Saturn’s Little Wavemaking Moon

Captured on January 15, this narrow-angle Cassini image shows an outer portion of Saturn’s A ring on the left and the ropy F ring crossing on the right. The thin black line near the A ring’s bright edge is the Keeler Gap, a 22-mile-wide space cleared by the passage of Daphnis, a shepherd moon barely 5 miles (about 7.5 km) across. As it travels around Saturn within the gap its gravity perturbs the fine icy particles within the rings, sending up rippling waves both before and behind it — visible here near the upper center.

From Cassini’s distance of 870,000 miles (1.4 million km) Daphnis itself is just barely visible as a single pixel within the Gap — can you see it? If not, click below…

There it is:

Highlighting Daphnis inside the Keeler Gap
Highlighting Daphnis inside the Keeler Gap

While lacking the murky mystery of Titan’s atmosphere, Enceladus’ dramatic jets and the tortured and cratered surfaces found on Dione, Rhea, Mimas and many of Saturn’s larger icy moons, little Daphnis has always fascinated me because of the scalloped waves it kicks up within Saturn’s rings. Eventually these waves settle back down, but at their highest they can extend a mile or two above and below the ring plane!

Daphnis' wake casts peaked shadows on the rings
Daphnis’ wake casts peaked shadows on the rings

This effect was most pronounced during Saturn’s spring equinox in August 2009 when sunlight was striking the rings edge-on, creating strong shadows from any areas of relief.

Imagine the impressive view you’d have if you were nearby, positioned just above the rings as Daphnis approached and hurtled past, the rings rising up in mile-high peaks from the moon’s gravity before smoothing out again. Incredible!

Daphnis seen by Cassini in June 2010 (NASA/JPL/SSI)
Daphnis seen by Cassini in June 2010 (NASA/JPL/SSI)

And I’m not the only one to imagine such a scene either — apparently artist Erik Svensson is also intrigued by Daphnis, enough to have been inspired to create the image below. How very cool!

Future explorers watch Daphnis speed past at the edge of Saturn's A ring (© Erik Svennson, all rights reserved. Used with permission.)
Future explorers watch Daphnis speed past at the edge of Saturn’s A ring (© Erik Svennson, all rights reserved. Used with permission.)

Like its larger shepherd moon sister Prometheus, Daphnis may be little but still has a big effect on the icy stuff that makes up Saturn’s iconic rings.

And for lots more views of Daphnis click here (but watch out, it may just become your favorite moon too!)

Image credits: NASA/JPL-Caltech/Space Science Institute.

Saturn to Shed its Spooky Spokes for Summer

As Saturn steadily moves along its 29.7-year-long orbit toward summertime in its northern hemisphere NASA’s Cassini spacecraft is along for the ride, giving astronomers a front-row seat to seasonal changes taking place on the ringed planet.

One of these fluctuations is the anticipated disappearance of the “spokes” found in the rings, a few of which can be seen above in an image captured on Dec. 20 of last year.

First identified by Voyager in 1980, spokes are ghostly streaks of varying size and brightness that stretch radially across Saturn’s ring system. They orbit around the planet with the ring particles and can last for hours before fading away.

Under the right lighting conditions spokes can appear dark, as seen in this image from Jan. 2010 (NASA/JPL/SSI)
Under the right lighting conditions spokes can appear dark, as seen in this image from Jan. 2010 (NASA/JPL/SSI)

One of the most elusive and transient of features found on Saturn, spokes are thought to be made up of larger microscopic particles of ice — each at least a micron or more — although exactly what makes them gather together isn’t yet known.

They are believed to be associated with interactions between ring particles and Saturn’s electromagnetic field.

“The spokes are most prominent at a point in the rings where the ring particles are moving at the same speed as Saturn’s electromagnetic field,” said Brad Wallis, Cassini rings discipline scientist. “That idea and variations of it are still the most prominent theories about the spokes.”

Other researchers have suggested that they may be caused by electron beams issuing outwards along magnetic field lines from lightning storms in Saturn’s atmosphere.

Regardless of how they are created, spokes are more often observed when sunlight is striking the rings edge-on — that is, during the spring and autumn equinoxes. Perhaps the increased solar radiation along Saturn’s equator increases the formation of lightning-generating storms, in turn creating more spokes? It’s only a guess, but Cassini — and astronomers — will be watching to see if these furtive features do in fact fail to appear during Saturn’s northern summer, the height of which arrives in 2016.

Read more about Saturn’s spokes here.

The Rings on the Planet Go ‘Round and ‘Round…

Raw wide-angle Cassini image of Saturn’s rings (NASA/JPL/SSI)

Recently I posted an image of two of Saturn’s shepherd moons, Pandora and Prometheus, captured by Cassini in a face-off across the spindly F ring. Now here’s a much wider-angle view of the gas giant’s rings, seen by Cassini  two days later on December 20, and the same two moons can still be seen staring each other down… two tiny points of light visible across the wavering line of the F ring at lower center.

This is just one raw image in a series of 56 that Cassini captured on the 20th, and I’ve combined them together to make a GIF animation — click below to watch:

Animation of Saturn’s rings made from raw images acquired by Cassini on Dec. 20, 2012 (NASA/JPL/SSI. Animation by J. Major)

In the animation you can see Pandora and Prometheus promenade around Saturn (detail at right) as well as a “spoke” of light material moving within the inner dark edge of the A ring. Also many clumps are visible in the thin F ring — caused by embedded moonlets and the gravitational influence of the shepherd moons.

Saturn’s enormous shadow engulfs the entire ring system at the top of the scene.

Cassini was moving relative to Saturn while these images were captured so some background stars make brief appearances, as well as a couple of pixel flares and a cosmic ray hit. These are common in Cassini images.

See more news and images from the Cassini mission here.

 

Saturn. In color.

Color-composite of Saturn, made from raw Cassini images acquired in visible light channels on 18 Nov. 2012. (NASA/JPL/SSI. Composite by Jason Major.)

Looking for an awesome view of Saturn as it would look from 1,951,681 kilometers (1,212,718 miles) away? Here you go.

Just my and Cassini’s way of reminding everyone how beautiful our own Solar System is! Lest we forget.

Saturn’s Fluctuating F Ring

Bright clumps of material spotted within Saturn’s ropy F ring (NASA/JPL/SSI)

Released today, this image acquired by NASA’s Cassini spacecraft shows some interesting structures forming within Saturn’s thinnest but most dynamic ring.

Of Saturn’s countless ring structures the F ring may very well be the most dynamic, if not the most fascinating. Orbiting Saturn just outside the edge of the A ring at a distance of 140,000 km (87,000 miles), the F ring is a hazy, ropy band of fine ice particles that shift, twist and occasionally gather into bright clumps… only to drift apart once more.

The F ring can range in width from 30 to 500 km (20-500 miles), depending on what’s going on in and outside of it.

The image above, originally captured by Cassini on June 28 and released today by the Cassini Imaging Central Laboratory for Operations (CICLOPS), shows a particularly bright clump of material at the outer edge of the F ring, as well as some finer structures and streamers forming within the inner bands. Due to the lighting geometry its thought that the clumps are mostly composed of dusty material.

Detail of the ghostly F ring structures (NASA/JPL/SSI)

The features seen here are likely due to the ring’s interactions with passing shepherd moons — such as the 148-km-wide Prometheus — or with small moonlets embedded within the ring itself. Mostly made of fine particles of dust and ice smaller than those found in smoke, the material orbiting within the F ring is extremely susceptible to external gravitational influences.

Original image scale is 4 km (3 miles) per pixel.

See more images from the entire Cassini mission on the CICLOPS site here (and for a look at more interesting ring dynamics check out these recent Cassini images of my personal favorite moon, Daphnis.)

 

Saturn Shows Off Its Shadow

Take a look up at the enormous shadow cast by Saturn onto its own rings in this raw image, acquired by NASA’s Cassini spacecraft on September 18, 2012.

Cassini captured this image from below Saturn’s ring plane at a distance of 1,393,386 miles (2,242,437 kilometers). It shows not only the gas giant’s shadow but also the wispy nature of the rings, which, although complex, extensive and highly reflective (the light seen on Saturn above is reflected light from the rings!) they are still very thin — less than a mile (about 1 km) on average and in some places as little as thirty feet (10 meters) thick.

Seen in the right light, some of the thin innermost rings can seem to nearly disappear entirely — especially when backlit by Saturn itself.

Views like the one above are once again possible because of Cassini’s new orbit, which takes it high above and below the ring plane, providing a new perspective for studying Saturn and its moons. Ultimately by next April the spacecraft will be orbiting Saturn at an inclination of about 62 degrees — that’d be like an orbit around Earth that goes from Alaska to the northernmost tip of Antarctica. (Find out how Cassini alters its orbit here.)

With this viewpoint Cassini will get some great views of Saturn’s north and south poles, which are gradually moving into their summer and winter seasons, respectively, during the ringed planet’s 29.5-Earth-year orbital period.

After more than 8 years in orbit Cassini is still fascinating us with enthralling images of Saturn on a regular basis. Read more about the Cassini mission here.

Cassini spots shepherd moons Pan (within the Encke Gap) and Prometheus (along the inner edge of the F ring) in an image acquired on Sept. 18, 2012

Images: NASA/JPL/Space Science Institute.

Changing Hues Signal Transition of Seasons at Saturn

The giant moon Titan passes in front of Saturn in this natural-color, wide-angle view from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

[SPOILER ALERT: Viewing these images will force you to change your computer wallpaper]

Here on Earth, it’s almost time for the burst of fall color that signals the change of seasons in the Northern Hemisphere. Saturn’s color too is transforming subtly as the gas giant slips into a Saturnian spring and autumn as seen in this series of true-color images from NASA’s Cassini spacecraft.

Titan, a moon larger than the planet Mercury, hangs before the rings and changing colors of Saturn in the first of four spectacular images release by NASA and the Cassini Imaging Central Laboratory for Operations (CICLOPS).

“For no other reason than that they are gorgeous, the Cassini imaging team is releasing today a set of fabulous images of Saturn and Titan…in living color…for your day-dreaming enjoyment,” said Carolyn Porco, Cassini imaging team lead based at the Space Science Institute in Boulder, Colordo, in an email blast.

When Cassini arrived at Saturn eight years ago, the planet’s northern hemisphere, locked in winter, showed azure blue. Now as winter passes to the southern hemisphere, the colors are reversing as the blue fades from the north and rises in the south.

“Note that our presence at Saturn for the last eight years has made possible the sighting of subtle changes with time, and one such change is obvious here,” Porco said. “As the seasons have advanced, and spring has come to the north and autumn to the south throughout the Saturn system, the azure blue in the northern winter Saturnian hemisphere that greeted Cassini upon its arrival in 2004 is now fading; and it is now the southern hemisphere, in its approach to winter, that is taking on a bluish hue.”

Scientists believe that the increasing blue color in the south likely is due to the increasing intensity of ultraviolet light from the Sun which produces the haze. Methane in the atmosphere also absorbs light toward the red end of the spectrum while reflecting blue light. This view looks from just above the ring plane with the Sun shining from above casting broad shadows on the colorful clouds of Saturn. The image was taken on May 6, 2012 from about 778,000 kilometers (483,000 miles) from Titan.

Some of the views, including this image of a vortex at Titan’s south pole are only possible because of a newly tilted, or inclined, orbit that takes Cassini high over the poles of Saturn and its moons. Scientists first noticed the detached mass of clouds over the south pole in March. The swirling mass of the vortex stands out clearly against the golden cloud deck surrounding Titan.

The recently formed south polar vortex stands out against Titan in this natural-color view from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

Sunlight scattering through Titan’s atmosphere forms a ring of color as NASA’s Cassini spacecraft cruises along the night side of Saturn’s largest moon. Image Credit: NASA/JPL-Caltech/SSI

A glowing hint of the polar vortex shows in this image looking toward the night-time, Saturn-facing side of Titan. Sunlight scattering through Titan’s atmosphere forms the ring of color in this image taken about 216,000 kilometers (134,000 miles) from Titan.

Saturn’s rings cut colorful Titan in half in this image from NASA’s Cassini spacecraft. Image Credit: NASA/JPL-Caltech/SSI

The rings obscure Titan in the final image of the quartet. The image is taken from just above the northern, sunlit side of the ring plane. Saturn’s shadow cast along the rings create the dark swath in the center of the image but if you look close, you can see a tiny sliver of Titan through the Cassini Division, the largest gap in Saturn’s wide rings.

“Cassini has been in orbit now for the last eight years, and despite the fact that we can’t know exactly what the next five years will show us, we can be certain that whatever it is will be wondrous,” said Porco.

About the author: John Williams is owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

Treasure Hunt for Cassini Reveals Tiny Moon Atlas

Saturn's tiny moon Atlas shines with the rings

Saturn’s tiny moon Atlas shines with the rings

While most eyes on Earth have been focused on the Red Planet and the eventful landing of the Curiosity Rover, other missions throughout the Solar System are delivering stunning vistas as well, such as this image from NASA’s Cassini spacecraft of tiny moon Atlas as it shines just above Saturn’s rings.

Can you find it?

Atlas, just 30 kilometers (or 19 miles) across, sits just above the ring plane in this image taken by Cassini’s narrow-angle camera on April 16, 2012 at a distance of 1.4 million kilometers (870,000 miles). At this distance, Atlas appears as a small white dot. Atlas orbits Saturn between the main rings and the thin F ring.

Cassini arrived at Saturn in 2004 and is now in its second extended mission called Cassini Solstice Mission. For the past two years, Cassini cruised in an equatorial orbit flying close over several moons including Titan and studying the planet’s iconic rings. Over the next three years, Cassini will hurtle high above the poles, sending the probe through the ring plane many times.

John Williams is a science writer and owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

The Return of the Rings!

Now that Cassini has gone off on a new trajectory taking it above and below the equatorial plane of Saturn, we’re back to getting some fantastic views of the rings — the likes of which haven’t been seen in over two and a half years!

The image above shows portions of the thin, ropy F ring and the outer A ring, which is split by the 202-mile (325-km) -wide Encke gap. The shepherd moon Pan can be seen cruising along in the gap along with several thin ringlets. Near the A ring’s outer edge is a narrower space called the Keeler gap — this is the home of the smaller shepherd moon Daphnis, which isn’t visible here (but is one of my personal favorites!)

The scalloped pattern on the inner edge of the Encke gap downstream from Pan and a spiral pattern moving inwards from that edge are created by the 12.5-mile-wide (20-km-wide) moon’s gravitational influence.

Other features that have returned for an encore performance are the so-called propellers, spiral sprays of icy ring material created by tiny micro-moons within the rings. Individually too small to discern (less than half a mile in diameter) these propeller moons kick up large clumps of reflective ring particles with their gravity as they travel through the rings, revealing their positions.

The three images above show a propeller within the A ring. Nicknamed “Sikorsky” after Russian-American aviator Igor Sikorsky, the entire structure is about 30 miles (50 km) across and is one of the more well-studied propellers.

Scientists are eager to understand the interactions of propellers in Saturn’s rings as they may hold a key to the evolution of similar systems, such as solar systems forming from disks of matter.

See a video of a propeller orbiting within the rings here, and here’s an image of one that’s large enough to cast a shadow!

“One of the main contributing factors to the enormous success we on the Cassini mission have enjoyed in the exploration of Saturn is the capability to view the planet and the bodies around it from a variety of directions,” Cassini Imaging Team Leader Carolyn Porco wrote earlier today. “Setting the spacecraft high into orbit above Saturn’s equator provides us direct views of the equatorial and middle latitudes on the planet and its moons, while guiding it to high inclination above the equator plane affords the opportunity to view the polar regions of these bodies and be treated to vertigo-inducing shots of the planet’s glorious rings.”

As always, keep up with the latest Cassini news on the mission site here, and read more about these images on the CICLOPS imaging team page here.

Image credits: NASA / JPL / Space Science Institute.

 

Ride Along with Rhea

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Assembled from 29 raw images taken by the Cassini orbiter on Monday, April 25, this animation brings us along an orbital ride with Rhea as it crosses Saturn’s nighttime face, the planet’s shadow cast across the ringplane. Sister moons Dione and Tethys travel the opposite lane in the background, eventually appearing to sink into Saturn’s atmosphere.

Rhea's heavily cratered surface, imaged by Cassini on October 2010. NASA/JPL/SSI

The exposure varies slightly from frame to frame due to the fact that they are not all taken with the same color channel filter.

Rhea (1,528 kilometers, or 949 miles, wide), Dione (1,123 kilometers, or 698 miles wide) and Tethys (1,066 kilometers, or 662 miles wide) are all very similar in composition and appearance. The moons are composed mostly of water ice and rock, each covered in craters of all sizes and crisscrossed by gouges, scarps and chasms. All three are tidally locked with Saturn, showing the same face to their parent planet in the same way that the Moon does with Earth.

The Cassini spacecraft was 2,227,878 km (1,384,339 miles) from Rhea when the images were taken.

(The original images have not been validated or calibrated. Validated/calibrated images will be archived with the NASA Planetary Data System in 2012.)

Image credit: NASA / JPL / Space Science Institute. Animation by Jason Major.