Posted on by Nancy Atkinson

Cassini the Artist: Shadows, Ringshine, Double Crescent Moons

Cassini art. Credit: NASA/JPL/Space Science Institute

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I often ponder whether the Cassini spacecraft is a better scientist or artist. I found three recent images from Cassini that definitely give the nod to artist, but surely there’s lots of great science here as well. In this image, Saturn casts its shadow on the rings, but it also shows how the rings reflect sunlight onto the dark side of the planet. Here Saturn appears dimly illuminated by this ringshine. This view looks toward the southern, unilluminated side of the rings from about 10 degrees below the ringplane, and was taken on Jan. 2, 2010 when Cassini was about 2.3 million kilometers (1.4 million miles) from Saturn. Below: beautiful moons.

Two moons, with Saturn's rings. Image Credit: NASA/JPL/Space Science Institute

While this image is stunningly gorgeous, perhaps the most amazing thing is that it was snapped by Cassini’s cameras just yesterday (March 15, 2010) and beamed back to Earth today! This is a raw, uncalibrated image and the only details posted about it is that the camera was pointing toward Tethys at approximately 2,410,546 kilometers away. Can anyone guess what the second moon is?

Double crescent moons. Credit: NASA/JPL/Space Science Institute.

Another beauty, Dione and Titan make a smiling pair of crescent moons. This image was taken on March 12, 2010 and received on Earth March 13, 2010. The camera was pointing toward Dione at approximately 2,211,699 kilometers away.

For more great images see the Cassini website, or the CICLOPS website

Posted on by Nancy Atkinson

More Jaw-Droppers from Cassini

The small moon Janus is almost hidden between the planet's rings and the larger moon Rhea.Credit: NASA/JPL/Space Science Institute

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The Cassini mission keeps churning out the hits, and here’s a collection of some of the latest stunning images released by the CICLOPS (Cassini Imaging for Central Operations) team. Above, the small moon Janus is almost hidden between the planet’s rings and the larger moon Rhea. The northern part of Janus can be seen peeking above the rings in this image of a “mutual event” where Janus (179 kilometers, 111 miles across) moved past Rhea (1,528 kilometers, 949 miles across). Mutual event observations such as this one, in which one moon passes close to or in front of another, help scientists refine their understanding of the orbits of Saturn’s moons. Click here to see a movie of the event.

Saturn's potato-shaped moon Prometheus is rendered in three dimensions in this close-up from Cassini. Credit: NASA/JPL/Space Science Institute

Grab your 3-D glasses for this one! This 3-D view is a close-up of Saturn’s potato-shaped moon Prometheus, showing the moon’s leading hemisphere. The image was created by combining two different black and white images that were taken from slightly different viewing angles. The images are combined so that the viewer’s left and right eye, respectively and separately, see a left and right image of the black and white stereo pair when viewed through red-blue glasses.

Saturn and Enceladus. Credit: NASA/JPL/Space Science Institute

At first glance, you might think this scene simply shows a bright chunk of Saturn, along with a crescent of the moon Enceladus at top right. But a closer look at the center of the image reveals a dramatic surprise: plumes of water ice spew out from the famed fractures known as “tiger stripes” near the south pole of the moon. And one other surprise: Although it may appear that Enceladus (504 kilometers, 313 miles across) is in the background here, the moon actually is closer to the spacecraft than Saturn is. This view looks most directly toward the side of Enceladus that faces away from Saturn. North on Enceladus is up and rotated 1 degree to the left.

For more great images, check out the CICLOPS website, or NASA’s Cassini website.

Posted on by Jean Tate

Cassini Survives Close Encounter of the Death Star Kind!

Cassini's Mimas, from 70,000 km (Credit: NASA/JPL/Space Science Institute)

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On February 13, 2010, Cassini flew by Saturn’s moon Mimas, coming as close as 9,500 km.

It passed directly over Herschel, a giant crater whose creation almost shattered the moon … and which, in its appearance in some earlier images, earned Mimas the nickname “Death Star”, after the iconic Star Wars prop.

The Cassini team has just released some “Raw Previews” of Cassini’s close encounter; time to feast your eyes.

35,000 km-distant Herschel, from Cassini (unprocessed image; credit: NASA/JPL/Space Science Institute)

The Cassini Equinox Mission, of which the Mimas flyby is but a small part, is a joint United States and European endeavor. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.
Herschel, from 16,000 km above (unprocessed image; credit: NASA/JPL/Space Science Institute)

Source: CICLOPS (Cassini Imaging Central Laboratory for Operations)

Posted on by Jean Tate

On New Year’s Eve, Cassini Will Stare at the Death Star’s Superlaser

Saturn's moon Mimas. Image credit: NASA/JPL/SSI

OK, it’s actually the Herschel crater on Mimas, a smallish moon of Saturn (and it’s the eve of Chinese New Year, February 13th, 2010), but it’s a cool headline, don’t you think?

Cassini will be very busy that day, which begins with a rare sunrise – the Sun goes behind Saturn (from Cassini’s perspective) – followed by a rare blackout, as the Earth goes behind Saturn. Then there’s three “Forward shields up!” moments, as Cassini tries to dodge a Klingon missile flies through regions of “increased ring particle concentration”, a couple of distant flybys (Epimetheus, Janus; ~100,000 km each), a ring-plane crossing, another “Shields up!” moment, and a 9,500 km close approach to Death Star Mimas. And the day ends with a distant (112,000 km) flyby of Tethys. Whew!

“Mimas bears the mark of a violent, giant impact from the past – the 140-kilometer-wide Herschel Crater – and scientists hope the encounter will help them explain why the moon was not blown to smithereens when the impact happened. They will also be trying to count smaller dings inside the basin of Herschel Crater so they can better estimate its age,” JPL’s Jia-Rui C. Cook said, “The Mimas flyby involves a significant amount of skill because the spacecraft will be passing through a dusty region to get there. Mission managers have planned for the Cassini spacecraft to lead with its high-gain antenna to provide a barrier of protection.”

To date, the best images of Mimas – and its Herschel crater – were obtained on August 2nd, 2005, during Cassin’s distant flyby.

Mimas is an inner moon of Saturn that averages 396 kilometers in diameter. The diameter of Herschel Crater is about one-third that of the entire moon. The walls of the crater are about 5 kilometers high, and parts of the floor are approximately 10 kilometers deep.

Map of Mimas (Credit: NASA/JPL/Space Science Institute )

Mimas would have beaten another of Saturn’s moons, Rhea, for the record of “most battered moon”, but for the fact that it was warmer – and so softer – for longer than Rhea (because it’s closer to Saturn), so many of the earliest craters were more degraded.

Have you heard of the “Mimas paradox”? Mimas’ orbit is more eccentric than Enceladus’, and is in resonance with Dione and Enceladus – so it should be heated, tidally, more than Enceladus – but its surface has not, apparently, changed for a very long time (while geysers on Enceladus show that it is still quite active). Further, the two moons seem to have similar compositions.

On this flyby, Cassini’s composite infrared spectrometer will be working to determine the thermal signature of the moon, and other instruments will be making measurements to learn more about the surface composition. Perhaps that will shed some light on the Mimas paradox.

Sources: Cassini Set to Do Retinal Scan of Saturnian Eyeball, Mimas (NASA/JPL)

Posted on by Nancy Atkinson

Hubble Captures Double Aurorae Light Show on Saturn

Hubble's view of Saturn with a double view of its fluttering aurorae. Credit: NASA, ESA and Jonathan Nichols (University of Leicester)


In January and March 2009, researchers using Hubble took advantage of a rare opportunity to record Saturn when its rings are edge-on, resulting in a unique look featuring both of the giant planet’s poles. And Saturn cooperated by providing an incredible double light show with Saturn’s own northern and southern lights. Since Saturn is only in this position every 15 years or so, this favorable orientation has allowed a sustained study of the two beautiful and dynamic aurorae.

Since it takes Saturn almost thirty years to orbit the Sun, the opportunity to image both of its poles occurs only twice in that period. Hubble has been snapping pictures of the planet at different angles since the beginning of the mission in 1990, but 2009 brought a unique chance for Hubble to image Saturn with the rings edge-on and both poles in view. At the same time Saturn was approaching its equinox so both poles were equally illuminated by the Sun’s rays.

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These recent observations go well beyond just a still image and have allowed researchers to monitor the behavior of both Saturn’s poles in the same shot over a sustained period of time. The movie they created from the data, collected over several days during January and March 2009, has aided astronomers studying both Saturn’s northern and southern aurorae. Given the rarity of such an event, this new footage will likely be the last and best equinox movie that Hubble captures of our planetary neighbor.

Despite its remoteness, the Sun’s influence is still felt by Saturn. The Sun constantly emits particles that reach all the planets of the Solar System as the solar wind. When this electrically charged stream gets close to a planet with a magnetic field, like Saturn or the Earth, the field traps the particles, bouncing them back and forth between its two poles. A natural consequence of the shape of the planet’s magnetic field, a series of invisible “traffic lanes” exist between the two poles along which the electrically charged particles are confined as they oscillate between the poles. The magnetic field is stronger at the poles and the particles tend to concentrate there, where they interact with atoms in the upper layers of the atmosphere, creating aurorae, the familiar glow that the inhabitants of the Earth’s polar regions know as the northern and southern lights.

At first glance the light show of Saturn’s aurorae appears symmetric at the two poles. However, analysing the new data in greater detail, astronomers have discovered some subtle differences between the northern and southern aurorae, which reveal important information about Saturn’s magnetic field. The northern auroral oval is slightly smaller and more intense than the southern one, implying that Saturn’s magnetic field is not equally distributed across the planet; it is slightly uneven and stronger in the north than the south. As a result, the electrically charged particles in the north are accelerated to higher energies as they are fired toward the atmosphere than those in the south. This confirms a previous result obtained by the space probe Cassini, in orbit around the ringed planet since 2004.

Source: ESA

Posted on by Nancy Atkinson

Saturn’s Rings Have Gone Plaid

Saturn's plaid rings. Credit: NASA/JPL/Space Science Institute

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Are Saturn’s rings spinning at ludicrous speeds? It appears they have gone plaid! The Cassini spacecraft has actually spied two types of waves in Saturn’s A ring: a spiral density wave on the left of the image and a more pronounced spiral bending wave near the middle. And the “plaid” look comes from the slight pixelation visible near the brightest and darkest lines, which the Cassini team says is an unavoidable result of the size of the camera’s sensor and of image processing.

And if you don’t get the “plaid” reference, go watch Spaceballs.

The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Jan. 11, 2010 at a distance of approximately 279,000 kilometers (173,000 miles) from Saturn.

Source: Cassini

Posted on by Nancy Atkinson

More Stunning Images and Discoveries Ahead: Cassini Mission Extended to 2017

Saturn from Cassini. Image credit: NASA/JPL/SSI

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With the new 2011 NASA budget allowing for more space science activities, the space agency has extended the Cassini mission to explore Saturn and its moons to 2017. “This is a mission that never stops providing us surprising scientific results and showing us eye popping new vistas,” said Jim Green, director of NASA’s planetary science division. “The historic traveler’s stunning discoveries and images have revolutionized our knowledge of Saturn and its moons.” This is the second mission extension for Cassini, and the new “Solstice Mission” will allow scientists to study seasonal and other long-term weather changes on the planet and its moons.

The Cassini mission will get $60 million per year to continue its study of the Saturn system.

“The extension presents a unique opportunity to follow seasonal changes of an outer planet system all the way from its winter to its summer,” said Bob Pappalardo, Cassini project scientist. “Some of Cassini’s most exciting discoveries still lie ahead.”

Cassini arrived just after Saturn’s northern winter solstice, and this extension continues until a few months past northern summer solstice in May 2017. The northern summer solstice marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.

The plumes of Enceladus as imaged by the most recent Cassini flyby. Image Credit: NASA/JPL/Space Science Institute

A complete seasonal period on Saturn has never been studied at this level of detail. The Solstice mission schedule calls for an additional 155 orbits around the planet, 54 flybys of Titan and 11 flybys of the icy moon Enceladus.

The mission extension also will allow scientists to continue observations of Saturn’s rings and the magnetic bubble around the planet known as the magnetosphere. The spacecraft will make repeated dives between Saturn and its rings to obtain in depth knowledge of the gas giant. During these dives, the spacecraft will study the internal structure of Saturn, its magnetic fluctuations and ring mass.

Cassini launched in October 1997 with the European Space Agency’s Huygens probe. The spacecraft arrived at Saturn in 2004. The probe was equipped with six instruments to study Titan, Saturn’s largest moon. Cassini’s 12 instruments have returned a daily stream of data from Saturn’s system for nearly six years.

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Artists impression of the Cassini spacecraft at Saturn. Credit: NASA

“The spacecraft is doing remarkably well, even as we endure the expected effects of age after logging 2.6 billion miles on its odometer,” said Bob Mitchell, Cassini program manager at JPL. “This extension is important because there is so much still to be learned at Saturn. The planet is full of secrets, and it doesn’t give them up easily.”

Cassini’s travel scrapbook includes more than 210,000 images; information gathered during more than 125 revolutions around Saturn; 67 flybys of Titan and eight close flybys of Enceladus. Cassini has revealed unexpected details in the planet’s signature rings, and observations of Titan have given scientists a glimpse of what Earth might have been like before life evolved.

For more info on the mission, check out the Cassini website.

Posted on by Nancy Atkinson

Scientists Find Water Ice Creates the Spokes in Saturn’s B Ring

Spokes visible in Saturn's B ring. Credit: NASA/JPL/Space Science Institute

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The mysterious spokes that sometimes appear in Saturn’s largest ring, the B ring, have been unexplained. But new measurements from Cassini’s Visual Infrared Mapping spectrometer (VIMS) suggests the radial spokes that sometimes form across the ring are entirely composed of water ice. The existence of the spokes were unexpected and were first observed when the Voyager spacecraft flew by Saturn in 1980. When Cassini arrived at Saturn in 2004, the spokes were not visible, but later appeared in 2005; the VIMS instrument was not able to observe the spokes until 2008. Even with this new information, the spokes are still mysterious, as they appear to be a seasonal phenomenon and can become visible and then fade within a few hours. The process that creates and dissipates the spokes is unknown.

Another view from Cassini of spokes. Credit: Credit: NASA/JPL/Space Science Institute

Early hypotheses on the spokes speculated that gravitational forces and/or electrostatic repulsion between ring particles played a role in creating the spokes. One clue was that the spokes are more commonly observed when Saturn’s rings are more nearly edge on to the Sun. Other scientists had suggested ice, but believed the spokes were composed mainly of smaller ice grains. However, the new data show a large portion of the grains are larger than expected; a micrometer or more in radius.

E. D’Aversa and his team from the Institute for Interplanetary Space Physics in Rome, Italy used the VIMS instrument on Cassini to observe the infrared spectrum emitted by these spokes on July 9, 2008. These were the first measurements of the complete reflectance spectrum of the spokes in a wide spectral range (0.35–0.51 ?m). The team said that radiative transfer modeling supports a pure water ice composition for the spoke’s grains, but their size distribution is found to be wider than previously thought.

The preliminary results showed a modal value of about 1.90 ?m (reff = 3.5 ?m, veff = 0.3) and a number density of about 0.01–0.1 grains/cm3. The researchers say the unexpected abundance of micron-sized grains in the spokes may have implications for the formation models since the energy requirement increases by at least one order of magnitude. Future observations could help constrain the size as well as shed more light on the how the spokes form, evolve and change.

Paper: The spectrum of a Saturn ring spoke from Cassini/VIMS

Posted on by Nicholos Wethington

A Double-Dose of Cassini Goodness

The Cassini mission is just a non-stop faucet of fantastic images! Here are two that were released today, for your viewing pleasure. The first image, above, is an eclipse of Saturn’s moon Tethys, which lies in the background, by Dione. The three images were each taken one minute apart.

As you can see, from Cassini’s perspective Dione passes right in front of Tethys. Make no mistake in thinking that these two Saturnian companions are close together in this shot, however; Dione, the moon in the foreground, is 2.2 million kilometers (1.4 million miles) from the Cassini spacecraft, while Tethys is 2.6 million kilometers (1.6 million miles) away.

An interesting feature of the image is how Tethys appears brighter on the side of the moon opposite the Sun. This is because Saturn, which lies out of the image to the right, is reflecting light from the Sun back onto the moon. Dione is not being backlit by Saturn from the vantage point of Cassini, so its face that is opposite the Sun appears darker.

Visible on Tethys is the Odysseus Crater, which spans a whopping 400km (240 miles). Given that Tethys is only 1,062 kilometers, or 660 miles across, the crater appears very large in comparison to the moon. It also makes the moon very much resemble the Death Star from Star Wars, don’t you think? These images were taken using Cassini’s narrow-angle camera on Nov. 28, 2009.

This second image is a synthetic aperture radar image of the surface of Saturn’s moon Titan. In the lower right and upper center of the image, the two wrinkly features are actually small Titanian mountains. What exactly causes the grooves in these mountains has still to be determined.

On Earth, the shifting of tectonic plates can form such structures, as well as the processes of water flowing, freezing, and melting.

Since Titan has an atmosphere composed mostly of methane and ethane, and experiences rain much like here on Earth, it’s quite possible that these processes are the cause of such features.

Because the illumination of this image comes from the radar on Cassini, the peaks of these formations should be the brightest. As is visible, this isn’t the case. Notice how the left side of the upper mountain in the image, and right side of the lower-right mountain are brighter. The materials that make up the darker and lighter areas are the cause for this lighting effect.

The image represents a patch of Titan’s surface 250 km (155 miles) high and 285 km (180 miles) wide, and the resolution is about 350 meters (1,150 feet) per pixel, and it was taken on December 28th, 2009.

Source: Cassini Equinox Mission, here and here.

Posted on by Nancy Atkinson

The Sound of Saturn’s Rings

This wonderful video was posted by Jennifer Ouellette on Discovery News, and I just had to share it. The sounds are actual recordings picked up by the Cassini spacecraft. I have heard the eerie audio before, but never had previously seen it paired up with moving images from the mission. The radio emissions, called Saturn kilometric radiation, are generated along with Saturn’s auroras, or northern and southern lights. Cassini’s Radio and Plasma Wave Science (RPWS) instrument takes high-resolution measurements that allow scientists to convert the radio waves into audio recordings by shifting the frequencies down into the audio frequency range.
Continue reading “The Sound of Saturn’s Rings”