Mimas Peeping Behind Dione

Saturn's moon Mimas peeps out from behind the larger moon Dione in this view from the Cassini spacecraft.

Mimas (246 miles, or 396 kilometers across) is near the bottom center of the image. Saturn's rings are also visible in the top right.

This view looks toward the anti-Saturn side of Dione (698 miles, or 1,123 kilometers across). North on Dione is up and rotated 20 degrees to the right. This view looks toward the northern, sunlit side of the rings from just above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on December 12, 2011. The view was obtained at a distance of approximately 377,000 miles (606,000 kilometers) from Mimas. The view was obtained at a distance of approximately 56,000 miles (91,000 kilometers) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 42 degrees. Image scale is 1,773 feet (541 meters) per pixel on Dione.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Daphnis Making Waves

The Cassini spacecraft catches Saturn's moon Daphnis making waves and casting shadows from the narrow Keeler Gap of the planet's A ring in this view taken around the time of Saturn's August 2009 equinox.

Daphnis (8 kilometers, or 5 miles across) is almost invisible in this view, but the shadows cast on the wide A ring can be seen below the center of the image. The Encke Gap of the A ring, which is wider than the Keeler Gap, is on the right. Saturn's thin F ring is on the left of the view. See PIA11629 for a similar, closer view.

More than a dozen background stars are visible in this image.

Daphnis has an inclined orbit and its gravitational pull perturbs the orbits of the particles of the A ring forming the Keeler Gap's edge and sculpts the edge into waves having both horizontal (radial) and out-of-plane components. Material on the inner edge of the gap orbits faster than the moon so that the waves there lead the moon in its orbit. Material on the outer edge moves slower than the moon, so waves there trail the moon. See PIA11656 to learn more about this process.

The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane, significantly darkens the rings, and causes out-of-plane structures to look anomalously bright and cast shadows across the rings. These scenes are possible only during the few months before and after Saturn's equinox which occurs only once in about 15 Earth years. Before and after equinox, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons (see PIA11657), but also the shadows of newly revealed vertical structures in the rings themselves (see PIA11665).

This view looks toward the northern, sunlit side of the rings from about 13 degrees above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on August 16, 2009. The view was acquired at a distance of approximately 2.1 million kilometers (1.3 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 108 degrees. Image scale is 12 kilometers (8 miles) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Lightning Strike on Saturn

These false-color mosaics from NASA's Cassini spacecraft capture lightning striking within the huge storm that encircled Saturn's northern hemisphere for much of 2011.

The larger mosaic on the left of the panel shows the lightning flash, which appears as a blue dot. The smaller mosaic on the right is composed of images taken 30 minutes later, and the lightning is not flashing at that time.

See PIA14904 for a mosaic showing a wider view wrapping around the planet also in which some blue lightning is visible in the clouds.

The white arrow in the annotated version of this panel points to the location where the lightning occurred in the clouds. The optical energy of this and other flashes on Saturn is comparable to the strongest of the flashes on Earth. The flash is approximately 120 miles (200 kilometers) in diameter when it exits the tops of the clouds. From this, scientists deduce that the lightning bolts originate in the clouds deeper down in Saturn's atmosphere where water droplets freeze. This is analogous to where lightning is created on Earth.

This lightning flash appears only in the filter sensitive to blue visible light, and the images were enhanced to increase the visibility of the lightning.

Images taken using red, green and blue spectral filters are usually combined to create a natural color view. Because visible red-light images were not available, images taken using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers were used in place of red. Also, the blue filter image was enhanced to increase the visibility of the lightning. The result is a type of false color image.

The images were obtained with the Cassini spacecraft narrow-angle camera on March 6, 2011, at a distance of approximately 2 million miles (3.3 million kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 83 degrees. These mosaics are simple cylindrical map projections, defined such that a square pixel subtends equal intervals of latitude and longitude. At higher latitudes, the pixel size in the north-south direction remains the same, but the pixel size (in terms of physical extent on the planet) in the east-west direction becomes smaller. The pixel size is set at the equator, where the distances along the sides are equal. This map has a pixel size of 12 miles (20 kilometers) at the equator.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Note: For more information, see Cassini Spots Daytime Lightning on Saturn.

Partial Eclipse of Enceladus, with Titan

Saturn's moon Enceladus is partially eclipsed by the planet in this Cassini spacecraft view which also features the moon Titan in the distance.

Cassini flew by Enceladus, shown in the center of the view, at a distance of about 16,000 miles (26,000 kilometers). The terminator between the day and night sides of Enceladus (313 miles, or 504 kilometers across) can be seen on the far left of the moon, while the shadow of the eclipsing planet runs across the bottom.

Titan (3,200 miles, or 5,150 kilometers across) is in the bottom right of this image and is about 684,000 miles (1.1 million kilometers) from the spacecraft. See PIA11508 to see Titan eclipsed by the planet.

This view looks toward the Saturn-facing sides of Enceladus and Titan. North is up.

The image was taken in visible light with the Cassini spacecraft wide-angle camera on October 1, 2011. The view was obtained at a Sun-Enceladus-spacecraft, or phase, angle of 29 degrees. Scale in the original image was 2 miles (3 kilometers) per pixel on Enceladus. The image was contrast enhanced and magnified by a factor of 1.5 to enhance the visibility of surface features.

Photo credit: NASA/JPL-Caltech/Space Science Institute

Titan's South Polar Vortex

This true color image captured by NASA'S Cassini spacecraft before a distant flyby of Saturn's moon Titan on June 27, 2012, shows a south polar vortex, or a swirling mass of gas around the pole in the atmosphere.

The south pole of Titan (3,200 miles, or 5,150 kilometers, across) is near the center of the view.

Since Cassini arrived in the Saturn system in 2004, Titan has had a visible "hood" high above the north pole (see PIA08137). It was northern winter at Cassini's arrival, and much of the high northern latitudes were in darkness. But the hood, an area of denser, high altitude haze compared to the rest of the moon's atmosphere, was high enough to be still illuminated by sunlight. The seasons have been changing since Saturn's August 2009 equinox signaled the beginning of spring in the northern hemisphere and fall in the southern hemisphere for the planet and its many moons. Now the high southern latitudes are moving into darkness. The formation of the vortex at Titan's south pole may be related to the coming southern winter and the start of what will be a south polar hood.

See PIA14920 for a movie captured with a similar view and showing the polar vortex in motion.

These new, more detailed images are only possible because of Cassini's newly inclined orbits, which are the next phase of Cassini Solstice Mission. Previously, Cassini was orbiting in the equatorial plane of the planet, and the imaging team's images of the polar vortex between late March and mid-May were taken from over Titan's equator. At that time, images showed a brightening or yellowing of the detached haze layer on the limb, or edge of the visible disk of the moon, over the south polar region.

Scientists think these new images show open cell convection. In open cells, air sinks in the center of the cell and rises at the edge, forming clouds at cell edges. However, because the scientists can't see the layer underneath the layer visible in these new images, they don't know what mechanisms may be at work.

Cosmic ray hits on the camera detectors appear as bright dots in the black and white version of the image (Figure 1).

Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft narrow-angle camera late on June 26, 2012 at a distance of approximately 301,000 miles (484,000 kilometers) from Titan. Image scale is 2 miles (3 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute; video credit: NASA/JPL-Caltech/Space Science Institute

Note: For more information, see The Titanian Seasons Turn, Turn, Turn; also, PIA14920: Titan's South Polar Vortex in Motion.

Formation of a High-Altitude Hood Over Titan's South Pole

False-color images from NASA's Cassini spacecraft show the development of a hood of high-altitude haze -- which appears orange in this image -- forming over the south pole of Saturn's moon Titan. These images were obtained on May 22 and June 7, 2012 by the visual and infrared mapping spectrometer in infrared wavelengths. Scientists assigned the colors red, green and blue to wavelengths mostly sensitive to the stratosphere, troposphere, and surface components, respectively. The newly discovered feature appears several hundred miles (kilometers) above the surface. When Cassini arrived at Saturn, it saw a hood of clouds and haze over Titan's north pole, which was experiencing winter. The south pole was basically clear, except for sporadic methane clouds. The seasons have been changing and the circulation in the upper atmosphere goes now from the illuminated north pole to the cooling south pole, causing downwellings over the south pole and formation of the hood.

Photo credit: NASA/JPL-Caltech/University of Arizona/LPGNantes

Pan Amid the Rings

NASA's Cassini spacecraft has recently resumed the kind of orbits that allow for spectacular views of Saturn's rings. This view, from Cassini's imaging camera, shows the outer A ring and the F ring. The wide gap in the image is the Encke Gap, where you see not only the embedded moon Pan but also several kinky, dusty ringlets. A wavy pattern on the inner edge of the Encke gap downstream from Pan and aspiral pattern moving inwards from that edge show Pan's gravitational influence. The narrow gap close to the outer edge is the Keeler gap.

Photo credit: NASA/JPL-Caltech/SSI

The Sikorsky Propeller

These three Cassini images show a propeller-shaped structure created by an unseen moon in Saturn's A ring. Propellers and other details of Saturn's rings are greeting scientists for the first time in two years, as Cassini's orbit took the spacecraft out of Saturn's equatorial plane in the spring of 2012, making face-on views of the rings possible again.

For years scientists have tracked this propeller, marked with red arrows here. These images are part of a growing catalog of "propeller" moons that, despite being too small to be seen, enhance their visibility by creating larger disturbances in the surrounding fabric of Saturn's rings.

This propeller, nicknamed "Sikorsky" after Russian-American aviator Igor Sikorsky, is about 30 miles (50 kilometers) long. See PIA12790, PIA12792 and PIA11672 to learn more about propellers.

In this most recent image, scientists knew they were observing a propeller they had seen before because Sikorsky was found close to the location predicted by a simple model of its motion. But its actual location did trail the predicted location by 6 degrees of longitude (8,000 miles, or 13,000 kilometers), underlining some of the changes known to occur in the orbits of propeller moons. These changes may occur because of interactions between the rings and the propeller moons. Scientists are eager to understand these interactions in Saturn's rings, as they may hold a key to similar systems such as solar systems forming from disks of matter.

In this most recent image, Sikorsky was found to trail its predicted position by 6 degrees of longitude (8,000 miles, or 13,000 kilometers), a discrepancy that underlines the changes that are known to occur in the orbits of propeller moons, possibly due to interactions between the rings and the embedded moons. Scientists are eager to understand these interactions in Saturn's rings, as they may hold a key to similar systems such as solar systems forming from disks of matter.

The Encke Gap of Saturn's A ring is on the right in the images. The A ring is the outermost of Saturn's main rings. This view looks toward the northern, sunlit side of the rings from about 12 degrees above the ringplane.

These images have not been cleaned of the effects of cosmic rays that struck the camera's sensor during exposure. These cosmic ray hits appear as small white specks or streaks on the images. These specks are not features in Saturn's rings. The image has been enhanced to aid visibility of compact objects like the propeller. The enhancement makes the edge of the Encke Gap appear dashed.

The images were taken in visible light with the Cassini spacecraft narrow-angle camera on June 5, 2012. The view was obtained at a distance of approximately 236,000 miles (380,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 24 degrees. Image scale is 1 mile (2 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/SSI/Cornell

Note: For more information, see Saturn's Rings are Back.

Bright Ejecta on Dione

Ejected material appears bright around some of Dione's craters in the image taken during the Cassini spacecraft's flyby of the moon on March 28, 2012.

This view is centered on terrain at 25 degrees north latitude, 128 degrees west longitude on Dione (698 miles, 1123 kilometers across).

See PIA10464 to see ejecta, or material thrown outward by the impact that formed a crater, covering a large area on the moon Rhea.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera. The view was acquired at a distance of approximately 28,000 miles (45,000 kilometers) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 55 degrees. Image scale is 876 feet (267 meters) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute

The Shadow of Enceladus on Saturn

Saturn's rings cast wide shadows on the planet, and the shadow of a moon also graces the gas giant in this scene from the Cassini spacecraft.

The moon Enceladus is not shown in this view, but it does cast a small, elongated shadow on the planet near the bottom of this view. The moon Mimas (246 miles, or 396 kilometers across) is visible as a bright dot on the far right of the image in the ring plane.

This view looks toward the southern, unilluminated side of the rings from about 2 degrees below the ringplane.

The image was taken with the Cassini spacecraft wide-angle camera on Jan. 14, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was acquired at a distance of approximately 1.7 million miles (2.8 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 51 degrees. Image scale is 105 miles (170 kilometers) per pixel.

Photo credit: NASA/JPL-Caltech/Space Science Institute