Starship Asterisk*

---

PIA12635: Don't Forget Telesto (Credit: NASA/JPL/SSI)

Don't Forget Telesto

Saturn's moon Dione dwarfs the moon Telesto in this Cassini spacecraft image.

Dione (1,123 kilometers, or 698 miles across) is the third largest of Saturn's moons, and it dominates this view. Tiny Telesto (25 kilometers, or 16 miles across) can be seen below and to the left of Dione.

This view looks toward the anti-Saturn side of Dione. North on Dione is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 4, 2010. The view was acquired at a distance of approximately 477,000 kilometers (296,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 72 degrees. Scale on Dione is 3 kilometers (2 miles) per pixel.

---

PIA12639: Bisected Crescent (Credit: NASA/JPL/SSI)

Bisected Crescent

The rings split the planet in two in this Cassini spacecraft view of a crescent Saturn.

Saturn's moon Tethys (1,062 kilometers, or 660 miles across) is the small dot on the left of the image, below the rings. This view looks toward the northern, sunlit side of the rings from just above the ringplane.

The image was taken with the Cassini spacecraft wide-angle camera on Nov. 28, 2009 using a spectral filter sensitive to wavelengths of near-infrared light centered at 752 nanometers. The view was obtained at a distance of approximately 2.5 million kilometers (1.5 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 103 degrees. Image scale is 143 kilometers (89 miles) per pixel.

While we humans carry on with our daily lives down here on Earth, perhaps stuck in traffic or reading blogs, or just enjoying a Springtime stroll, a school-bus-sized spacecraft called Cassini continues to gather data and images for us - 1.4 billion kilometers (870 million miles) away. Over the past months, NASA's Cassini spacecraft has made several close flybys of Saturn's moons, caught the Sun's reflection glinting off a lake on Titan, and has brought us even more tantalizing images of ongoing cryovolcanism on Enceladus. Collected here are a handful of recent images from the Saturnian system. (30 photos total)

---

PIA12643: Rings, Rhea and Janus (Credit: NASA/JPL/SSI)

Rings, Rhea and Janus

Saturn's rings occupy the foreground of this image. The small moon Janus appears to hover above, while the far larger moon Rhea is partially obscured by the rings.

Janus appears to be located directly over the rings, but the moon is actually further away, at a range of about 1.1 million kilometers (684,000 miles) from the Cassini spacecraft. Rhea is 1.6 million kilometers (994,000 miles) from the spacecraft. This view looks toward the trailing hemisphere of Janus (179 kilometers, or 111 miles across) and the Saturn-facing side of Rhea (1,528 kilometers, or 949 miles across).

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

---

PIA12644: Odysseus in Profile (Credit: NASA/JPL/SSI)

Tethys: Odysseus in Profile

Tethys' huge Odysseus Crater is brightly lit in the northern latitudes of this Saturnian moon in this Cassini spacecraft view.

The crater is seen almost edge-on in the upper left of the image. See PIA07693: The Great Basin for a closer view of this crater. Lit terrain seen here is on the leading hemisphere of Tethys (1,062 kilometers, or 660 miles across). North on Tethys is up and rotated 1 degree to the left.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 9, 2010. The view was acquired at a distance of approximately 1.5 million kilometers (932,000 miles) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 75 degrees. Image scale is 9 kilometers (6 miles) per pixel.

---

PIA12655: Titan's Dark Senkyo (Credit: NASA/JPL/SSI)

The Cassini spacecraft looks toward the dark Senkyo region on Saturn's moon Titan.

Senkyo is the dark region towards the right. Two other dark regions, Aztlan (to the left, slanting down below the equator) and Fensal (left, north of Aztlan), are also shown here. The bright area below Aztlan is called Tsegihi. See Details of Dark Senkyo for a closer view of Senkyo and to learn more. This view looks toward the Saturn-facing side of Titan (5,150 kilometers, or 3,200 miles across). North on Titan is up and rotated 9 degrees to the left.

The image was taken with the Cassini spacecraft narrow-angle camera on April 8, 2010 using a spectral filter sensitive to wavelengths of near-infrared light centered at 938 nanometers. The view was obtained at a distance of approximately 2.1 million kilometers (1.3 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 33 degrees. Image scale is 12 kilometers (7 miles) per pixel.

---

PIA12670: Epimetheus Before Janus (Credit: NASA/JPL/SSI)

Saturn's moon Epimetheus moves in front of the larger moon Janus as seen by the Cassini spacecraft.

This view looks toward the leading hemispheres of Epimetheus (113 kilometers, or 70 miles across) and Janus (179 kilometers, or 111 miles across). The moons are lit by sunlight on the left and light reflected off Saturn on the right.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on April 2, 2010. The view was obtained at a distance of approximately 2.1 million kilometers (1.3 million miles) from Epimetheus and at a Sun-Epimetheus-spacecraft, or phase, angle of 120 degrees. The view was obtained at a distance of approximately 2.2 million kilometers (1.4 million miles) from Janus and at a Sun-Janus-spacecraft, or phase, angle of 120 degrees as well. Scale in the original image was about 13 kilometers (8 miles) per pixel on both moons. The image has been magnified by a factor of two and contrast-enhanced to aid visibility.

Click to view full size image

A Closer Look at Daphnis

NASA's Cassini spacecraft has captured the closest images of Saturn's moon Daphnis to date. In these raw images obtained on July 5, 2010, the moon can be seen orbiting in a rift known as the Keeler Gap in one of Saturn's rings.

This raw, unprocessed image of Saturn's moon Daphnis orbiting in a rift in Saturn's rings was taken on July 5, 2010, by NASA's Cassini spacecraft. The camera was pointing toward Daphnis, 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 2011.

Credit: NASA/JPL/SSI

As promised last week, Cassini has delivered its best photos yet of the tiny moon Daphnis, the ringmoon that is responsible for carving out the skinny Keeler gap at the outer edge of Saturn's A ring. In addition to carving out the gap, its slight up-and-down motions, coupled with the fact that the particles in the ring that are closer to Saturn move faster in their orbits than Daphnis does, Daphnis excites vertical wave structures in the edge of the gap that make the sawtooth patterns visible in this image.

Saturn's moon Daphnis is only 8 kilometers wide, but it has a fairly substantial effect on the A ring, making waves on the ring's edge. According to Carolyn Porco on Twitter, this is the closest look yet at this mini, moving moon. Daphnis resides in the Keeler Gap, which is about 42 km wide, but the moon's eccentric orbit causes its distance from Saturn to vary by almost 9 km, and its inclination causes it to move up and down by about 17 km. That may not sound like much, but within a small gap, this variability causes the waves seen in the edges of the gap. We've only known about Daphnis' existence since 2005, one of the many discoveries made by the Cassini spacecraft, and this is the first image where Daphnis is more than just a little dot.

---

PIA12671: A Look at Belet (Credit: NASA/JPL/SSI)

Titan: A Look at Belet

The Cassini spacecraft looks toward Saturn's largest moon and maps the dark Belet region on Titan.

Lit terrain seen here is in the area between the trailing hemisphere and Saturn-facing side of Titan (5,150 kilometers, or 3,200 miles across). North on Titan is up.

The image was taken with the Cassini spacecraft narrow-angle camera on April 24, 2010 using a spectral filter sensitive to wavelengths of ultraviolet light centered at 938 nanometers. The view was acquired at a distance of approximately 1.9 million kilometers (1.2 million miles) from Titan and at a Sun-Titan-spacecraft, or phase, angle of 82 degrees. Image scale is 11 kilometers (7 miles) per pixel.

---

PIA12672: Sizeable Swirls (Credit: NASA/JPL/SSI)

Saturn: Sizeable Swirls

Huge clouds swirl through the southern latitudes of Saturn where the rings cast dramatic shadows.

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

The image was taken with the Cassini spacecraft wide-angle camera on April 30, 2010 using a spectral filter sensitive to wavelengths of near-infrared light centered at 728 nanometers. The view was obtained at a distance of approximately 1.4 million kilometers (870,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 67 degrees. Image scale is 79 kilometers (49 miles) per pixel.

I love the splashy full-color pictures of Saturn, but sometimes grayscale
(or what is commonly, and incorrectly, called black-and-white)
is what’s needed to capture a mood. Take a look ... Sigh. Oh my ...

---

PIA12673: Differently Aged Terrain (Credit: NASA/JPL/SSI)

The Cassini spacecraft examines old and new terrain on Saturn's fascinating Enceladus, a moon where jets of water ice particles and vapor spew from the south pole.

Newly created terrain is at the bottom, in the center and on the left of this view. Older, cratered terrain is on the right. See PIA11685: New to Old on Enceladus for another view of this area and more information about its geology. This image was captured during Cassini's Nov. 21, 2009, flyby of the moon. This view looks toward the leading hemisphere of Enceladus (504 kilometers, or 313 miles across). North on Enceladus is up and rotated 3 degrees to the right.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera. The view was obtained at a distance of approximately 133,000 kilometers (83,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 46 degrees. Image scale is 796 meters (2,612 feet) per pixel.

Click to view full size image

PIA12674: Flying by Dione

Wispy terrain stretches across the trailing hemisphere of Saturn's moon Dione on the right of this Cassini image taken during the spacecraft's flyby on April 7, 2010.

See PIA06163: Highest Resolution View of Dione for an older, closer view of Dione's wispy fractures. This view looks toward the Saturn-facing side of Dione (1,123 kilometers, or 698 miles across). North on Dione is up and rotated 1 degree to the right.

The image was taken in visible light with the Cassini spacecraft wide-angle camera. The view was acquired at a distance of approximately 40,000 kilometers (25,000 miles) from Dione and at a sun-Dione-spacecraft, or phase, angle of 11 degrees. Image scale is 2 kilometers (1 mile) per pixel.

Credit: NASA/JPL/SSI

• Other Images: http://asterisk.apod.com/vie ... 29&t=19336

mexhunter wrote:This picture seems to me sublime.
Arguably, it is the moon of the moon.

PIA12638: Big and Small Before Rings

Saturn's moon Rhea looms "over" a smaller and more distant Epimetheus against a striking background of planet and rings.

The two moons aren't actually close to each other. The view was obtained at a distance of approximately 1.2 million kilometers (746,000 miles) from Rhea and 1.6 million kilometers (994,000 miles) from Epimetheus.

Lit terrain seen here is in the area between the trailing hemisphere and anti-Saturn side of Rhea (1,528 kilometers, or 949 miles across). Lit terrain seen on Epimetheus (113 kilometers, or 70 miles across) is mostly on the Saturn-facing side. This view looks toward the sunlit side of the rings from just above the ringplane.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on March 24, 2010. Image scale is 7 kilometers (4 miles) per pixel on Rhea and 10 kilometers (6 miles) per pixel on Epimetheus.

Credit: NASA/JPL/SSI

[img3="Multiple F-Ring "Fans""]http://photojournal.jpl.nasa.gov/jpeg/PIA12784.jpg[/img3]

Click to play embedded YouTube video.

The Effect of Prometheus on the F Ring

Click to play embedded YouTube video.

Catching a Cluster of Stars

While orbiting Saturn for the last six years, NASA’s Cassini spacecraft has kept a close eye on the collisions and disturbances in the gas giant’s rings. They provide the only nearby natural laboratory for scientists to see the processes that must have occurred in our early solar system, as planets and moons coalesced out of disks of debris.

New images from Cassini show icy particles in Saturn’s F ring clumping into giant snowballs as the moon Prometheus makes multiple swings by the ring. The gravitational pull of the moon sloshes ring material around, creating wake channels that trigger the formation of objects as large as 20 kilometers (12 miles) in diameter.

“Scientists have never seen objects actually form before,” said Carl Murray, a Cassini imaging team member based at Queen Mary, University of London. “We now have direct evidence of that process and the rowdy dance between the moons and bits of space debris.”

Murray discussed the findings today (July 20, 2010) at the Committee on Space Research meeting in Bremen, Germany, and they are published online by the journal Astrophysical Journal Letters on July 14, 2010. A new animation based on imaging data shows how one of the moons interacts with the F ring and creates dense, sticky areas of ring material.

Saturn's thin, kinky F ring was discovered by NASA’s Pioneer 11 spacecraft in 1979. Prometheus and Pandora, the small “shepherding” moons on either side of the F ring, were discovered a year later by NASA’s Voyager 1. In the years since, the F ring has rarely looked the same twice, and scientists have been watching the impish behavior of the two shepherding moons for clues.

Prometheus, the larger and closer to Saturn of the two moons, appears to be the primary source of the disturbances. At its longest, the potato-shaped moon is 148 kilometers (92 miles) across. It cruises around Saturn at a speed slightly greater than the speed of the much smaller F ring particles, but in an orbit that is just offset. As a result of its faster motion, Prometheus laps the F ring particles and stirs up particles in the same segment once in about every 68 days.

“Some of these objects will get ripped apart the next time Prometheus whips around,” Murray said. “But some escape. Every time they survive an encounter, they can grow and become more and more stable.”

Cassini scientists using the ultraviolet imaging spectrograph previously detected thickened blobs near the F ring by noting when starlight was partially blocked. These objects may be related to the clumps seen by Murray and colleagues.

The newly-found F ring objects appear dense enough to have what scientists call “self-gravity.” That means they can attract more particles to themselves and snowball in size as ring particles bounce around in Prometheus’s wake, Murray said. The objects could be about as dense as Prometheus, though only about one-fourteenth as dense as Earth.

What gives the F ring snowballs a particularly good chance of survival is their special location in the Saturn system. The F ring resides at a balancing point between the tidal force of Saturn trying to break objects apart and self-gravity pulling objects together. One current theory suggests that the F ring may be only a million years old, but gets replenished every few million years by moonlets drifting outward from the main rings. However, the giant snowballs that form and break up probably have lifetimes of only a few months.

The new findings could also help explain the origin of a mysterious object about 5 to 10 kilometers (3 to 6 miles) in diameter that Cassini scientists spotted in 2004 and have provisionally dubbed S/2004 S 6. This object occasionally bumps into the F ring and produces jets of debris.

Credit: NASA/JPL/SSI

See Related Multimedia

bystander wrote:[img3="Multiple F-Ring "Fans""]http://photojournal.jpl.nasa.gov/jpeg/PIA12784.jpg[/img3]

Click to view full size image

Fleeing the Scene

Saturn's moon Prometheus, having perturbed the planet's thin F ring, moves away as it continues in its orbit.

The gravity of potato-shaped Prometheus (86 kilometers, 53 miles across) periodically creates streamer-channels in the F ring, and the moon's handiwork can be seen in the dark channels here.

This view looks toward the northern, sunlit side of the rings from about 10 degrees above the ringplane. A star is visible through the rings near the center right of the image.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on June 1, 2010. The view was acquired at a distance of approximately 1.3 million kilometers (808,000 miles) from Saturn. Image scale is 7 kilometers (5 miles) per pixel.

Credit: NASA/JPL/SSI

http://asterisk.apod.com/vie ... 65#p127565