two large impact basins are seen top, as they have been battered by subsequent impacts. Enhanced color view. Pictures taken on Dec. 23, 2005. picture courtesy NASA/JPL/Space Science Institute |
 | This intense false-color picture of Rhea taken on Jan. 18, 2006 is showing a dramatic view of the moon. picture courtesy NASA/JPL/Space Science Institute |
 | Bright streaks also are found at Rhea, as they seem to originate in the north polar regions. Image in the visible, dated Oct. 11, 2006. picture courtesy NASA/JPL/Space Science Institute |
Pictures dating from before the flyby:
 | In a somewhat distant flyby, Cassini took this close view of Rhea on April 14th, 2005 at a distance of 153,000 mi (247,000 km). A bright, rayed, hence likely relatively young crater is seen, as Rhea seems heavily cratered. North is up and about 15° to the left. picture courtesy NASA/JPL/Space Science Institute |
 | Rhea seen on Nov. 1, 2004. Rhea is Saturn's second-largest moon. It will be imaged next Nov. 26, 2005 at a distance of 311 miles (500 km) only. picture courtesy NASA/JPL/Space Science Institute |
 | Rhea seen on Nov. 10, 2004. What might be a Copernicus-style, fresh impact crater is seen near the limb as a large crater may be seen just on the terminator. picture courtesy NASA/JPL/Space Science Institute |
 | A view (top left) of Rhea northern basin, named Tirawa. It was discovered in Voyager images. This ancient impact site is approximately 220-mile (360-km) across. Another, perhaps larger basin sits to the south of Tirawa and is partly in shadow. The picture was taken June 2, 2005, at a distance of approximately 1.1 million mi (1.8 million km). picture courtesy NASA/JPL/Space Science Institute |
 | Crater terrain at Rhea, Dec. 9, 2004. picture courtesy NASA/JPL/Space Science Institute |
 | Crater terrain at Rhea, Dec. 12, 2004. picture courtesy NASA/JPL/Space Science Institute |
 | Color view of Rhea. Unusual polygonal-rimed craters are seen in the lower left portion. picture courtesy NASA/JPL/Space Science Institute |
 | Bright splat at Rhea is coating much of the moon's leading hemisphere. The bright feature may be impact-related. picture courtesy NASA/JPL/Space Science Institute |
 | Another view of the bright splat. We corrected the original picture for a better view of it. picture site 'Amateur Astronomy' based on a picture NASA/JPL/Space Science Institute |
 | Over Rhea's south polar regions. picture courtesy NASA/JPL/Space Science Institute |
 | Rhea's southern regions. An interesting thing about these faraways moons is that, despite their icy composition is different from the rocky planets, their surface is strangely reminding of bodies like the Moon or Mercury. The large crater, center left, is "Izanagi" as it's only one among others of such large impact basins at Rhea (picture taken on Aug. 1, 2005 at a distance of 158,000 miles (255,000 km). picture courtesy NASA/JPL/Space Science Institute |
 | The large crater, center left, is "Izanagi" as it's only one among others of such large impact basins at Rhea like the one immediately above attests (picture taken on Aug. 1, 2005). picture courtesy NASA/JPL/Space Science Institute |
 | Rayed crater (right) and large, round basin (on the terminator). picture courtesy NASA/JPL/Space Science Institute |
Pictures dating from after the flyby:
 | Rhea seen in visible light on March 21st, 2006. The surface is ancient, likely some billions years. picture courtesy NASA/JPL/Space Science Institute |
 | The wisps at Rhea likely are networks of fractures, like on Dione, as they cut across older, cratered terrain. In addition, a set of thin, north-south trending lineaments (also likely fractures) is visible on the left side of the moon. picture courtesy NASA/JPL/Space Science Institute |
 | This view of Rhea is showing a color zonage from North (top) to South (bottom). The view here is in black and white, as the zonage translates into hues of grey. picture courtesy NASA/JPL/Space Science Institute |
 | A crater area between day and night as seen during a flyby 100 miles (200 kilometers) away from Rhea's surface in 2011. picture courtesy NASA/JPL/SSI |
 | This view is showing hemispheric color differences on Rhea in false-colors. The image shows the side of the moon that always faces the planet with the left half of the visible disk of Rhea facing in the direction of Rhea's orbital motion around Saturn, while the right side faces the trailing direction. It is not unusual for large icy Saturnian satellites to exhibit hemispheric albedo and color differences, as likely related to systematic regional changes in surface composition or the sizes and mechanical structure of grains making up the icy soil. Such large-scale variations can arise from numerous processes, such as meteoritic debris preferentially hitting one side of Rhea. The differences can also arise from "magnetic sweeping," a process that happens when ions that are trapped in Saturn's magnetic field drag over and implant themselves in Rhea's icy surface. The slightly reddish false-color hues near Rhea's poles identify subtle composition changes that might be caused by differences in the surface exposure to meteoric debris falling into the moon or implantation of ions. These differences could vary by latitude. picture courtesy NASA/JPL/SSI |
 | A other view of the battered surface of Rhea as seen in May 2012. picture courtesy NASA/JPL-Caltech/Space Science Institute |
 | That image constitutes Cassini's final observation of Rhea, looking down at Rhea's northern hemisphere. The northern rim of the giant Tirawa impact basin can be seen along the limb at left. picture courtesy NASA/JPL-Caltech/Space Science Institute |
Cassini flew by Tethys on September 24th, 2005 by a distance of 930 miles (1,500 km). The spacecraft is planned to be back there in the summer of 2007. The spacecraft had as a plan to image parts of the giant Ithaca Chasma canyon system and the southern polar regions. Ithaca Chasma has been seen hammered by impact craters, which means this rift is old. Some craters at Tethys have been seen bright-floored. Further studies of Tethys showed a subtle color difference between the moon's Saturn-facing side as opposed to the trailing side. Like most moons in the solar system, Saturn's moon Tethys is covered by impact craters. While Tethys is 660 miles (1,062 kilometers) across, the crater Odysseus is 280 miles (450 kilometers) across, covering about 18 percent of the moon's surface area. A comparably sized crater on Earth would be as large as Africa! Craters at Tethys are overprinting older, large basins. Further studies, on the other hand, hinted to that some kind of geological activity, or even volcanism likely occurs at Dione and makes that the moon is dilapidating icy, ionized particles into Saturn's magnetic field's plasma. A part of Tethys seems more reflective, in the ultraviolet, than the other. Red arcs are narrow, curved lines on Tethys could be exposed ice with chemical impurities, or the result of outgassing from inside Tethys. They could also be associated with features like fractures that are below the resolution of the available images. Except for a few small craters on Saturn's moon Dione, reddish-tinted features are rare on other moons of Saturn. Many reddish features do occur, however, on the geologically young surface of Jupiter's moon Europa
 | Centered on Ithaca Chasma rift, a fine view of Tethys. picture courtesy NASA/JPL/Space Science Institute |
 | Ithaca Chasma is seen edge-view on this picture taken Dec. 25, 2005. picture courtesy NASA/JPL/Space Science Institute |
 | The peaked crater Telemachus is well seen here, with, at its upper left, and eroded crater named Teiresias. picture courtesy NASA/JPL/Space Science Institute |
 | This southernmost extent of Ithaca Chasma is showing bright-floored craters and steep cliffs. A stunning view!. picture courtesy NASA/JPL/Space Science Institute |
 | Natural color view obtained by our site from a false-color view of Cassini. The variety of hues at such a small scale might hint to a mixture of different surface materials. picture courtesy NASA/JPL/Space Science Institute, modified site 'Amateur Astronomy' |
 | View, in the ultraviolet, of Odysseus. The basin is 280-mile (450-km) wide. View dated December 24th, 2005. The giant impact basin Odysseus may feature differences in either the composition or structure of the terrain exposed. At 280 miles it is one of the largest impact craters of Saturn's icy moons, and may have significantly altered the geologic history of Tethys. picture courtesy NASA/JPL/Space Science Institute |
The following pictures date back to before the flyby:
 | Tethys is seen here beyond Saturn south pole. A large feature is seen at the moon, which might be a row of three craters. Saturn was (2.4 million miles (3.9 million km) from Cassini. picture courtesy NASA/JPL/Space Science Institute |
 | Tethys seen October 28th, 2004 at a distance of 159,000 miles (256,000 km). The surface is saturated by craters as a grooved terrain is seen at the top of the picture. picture courtesy NASA/JPL/Space Science Institute |
 | Another view of Tethys. The great rift Ithaca Chasma is seen along as a vast, 185-mile (300 km) wide multi-ringed feature may be seen at its lower right. The rift is 60-miles (100 km) wide in some places as it runs three-fourths the way around the moon. picture courtesy NASA/JPL/Space Science Institute |
 | Another view of Ithaca Chasma. The Ithaca Chasma, at the lower right on this picture, is a canyon system stretching on a distance of 620 mi (1,000 km), with an average width of 60 mi (100 km). The canyon might have been created by the impact that gave birth to the giant crater Odysseus. picture courtesy NASA/JPL/Space Science Institute |
 | Tethys is featuring too this large, 280-mile wide (450 km) crater, called "Odysseus". It's not unlike a similar feature seen at Mimas (Herschel). A large, dark, equatorial band is seen too on this picture. picture courtesy NASA/JPL/Space Science Institute |
 | "Carthage Linea" pointing to Crater Turnus, left; Palatine Linea bottom right. picture courtesy NASA/JPL/Space Science Institute |
 | 280-mile wide (450 km) Odysseus basin is at top right. Another large impact basin is seen as is a brightness banding. North is up and tilted 20° to the left. picture courtesy NASA/JPL/Space Science Institute |
 | Another view of crater Odysseus. picture courtesy NASA/JPL/Space Science Institute |
The following pictures date back to after the flyby:
 | The 150-mile (245-km) wide crater Melanthius, in the southern terrain of Tethys, is seen here. Left, on the other hand, a distinct boundary in crater abundance is seen. picture courtesy NASA/JPL/Space Science Institute |
 | A thermal shape feature seen at Mimas in 2010 was also found at Tethys in 2012. That likely is hinting to that the process creating such features are current in the Saturnian system. That thermal shape on the Saturnian moons, which might also exist in the Jovian system, occurs because of the way high-energy electrons bombard low latitudes on the side of the moon that faces forward as it orbits around Saturn. The bombardment turns that part of the fluffy surface into hard-packed ice. As a result, the altered surface does not heat as rapidly in the sunshine or cool down as quickly at night as the rest of the surface. Tethys is also bombarded by icy particles from Enceladus' plumes making the surface alteration occurring more quickly than its recoating by plume particles. At Tethys, unlike Mimas, the thermal pattern can also be seen subtly in visible-light images of the surface, as a dark lens-shaped region first noticed by NASA's Voyager spacecraft in 1980. picture courtesy NASA/JPL-Caltech/GSFC/SWRI |
 | Another view of the Odysseus Crater. The Odysseus Crater is a enormous impact crater, which is about 280 miles (450 kilometers) across, with its ring of steep cliffs and the mountains that rise at its center. Odysseus is on the leading hemisphere of Tethys. North is up. picture courtesy NASA/JPL-Caltech/Space Science Institute |
