Tag Archives: Cassini

The kittens of Saturn’s rings

The scientists who used Cassini to identify about 60 transient clumps in Saturn’s rings have dubbed them “kittens” and have been naming them appropriately.

Saturn’s kittens are a group of small clumps and baby moons, or moonlets, that occupy the planet’s F ring. Like the rest of Saturn’s rings, this thin outer ring is made up of countless particles that range in size. When enough of those particles bump into one another and stick together, they aggregate into larger clumps — and become eligible for a kitten name.

So far, the list of Saturn’s kitten names includes several classics, like Fluffy, Garfield, Socks and Whiskers. These are unofficial nicknames for more-complicated (and less adorable) official titles like “Alpha Leonis Rev 9” (aka, Mittens). The technical names for these features come from events called stellar occultations, during which Cassini was able to detect the little clumps. In a stellar occultation, a star passes behind Saturn’s rings from Cassini’s point of view.

Most of these clumps will likely never be found again, so their unofficial kitten names are essentially just for fun.


Cassini’s last image of Iapetus


The image on the right is a cropped and scaled up version of one of Cassini’s last images of Saturn’s moon, Iapetus.

The moon is unique in that its east and west hemispheres have completely opposite albedos, with one being very dark and the other very bright. It also has a very distinctive large crater, seen in this image. Scientists do not quite understand what causes the dichotomy, though they have models that partly explain it, partly from material being deposited on the moon’s leading hemisphere combined with the temperature differences at different latitudes.

The cause of the extreme brightness dichotomy on Iapetus is likely to be thermal segregation of water ice on a global scale. Thermal effects are usually expected to act latitudinally. That is, polar areas are colder than equatorial terrain in most cases due to the more oblique angle of the solar irradiation. Therefore, an additional process is required to explain the longitudinal difference as well. In one model, dark, reddish dust coming in from space and preferentially deposited on the leading side forms a small, but crucial difference between the leading and trailing hemispheres, which is sufficient to allow the thermal effect to evaporate the water ice on the leading side completely, but only marginally on the trailing side.

It was this moon’s strange dichotomy that had Arthur Clarke use it in 2001: A Space Odyssey. While Cassini’s images clearly prove that the brightness difference was not created by an alien civilization, as imagined by Clarke, those images have not really provided us a full explanation for its cause. The uncertainty of science marches on!


Cassini’s mission ends

Enceladus as seen by Cassini two days before mission end

After a seven year journey and thirteen years in orbit around Saturn, Cassini’s mission ended early this morning with a dive into Saturn’s atmosphere.

The image above, cropped to show here, is actually one from a short movie, showing Enceladus setting behind the horizon of Saturn. The images were taking two days ago, but provide a fitting image for the mission’s end.

Some of the best images from the dive, including Cassini’s last image, can be found here.

While most of the press will rightly wax eloquent about the magnificence of this mission, my focus remains on what will come next. We no longer have any way to observe what is happening on Saturn. We are blind. We should not be.


Cassini on final approach to Saturn

Engineers have confirmed that Cassini is now on its final approach to Saturn, with a scheduled dive into the gas giant set for Friday, September 15.

The mission’s final calculations predict loss of contact with the Cassini spacecraft will take place on Sept. 15 at 7:55 a.m. EDT (4:55 a.m. PDT). Cassini will enter Saturn’s atmosphere approximately one minute earlier, at an altitude of about 1,190 miles (1,915 kilometers) above the planet’s estimated cloud tops (the altitude where the air pressure is 1-bar, equivalent to sea level on Earth). During its dive into the atmosphere, the spacecraft’s speed will be approximately 70,000 miles (113,000 kilometers) per hour. The final plunge will take place on the day side of Saturn, near local noon, with the spacecraft entering the atmosphere around 10 degrees north latitude.

We will get Cassini’s last images about 90 minutes after its death.


An oral history of the Cassini mission to Saturn

Link here. Those who have read my book on the building of the Hubble Space Telescope will recognize many of the same people and political maneuvers used to get the project off the ground and funded.

Note too that the idea of Cassini was first proposed in 1982, but it didn’t actually launch until 1997. Fifteen years. While today I think such a spacecraft could go from concept to launch much faster, this timeline gives us a guide on when the next Saturn orbiter might launch. At the earliest do not expect another mission to Saturn to launch before 2025.


Cassini says goodbye to Saturn

Saturn, October 2016

Cool image time! The picture above, reduced in resolution to show here, was taken in October 2016 during one of Cassini’s last distant orbits that gave it a global view of Saturn and its rings. Since it began its dives close to the gas giant such views have not been possible.

The mission ends this coming Saturday with a dive into Saturn. It was launched in October 1997, and after a seven year journey has spent the last thirteen years in orbit around the planet, providing us the first long term glimpse of a gas giant as its seasons evolved.

Cassini has been orbiting Saturn for nearly a half of a Saturnian year but that journey is nearing its end. This extended stay has permitted observations of the long-term variability of the planet, moons, rings, and magnetosphere, observations not possible from short, fly-by style missions.

When the spacecraft arrived at Saturn in 2004, the planet’s northern hemisphere, seen here at top, was in darkness, just beginning to emerge from winter (see Cassini’s Holiday Greetings​). Now at journey’s end, the entire north pole is bathed in the continuous sunlight of summer.

The spacecraft was also able to observe the seasonal changes that occurred to Titan. It also studied the plumes coming from the tiger stripe cracks on Enceladus, shown below the fold in a movie created by Cassini over a 14 hour time period in August 2017.

I expect that scientists will be exploring Cassini’s data archive for decades, finding many things not noticed in their initial viewing. Unfortunately, we will not have another spacecraft taking new pictures in orbit around Saturn to compare with Cassini’s past images for many decades to come. On Saturday, we go blind.
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Saturn’s magnificent rings

Saturn's rings

The Cassini science team released two sets of images taken by the spacecraft of Saturn’s rings.

The image above, reduced in resolution to show here, is from the second link. As they note,

The pale tan color is generally not perceptible with the naked eye in telescope views, especially given that Saturn has a similar hue.

The material responsible for bestowing this color on the rings—which are mostly water ice and would otherwise appear white—is a matter of intense debate among ring scientists that will hopefully be settled by new in-situ observations before the end of Cassini’s mission.

The different ringlets seen here are part of what is called the “irregular structure” of the B ring. Cassini radio occultations of the rings have shown that these features have extremely sharp boundaries on even smaller scales (radially, or along the direction outward from Saturn) than the camera can resolve here. Closer to Saturn, the irregular structures become fuzzier and more rounded, less opaque, and their color contrast diminishes.

Check out both. They reveal to me that our understanding of these rings remains essentially nil, even after more than a dozen years of study by Cassini.


Cassini movie flying past Saturn’s rings

movie of Cassini flying past Saturn's rings

Cool image time! The Cassini science team has assembled a short movie from 21 images taken by the spacecraft during its August 20th dive between the rings and Saturn. That animation is to the right.

Only two weeks remain in the Cassini mission. The spacecraft dives into Saturn on September 15.

The spacecraft is expected to lose radio contact with Earth within about one to two minutes after beginning its descent into Saturn’s upper atmosphere. But on the way down, before contact is lost, eight of Cassini’s 12 science instruments will be operating. In particular, the spacecraft‘s ion and neutral mass spectrometer (INMS), which will be directly sampling the atmosphere’s composition, potentially returning insights into the giant planet’s formation and evolution. On the day before the plunge, other Cassini instruments will make detailed, high-resolution observations of Saturn’s auroras, temperature, and the vortices at the planet’s poles. Cassini’s imaging camera will be off during this final descent, having taken a last look at the Saturn system the previous day (Sept. 14).

The second link above gives a detailed moment-by-moment breakdown of the final six days.

I would have posted this earlier this week, but my limited internet access made it impossible. Sorry about that.


The gentle storms of Saturn

Saturn's gentle storms

Cool image time! The Cassini image above, cropped and reduced slightly, shows a close-up view of Saturn’s cloud tops, taken during Cassini’s May 18, 2017 fly-by.

Clouds on Saturn take on the appearance of strokes from a cosmic brush thanks to the wavy way that fluids interact in Saturn’s atmosphere. Neighboring bands of clouds move at different speeds and directions depending on their latitudes. This generates turbulence where bands meet and leads to the wavy structure along the interfaces.

What I see is a much less turbulent storm pattern, when compared with Jupiter. This is not to say that the weather of Saturn is quiet or peaceful, for it certainly cannot be, considering the gas giant’s size and the depth of the atmosphere. Still, this image suggests that the turbulence is less violent here, possibly because Saturn is farther from the Sun and is hit with less solar energy, and because Saturn is smaller and thus produces less of its own internal energy.

Either way, it is beautiful and mysterious, in the way are all such images of alien places.


Cassini’s last close look at Titan

Titan's magic lake district

The Cassini science team has released the last radar swath that the spacecraft will take of Titan, imaged on April 22.

You can see the full swath up close here. The image above is my crop of the section on the swath’s right portion, showing the shoreline of the hydrocarbon lake Ligeia Mare, where periodically an island has been seen by radar to intermittently appear and disappear.

No “island” feature was observed during this pass. Scientists continue to work on what the transient feature might have been, with waves and bubbles being two possibilities.

The fly-by also took the first, and last, depth measurement of 8 other lakes, finding that they all had the same depth, suggesting they are connected by an underground “water” table. In this case, it ain’t water, but liquid hydrocarbons like methane.


Cassini’s last five orbits of Saturn

Cassini is about to begin its last of five orbits of Saturn, before it is sent into the planet’s atmosphere to burn up.

Cassini will make the first of these five passes over Saturn at 12:22 a.m. EDT Monday, Aug. 14. The spacecraft’s point of closest approach to Saturn during these passes will be between about 1,010 and 1,060 miles (1,630 and 1,710 kilometers) above Saturn’s cloud tops.

The spacecraft is expected to encounter atmosphere dense enough to require the use of its small rocket thrusters to maintain stability – conditions similar to those encountered during many of Cassini’s close flybys of Saturn’s moon Titan, which has its own dense atmosphere. “Cassini’s Titan flybys prepared us for these rapid passes through Saturn’s upper atmosphere,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory (JPL) in California. “Thanks to our past experience, the team is confident that we understand how the spacecraft will behave at the atmospheric densities our models predict.”


Looking down at Saturn’s rings

Looking down at Saturn's rings

Cool image time! The image on the right, reduced in resolution to show here, was taken by Cassini in May and looks down at the outer rings of Saturn. The moon Prometheus can also be seen in the large gap between the main rings and the outermost F ring.

Most of the small moon’s surface is in darkness due to the viewing geometry here. Cassini was positioned behind Saturn and Prometheus with respect to the sun, looking toward the moon’s dark side and just a bit of the moon’s sunlit northern hemisphere.

Also visible here is a distinct difference in brightness between the outermost section of Saturn’s A ring (left of center) and rest of the ring, interior to the Keeler Gap (lower left).

The image clearly shows the gravitational influence of the moon on the outer ring. As Prometheus orbits past the F ring its mass creates waves through the ring’s materials.


The endless bands of Saturn

Cool image time. One of the images released by the Cassini science team this week when it announced the first results from the spacecraft’s weekly dives between Saturn and its innermost rings was a short video made from 137 images taken on its first dive on April 26, 2017.

It is absolutely worthwhile to view this video. It begins at Saturn’s north pole, looking down into what appears to be a bottomless vortex, and continues south to almost the equator. Along the way the movie captures what seems to be innumerable horizontal bands across the gas giant’s surface. Not only are do we see the major bands that have been observed from Earth for centuries, there are bands within bands, and bands within those bands. Like a fractal it appears that the deeper you go, the more horizontal jet streams you see.

Like Juno at Jupiter, the mysteries of a gas giant like Saturn is overwhelming. This is a big and very active planet. We understand almost nothing about its weather systems, its atmosphere, and its interior. And this glimpse by Cassini is only that, a mere glimpse. When Cassini’s mission ends in September, it will leave us a treasure trove of knowledge. It will also leave us a much larger library of unanswered questions, all of which will remain unanswered until we can return, decades hence, with new probes..


First results from Cassini’s dives between Saturn and its rings

The first results from Cassini’s weekly dives between Saturn and its innermost rings have now been released.

The big surprise so far is the lack of a tilt to Saturn’s magnetic field.

Based on data collected by Cassini’s magnetometer instrument, Saturn’s magnetic field appears to be surprisingly well-aligned with the planet’s rotation axis. The tilt is much smaller than 0.06 degrees — which is the lower limit the spacecraft’s magnetometer data placed on the value prior to the start of the Grand Finale.

This observation is at odds with scientists’ theoretical understanding of how magnetic fields are generated. Planetary magnetic fields are understood to require some degree of tilt to sustain currents flowing through the liquid metal deep inside the planets (in Saturn’s case, thought to be liquid metallic hydrogen). With no tilt, the currents would eventually subside and the field would disappear.

Any tilt to the magnetic field would make the daily wobble of the planet’s deep interior observable, thus revealing the true length of Saturn’s day, which has so far proven elusive.

They also have gotten lots of much better images of the planet’s cloud tops.


Titan’s clearing northern skies

Titan's clearing northern skies

The image of Titan on the right, reduced in resolution to show here, was taken by Cassini less than a week ago, on June 9, as it continues its last orbits of Saturn prior to crashing into the gas giant’s atmosphere in September.

NASA’s Cassini spacecraft sees bright methane clouds drifting in the summer skies of Saturn’s moon Titan, along with dark hydrocarbon lakes and seas clustered around the north pole. Compared to earlier in Cassini’s mission, most of the surface in the moon’s northern high latitudes is now illuminated by the sun. …Summer solstice in the Saturn system occurred on May 24, 2017.

When Cassini arrived more than a decade ago, it was winter on Titan’s northern hemisphere, and the atmosphere was thick with haze. Now the sky is clearing as the stormy weather shifts to the winter in the southern hemisphere.

As with yesterday’s global map of Mimas, this image is in many ways a farewell look at Titan. While Cassini will likely get a few more global images of the Saturn moon before the mission ends in September, this image essentially marks the end of our ability to observe this strange planet closely, for decades to come. When Cassini crashes into Saturn, our vision at Saturn will go blind. And no one knows when our sight there will return, as no mission is presently in the works, or is even being considered, to return to Saturn.


A new map of Mimas

Global map of Mimas

The Cassini science team has released what will be the best map of Saturn’s moon Mimas for many decades to come. A reduced resolution version is above, and was updated after the most recent fly-bys in November 2016 and February 2017.

The moon’s large, distinguishing crater, Herschel, is seen on the map at left. The map is an equidistant (simple cylindrical) projection and has a scale of 710 feet (216 meters) per pixel at the equator. The mean radius of Mimas used for projection of this map is 123.2 miles (198.2 kilometers). The resolution of the map is 16 pixels per degree.

Since Cassini is in its final orbits and will crash into Saturn in September, and no other Saturn mission is even being planned, do not expect a better map for a very long time.


Pole of Saturn’s moon Enceladus shifted 55 degrees in the past

Data from Cassini now suggests that the moon Enceladus shifted its pole as much as 55 degrees sometime in the past, possibly due to an impact.

Whether it was caused by an impact or some other process, Tajeddine and colleagues think the disruption and creation of the tiger-stripe terrain [at south pole] caused some of Enceladus’ mass to be redistributed, making the moon’s rotation unsteady and wobbly. The rotation would have eventually stabilized, likely taking more than a million years. By the time the rotation settled down, the north-south axis would have reoriented to pass through different points on the surface — a mechanism researchers call “true polar wander.”


After 7 years Cassini reaches Saturn’s solstice

In 2010 NASA extended the Cassini mission orbiting Saturn for seven years to the planet’s next solstice, so that the spacecraft could observe Saturn, its moons, and its rings, for one full season of its 28 year orbit.

Today, Cassini reached that target.

NASA’s Cassini spacecraft still has a few months to go before it completes its mission in September, but the veteran Saturn explorer reaches a new milestone today. Saturn’s solstice — that is, the longest day of summer in the northern hemisphere and the shortest day of winter in the southern hemisphere — arrives today for the planet and its moons. The Saturnian solstice occurs about every 15 Earth years as the planet and its entourage slowly orbit the sun, with the north and south hemispheres alternating their roles as the summer and winter poles.

The article provides a detailed review of all the changes that have occurred during this long time period.


Propellers by the dozens


Cool image time! The latest image releases from Cassini, taken during its recent close fly-by campaign of the rings of Saturn, focus on the propeller features produced in the rings by larger ring objects. The image on the right, reduced to show here, reveals dozens of propellers of all shapes and sizes.

The original discovery of propellers in this region in Saturn’s rings … was made using several images taken from very close to the rings during Cassini’s 2004 arrival at Saturn. Those discovery images were of low resolution and were difficult to interpret, and there were few clues as to how the small propellers seen in those images were related to the larger propellers Cassini observed later in the mission….

This image, for the first time, shows swarms of propellers of a wide range of sizes, putting the ones Cassini observed in its Saturn arrival images in context. Scientists will use this information to derive a “particle size distribution” for propeller moons, which is an important clue to their origins.

The parallel pattern of rings in the center of the image is a series of density waves in the ring structure, caused by an interaction with one of Saturn’s larger nearby moons.

They have also released the best view we can now expect of a propeller by Cassini.

This is the third and final propeller to be targeted for a close flyby observation during Cassini’s ring-grazing orbits (the period from Nov. 2016 to April 2017 when Cassini’s orbit passed just outside the main rings). …Because propellers are seen in the outermost parts of the main rings, the ring-grazing orbits provided Cassini’s best opportunity to see them up close.

Cassini is now diving between the rings and the planet, so the propellers are farther away.


Saturn’s north pole hexagon jet stream

Saturn's north polar hexagon jet stream

Cool image time! The image on the right, reduced and cropped to show here, was taken by Cassini in January as it was preparing to head into its final 22 orbital dives between Saturn and its rings. The image shows the gas giant’s north polar, with all its magnificent features. As the press release notes, the north pole was in shadow for the first part of Cassini’s mission, and only in recent years has finally moved into sunlight so that the spaceship can see and image it.

Although the sunlight falling on the north pole of Saturn is enough to allow us to image and study the region, it does not provide much warmth. In addition to being low in the sky (just like summer at Earth’s poles), the sun is nearly ten times as distant from Saturn as from Earth. This results in the sunlight being only about 1 percent as intense as at our planet.

This view looks toward Saturn from about 31 degrees above the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on Jan. 22, 2017 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 939 nanometers.

Be sure to look at the full image.


Cassini science team releases movie of images from first ring dive

The Cassini science team has released a movie compiled from images taken during the spacecraft’s first dive between Saturn and its rings.

I have embedded the movie below the fold. It cuts off before the spacecraft’s closest approach because they took a very conservative approach to this fly-by, turning the vehicle so that its antenna dish protected it. This prevented the taking of the best images. The second dive, that occurred yesterday, will have better images.
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Cassini finds gap in Saturn’s rings surprisingly empty

The uncertainty of science: The data from Cassini’s first dive through the gap between Saturn and its innermost ring suggests that the space there has much less material than predicted.

Cassini’s Radio and Plasma Wave Science (RPWS) instrument was one of two science instruments with sensors that poke out from the protective shield of the antenna (the other being Cassini’s magnetometer). RPWS detected the hits of hundreds of ring particles per second when it crossed the ring plane just outside of Saturn’s main rings, but only detected a few pings on April 26. When RPWS data are converted to an audio format, dust particles hitting the instrument’s antennas sound like pops and cracks, covering up the usual whistles and squeaks of waves in the charged particle environment that the instrument is designed to detect. The RPWS team expected to hear a lot of pops and cracks on crossing the ring plane inside the gap, but instead, the whistles and squeaks came through surprisingly clearly on April 26.

“It was a bit disorienting — we weren’t hearing what we expected to hear,” said William Kurth, RPWS team lead at the University of Iowa, Iowa City. “I’ve listened to our data from the first dive several times and I can probably count on my hands the number of dust particle impacts I hear.” The team’s analysis suggests Cassini only encountered a few particles as it crossed the gap — none larger than those in smoke (about 1 micron across).

The second dive through the rings will occur tomorrow, with data sent down the next day. Because the gap is emptier than expected, they will not have to protect the spacecraft so thoroughly, and will thus have more instruments gathering data during the fly through.


Cassini successfully completes first dive between Saturn and its rings

The Cassini spacecraft has successfully survived its close flyby of Saturn, diving between the rings and the top of the planet’s cloud tops.

As it dove through the gap, Cassini came within about 1,900 miles (3,000 kilometers) of Saturn’s cloud tops (where the air pressure is 1 bar — comparable to the atmospheric pressure of Earth at sea level) and within about 200 miles (300 kilometers) of the innermost visible edge of the rings.

Cassini is beaming down its images and data now, with the images to be available later today.


Cassini about to make first dive into Saturn’s rings

Cassini will make its first dive through a gap in Saturn’s ring today, and this link provides details.

Because that gap is a region no spacecraft has ever explored, Cassini will use its dish-shaped high-gain antenna (13 feet or 4 meters across) as a protective shield while passing through the ring plane. No particles larger than smoke particles are expected, but the precautionary measure is being taken on the first dive. The Cassini team will use data collected by one of the spacecraft’s science instruments (the Radio and Plasma Wave Subsystem, or RPWS) to ascertain the size and density of ring particles in the gap in advance of future dives. As a result of its antenna-forward orientation, the spacecraft will be out of contact with Earth during the dive.

The first images are not expected until mid-day tomorrow.


Cassini makes last fly-by of Titan

Cassini on April 21 made its last fly-by of Titan as the spacecraft is prepared for its final 22 orbits of Saturn.

The flyby also put Cassini on course for its dramatic last act, known as the Grand Finale. As the spacecraft passed over Titan, the moon’s gravity bent its path, reshaping the robotic probe’s orbit slightly so that instead of passing just outside Saturn’s main rings, Cassini will begin a series of 22 dives between the rings and the planet on April 26. The mission will conclude with a science-rich plunge into Saturn’s atmosphere on Sept. 15. “With this flyby we’re committed to the Grand Finale,” said Earl Maize, Cassini project manager at JPL. “The spacecraft is now on a ballistic path, so that even if we were to forgo future small course adjustments using thrusters, we would still enter Saturn’s atmosphere on Sept. 15 no matter what.”

The flyby zipped past Titan only a little more than 600 miles above its surface.


Water plumes on Europa plus hydrogen in Enceladus plumes

Scientists have detected more evidence of underground oceans on both Europa (orbiting Jupiter) and Enceladus (orbiting Saturn).

In the case of Europa, the Hubble Space Telescope has once again detected plumes of water ice being shot up from cracks in the moon’s surface. This second detection confirms the first from two years ago.

In the case of Enceladus, Cassini data has detected the presence of hydrogen in the plumes totaling 1% of the total material in the plumes.

The Europa story is significant, in that it confirms that the moon is still active geologically, and that the underground ocean is interacting with the outside world by ejecting material from it to the surface. This increases the odds that there will be some very intriguing chemistry in that ocean, including the possibility of organic life.

The Enceladus story puzzles me. We already know that the plumes there are made of water, which in itself is one third hydrogen. Why should anyone be surprised that a portion of that water gets split so that some of the hydrogen gets released as an atom instead of part of the water molecule. In fact, this discovery does not seem to me to be much of a discovery at all, but simply a confirmation that the plumes have the materials from the water ocean below the surface. That NASA has pushed it this week so hard in conjunction with their future Europa Clipper mission suggests that this part of the press story is really about lobbying for funds and has little to do with science.


The rings of Saturn

The rings of Saturn up close

Cool image time! The image to the right, cropped to post here, is part of one of the closest and highest resolution images that Cassini has yet taken of Saturn’s rings. The image was taken in January during one of the spacecraft’s ring grazing orbits, and has a resolution of 2,300 feet per pixel. And yet, as noted by the Cassini science team, “Even at this level of detail, it is still not fine enough to resolve the individual particles that make up the ring.”

In prepping the image, all I did was crop it to show the closest rings. I purposely did not reduce its resolution, so that you can see that no individual particles are visible. The rings of Saturn are truly made up of billions of small objects, behaving in many ways like liquid floating in the gravity well of Saturn. If you don’t believe me, download the full image and zoom in on it as much as you like. All you will see are pixels.

The fundamental science question therefore is not how Saturn’s rings behave (though this is certainly important and quite fascinating) but why did those rings end up the way they are. No other planet has rings anything like Saturn’s in their density and make-up. Why? Are Saturn’s rings a normal process that only occurs for short times around planets, which is why only Saturn has these types of rings at present? Or is it a rare event, so rare that we happen to be very lucky to see such a thing at all?

Even more important, Saturn’s rings and their behavior are likely linked closely to the same phenomenon that describe the formation of planets around a star. The more we can learn about why these rings exist, the more we will learn about why planets exist, both here circling the Sun as well as around stars everywhere else.


Saturn’s weird moon Pan


New images from Cassini have provided scientists their first sharp images of Saturn’s moon Pan, and what those images show is something really weird. The image on the right is only one sample, with the link providing more.

Pan orbits in a gap between two rings, and the ridge might have accumulated from material from those rings. Then again, maybe not. It will take more data to I think completely unravel how this moon got to look like it does.


A propeller in Saturn’s A ring

A propeller in Saturn's A ring

Cool image time! The image on the right, cropped and reduced to show here, captures the same propeller feature in Saturn’s A ring, with the top image showing the sunlight side and the bottom image the side away from the Sun.

Cassini scientists have been tracking the orbit of this object for the past decade, tracing the effect that the ring has upon it. Now, as Cassini has moved in close to the ring as part of its ring-grazing orbits, it was able to obtain this extreme close-up view of the propeller, enabling researchers to examine its effects on the ring. These views, and others like them, will inform models and studies in new ways going forward.

…The propeller’s central moonlet would only be a couple of pixels across in these images, and may not actually be resolved here. The lit-side image shows that a bright, narrow band of material connects the moonlet directly to the larger ring, in agreement with dynamical models. That same thin band of material may also be obscuring the moonlet from view.

Lengthwise along the propeller is a gap in the ring that the moonlet has pried open. The gap appears dark on both the lit and unlit sides. Flanking the gap near the moonlet are regions of enhanced density, which appear bright on the lit side and more mottled on the unlit side.

The scale of the two images is slightly different, 0.33 and 0.44 miles, as they were taken as Cassini was zipping past during one of its ring-grazing orbits on February 21.

To my eye, the effect here faintly resembles a wake produced by a boat in water, except that the wake moves in opposite directions on opposite sides of the tiny moonlet as it plows through the A ring.

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