Astronomy Picture of the Day Search Results for "Enceladus"

APOD: 2024 August 25 – Fresh Tiger Stripes on Saturns Enceladus
Explanation: Do underground oceans vent through canyons on Saturn's moon Enceladus? Long features dubbed tiger stripes are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring. Evidence for this has come from the robot Cassini spacecraft that orbited Saturn from 2004 to 2017. Pictured here, a high resolution image of Enceladus is shown from a close flyby. The unusual surface features dubbed tiger stripes are visible in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead. An analysis of ejected ice grains has yielded evidence that complex organic molecules exist inside Enceladus. These large carbon-rich molecules bolster -- but do not prove -- that oceans under Enceladus' surface could contain life.

APOD: 2023 December 16 - Crescent Enceladus
Explanation: Peering from the shadows, the Saturn-facing hemisphere of tantalizing inner moon Enceladus poses in this Cassini spacecraft image. North is up in the dramatic scene captured during November 2016 as Cassini's camera was pointed in a nearly sunward direction about 130,000 kilometers from the moon's bright crescent. In fact, the distant world reflects over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as fresh snow. A mere 500 kilometers in diameter, Enceladus is a surprisingly active moon. Data and images collected during Cassini's flybys have revealed water vapor and ice grains spewing from south polar geysers and evidence of an ocean of liquid water hidden beneath the moon's icy crust.

APOD: 2023 February 5 – Enceladus by Saturnshine
Explanation: This moon is shining by the light of its planet. Specifically, a large portion of Enceladus pictured here is illuminated primarily by sunlight first reflected from the planet Saturn. The result is that the normally snow-white moon appears in the gold color of Saturn's cloud tops. As most of the illumination comes from the image left, a labyrinth of ridges throws notable shadows just to the right of the image center, while the kilometer-deep canyon Labtayt Sulci is visible just below. The bright thin crescent on the far right is the only part of Enceladus directly lit by the Sun. The featured image was taken in 2011 by the robotic Cassini spacecraft during a close pass by the enigmatic moon. Inspection of the lower left part of this digitally sharpened image reveals plumes of ice crystals thought to originate in a below-surface sea.

APOD: 2020 September 24 - Enceladus in Infrared
Explanation: One of our Solar System's most tantalizing worlds, icy Saturnian moon Enceladus appears in these detailed hemisphere views from the Cassini spacecraft. In false color, the five panels present 13 years of infrared image data from Cassini's Visual and Infrared Mapping Spectrometer and Imaging Science Subsystem. Fresh ice is colored red, and the most dramatic features look like long gashes in the 500 kilometer diameter moon's south polar region. They correspond to the location of tiger stripes, surface fractures that likely connect to an ocean beneath the Enceladus ice shell. The fractures are the source of the moon's icy plumes that continuously spew into space. The plumes were discovered by by Cassini in 2005. Now, reddish hues in the northern half of the leading hemisphere view also indicate a recent resurfacing of other regions of the geologically active moon, a world that may hold conditions suitable for life.

APOD: 2020 May 19 - Posters of the Solar System
Explanation: Would you like a NASA astronomy-exploration poster? You are just one page-print away. Any of the panels you see on the featured image can appear on your wall. Moreover, this NASA page has, typically, several more posters of each of the Solar System objects depicted. These posters highlight many of the places humanity, through NASA, has explored in the past 50 years, including our Sun, and planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Moons of Jupiter that have been posterized include Europa, Ganymede, Callisto, and Io, while moons of Saturn that can be framed include Enceladus and Titan. Images of Pluto, Ceres, comets and asteroids are also presented, while six deep space scenes -- well beyond our Solar System -- can also be prominently displayed. If you lack wall space or blank poster sheets don't despair -- you can still print many of these out as trading cards.

APOD: 2020 April 27 - Fresh Tiger Stripes on Saturns Enceladus
Explanation: How will humanity first learn of extraterrestrial life? One possibility is to find it under the icy surface of Saturn's moon Enceladus. A reason to think that life may exist there are long features -- dubbed tiger stripes -- that are known to be spewing ice from the moon's icy interior into space. These surface cracks create clouds of fine ice particles over the moon's South Pole and create Saturn's mysterious E-ring. Evidence for this has come from the robot Cassini spacecraft that orbited Saturn from 2004 to 2017. Pictured here, a high resolution image of Enceladus is shown from a close flyby. The unusual surface tiger stripes are shown in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead. A recent analysis of ejected ice grains has yielded evidence that complex organic molecules exist inside Enceladus. These large carbon-rich molecules bolster -- but do not prove -- that oceans under Enceladus' surface could contain life. Another Solar System moon that might contain underground life is Europa.

APOD: 2020 April 19 - Cassini Approaches Saturn
Explanation: What would it look like to approach Saturn in a spaceship? One doesn't have to just imagine -- the Cassini spacecraft did just this in 2004, recording thousands of images along the way, and hundreds of thousands more since entering orbit. Some of Cassini's early images have been digitally tweaked, cropped, and compiled into the featured inspiring video which is part of a larger developing IMAX movie project named In Saturn's Rings. In the concluding sequence, Saturn looms increasingly large on approach as cloudy Titan swoops below. With Saturn whirling around in the background, Cassini is next depicted flying over Mimas, with large Herschel Crater clearly visible. Saturn's majestic rings then take over the show as Cassini crosses Saturn's thin ring plane. Dark shadows of the ring appear on Saturn itself. Finally, the enigmatic ice-geyser moon Enceladus appears in the distance and then is approached just as the video clip ends. After more than a decade of exploration and discovery, the Cassini spacecraft ran low on fuel in 2017 was directed to enter Saturn's atmosphere, where it surely melted.

APOD: 2019 December 29 - Cassini Spacecraft Crosses Saturn's Ring Plane
Explanation: If this is Saturn, where are the rings? When Saturn's "appendages" disappeared in 1612, Galileo did not understand why. Later that century, it became understood that Saturn's unusual protrusions were rings and that when the Earth crosses the ring plane, the edge-on rings will appear to disappear. This is because Saturn's rings are confined to a plane many times thinner, in proportion, than a razor blade. In modern times, the robot Cassini spacecraft orbiting Saturn frequently crossed Saturn's ring plane during its mission to Saturn, from 2004 to 2017. A series of plane crossing images from 2005 February was dug out of the vast online Cassini raw image archive by interested Spanish amateur Fernando Garcia Navarro. Pictured here, digitally cropped and set in representative colors, is the striking result. Saturn's thin ring plane appears in blue, bands and clouds in Saturn's upper atmosphere appear in gold. Details of Saturn's rings can be seen in the high dark shadows across the top of this image, taken back in 2005. The moons Dione and Enceladus appear as bumps in the rings.

APOD: 2019 October 17 - Moons of Saturn
Explanation: On July 29, 2011 the Cassini spacecraft's narrow-angle camera took this snapshot and captured 5 of Saturn's moons, from just above the ringplane. Left to right are small moons Janus and Pandora respectively 179 and 81 kilometers across, shiny 504 kilometer diameter Enceladus, and Mimas, 396 kilometers across, seen just next to Rhea. Cut off by the right edge of the frame, Rhea is Saturn's second largest moon at 1,528 kilometers across. So how many moons does Saturn have? Twenty new found outer satellites bring its total to 82 known moons, and since Jupiter's moon total stands at 79, Saturn is the Solar System's new moon king. The newly announced Saturnian satellites are all very small, 5 kilometers or so in diameter, and most are in retrograde orbits inclined to Saturn's ringplane. You can help name Saturn's new moons, but you should understand the rules. Hint: A knowledge of Norse, Inuit, and Gallic mythology will help.

APOD: 2019 May 5 - Saturn, Titan, Rings, and Haze
Explanation: This is not a solar eclipse. Pictured here is a busy vista of moons and rings taken at Saturn. The large circular object in the center of the image is Titan, the largest moon of Saturn and one of the most intriguing objects in the entire Solar System. The dark spot in the center is the main solid part of the moon. The bright surrounding ring is atmospheric haze above Titan, gas that is scattering sunlight to a camera operating onboard the robotic Cassini spacecraft. Cutting horizontally across the image are the rings of Saturn, seen nearly edge on. At the lower right of Titan is Enceladus, a small moon of Saturn. Since the image was taken pointing nearly at the Sun, the surfaces of Titan and Enceladus appear in silhouette, and the rings of Saturn appear similar to a photographic negative. Now if you look really really closely at Enceladus, you can see a hint of icy jets shooting out toward the bottom of the image. It is these jets that inspired future proposals to land on Enceladus, burrow into the ice, and search for signs of extraterrestrial life.

APOD: 2019 March 9 - Crescent Enceladus
Explanation: Peering from the shadows, the Saturn-facing hemisphere of tantalizing inner moon Enceladus poses in this Cassini spacecraft image. North is up in the dramatic scene captured during November 2016 as Cassini's camera was pointed in a nearly sunward direction about 130,000 kilometers from the moon's bright crescent. In fact, the distant world reflects over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as fresh snow. A mere 500 kilometers in diameter, Enceladus is a surprisingly active moon. Data collected during Cassini's flybys and years of images have revealed the presence of remarkable south polar geysers and a possible global ocean of liquid water beneath an icy crust.

APOD: 2018 July 1 - Fresh Tiger Stripes on Saturn's Enceladus
Explanation: Do underground oceans vent through the tiger stripes on Saturn's moon Enceladus? Long features dubbed tiger stripes are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring. Evidence for this has come from the robot Cassini spacecraft that orbited Saturn from 2004 to 2017. Pictured here, a high resolution image of Enceladus is shown from a close flyby. The unusual surface features dubbed tiger stripes are visible in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas,approximately the same size, appears quite dead. A recent analysis of ejected ice grains has yielded evidence that complex organic molecules exist inside Enceladus. These large carbon-rich molecules bolster -- but do not prove -- that oceans under Enceladus' surface could contain life.

APOD: 2018 February 15 - Enceladus in Silhouette
Explanation: One of our Solar System's most tantalizing worlds, Enceladus is backlit by the Sun in this Cassini spacecraft image from November 1, 2009. The dramatic illumination reveals the plumes that continuously spew into space from the south pole of Saturn's 500 kilometer diameter moon. Discovered by Cassini in 2005, the icy plumes are likely connected to an ocean beneath the ice shell of Enceladus. They supply material directly to Saturn's outer, tenuous E ring and make the surface of Enceladus as reflective as snow. Across the scene, Saturn's icy rings scatter sunlight toward Cassini's cameras. Beyond the rings, the night side of 80 kilometer diameter moon Pandora is faintly lit by Saturnlight.

APOD: 2017 September 11 - Cassini Approaches Saturn
Explanation: What would it look like to approach Saturn in a spaceship? One doesn't have to just imagine -- the Cassini spacecraft did just this in 2004, recording thousands of images along the way, and hundreds of thousands more since entering orbit. Some of Cassini's early images have been digitally tweaked, cropped, and compiled into the featured inspiring video which is part of a larger developing IMAX movie project named In Saturn's Rings. In the concluding sequence, Saturn looms increasingly large on approach as cloudy Titan swoops below. With Saturn whirling around in the background, Cassini is next depicted flying over Mimas, with large Herschel Crater clearly visible. Saturn's majestic rings then take over the show as Cassini crosses Saturn's thin ring plane. Dark shadows of the ring appear on Saturn itself. Finally, the enigmatic ice-geyser moon Enceladus appears in the distance and then is approached just as the video clip ends. The Cassini spacecraft itself, low on fuel, is scheduled to end on Friday when it will be directed to approach so close to Saturn that it falls in and melts.

APOD: 2017 August 29 - Saturn in Blue and Gold
Explanation: Why is Saturn partly blue? The featured picture of Saturn approximates what a human would see if hovering close to the giant ringed world. The image was taken in 2006 March by the robot Cassini spacecraft now orbiting Saturn. Here Saturn's majestic rings appear directly only as a thin vertical line. The rings show their complex structure in the dark shadows they create on the image left. Saturn's fountain moon Enceladus, only about 500 kilometers across, is seen as the bump in the plane of the rings. The northern hemisphere of Saturn can appear partly blue for the same reason that Earth's skies can appear blue -- molecules in the cloudless portions of both planet's atmospheres are better at scattering blue light than red. When looking deep into Saturn's clouds, however, the natural gold hue of Saturn's clouds becomes dominant. It is not known why southern Saturn does not show the same blue hue -- one hypothesis holds that clouds are higher there. It is also not known why Saturn's clouds are colored gold. Next month, Cassini will end its mission with a final dramatic dive into Saturn's atmosphere.

APOD: 2017 April 16 - Life Enabling Plumes above Enceladus
Explanation: Does Enceladus have underground oceans that could support life? The discovery of jets spewing water vapor and ice was detected by the Saturn-orbiting Cassini spacecraft in 2005. The origin of the water feeding the jets, however, was originally unknown. Since discovery, evidence has been accumulating that Enceladus has a deep underground sea, warmed by tidal flexing. Pictured here, the textured surface of Enceladus is visible in the foreground, while rows of plumes rise from ice fractures in the distance. These jets are made more visible by the Sun angle and the encroaching shadow of night. A recent fly-through has found evidence that a plume -- and so surely the underlying sea -- is rich in molecular hydrogen, a viable food source for microbes that could potentially be living there.

APOD: 2017 February 9 - Crescent Enceladus
Explanation: Peering from the shadows, the Saturn-facing hemisphere of tantalizing inner moon Enceladus poses in this Cassini spacecraft image. North is up in the dramatic scene captured last November as Cassini's camera was pointed in a nearly sunward direction about 130,000 kilometers from the moon's bright crescent. In fact, the distant world reflects over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as fresh snow. A mere 500 kilometers in diameter, Enceladus is a surprisingly active moon. Data collected during Cassini's flybys and years of images have revealed the presence of remarkable south polar geysers and a possible global ocean of liquid water beneath an icy crust.

APOD: 2015 December 3 - Enceladus: Ringside Water World
Explanation: Saturn's icy moon Enceladus poses above the gas giant's icy rings in this Cassini spacecraft image. The dramatic scene was captured on July 29, while Cassini cruised just below the ring plane, its cameras looking back in a nearly sunward direction about 1 million kilometers from the moon's bright crescent. At 500 kilometers in diameter, Enceladus is a surprisingly active moon though, its remarkable south polar geysers are visible venting beyond a dark southern limb. In fact, data collected during Cassini's flybys and years of images have recently revealed the presence of a global ocean of liquid water beneath this moon's icy crust. Demonstrating the tantalizing liquid layer's global extent, the careful analysis indicates surface and core are not rigidly connected, with Enceladus rocking slightly back and forth in its orbit.

APOD: 2015 October 21 - The Fractured North Pole of Saturn's Enceladus
Explanation: The north pole of Saturn's moon Enceladus is unexpectedly fascinating and complex. Previous to the latest flyby of the robotic Cassini spacecraft, the northern region was known mostly for its unusually high abundance of craters. Last week's flyby, however, returned images of unprecedented detail, including the featured image showing the expected craters coupled with an unexpected and circuitous pattern of picturesque cracks and fractures. Broken terrain has been recorded at lower latitudes, with deep canyons dubbed Tiger Stripes near Enceladus' South Pole. The fractures may further indicate global interplay between the surface and potential seas underneath, seas that future missions might target for signs of life.

APOD: 2015 September 20 - Global Ocean Suspected on Saturn's Enceladus
Explanation: Do some surface features on Enceladus roll like a conveyor belt? A leading interpretation of images taken of Saturn's most explosive moon indicate that they do. This form of asymmetric tectonic activity, very unusual on Earth, likely holds clues to the internal structure of Enceladus, which may contain subsurface seas where life might be able to develop. Pictured above is a composite of 28 images taken by the robotic Cassini spacecraft in 2008 just after swooping by the ice-spewing orb. Inspection of these images show clear tectonic displacements where large portions of the surface all appear to move all in one direction. On the image right appears one of the most prominent tectonic divides: Labtayt Sulci, a canyon about one kilometer deep. The magnitude of Enceladus' wobble as it orbits Saturn might indicate damping by a globally extending underground ocean layer.

APOD: 2015 July 8 - In the Company of Dione
Explanation: That is not our Moon. It's Dione, and it’s a moon of Saturn. The robotic Cassini spacecraft took the featured image during a flyby of Saturn's cratered Moon last month. Perhaps what makes this image so interesting, though, is the background. First, the large orb looming behind Dione is Saturn itself, faintly lit by sunlight first reflected from the rings. Next, the thin lines running diagonally across the image are the rings of Saturn themselves. The millions of icy rocks that compose Saturn's spectacular rings all orbit Saturn in the same plane, and so appear surprisingly thin when seen nearly edge-on. Front and center, Dione appears in crescent phase, partially lit by the Sun that is off to the lower left. A careful inspection of the ring plane should also locate the moon Enceladus on the upper right.

APOD: 2014 November 7 - The Map of Dione
Explanation: This cylindrical projection global map is one of six new color maps of Saturn's midsized icy moons, constructed using 10 years of image data from the Cassini spacecraft. Discovered by Cassini (the astronomer) in 1684, Dione is about 1,120 kilometers across. Based on data extending from infrared to ultraviolet, the full resolution of this latest space-age map is 250 meters per pixel. The remarkable brightness difference between the tidally locked moon's lighter leading hemisphere (right) and darker trailing hemisphere clearly stands out. Like other Saturn moons orbiting within the broad E-ring, Dione's leading hemisphere is kept shiny as it picks up a coating of the faint ring's icy material. The E-ring material is constantly replenished by geysers on moon Enceladus' south pole. Lighter, younger surface fractures also appear to cross the dark, cratered trailing hemisphere.

APOD: 2014 September 19 - Potentially Habitable Moons
Explanation: For astrobiologists, these may be the four most tantalizing moons in our Solar System. Shown at the same scale, their exploration by interplanetary spacecraft has launched the idea that moons, not just planets, could have environments supporting life. The Galileo mission to Jupiter discovered Europa's global subsurface ocean of liquid water and indications of Ganymede's interior seas. At Saturn, the Cassini probe detected erupting fountains of water ice from Enceladus indicating warmer subsurface water on even that small moon, while finding surface lakes of frigid but still liquid hydrocarbons beneath the dense atmosphere of large moon Titan. Now looking beyond the Solar System, new research suggests that sizable exomoons, could actually outnumber exoplanets in stellar habitable zones. That would make moons the most common type of habitable world in the Universe.

APOD: 2014 August 4 - Shadows and Plumes Across Enceladus
Explanation: Why does Enceladus have ice plumes? The discovery of jets spewing water vapor and ice was detected by the Saturn-orbiting Cassini spacecraft in 2005. The origin of the water feeding the jets, however, remained a topic of research. A leading hypothesis held that the source might originate from a deep underground sea, but another hypothesis indicated that it might just be ice melted off walls of deep rifts by the moon's tidal flexing and heating. Pictured above, the textured surface of Enceladus is visible in the foreground, while rows of plumes rise from ice fractures in the distance. These jets are made more visible by the Sun angle and the encroaching shadow of night. Recent study of over a hundred images like this -- of geysers crossing Enceladus' South Pole, together with regional heat maps, indicate that these plumes likely originate from a hidden sea, incresaing the chance that this frosty globe might be harboring life.

APOD: 2014 April 13 - Saturn in Blue and Gold
Explanation: Why is Saturn partly blue? The above picture of Saturn approximates what a human would see if hovering close to the giant ringed world. The above picture was taken in 2006 March by the robot Cassini spacecraft now orbiting Saturn. Here Saturn's majestic rings appear directly only as a thin vertical line. The rings show their complex structure in the dark shadows they create on the image left. Saturn's fountain moon Enceladus, only about 500 kilometers across, is seen as the bump in the plane of the rings. The northern hemisphere of Saturn can appear partly blue for the same reason that Earth's skies can appear blue -- molecules in the cloudless portions of both planet's atmospheres are better at scattering blue light than red. When looking deep into Saturn's clouds, however, the natural gold hue of Saturn's clouds becomes dominant. It is not known why southern Saturn does not show the same blue hue -- one hypothesis holds that clouds are higher there. It is also not known why Saturn's clouds are colored gold.

APOD: 2014 April 6 - Fresh Tiger Stripes on Saturns Enceladus
Explanation: Do underground oceans vent through the tiger stripes on Saturn's moon Enceladus? Long features dubbed tiger stripes are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring. Evidence for this has come from the robot Cassini spacecraft now orbiting Saturn. Pictured above, a high resolution image of Enceladus is shown from a close flyby. The unusual surface features dubbed tiger stripes are visible in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead. Most recently, an analysis of slight gravity deviations has given an independent indication of underground oceans. Such research is particularly interesting since such oceans would be candidates to contain life.

APOD: 2013 December 15 - Gibbous Europa
Explanation: Although the phase of this moon might appear familiar, the moon itself might not. In fact, this gibbous phase shows part of Jupiter's moon Europa. The robot spacecraft Galileo captured this image mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible are plains of bright ice, cracks that run to the horizon, and dark patches that likely contain both ice and dirt. Raised terrain is particularly apparent near the terminator, where it casts shadows. Europa is nearly the same size as Earth's Moon, but much smoother, showing few highlands or large impact craters. Evidence and images from the Galileo spacecraft, indicated that liquid oceans might exist below the icy surface. To test speculation that these seas hold life, ESA has started preliminary development of the Jupiter Icy Moons Explorer (JUICE), a spacecraft proposed for launch around 2022 that would further explore Jupiter and in particular Europa. Recent observations by the Hubble Space Telescope have uncovered new evidence that Europa, like Saturn's moon Enceladus, has ice venting from its surface.

APOD: 2013 November 13 - In the Shadow of Saturn
Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn drifted in giant planet's shadow earlier this year and looked back toward the eclipsed Sun. Cassini saw a unique and celebrated view. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, Saturn's expansive ring system appears as majestic as always even from this odd angle. Ring particles, many glowing only as irregular crescents, slightly scatter sunlight toward Cassini in this natural color image. Several moons and ring features are also discernible. Appearing quite prominently is Saturn's E ring, the ring created by the unusual ice-fountains of the moon Enceladus and the outermost ring visible above. To the upper left, far in the distance, are the planets Mars and Venus. To the lower right, however, is perhaps the most wondrous spectacle of all: the almost invisible, nearly ignorable, pale blue dot of Earth.

APOD: 2013 July 29 - Saturn, Titan, Rings, and Haze
Explanation: This is not a solar eclipse. Pictured above is a busy vista of moons and rings taken at Saturn. The large circular object in the center of the image is Titan, the largest moon of Saturn and one of the most intriguing objects in the entire Solar System. The dark spot in the center is the main solid part of the moon. The bright surrounding ring is atmospheric haze above Titan, gas that is scattering sunlight to a camera operating onboard the robotic Cassini spacecraft. Cutting horizontally across the image are the rings of Saturn, seen nearly edge on. At the lower right of Titan is Enceladus, a small moon of Saturn. Since the image was taken pointing nearly at the Sun, the surfaces of Titan and Enceladus appear in silhouette, and the rings of Saturn appear similar to a photographic negative. Now if you look really really closely at Enceladus, you can see a hint of icy jets shooting out toward the bottom of the image. It is these jets that inspired future proposals to land on Enceladus, burrow into the ice, and search for signs of extraterrestrial life.

APOD: 2013 March 29 - Ringside with Rhea
Explanation: Orbiting in the plane of Saturn's rings, Saturnian moons have a perpetual ringside view of the gas giant planet. Of course, while passing near the ring plane the Cassini spacecraft also shares their stunning perspective. The thin rings themselves slice across the middle of this Cassini snapshot from April 2011. The scene looks toward the dark night side of Saturn, in the frame at the left, and the still sunlit side of the rings from just above the ringplane. Centered, over 1,500 kilometers across, Rhea is Saturn's second largest moon and is closest to the spacecraft, around 2.2 million kilometers away. To Rhea's right, shiny, 500 kilometer diameter Enceladus is about 3 million kilometers distant. Dione, 1,100 kilometers wide, is 3.1 million kilometers from Cassini's camera on the left, partly blocked by Saturn's night side.

APOD: 2012 December 22 - Saturn at Night
Explanation: Splendors seldom seen are revealed in this glorious picture from Saturn's shadow. Imaged by Cassini on October 17, 2012 during its 174th orbit, the ringed planet's night side is viewed from a perspective 19 degrees below the ring plane at a distance of about 800,000 kilometers with the Sun almost directly behind the planet. A 60 frame mosaic, images made with infrared, red, and violet filters were combined to create an enhanced, false-color view. Strongly backlit, the rings look bright away from the planet but dark in silhouette against the gas giant. Above center, they reflect a faint, eerie light on the cloud tops while Saturn casts its own dark shadow on the rings. A similar Cassini image from 2006 also featured planet Earth as a pale blue dot in the distance. Instead, this scene includes icy moons Enceladus (closer to the rings) and Tethys below the rings on the left.

APOD: 2012 September 16 - Saturn: Bright Tethys and Ancient Rings
Explanation: How old are Saturn's rings? No one is quite sure. One possibility is that the rings formed relatively recently in our Solar System's history, perhaps only about 100 million years ago when a moon-sized object broke up near Saturn. Evidence for a young ring age includes a basic stability analysis for rings, and the fact that the rings are so bright and relatively unaffected by numerous small dark meteor impacts. More recent evidence, however, raises the possibility that some of Saturn's rings may be billions of years old and so almost as old as Saturn itself. Inspection of images by the Saturn-orbiting Cassini spacecraft indicates that some of Saturn's ring particles temporarily bunch and collide, effectively recycling ring particles by bringing fresh bright ices to the surface. Seen here, Saturn's rings were imaged in their true colors by the robotic Cassini in late October. Icy bright Tethys, a moon of Saturn likely brightened by a sandblasting rain of ice from sister moon Enceladus, is visible in front of the darker rings.

APOD: 2012 April 14 - Six Moons of Saturn
Explanation: How many moons does Saturn have? So far 62 have been discovered, the smallest only a fraction of a kilometer across. Six of its largest satellites can be seen here, though, in a sharp Saturnian family portrait taken on March 9. Larger than Earth's Moon and even slightly larger than Mercury, Titan has a diameter of 5,150 kilometers and starts the line-up at the lower left. Continuing to the right across the frame are Mimas, Tethys, [Saturn], Enceladus, Dione, and Rhea at far right. Saturn's first known natural satellite, Titan was discovered in 1655 by Dutch astronomer Christiaan Huygens, while most recently the satellite provisionally designated S/2009 S1 was found by the Cassini Imaging Science Team in 2009. Tonight, Saturn reaches opposition in planet Earth's sky, offering the best telescopic views of the ringed planet and moons.

APOD: 2012 February 8 - Enceladus Backlit by Saturn
Explanation: This moon is shining by the light of its planet. Specifically, a large portion of Enceladus pictured above is illuminated primarily by sunlight first reflected from the planet Saturn. The result is that the normally snow-white moon appears in the gold color of Saturn's cloud tops. As most of the illumination comes from the image left, a labyrinth of ridges throws notable shadows just to the right of the image center, while the kilometer-deep canyon Labtayt Sulci is visible just below. The bright thin crescent on the far right is the only part of Enceladus directly lit by the Sun. The above image was taken last year by the robotic Cassini spacecraft during a close pass by by the enigmatic moon. Inspection of the lower part of this digitally sharpened image reveals plumes of ice crystals thought to originate in a below-surface sea.

APOD: 2011 September 4 - In the Shadow of Saturn
Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn drifted in giant planet's shadow for about 12 hours in 2006 and looked back toward the eclipsed Sun. Cassini saw a view unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn, slightly scattering sunlight, in this exaggerated color image. Saturn's rings light up so much that new rings were discovered, although they are hard to see in the image. Seen in spectacular detail, however, is Saturn's E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus and the outermost ring visible above. Far in the distance, at the left, just above the bright main rings, is the almost ignorable pale blue dot of Earth.

APOD: 2011 May 12 - Enceladus Looms
Explanation: A sunlit crescent of Saturn's moon Enceladus looms above the night side of Saturn in this dramatic image from the Cassini spacecraft. Captured on August 13, 2010 looking in a sunward direction during a flyby of the icy moon, the view also traces layers in the upper atmosphere of Saturn scattering sunlight along the planet's bright limb. Closer to the spacecraft than Saturn, Enceladus is a mere 60,000 kilometers from Cassini's camera. The south polar region of the 500 kilometer-diameter moon is illuminated, including plumes of water vapor and icy particles spraying above the long fissures in the moon's surface. The fissures have been dubbed tiger stripes. First discovered in Cassini images from 2005, the plumes are strong evidence that liquid water exists near the surface of surprisingly active Enceladus.

APOD: 2011 March 15 - Cassini Approaches Saturn
Explanation: What would it look like to approach Saturn in a spaceship? One doesn't have to just imagine -- the Cassini spacecraft did just this in 2004, recording thousands of images along the way, and thousands more since entering orbit. Recently, some of these images have been digitally tweaked, cropped, and compiled into the above inspiring video which is part of a larger developing IMAX movie project named Outside In. In the last sequence, Saturn looms increasingly large on approach as cloudy Titan swoops below. With Saturn whirling around in the background, Cassini is next depicted flying over Mimas, with large Herschel Crater clearly visible. Saturn's majestic rings then take over the show as Cassini crosses Saturn's thin ring plane. Dark shadows of the ring appear on Saturn itself. Finally, the enigmatic ice-geyser moon Enceladus appears in the distance and then is approached just as the video clip ends.

APOD: 2011 March 8 - Titan, Rings, and Saturn from Cassini
Explanation: How thin are the rings of Saturn? Brightness measurements from different angles have shown Saturn's rings to be about one kilometer thick, making them many times thinner, in relative proportion, than a razor blade. This thinness sometimes appears in dramatic fashion during an image taken nearly along the ring plane. The robot Cassini spacecraft now orbiting Saturn has now captured another shot that dramatically highlights the ring's thinness. The above image was taken in mid January in infrared and polarized light. Titan looms just over the thin rings, while dark ring shadows on Saturn show the Sun to be above the ring plane. Close inspection of the image will show the smaller moon Enceladus on the far right. Cassini, humanity's first mission to orbit Saturn, currently has operations planned until 2017.

APOD: 2009 December 8 - Ice Moon Tethys from Saturn Orbiting Cassini
Explanation: What processes formed the unusual surface of Saturn's moon Tethys? To help find out, NASA sent the robotic Cassini spacecraft right past the enigmatic ice moon in 2005. Pictured above is one of the highest resolution images of an entire face of Tethys yet created. The pervasive white color of Tethys is thought to be created by fresh ice particles continually falling onto the moon from Saturn's diffuse E-ring -- particles expelled by Saturn's moon Enceladus. Some of the unusual cratering patterns on Tethys remain less well understood, however. Close inspection of the above image of Tethys' south pole will reveal a great rift running diagonally down from the middle: Ithaca Chasma. A leading theory for the creation of this great canyon is anchored in the tremendous moon-wide surface cracking that likely occurred when Tethys' internal oceans froze. If so, Tethys may once have harbored internal oceans, possibly similar to the underground oceans some hypothesize to exist under the surface of Enceladus today. Might ancient life be frozen down there?

APOD: 2009 November 24 - Cassini Flyby Shows Enceladus Venting
Explanation: What's happening on the surface of Saturn's moon Enceladus? Enormous ice jets are erupting. Giant plumes of ice have been photographed in dramatic fashion by the robotic Cassini spacecraft during this past weekend's flyby of Saturn's moon Enceladus. Pictured above, numerous plumes are seen rising from long tiger-stripe canyons across Enceladus' craggy surface. Several ice jets are even visible in the shadowed region of crescent Enceladus as they reach high enough to scatter sunlight. Other plumes, near the top of the above image, appear visible just over the moon's sunlit edge. That Enceladus vents fountains of ice was first discovered on Cassini images in 2005, and has been under close study ever since. Continued study of the ice plumes may yield further clues as to whether underground oceans, candidates for containing life, exist on this distant ice world.

APOD: 2009 June 28 - Fresh Tiger Stripes on Saturn's Enceladus
Explanation: Do underground oceans vent through the tiger stripes on Saturn's moon Enceladus? Long features dubbed tiger stripes are known to be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring. Evidence for this has come from the robot Cassini spacecraft now orbiting Saturn. Pictured above, a high resolution image of Enceladus is shown from a close flyby. The unusual surface features dubbed tiger stripes are visible in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead. Most recently, an analysis of dust captured by Cassini found evidence for sodium as expected in a deep salty ocean. Conversely however, recent Earth-based observations of ice ejected by Enceladus into Saturn's E-Ring showed no evidence of the expected sodium. Such research is particularly interesting since such an ocean would be a candidate to contain life.

APOD: 2009 March 19 - Saturn: Moons in Transit
Explanation: Every 14 to 15 years, Saturn's rings are tilted edge-on to our line of sight. As the bright, beautiful rings seem to grow narrower it becomes increasingly difficult to see them, even with large telescopes. But it does provide the opportunity to watch multiple transits of Saturn's moons. During a transit, a sunlit moon and its shadow glide across the cloudy face of the gas giant. Recorded on February 24, this Hubble image is part of a sequence showing the transit of four of Saturn's moons. From left to right are Enceladus and shadow, Dione and shadow, and Saturn's largest moon Titan. Small moon Mimas is just touching Saturn's disk near the ring plane at the far right. The shadows of Titan and Mimas have both moved off the right side of the disk. Saturn itself has an equatorial diameter of about 120,000 kilometers.

APOD: 2009 January 11 - In the Shadow of Saturn
Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn recently drifted in giant planet's shadow for about 12 hours and looked back toward the eclipsed Sun. Cassini saw a view unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn, slightly scattering sunlight, in this exaggerated color image. Saturn's rings light up so much that new rings were discovered, although they are hard to see in the image. Seen in spectacular detail, however, is Saturn's E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus and the outermost ring visible above. Far in the distance, at the left, just above the bright main rings, is the almost ignorable pale blue dot of Earth.

APOD: 2008 December 22 - Labtayt Sulci on Saturns Enceladus
Explanation: Do some surface features on Enceladus roll like a conveyor belt? A leading interpretation of recent images taken of Saturn's most explosive moon indicate that they do. This form of asymmetric tectonic activity, very unusual on Earth, likely holds clues to the internal structure of Enceladus, which may contain subsurface seas where life might be able to develop. Pictured above is a composite of 28 images taken by the robotic Cassini spacecraft in October just after swooping by the ice-spewing orb. Inspection of these images show clear tectonic displacements where large portions of the surface all appear to move all in one direction. Near the top of the image appears one of the most prominent tectonic divides: Labtayt Sulci, a canyon about one kilometer deep.

APOD: 2008 November 5 - Seventeen Hundred Kilometers Above Enceladus
Explanation: Above is one of the closest pictures yet obtained of Saturn's ice-spewing moon Enceladus. The image was taken from about 1,700 kilometers up as the robotic Cassini spacecraft zoomed by the fractured ice ball last week. Features the size of a bus are resolvable in this highly detailed image taken of Enceladus' active tiger stripe region. Very different from most other moons and planets, grooves and hills dot an alien moonscape devoid of craters. Space pioneers might wonder where, on such a highly textured surface, a future probe might land in search of freshly deposited ice, subsurface seas, or even indicators of life. Although appearing dark in the above contrast-enhanced image, the surface of Enceladus is covered with some of the brightest ice in the entire Solar System, reflecting about 99 percent of the light it receives. To help better understand this enigmatic world, Cassini is scheduled to swoop by Enceladus at least five more times.

APOD: 2008 October 14 - An Enceladus Tiger Stripe from Cassini
Explanation: What creates the unusual tiger stripes on Saturn's moon Enceladus? No one is sure. To help find out, scientists programmed the robotic Cassini spacecraft to dive right past the plume-spewing moon last week. Previously, the tiger stripe regions were found to be expelling plumes of water-ice, fueling speculation that liquid seas might occur beneath Enceladus' frozen exterior. Such seas are so interesting because they are candidates to contain extraterrestrial life. Important processes in tiger stripe formation may include heating from below and moonquakes. Visible above is terrain on Enceladus so young that only a few craters are visible. This newly released raw image shows at least one type of false artifact, however, as seeming chains of craters are not so evident in other concurrently released images of the same region. The large tiger stripe across the image middle is impressive not only for its length and breadth, but because a large internal shadow makes it also appear quite deep. Cassini will next fly by Enceladus on October 31.

APOD: 2008 October 13 - Cassini Passes Through Ice Plumes of Enceladus
Explanation: What telling impurities taint the ice plumes of Enceladus? To help answer this question, the robotic Cassini spacecraft dove last week to within 30 kilometers of Saturn's ice-plume emitting moon. At this closest-ever approach, Cassini attempted to sniff and obtain chemical data on particles ejected from Enceladus' regular surface, while at other times Cassini flew right through -- and sampled -- ice geysers directly. Searches in the data for impurity clues in the water-ice dominated plumes and surface ejecta are progressing. Although the main purpose of this flyby was particle analysis, several interesting images are emerging. Visible in the above image, for example, is an unusual gray sheen running vertically up the image center that might be water vapor escaping from surface canyons. Other notable features visible above include vast plains of craterless icy grooves, the day-night terminator across the image left, and an area near the top comparatively rich in craters. Cassini is scheduled to buzz by Enceladus in an imaging run near the end of this month.

APOD: 2008 July 20 - Crescent Rhea Occults Crescent Saturn
Explanation: Soft hues, partially lit orbs, a thin trace of the ring, and slight shadows highlight this understated view of the majestic surroundings of the giant planet Saturn. Looking nearly back toward the Sun, the robot Cassini spacecraft now orbiting Saturn captured crescent phases of Saturn and its moon Rhea in color a few years ago. As striking as the above image is, it is but a single frame from a recently released 60-frame silent movie where Rhea can be seen gliding in front of its parent world. Since Cassini was nearly in the plane of Saturn's rings, the normally impressive rings are visible here only as a thin line across the image center. Although Cassini has now concluded its primary mission, its past successes and opportunistic location have prompted NASA to start a two-year Equinox Mission, further exploring not only Saturn's enigmatic moons Titan and Enceladus, but Saturn herself as her grand rings tilt right at the Sun in August 2009.

APOD: 2008 March 31 - Close Up of Enceladus Tiger Stripes
Explanation: Could life exist beneath Enceladus? A recent flyby of Saturn's icy moon has bolstered this fascinating idea. Two years ago, images from the robotic Cassini spacecraft orbiting Saturn led astronomers to the undeniable conclusion that Saturn's moon Enceladus was spewing fountains of gas and ice crystals through cracks in its surface dubbed tiger stripes. Last month, Cassini dove through some of these plumes and determined that they contained water vapor laced with small amounts of methane as well as simple and complex organic molecules. Surprisingly, the plumes of Enceladus appear similar in make-up to many comets. What's more, the temperature and density of the plumes indicate they might have originated from a warmer source -- possibly a liquid source -- beneath the surface. A liquid water sea containing organic molecules is a good place to look for life. Pictured above is a vertically exaggerated close-up of some long, venting tiger stripes. The computer composite was generated from images and shadows taken during recent Cassini flybys. Nine more flybys of Enceladus by Cassini are planned.

APOD: 2008 March 17 - Thirty Thousand Kilometers Above Enceladus
Explanation: What does the surface of Saturn's ice-spewing moon Enceladus look like? To help find out, the robotic Cassini spacecraft now orbiting Saturn was sent soaring past the cryovolcanic moon and even right through one of Enceladus' ice plumes. Cassini closed to about 52 kilometers during its closest encounter to date. The above unprocessed image was taken looking down from the north, from about 30,000 kilometers away. Visible are at least two types of terrain. The first type of terrain has more craters than occur near Enceladus' South Pole. The other type of terrain has few craters but many ridges and grooves that may have been created by surface-shifting tectonic activity. Exogeologists are currently poring over this and other Cassini images from last Wednesday's flyby to better understand the moon's patch-work surface, its unusual ice-geysers, and its potential to support life. Cassini is scheduled to fly by Enceladus at least nine more times, including an even closer pass of just 25 kilometers this coming October.

APOD: 2007 December 17 - Saturn's Ancient Rings
Explanation: How old are Saturn's rings? No one is quite sure. One possibility is that the rings formed relatively recently in our Solar System's history, perhaps only about 100 million years ago when a moon-sized object broke up near Saturn. Evidence for a young ring age includes a basic stability analysis for rings, and the fact that the rings are so bright and relatively unaffected by numerous small dark meteor impacts. New evidence, however, raises the possibility that some of Saturn's rings may be billions of years old and so almost as old as Saturn itself. Inspection of images by the Saturn-orbiting Cassini spacecraft indicates that some of Saturn's ring particles temporarily bunch and collide, effectively recycling ring particles by bringing fresh bright ices to the surface. Seen here, Saturn's rings were imaged in their true colors by the robotic Cassini in late October. Icy bright Tethys, a moon of Saturn likely brightened by a sandblasting rain of ice from sister moon Enceladus, is visible in front of the darker rings.

APOD: 2007 October 13 - Enceladus Ice Geysers
Explanation: Ice geysers erupt on Enceladus, bright and shiny inner moon of Saturn. Shown in this false-color image, a backlit view of the moon's southern limb, the majestic, icy plumes were discovered by instruments on the Cassini Spacecraft during close encounters with Enceladus in November of 2005. Eight source locations for these geysers have now been identified along substantial surface fractures in the moon's south polar region. Researchers suspect the geysers arise from near-surface pockets of liquid water with temperatures near 273 kelvins (0 degrees C). That's hot when compared to the distant moon's surface temperature of 73 kelvins (-200 degrees C). The cryovolcanism is a dramatic sign that tiny, 500km-diameter Enceladus is surprisingly active. Enceladus ice geysers also likely produce Saturn's faint but extended E ring.

APOD: 2007 March 27 - Enceladus Creates Saturns E Ring
Explanation: The active moon Enceladus appears to be making Saturn's E ring. An amazing picture showing the moon at work was taken late last year by the Saturn-orbiting Cassini spacecraft and is shown above. Enceladus is the dark spot inside the bright flare, right near the center of Saturn's E ring. Streams of ice and water vapor can be seen pouring off Enceladus into the E ring. The above bright image of the normally faint E-ring was made possible by aligning Cassini so that Saturn blocked the Sun. From that perspective, small ring particles reflect incoming sunlight more efficiently. Cassini has now been orbiting Saturn for almost three years, and is scheduled to swoop by the unexpectedly cryovolcanic Enceladus at least several more times.

APOD: 2007 January 31 - Movie: Cassini Crosses Saturn's Ring Plane
Explanation: What would the rings of Saturn look like if you passed right through the ring plane? To find out, NASA aimed cameras from the Cassini spacecraft right at Saturn's rings as the robotic explorer passed from the sunlit side of the rings to the shadowed side. Resulting images from a vantage point outside the rings and most moons, but inside the orbit of Titan, have been gathered together in the above time-lapse movie. The dramatic movie demonstrates that ring particle density and reflectivity makes some parts of the shadowed side nearly the photographic negative of the sunlit side, but nearly empty regions remain continually dark. Visible also are Saturn-orbiting moons Enceladus, Mimas, Janus, Epimetheus, Prometheus, and Pandora. The extreme thinness of Saturn's rings can be appreciated from frames taken near the crossing time.

APOD: 2006 December 31 - A Year of Extraterrestrial Fountains and Flows
Explanation: The past year was extraordinary for the discovery of extraterrestrial fountains and flows -- some offering new potential in the search for liquid water and the origin of life beyond planet Earth.. Increased evidence was uncovered that fountains spurt not only from Saturn's moon Enceladus, but from the dunes of Mars as well. Lakes were found on Saturn's moon Titan, and the residual of a flowing liquid was discovered on the walls of Martian craters. The diverse Solar System fluidity may involve forms of slushy water-ice, methane, or sublimating carbon dioxide. Pictured above, the light-colored path below the image center is hypothesized to have been created sometime in just the past few years by liquid water flowing across the surface of Mars.

APOD: 2006 October 16 - In the Shadow of Saturn
Explanation: In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft now orbiting Saturn recently drifted in giant planet's shadow for about 12 hours and looked back toward the eclipsed Sun. Cassini saw a view unlike any other. First, the night side of Saturn is seen to be partly lit by light reflected from its own majestic ring system. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn and slightly scattering sunlight, in the above exaggerated color image. Saturn's rings light up so much that new rings were discovered, although they are hard to see in the above image. Visible in spectacular detail, however, is Saturn's E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus, and the outermost ring visible above. Far in the distance, visible on the image left just above the bright main rings, is the almost ignorable pale blue dot of Earth.

APOD: 2006 June 27 - The Moving Moons of Saturn
Explanation: The moons of Saturn never stop. A space traveler orbiting the ringed giant planet would witness a continuing silent dance where Saturn's multiple moons pass near each other in numerous combinations. Like a miniature Solar System, the innermost moons orbit Saturn the fastest. The above movie was centered on Saturn's moon Rhea, so that the moons Mimas and Enceladus appear to glide by. At 1,500 kilometers across, Rhea is over three times larger than the comparably sized Mimas and Enceladus. The Sun illuminates the scene from the lower right, giving all of the moons the same crescent phase. The above time lapse movie was created by the Saturn-orbiting robotic Cassini spacecraft over a period of about 40 minutes.

APOD: 2006 June 8 - Enceladus Ice Volcanos
Explanation: In this stunning Saturnian vista - one in a series of artist's visions of volcanos on alien worlds - icy geysers erupt along narrow fractures in inner moon Enceladus. The majestic plumes were actually discovered by instruments on the Cassini Spacecraft during close encounters with bright and shiny Enceladus last year. Researchers now suspect the plumes originate from near-surface pockets of liquid water with temperatures near 273 kelvins (0 degrees C) - hot when compared to the distant moon's surface temperature of 73 kelvins (-200 degrees C). A dramatic sign that tiny, 500km-diameter Enceladus is surprisingly active, these ice volcanos hold out another potential site in the search for water and origin of life beyond planet Earth. Enceladus' ice volcanos also likely produce Saturn's faint but extended E ring.

APOD: 2006 May 3 - Saturn in Blue and Gold
Explanation: Why is Saturn partly blue? The above picture of Saturn approximates what a human would see if hovering close to the giant ringed world. The above picture was taken in mid-March by the robot Cassini spacecraft now orbiting Saturn. Here Saturn's majestic rings appear directly only as a thin vertical line. The rings show their complex structure in the dark shadows they create on the image left. Saturn's fountain moon Enceladus, only about 500 kilometers across, is seen as the bump in the plane of the rings. The northern hemisphere of Saturn can appear partly blue for the same reason that Earth's skies can appear blue -- molecules in the cloudless portions of both planet's atmospheres are better at scattering blue light than red. When looking deep into Saturn's clouds, however, the natural gold hue of Saturn's clouds becomes dominant. It is not known why southern Saturn does not show the same blue hue -- one hypothesis holds that clouds are higher there. It is also not known why Saturn's clouds are colored gold.

APOD: 2006 March 22 - Enceladus Near Saturn
Explanation: Some images of Saturn appear surreal. Earlier this year, the robot spacecraft Cassini now orbiting Saturn took this surreal image of the gas giant Saturn, its majestic rings, and its enigmatic world Enceladus all in one frame. Enceladus, recently found to emit jets of ice from possible underground seas, appears white as its surface is covered with relatively clean water-ice. Below Enceladus are the rings of Saturn, seen nearly edge on. Compared to Enceladus, Saturn's rings show their comparatively high density of dirt with their golden-brown color in this natural color image. The planet Saturn, in the background, appears relatively featureless with the exception of thin ring shadows visible on the upper left. The terminator between night and day is seen vertically across the face of this distant world.

APOD: 2006 March 10 - Enceladus and the Search for Water
Explanation: Based on data from Cassini spacecraft instruments, researchers are now arguing that liquid water reservoirs exist only tens of meters below the surface of Saturn's small (500 kilometer diameter) but active moon Enceladus. The exciting new results center around towering jets and plumes of material erupting from the moon's surface. The plumes originate in the long tiger stripe fractures of the south polar region pictured here. Detailed models suport conclusions that the plumes arise from near-surface pockets of liquid water at temperatures of 273 kelvins (0 degrees Celsius), even though Enceladus has a surface temperature of about 73 kelvins (-200 degrees Celsius). Clearly an important step in the search for water and the potential for the origin of life beyond planet Earth, such near-surface reservoirs of water would be far more accessible than, for example, the internal ocean detected on the Jovian moon Europa.

APOD: 2005 December 19 - Thin Rings Around Polarized Saturn
Explanation: How thin are the rings of Saturn? Brightness measurements from different angles have shown Saturn's rings to be about one kilometer thick, making them many times thinner, in relative proportion, than a razor blade. This thinness sometimes appears in dramatic fashion during an image taken nearly along the ring plane. The robot Cassini spacecraft now orbiting Saturn has now captured another shot that dramatically highlights the ring's thinness. The above artistic looking image was taken early last month in infrared polarized light. If alone in space, the unlit part of Saturn would be much darker. Reflection of light off of moons like Enceladus (pictured) and the billions of small particles in Saturn's rings, however, gives the giant space orb an unusual glow, an effect highlighted in polarized light.

APOD: 2005 December 5 - Ice Fountains Discovered on Saturns Enceladus
Explanation: Fountains of ice shoot out from Saturn's moon Enceladus. Clear discovery images of the fountains were made using observations from the robot Cassini spacecraft currently orbiting Saturn. During a recent pass, Cassini was programmed to look back toward the Sun where Enceladus would appear as a thin crescent. From this vantage point, particles emitted from the surface would better show themselves by reflecting sunlight. The tactic was successful -- the above frame shows several plumes emanating from regions previously known to contain gashes in the surface dubbed tiger stripes. Cassini detected an increase in particle emissions from these regions during a July flyby. Some of these ice particles likely contribute to the make up of Saturn's mysterious E ring.

APOD: 2005 September 6 - Fresh Tiger Stripes on Saturns Enceladus
Explanation: The tiger stripes on Saturn's moon Enceladus might be active. Even today, they may be spewing ice from the moon's icy interior into space, creating a cloud of fine ice particles over the moon's South Pole and creating Saturn's mysterious E-ring. Recent evidence for this has come from the robot Cassini spacecraft now orbiting Saturn. Cassini detected a marked increase in particle collisions during its July flyby only 270 kilometers over a South Polar region of Enceladus. Pictured above, a high resolution image of Enceladus is shown from the close flyby. The unusual surface features dubbed tiger stripes are visible on the left in false-color blue. Why Enceladus is active remains a mystery, as the neighboring moon Mimas, approximately the same size, appears quite dead.

APOD: 2005 June 6 - Saturn: Dirty Rings and a Clean Moon
Explanation: Eating surface ice from Enceladus might be healthier than eating ice from Saturn's rings -- it certainly appears cleaner. From their apparent densities and reflectance properties, both the rings of Saturn and its shiniest moon, Enceladus, are thought to be composed predominantly of water ice. For reasons that are not yet understood, however, many of Saturn's ring particles have become partly coated with some sort of relatively dark dust, while the surface of Enceladus appears comparatively bright and clean. The contrast between the two can be seen in the above image taken last month by the robot Cassini spacecraft now in orbit around Saturn. Bright Enceladus shines in the background in contrast to the darker foreground rings. The reason why Enceladus is so bright is currently unknown but might involve bringing fresh water to its surface with water volcanoes.

APOD: 2005 April 18 - Saturnian Moon and Rings
Explanation: When can a robot produce art? When it glides past the rings of Saturn. As the robot spacecraft Cassini orbiting Saturn crossed outside the famous photogenic ring plane of the expansive planet, the rings were imaged from the outside, nearly edge on, and in the shadow of Saturn. From the upper left, ring features include the A ring, the Cassini gap, the B ring, and the darker C ring that includes the Titan gap and a gap yet unnamed. Last month when the above image was taken, the gliding spacecraft was about one million kilometers from foreground Enceladus, a small Saturnian moon only about 500 kilometers across. Cassini is scheduled to continue its 70 orbit tour of Saturn over the next three years, sending back images of the gas giant, its rings, and its moons that will be studied for decades to come.

APOD: 2005 March 17 - Enceladus Close Up
Explanation: The surface of Enceladus is as white as fresh snow. Still, an impressive variety of terrain is revealed in this contrast enhanced image. At a resolution of about 30 meters per pixel, the close-up view spans over 20 kilometers - recorded during the touring Cassini spacecraft's March flyby of the icy Saturnian moon. Enceladus is known to be the most reflective moon in the solar system, and the recent Cassini encounters have also detected the presence of an atmosphere, making Enceladus the second moon of Saturn with such a distinction. In fact, Enceladus' fresh looking surface and significant atmosphere both indicate that the tiny, 500 kilometer diameter moon is active. Researchers suspect that ice volcanos or geysers coat the surface with fresh material and replenish the moon's atmosphere, ultimately providing the icy particles that compose Saturn's tenuous E ring.

APOD: 2005 February 24 - Ski Enceladus
Explanation: Small, icy, inner moon of Saturn, Enceladus is only about 500 kilometers in diameter. But the distant world does reflect over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as fresh snow. Seen here in a sharp view from the Cassini spacecraft's recent flyby, Enceladus shows a variety of surface features and very few impact craters - indicating that it has been an active world even though this tiny moon should have completely cooled off long ago. In fact, the resurfaced appearance of Enceladus could be the result of liquid water geysers or water volcanos. Since Enceladus orbits within the outer E ring of Saturn, the moon's surface may be kept snow-bright as it is continuously bombarded with icy ring particles. Eruptions on Enceladus itself would in turn supply material to the E ring. Interplanetary ski bums take note: tiny Enceladus has only about 1/100th the surface gravity of planet Earth and a surface temperature of -200 degrees C (-330 degrees F).

APOD: 2003 August 17 - Natural Saturn On The Cassini Cruise
Explanation: What could you see approaching Saturn aboard an interplanetary cruise ship? Your view would likely resemble this subtly shaded image of the gorgeous ringed gas giant. Processed by the Hubble Heritage project, the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn with cloud bands, storms, nearly edge-on rings, and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently en route, the Cassini spacecraft. Cassini flew by Jupiter at the turn of the millennium and is scheduled to arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun, Cassini will tour the Saturnian system, conducting a remote, robotic exploration with software and instruments designed by denizens of planet Earth.

APOD: 2002 May 11 - Natural Saturn On The Cassini Cruise
Explanation: What could you see approaching Saturn aboard an interplanetary cruise ship? Your view would likely resemble this subtly shaded image of the gorgeous ringed gas giant. Processed by the Hubble Heritage project, the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn with cloud bands, storms, nearly edge-on rings, and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently enroute, the Cassini spacecraft. Cassini flew by Jupiter at the turn of the millennium and is scheduled to arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun, Cassini will tour the Saturnian system, conducting a remote, robotic exploration with software and instruments designed by denizens of planet Earth.

APOD: 2002 January 24 - Ski Enceladus
Explanation: A small inner moon of Saturn, Enceladus is only about 500 kilometers in diameter. But the cold, distant world does reflect over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as new-fallen snow. Seen here in a mosaic of Voyager 2 images from 1981, Enceladus shows a variety of surface features and very few impact craters - indicating that it is an active world even though this ice moon should have completely cooled off long ago. In fact the fresh, resurfaced appearance of Enceladus suggests that an internal mechanism, perhaps driven by tidal pumping, generates heat and supplies liquid water to geysers or water volcanos. Since Enceladus orbits within the tenuous outer E ring of Saturn, the moon's surface may be kept snow-bright as it is continuously bombarded with icy ring particles. Eruptions on Enceladus itself would in turn supply material to the E ring. Interplanetary ski bums take note: tiny Enceladus has only about one hundredth the surface gravity of planet Earth.

APOD: 2000 January 29 - Natural Saturn On The Cassini Cruise
Explanation: What could you see approaching Saturn aboard an interplanetary cruise ship? Your view would likely resemble this subtly shaded image of the gorgeous ringed gas giant. Processed by the Hubble Heritage project, the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn with cloud bands, storms, nearly edge-on rings, and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently enroute - the Cassini spacecraft, launched in 1997 and scheduled to arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun, Cassini will tour the Saturnian system, conducting a remote, robotic exploration with software and instruments designed by denizens of planet Earth. But where is Cassini now? Still about 980 million kilometers from Saturn, last Sunday the spacecraft flew by asteroid 2685 Masursky.

APOD: November 5, 1998 - Natural Saturn On The Cassini Cruise
Explanation: What you could see approaching Saturn aboard an interplanetary cruise ship would closely resemble this subtly shaded view of the gorgeous ringed gas giant. Processed by the Hubble Heritage project, the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn with cloud bands, storms, nearly edge-on rings, and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently enroute - the Cassini spacecraft, launched just over a year ago and scheduled to arrive at Saturn in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun, Cassini will tour the Saturnian system, conducting a remote, robotic exploration with software and instruments designed by denizens of planet Earth.

APOD: October 18, 1998 - Saturns Rings Seen Sideways
Explanation: Saturn's rings are actually very thin. This picture from the Hubble Space Telescope was taken on August 6, 1995 when the rings lined up sideways as seen from Earth. Saturn's largest moon Titan is seen on the left, and Titan's shadow can be seen on Saturn's cloud tops! Titan itself looks a brownish color because of its thick atmosphere. Four other moons of Saturn can be seen just above the ring plane, which are, from left to right: Mimas, Tethys, Janus, and Enceladus. If you look carefully, you will note that the dark band across the planet is actually the shadow of the rings, and is slightly displaced from the real rings - which are best seen away from the planet. Saturn's rings are not solid - they are composed of ice chunks which range in size from a grain of sand to a house.

APOD: May 24, 1997 - Saturn's Rings Seen Sideways
Explanation: Saturn's rings are actually very thin. This picture from the Hubble Space Telescope was taken on August 6, 1995 when the rings lined up sideways as seen from Earth. Saturn's largest moon Titan is seen on the left, and Titan's shadow can be seen on Saturn's cloud tops! Titan itself looks a brownish color because of its thick atmosphere. Four other moon's of Saturn can be seen just above the ring plane, which are, from left to right: Mimas, Tethys, Janus, and Enceladus. If you look carefully, you will note that the dark band across the planet is actually the shadow of the rings, and is slightly displaced from the real rings - which are best seen away from the planet. Saturn's rings are not solid - they are composed of ice chunks which range in size from a grain of sand to a house.

APOD: April 29, 1996 - Saturn's Rings Seen Sideways
Explanation: Saturn's rings are actually very thin. This picture from the Hubble Space Telescope was taken on August 6, 1995 when the rings lined up sideways as seen from Earth. Saturn's largest moon Titan is seen on the left, and Titan's shadow can be seen on Saturn's cloud tops! Titan itself looks a brownish color because of its thick atmosphere. Four other moon's of Saturn can be seen just above the ring plane, which are, from left to right: Mimas, Tethys, Janus, and Enceladus. If you look carefully, you will note that the dark band across the planet is actually the shadow of the rings, and is slightly displaced from the real rings - which are best seen away from the planet. Saturn's rings are not solid - they are composed of ice chunks which range in size from a grain of sand to a house.

APOD: November 25, 1995 - Saturn's Cleanest Moon: Enceladus
Explanation: Enceladus orbits Saturn between the smaller Mimas and the larger Tethys. Enceladus is composed mostly of water ice and has the cleanest and purest ice surface in the Solar System. It's surface therefore appears nearly white. The surface also has many unusual groves and relatively few craters, like Jupiter's moon Ganymede. This indicates that the surface is young and/or newly reformed. To explain this, some astronomers speculate that Enceladus is susceptible to some sort of volcanic activity. Enceladus was originally discovered in 1789 by William Herschel.