Iapetus

These two global images of Iapetus show the extreme brightness dichotomy on the surface of this peculiar Saturnian moon. The left-hand panel shows the moon's leading hemisphere and the right-hand panel shows the moon's trailing side. While low and mid latitudes of the leading side exhibit a surface almost as dark as charcoal, broad tracts of the trailing side are almost as bright as snow. The dark terrain covers about 40 percent of the surface and is named Cassini Regio. The names of the bright terrain are Roncevaux Terra (north) and Saragossa Terra (south).

On both hemispheres, the dominant landforms are impact craters. The largest known well-preserved basin on Iapetus, called Turgis, has a diameter of about 580 kilometers (360 miles). It lies at 17 degrees north latitude, 28 degrees west longitude at the eastern edge of the dark Cassini Regio and is visible on the right side of the left-hand panel. The prominent basin on the southern trailing side (at the lower left of the right-hand panel) is Engelier. Engelier is located at 41 degrees south latitude, 265 degrees west longitude, and has a diameter of about 504 kilometers (313 miles). Its formation destroyed about half of Gerin, another large basin on Iapetus. Gerin is located at 46 degrees south latitude, 233 degrees west longitude, and has a diameter of about 445 kilometers (276 miles). Tortelosa Montes, a part of the giant equatorial ridge that was discovered in Cassini images on December 25, 2004, is visible in the left panel as a thin line within Cassini Regio, and as a tall prominence at the western limb. It continues onto the trailing side (right side of right panel), where the bright western flanks of the Carcassone Montes appear as dominant bright spots within the western edge of Cassini Regio.

The cause of the extreme brightness dichotomy on Iapetus is likely to be thermal segregation of water ice on a global scale. Thermal effects are usually expected to act latitudinally. That is, polar areas are colder than equatorial terrain in most cases due to the more oblique angle of the solar irradiation. Therefore, an additional process is required to explain the longitudinal difference as well. In one model, dark, reddish dust coming in from space and preferentially deposited on the leading side forms a small, but crucial difference between the leading and trailing hemispheres, which is sufficient to allow the thermal effect to evaporate the water ice on the leading side completely, but only marginally on the trailing side. See PIA11689 to learn more. Iapetus' extremely slow rotation rate (1,904 hours), its distance from the sun, its relatively small size and surface gravity, and its outer position within the regular satellite system of Saturn are also crucial contributing conditions for this mechanism to work as observed.

North on Iapetus is approximately up in the images. Iapetus has a diameter of 1471 kilometers (914 miles).

The right-hand panel, released previously as PIA08384, shows a mosaic of 60 different images, obtained on September 10, 2007.

The left-hand panel is a color composite of three images obtained through infrared, green and ultraviolet spectral filters (centered at 752, 568 and 338 nanometers, respectively) by Cassini's narrow-angle camera on December 27, 2004. The view was acquired at a distance of approximately 717,000 kilometers (446,000 miles) from Iapetus and at a sun-Iapetus-spacecraft, or phase, angle of 22 degrees.

Scale in the original image on the left was about 4 kilometers (2.5 miles) per pixel. For ease of comparison, the scales in both the left and right images were set to 1,400 meters (4,600 feet) per pixel.

Photo credit: NASA/JPL/Space Science Institute

Note: For more information, see Saturn is Like an Antiques Shop, Cassini Suggests.

Dione, Rhea and Enceladus

The Cassini spacecraft observes three of Saturn's moons set against the darkened night side of the planet.

Saturn is present on the left this image but is too dark to see. Rhea (1,528 kilometers, or 949 miles across) is closest to Cassini here and appears largest at the center of the image. Enceladus (504 kilometers, or 313 miles across) is to the right of Rhea. Dione (1,123 kilometers, or 698 miles across) is to the left of Rhea, partly obscured by Saturn.

This view looks toward the northern, sunlit side of the rings from just above the ringplane.

The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on April 25, 2011. The view was obtained at a distance of approximately 2.2 million kilometers (1.4 million miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 67 degrees. Image scale is 13 kilometers (8 miles) per pixel on Rhea. The view was obtained at a distance of approximately 3 million kilometers (1.9 million miles) from Enceladus and at a phase angle of 67 degrees. Image scale is 18 kilometers (11 miles) per pixel on Enceladus. The view was obtained at a distance of approximately 3.1 million kilometers (1.9 million miles) from Dione and at a phase angle of 67 degrees. Image scale is 19 kilometers (12 miles) per pixel on Dione.

Photo credit: NASA/JPL/Space Science Institute

Rhea

The surface of Saturn's moon Rhea bears witness to its violent history. Each crater seen here records an impact in the moon's past.

On some of Rhea's terrains, craters are so densely packed that they lie on top of each other, newer impacts often erasing the older craters. Rhea is 949 miles, or 1,528 kilometers across.

This view is centered on terrain at 38 degrees north latitude, 290 degrees west longitude. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on December 22, 2012.

The view was acquired at a distance of approximately 19,000 miles (31,000 kilometers) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 30 degrees. Image scale is 600 feet (183 meters) per pixel.

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

Saturn and Mimas

Saturn and its north polar hexagon dwarf Mimas as the moon peeks over the planet's limb. Saturn's A ring also makes an appearance on the far right. Mimas is 246 miles (396 kilometers) across.

This view looks toward the sunlit side of the rings from about 21 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on November 28, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 495,000 miles (797,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 4 degrees. Image scale is 27 miles (44 kilometers) per pixel.

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

Impact Craters on Rhea

N00203890.jpg was taken on March 09, 2013 and received on Earth March 10, 2013. The camera was pointing toward RHEA at approximately 2,348 miles (3,778 kilometers) away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2014.

Photo credit: NASA/JPL/Space Science Institute

Note: For more information, see Cassini Returns Images of Battered Saturn Moon.

Unusual Arc on Rhea

N00203884.jpg was taken on March 09, 2013 and received on Earth March 10, 2013. The camera was pointing toward RHEA at approximately 1,727 miles (2,779 kilometers) away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2014.

Photo credit: NASA/JPL/Space Science Institute

Note: For more information, see Cassini Returns Images of Battered Saturn Moon.

Rhea

N00203868.jpg was taken on March 09, 2013 and received on Earth March 10, 2013. The camera was pointing toward RHEA at approximately 39,072 miles (62,880 kilometers) away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated. A validated/calibrated image will be archived with the NASA Planetary Data System in 2014.

Photo credit: NASA/JPL/Space Science Institute

Note: For more information, see Cassini Returns Images of Battered Saturn Moon.

Urmia Lacus and Sionascaig Lacus

From the USGS Astrogeology Science Center:

The IAU Working Group for Planetary System Nomenclature has approved the names Urmia Lacus and Sionascaig Lacus for use on Titan. For more information, see the IAU Gazetteer of Planetary Nomenclature.

Rhea

This image was taken on March 10, 2013, and received on Earth March 10, 2013 by NASA's Cassini spacecraft. The camera was pointing toward Rhea at approximately 174,181 miles (280,317 kilometers) away, and the image was taken using the CL1 and CL2 filters. This image has not been validated or calibrated.

Photo credit: NASA/JPL/Space Science Institute

Note: For more information, see Cassini Returns Images of Battered Saturn Moon.

B-Rings Spokes and Atlas

The ghostly spokes in Saturn's B ring continue to put on a show for the Cassini spacecraft cameras in this recent image. The spokes, believed to be a seasonal phenomenon, are expected to disappear as Saturn nears its northern hemisphere summer. Scientists continue to monitor the spokes to better understand their origin and evolution.

The small moon Atlas also appears here barely visible in between the A ring and the F ring, which is the thin ring located furthest from Saturn, as the fainter dot close to the A ring. Atlas is closer to the bottom of the image. A bright star also appears in the gap between the two rings, and there are six other stars visible (one through the C ring, near the planet).

This view looks toward the unilluminated side of the rings from about 49 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on December 20, 2012.

The view was obtained at a distance of approximately 840,000 miles (1.4 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 105 degrees. Image scale is 48 miles (77 kilometers) per pixel.

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

Venus by Cassini

Dawn on Saturn is greeted across the vastness of interplanetary space by the morning star, Venus, in this image from NASA's Cassini spacecraft. Venus appears just off the edge of the planet, in the upper part of the image, directly above the white streak of Saturn's G ring. Lower down, Saturn's E ring makes an appearance, looking blue thanks to the scattering properties of the dust that comprises the ring. A bright spot near the E ring is a distant star.

Venus is, along with Mercury, Earth, and Mars, one of the rocky "terrestrial" planets in the solar system that orbit relatively close to the sun. Though Venus has an atmosphere of carbon dioxide that reaches nearly 900 degrees Fahrenheit (500 degrees Celsius) and a surface pressure 100 times that of Earth's, it is considered a twin to our planet because of their similar size, mass, rocky composition and orbit. Venus is covered in thick sulfuric acid clouds, making it very bright.

This view looks toward the unilluminated side of the rings from about 21 degrees below the ring plane.

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 wide-angle camera on January 4, 2013, at a distance of approximately 371,000 miles (597,000 kilometers) from Saturn. Image scale is 20 miles (32 kilometers) per pixel.

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

Venus Through Saturn's Rings

Peering over the shoulder of giant Saturn, through its rings, and across interplanetary space, NASA's Cassini spacecraft spies the bright, cloudy terrestrial planet, Venus. The vast distance from Saturn means that Venus only shows up as a white dot, just above and to the right of the image center.

Venus, along with Mercury, Earth, and Mars, is one of the rocky 'terrestrial' planets in the solar system that orbit relatively close to the sun. Though Venus has an atmosphere of carbon dioxide that reaches nearly 900 degrees Fahrenheit (500 degrees Celsius) and a surface pressure 100 times that of Earth, it is considered a twin to our planet because of their similar size, mass, rocky composition and orbit. Venus is covered in thick sulfuric acid clouds, making it very bright.

This view looks toward the unilluminated side of the rings from about 17 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on November 10, 2012.

This is a true-color picture of Saturn and Venus. A false-color mosaic including an image very similar to this one can be seen at PIA14934.

The bright arc is the limb of Saturn. A portion of the rings is seen in silhouette against the face of Saturn, which itself is faintly illuminated by sunlight scattered off the rings. The view was obtained at a distance of approximately 498,000 miles (802,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 178 degrees. Image scale is 28 miles (44 kilometers) per pixel.

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

Dione

The famed wispy terrain on Saturn's moon Dione is front and center in this recent Cassini spacecraft image. The "wisps" are fresh fractures on the trailing hemisphere of the moon's icy surface.

See PIA10560 to learn more about Dione's wispy terrain.

This view is centered on 55 degrees north latitude and 85 degrees west longitude on Dione (698 miles, or 1,123 kilometers across). North is up and rotated 39 degrees to the left.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on December 23, 2012. The view was obtained at a distance of approximately 153,000 miles (246,000 kilometers) from Dione. Image scale is 0.9 miles (1.5 kilometers) per pixel.

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