Pan in the Encke Gap

Saturn's innermost moon Pan orbits the giant planet seemingly alone in a ring gap its own gravity creates.

Pan (17 miles, or 28 kilometers across) maintains the Encke Gap in Saturn's A ring by gravitationally nudging the ring particles back into the rings when they stray in the gap. Scientists think similar processes might be at work as forming planets clear gaps in the circumstellar disks from which they form.

This view looks toward the sunlit side of the rings from about 38 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 3, 2014.

The view was acquired at a distance of approximately 2 million miles (3.2 million kilometers) from Pan and at a Sun-Pan-spacecraft, or phase, angle of 56 degrees. Image scale is 12 miles (19 kilometers) per pixel.

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

Mimas and Ring Shadow

As if trying to get our attention, Mimas is positioned against the shadow of Saturn's rings, bright on dark. As we near summer in Saturn's northern hemisphere, the rings cast ever larger shadows on the planet.

With a reflectivity of about 96 percent, Mimas (246 miles, or 396 kilometers across) appears bright against the less-reflective Saturn.

This view looks toward the sunlit side of the rings from about 10 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on July 13, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was acquired at a distance of approximately 1.1 million miles (1.8 million kilometers) from Saturn and approximately 1 million miles (1.6 million kilometers) from Mimas. Image scale is 67 miles (108 kilometers) per pixel at Saturn and 60 miles (97 kilometers) per pixel at Mimas.

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

Titan's Subsurface Reservoirs

Hundreds of lakes and seas are spread across the surface of Saturn's moon Titan. These lakes are filled with hydrocarbons, a form of organic compound that is also found naturally on Earth and includes methane.

While most of the liquid in the lakes is thought to be replenished by rainfall from clouds in Titan's atmosphere, the cycling of liquid between the subsurface, surface and atmosphere is still not well understood.

Scientists have modeled how a subsurface reservoir ('alkanofer') of liquid hydrocarbons, filled with rainfall runoff, would diffuse throughout Titan's porous icy crust. They found that this diffusion could cause a new reservoir – formed from clathrates - to form where the bottom of the original reservoir meets layers of non-porous ice.

Clathrates are compounds that form a crystal structure with small cages that trap other substances like methane and ethane. Titan's subsurface clathrate reservoirs would interact with and fractionate (separate) the liquid phase within the original underground hydrocarbon lake, slowly changing its composition. Eventually, subsurface lakes that had come into contact with the clathrate layer would mainly be composed of either propane or ethane, depending on the type of clathrate that had formed.

Importantly, this would continue up to Titan's surface. Lakes fed by these propane or ethane subsurface reservoirs would show the same kind of composition, whereas those fed by rainfall would be different and contain methane, nitrogen, and trace amounts of argon and carbon monoxide. The composition of the lake would indicate what was happening deep underground.

Illustration credit: ESA/ATG medialab

Note: For more information, see PIA18417: Titan's Subsurface Reservoirs (Artist's Concept) and Icy Aquifers on Titan Transform Methane Rainfall.

Two Ringlets in the Encke Gap

Although it appears empty from a distance, the Encke gap in Saturn's A ring has three ringlets threaded through it, two of which are visible here.

Each ringlet has dynamical structure such as the clumps seen in this image. The clumps move about and even appear and disappear, in part due to the gravitational effects of Pan.

This view looks toward the sunlit side of the rings from about 27 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 11, 2013.

The view was obtained at a distance of approximately 199,000 miles (321,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 121 degrees. Image scale is 1 mile (2 kilometers) per pixel.

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

Saturn From Above

Saturn reigns supreme, encircled by its retinue of rings.

Although all four giant planets have ring systems, Saturn's is by far the most massive and impressive. Scientists are trying to understand why by studying how the rings have formed and how they have evolved over time.

Also seen in this image is Saturn's famous north polar vortex and hexagon.

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 May 4, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was acquired at a distance of approximately 2 million miles (3 million kilometers) from Saturn. Image scale is 110 miles (180 kilometers) per pixel.

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

Note: For more information, see Supreme Saturn.

Methane Clouds Over Titan's Ligeia Mare

This animated sequence of Cassini images shows methane clouds moving above the large methane sea on Saturn's moon Titan known as Ligeia Mare.

The spacecraft captured the views between July 20 and July 22, 2014, as it departed Titan following a flyby. Cassini tracked the system of clouds as it developed and dissipated over Ligeia Mare during this two-day period. Measurements of the cloud motions indicate wind speeds of around 7 to 10 miles per hour (3 to 4.5 meters per second).

The timing between exposures in the sequence varies. In particular, there is a 17.5-hour jump between the second and third frames. Most other frames are separated by one to two hours.

A separate view, PIA18421, shows the location of these clouds relative to features in Titan's north polar region.

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

Note: For more information, see Cassini Tracks Clouds Developing Over a Titan Sea.

Rhea and Epimetheus

Saturn has a great many more moons than our planet – a whopping 62. A single moon, Titan, accounts for an overwhelming 96% of all the material orbit the planet, with a group of six other smaller moons dominating the rest. The other 55 small satellites whizzing around Saturn make up the tiny remainder along with the gas giant’s famous rings.

One of the subjects of this Cassini image, Rhea, belongs to that group of six. Set against a backdrop showing Saturn and its intricate system of icy rings, Rhea dominates the scene and dwarfs its tiny companion, one of the 55 small satellites known as Epimetheus.

Although they appear to be close to one another, this is a trick of perspective – this view was obtained when Cassini was some 1.2 million km from Rhea, and 1.6 million km from Epimetheus, meaning the moons themselves had a hefty separation of 400,000 km.

However, even if they were nearer to each other, Rhea would still loom large over Epimetheus: at 1528 km across and just under half the size of our own Moon, Rhea is well over 10 times the size of Epimetheus, which is a modest 113 km across.

As is traditional for the earliest discovered moons of Saturn, both are named after figures from Greek mythology: the Titan Rhea (“mother of the gods”) and Prometheus’ brother Epimetheus (“after thinker” or “hindsight”).

This image was taken by Cassini’s narrow-angle camera on 24 March 2010. A monochrome version was previously released by NASA as PIA12638: Big and Small Before Rings.

Image credit: Image data credit: NASA/JPL-Caltech/Space Science Institute; Processed image copyright: G. Ugarković

Pandora and the Rings

The F ring shepherd Pandora is captured here along with other well-known examples of how Saturn’s moons shape the rings. From the narrow F ring, to the gaps in the A ring, to the Cassini Division, Saturn's rings are a masterpiece of gravitational sculpting by the moons.

Pandora (50 miles, or 81 kilometers across), along with its fellow shepherd Prometheus (53 miles, or 86 kilometers across), helps confine the F ring and keep it from spreading.

This view looks toward the unilluminated side of the rings from about 31 degrees below the ringplane. The image was taken in visible 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 Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 63 degrees. Image scale is 32 miles (51 kilometers) per pixel.

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

Note: For more information, see Shepherd and Flock.

Saturn's North Polar Vortex

Like a giant eye for the giant planet, Saturn's great vortex at its north pole appears to stare back at Cassini as Cassini stares at it.

Measurements have sized the "eye" at a staggering 1,240 miles (2,000 kilometers) across with cloud speeds as fast as 330 miles per hour (150 meters per second). For color views of the eye and the surrounding region, see PIA14946 and PIA14944.

The image was taken with the Cassini spacecraft narrow-angle camera on April 2, 2014 using a combination of spectral filters which preferentially admit wavelengths of near-infrared light centered at 748 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 8 miles (13 kilometers) per pixel.

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

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.