Elevated View of Enceladus' South Pole

This dramatic view looks across the region of Enceladus' geyser basin and down on the ends of the Baghdad and Damascus fractures that face Saturn. The image, which looks approximately in the direction of Saturn, was taken from a more elevated viewpoint than other Cassini survey images of this area of the moon's south pole.

The geysering segments of the fractures seen here are among the most active and warmest in the whole region. As seen from the spacecraft from an elevation angle of 25 degrees south, the jets are projected against the bright surface as opposed to black sky. Consequently, despite the pronounced activity, the jets appear fuzzy, or indistinct, in this image and their tilts are consequently not measurable. Though their source locations are clearly seen, this image was not used in the process of triangulation, but instead it was used to confirm source locations determined from triangulation using other images.

The image was taken with Cassini's narrow-angle camera through the clear filter on August 13, 2010, with an image scale about 230 feet (70 meters) per pixel and a Sun-Enceladus-spacecraft, or phase, angle of about 151 degrees.

This image was one of those used to confirm the sources of Enceladus' geysers as described in a paper by Porco, DiNino, and Nimmo, and published in the online version of the Astronomical Journal in July 2014: http://dx.doi.org/10.1088/0004-6256/148/3/45.

A companion paper, by Nimmo et al. is available at: http://dx.doi.org/10.1088/0004-6256/148/3/46.

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

Note: For more information, see PIA17186: Geyser Basin in 3-D, PIA17187: Enceladus' Plume Brightness Variations, PIA17188: Surveyor's Map of Enceladus' Geyser Basin, PIA17189: What Lies Beneath: Close Up View (Artist's Concept), PIA17190: What Lies Beneath: Regional View (Artist's Concept), and Cassini Spacecraft Reveals 101 Geysers and More on Icy Saturn Moon.

Enceladus Geysers

This Cassini narrow-angle camera image -- one of those acquired in the survey conducted by the Cassini imaging science team of the geyser basin at the south pole of Enceladus -- was taken as Cassini was looking across the moon's south pole. At the time, the spacecraft was essentially in the moon's equatorial plane. The image scale is 1280 feet (390 meters) per pixel and the sun-Enceladus-spacecraft, or phase, angle is 162.5 degrees.

The image was taken through the clear filter of the narrow angle camera on November 30, 2010, 1.4 years after southern autumnal equinox. The shadow of the body of Enceladus on the lower portions of the jets is clearly seen.

In an annotated version of the image, the colored lines represent the projection of Enceladus' shadow on a plane normal to the branch of the Cairo fracture (yellow line), normal to the Baghdad fracture (blue line) and normal to the Damascus fracture (pink line).

Post-equinox images like this, clearly showing the different projected locations of the intersection between the shadow and the curtain of jets from each fracture, were useful for scientists in checking the triangulated positions of the geysers, as described in a paper by Porco, DiNino, and Nimmo, and published in the online version of the Astronomical Journal in July 2014: http://dx.doi.org/10.1088/0004-6256/148/3/45.

A companion paper, by Nimmo et al. is available at: http://dx.doi.org/10.1088/0004-6256/148/3/46.

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

Note: For more information, see 101 Geysers on Icy Saturn Moon.

Tethys

Tethys, like many moons in the solar system, keeps one face pointed towards the planet around which it orbits. Tethys' anti-Saturn face is seen here, fully illuminated, basking in sunlight. On the right side of the moon in this image is the huge crater Odysseus.

The Odysseus crater is 280 miles (450 kilometers) across while Tethys is 660 miles (1,062 kilometers) across. See PIA07693 for a closer view and more information on the Odysseus crater.

This view looks toward the anti-Saturn side of Tethys. North on Tethys is up and rotated 33 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 15, 2013.

The view was acquired at a distance of approximately 503,000 miles (809,000 kilometers) from Tethys. Image scale is 3 miles (5 kilometers) per pixel.

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

Crescent Saturn

Saturn appears to Cassini's cameras as a thin, sunlit crescent in this unearthly view. Citizens of Earth, being so much closer to the Sun than Saturn, never get to enjoy a view of Saturn like this without the aid of our robot envoys.

Parts of the night side of Saturn show faint illumination due to light reflected off the rings back onto the planet, an effect dubbed "ringshine." This view looks toward the unilluminated side of the rings from about 43 degrees below the ringplane. The image was taken in green light with the Cassini spacecraft wide-angle camera on August 4, 2013.

The view was obtained at a distance of approximately 1.2 million miles (2 million kilometers) from Saturn. Image scale is 75 miles (120 kilometers) per pixel.

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

Prometheus and the Rings

Seen within the vast expanse of Saturn's rings, Prometheus appears as little more than a dot. But that little moon still manages to shape the F ring, confining it to its narrow domain.

Prometheus (53 miles, or 86 kilometers across) and its fellow moon Pandora (50 miles, or 81 kilometers across) orbit beside the F ring and keep the ring from spreading outward through a process dubbed "shepherding."

This view looks toward the unilluminated side of the rings from about 45 degrees below the ringplane. The image was taken in green light with the Cassini spacecraft wide-angle camera on March 8, 2014.

The view was obtained at a distance of approximately 533,000 miles (858,000 kilometers) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 90 degrees. Image scale is 32 miles (51 kilometers) per pixel.

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

Saturn's North Polar Vortex and Rings

The Cassini spacecraft captures three magnificent sights at once: Saturn's north polar vortex and hexagon along with its expansive rings.

The hexagon, which is wider than two Earths, owes its appearance to the jet stream that forms its perimeter. The jet stream forms a six-lobed, stationary wave which wraps around the north polar regions at a latitude of roughly 77 degrees North.

This view looks toward the sunlit side of the rings from about 37 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on April 2, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 1.4 million miles (2.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 43 degrees. Image scale is 81 miles (131 kilometers) per pixel.

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

Titan's Ocean Perhaps as Salty as the Dead Sea

Researchers found that Titan's ice shell, which overlies a very salty ocean, varies in thickness around the moon, suggesting the crust is in the process of becoming rigid.

Scientists analyzing data from NASA's Cassini mission have firm evidence the ocean inside Saturn's largest moon, Titan, might be as salty as Earth's Dead Sea.

The new results come from a study of gravity and topography data collected during Cassini's repeated flybys of Titan during the past 10 years. Using the Cassini data, researchers presented a model structure for Titan, resulting in an improved understanding of the structure of the moon's outer ice shell. The findings are published in this week's edition of the journal Icarus.

"Titan continues to prove itself as an endlessly fascinating world, and with our long-lived Cassini spacecraft, we're unlocking new mysteries as fast as we solve old ones," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, who was not involved in the study.

Additional findings support previous indications the moon's icy shell is rigid and in the process of freezing solid. Researchers found that a relatively high density was required for Titan's ocean in order to explain the gravity data. This indicates the ocean is probably an extremely salty brine of water mixed with dissolved salts likely composed of sulfur, sodium and potassium. The density indicated for this brine would give the ocean a salt content roughly equal to the saltiest bodies of water on Earth.

"This is an extremely salty ocean by Earth standards," said the paper's lead author, Giuseppe Mitri of the University of Nantes in France. "Knowing this may change the way we view this ocean as a possible abode for present-day life, but conditions might have been very different there in the past."

Cassini data also indicate the thickness of Titan's ice crust varies slightly from place to place. The researchers said this can best be explained if the moon's outer shell is stiff, as would be the case if the ocean were slowly crystallizing and turning to ice. Otherwise, the moon's shape would tend to even itself out over time, like warm candle wax. This freezing process would have important implications for the habitability of Titan's ocean, as it would limit the ability of materials to exchange between the surface and the ocean.

A further consequence of a rigid ice shell, according to the study, is any outgassing of methane into Titan's atmosphere must happen at scattered "hot spots" -- like the hot spot on Earth that gave rise to the Hawaiian Island chain. Titan's methane does not appear to result from convection or plate tectonics recycling its ice shell.

How methane gets into the moon's atmosphere has long been of great interest to researchers, as molecules of this gas are broken apart by sunlight on short geological timescales. Titan's present atmosphere contains about five percent methane. This means some process, thought to be geological in nature, must be replenishing the gas. The study indicates that whatever process is responsible, the restoration of Titan's methane is localized and intermittent.

"Our work suggests looking for signs of methane outgassing will be difficult with Cassini, and may require a future mission that can find localized methane sources," said Jonathan Lunine, a scientist on the Cassini mission at Cornell University, Ithaca, New York, and one of the paper's co-authors. "As on Mars, this is a challenging task."

Image credit: NASA/JPL-Caltech/SSI/Univ. of Arizona/G. Mitri/University of Nantes

Note: For more information, see Saturn's Moon Titan Has a Very Salty Ocean.

Saturn's Shadows and Mimas

It may seem odd to think of planets casting shadows out in the inky blackness of space, but it is a common phenomenon. Earth’s shadow obscures the Moon during a lunar eclipse, and Jupiter’s moons cast small shadows onto their parent planet.

One of the best places in our Solar System to spot intriguing and beautiful celestial shadows is at Saturn. On 1 July, the international Cassini mission celebrates 10 years of exploring Saturn, its rings and its moons, an endeavor that has produced invaluable science but also stunning images like this.

Drifting along in the foreground, small and serene, is Saturn’s icy moon Mimas. The blue backdrop may at first appear to be the gas giant’s famous and impressive set of rings, with pale and dark regions separated by long inky black slashes, but it is actually the northern hemisphere of Saturn itself. The dark lines slicing across the frame are shadows cast by the rings onto the planet.

Although we may not associate the color blue with Saturn, when Cassini arrived at the planet the northernmost regions displayed the delicate blue palette shown in this image. As this region of Saturn is generally quite free of cloud, scattering by molecules in the atmosphere causes sunlight to take a longer path through the atmosphere. The light is scattered predominantly at shorter – bluer – wavelengths. This is similar to why the sky on Earth appears blue to our eyes.

Seasonal changes over the years since this photo was taken have turned the blue into Saturn's more familiar golden hue. The reverse is occurring in the south, which is slowly becoming bluer.

This image is composed of infrared, optical and ultraviolet observations from Cassini’s narrow-angle camera on 18 January 2005. The colors closely match what the scene would look like in true color.

This image was first published on the NASA Cassini website, in 2005.

Image credit: NASA/JPL/Space Science Institute

Dione

When imaged with the Sun nearly at our backs, Dione's heavily scarred surface lacks the shadows that emphasize the surface topography. However, this geometry highlights variations in surface brightness, which provide further evidence of Dione's active and often violent past.

The surface of Dione (698 miles, or 1,123 kilometers across) is covered in craters, reminding us of the impacts that have shaped all of the worlds of our solar system. Dione's surface also bears linear features that suggest geological activity in the past. See PIA07638 for more information.

Lit terrain seen here is on the Saturn-facing hemisphere of Dione. North on Dione is up and rotated 33 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 27, 2013.

The view was obtained at a distance of approximately 810,000 miles (1.3 million kilometers) from Dione. Image scale is 5 miles (8 kilometers) per pixel.

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