Category Archives: Cassini

Prometheus at Work


From JPL:
Most planetary rings appear to be shaped, at least in part, by moons orbiting their planets, but nowhere is that more evident than in Saturn’s F ring. Filled with kinks, jets, strands and gores, the F ring has been sculpted by its two neighboring moons Prometheus (seen here) and Pandora. Even more amazing is the fact that the moons remain hard at work reshaping the ring even today.

Prometheus (53 miles, or 86 kilometers across) shapes the F ring through consistent, repeated gravitational nudges and occasionally enters the ring itself (clearing out material and creating a “gore” feature, see PIA12785). Although the gravitational force of Prometheus is much smaller than that of Saturn, even small nudges can tweak the ring particles’ orbits to create new patterns in the ring.

This view looks toward the sunlit side of the rings from about 12 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 21 2016.

Image and caption: NASA/JPL-Caltech/Space Science Institute

Polar Vortex on Saturn

Wow, just look at that polar vortex of Saturn in fine detail from Cassini!  For the knowledge gained on missions like this versus the cost, it is money well spent.  We should be doing more.


Here’s the details from NASA/JPL/Space Science Institute:
Sitting at Saturn’s south pole is a vortex of monstrous proportions. The dark ‘eye’ of this feature is some 8000 km across, or about two thirds the diameter of Earth.

This image is 10 times more detailed than any previous picture of the polar vortex and shows a level of detail inside the eye that was not previously observable. Earlier images showed towering clouds around the edge of this vortex, but inside the air was thought to be mostly transparent. Here, however, a multitude of features is revealed.
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The Crescent of Titan


Here is an image of the Saturn moon Titan.  The moon – sun – Cassini geometry was such we see Titan in a crescent phase.  Cassini’s camera took the image using the clear and blue band filters.  This is a raw image meaning it is just as it was transmitted with no processing on the ground.

The image was taken on 05 April 2016 at 11:44 UTC and received on  Earth a bit less than six hours later.

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

Real Ring Art and More


This Cassini image gives us a unique almost chaotic view of Saturn’s rings that look something like modern art. How does it work? The image was taken 14 degrees above the ring plane and we see the rings and their shadows on the planet.

The other thing we can see is the tiny moon Pan. Look in the narrow ring gap (known as the Encke Gap) about in the center of the image (click to enlarge it). Pan is just 28 km / 17 miles across.

Image: NASA/JPL-Caltech/Space Science Institute

and MORE:

Y-Shaped Discontinuities


The what-discontinuities?

An excellent image by the Cassini orbiter. The “Y-shaped discontinuity” is just amazing — see below. Click the image and take a minute or two to admire the surface detail.  BTW –  I found and fixed a few image link problems.

From the Cassini team:
A sinuous feature snakes northward from Enceladus’ south pole like a giant tentacle. This feature, which stretches from the terminator near center, toward upper left, is actually tectonic in nature, created by stresses in Enceladus’ icy shell.

Geologists call features like these on Enceladus (313 miles or 504 kilometers across) “Y-shaped discontinuities.” These are thought to arise when surface material attempts to push northward, compressing or displacing existing ice along the way. Such features are also believed to be relatively young based on their lack of impact craters — a reminder of how surprisingly geologically active Enceladus is.

This view looks towards the trailing hemisphere of Enceladus. North is up. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Feb. 15, 2016.

The view was obtained at a distance of approximately 60,000 miles (100,000 kilometers) from Enceladus. Image scale is 1,900 feet (580 meters) per pixel.

The Cassini Division


The Cassini site has a labeled picture here you might find helpful.


Keep an eye out for local Yuri’s Night Celebrations, you probably have one near you (no matter where you are and it’s a good bet a scope will be on Jupiter and/or Saturn.  Both are so worth the look if you’ve never seen them for yourself, especially Saturn – it is dazzling!

From the Cassini site:

It’s difficult to get a sense of scale when viewing Saturn’s rings, but the Cassini Division (seen here between the bright B ring and dimmer A ring) is almost as wide as the planet Mercury. (See PIA11142 for a labeled panorama of features in the rings.)

The 2,980-mile-wide (4,800-kilometer-wide) division in Saturn’s rings is thought to be caused by the moon Mimas. Particles within the division orbit Saturn almost exactly twice for every time that Mimas orbits, leading to a build-up of gravitational nudges from the moon. These repeated gravitational interactions sculpt the outer edge of the B ring and keep its particles from drifting into the Cassini Division.

This view looks toward the sunlit side of the rings from about 4 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 28, 2016.

The view was acquired at a distance of approximately 740,000 miles (1.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 76 degrees. Image scale is 4 miles (7 kilometers) per pixel.

Cassini and Planet 9


LOL. I’ve been getting quite a kick out of some of the hoopla surrounding “Planet 9” and saw the stories about how Cassini’s orbit was getting knocked about by the gravity of said planet.

I’ve even seen claims that NASA  is projecting a huge hologram into the sky in order to hide the sight of “Planet 9” coming right at us, after all according to these people,  it is supposed to be on a track to hit is in April and by my reckoning there is less than three-weeks left.

One tiny problem, we don’t even know for sure if “Planet 9” even exists, to say nothing about the rest of it. Although I would love to believe NASA could produce a big hologram like that, but no sadly they can’t.  Oh well, it makes for some good science fiction.

Anyway to address the Cassini’s orbital perturbations,  the Cassini team has this to say:

Saturn Spacecraft Not Affected by Hypothetical Planet 9

Contrary to recent reports, NASA’s Cassini spacecraft is not experiencing unexplained deviations in its orbit around Saturn, according to mission managers and orbit determination experts at NASA’s Jet Propulsion Laboratory in Pasadena, California.

Several recent news stories have reported that a mysterious anomaly in Cassini’s orbit could potentially be explained by the gravitational tug of a theorized massive new planet in our solar system, lurking far beyond the orbit of Neptune. While the proposed planet’s existence may eventually be confirmed by other means, mission navigators have observed no unexplained deviations in the spacecraft’s orbit since its arrival there in 2004.

“An undiscovered planet outside the orbit of Neptune, 10 times the mass of Earth, would affect the orbit of Saturn, not Cassini,” said William Folkner, a planetary scientist at JPL. Folkner develops planetary orbit information used for NASA’s high-precision spacecraft navigation. “This could produce a signature in the measurements of Cassini while in orbit about Saturn if the planet was close enough to the sun. But we do not see any unexplained signature above the level of the measurement noise in Cassini data taken from 2004 to 2016.”

A recent paper predicts that, if data tracking Cassini’s position were available out to the year 2020, they might be used to reveal a “most probable” location for the new planet in its long orbit around the sun. However, Cassini’s mission is planned to end in late 2017, when the spacecraft — too low on fuel to continue on a longer mission — will plunge into Saturn’s atmosphere.

“Although we’d love it if Cassini could help detect a new planet in the solar system, we do not see any perturbations in our orbit that we cannot explain with our current models,” said Earl Maize, Cassini project manager at JPL.

Image and press release: The Cassini-Huygens mission is a cooperative project of NASA, ESA and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate in Washington.

Moon Duo


When taking images in directions opposite from the sun, most objects appear dark. Surprisingly, however, some of Saturn’s rings get brighter.

Parts of Saturn’s main rings appear dark in backlit views, particularly the dense B ring (as can been seen in PIA14934). However, some rings are comparatively tenuous and made up of dust particles that tend to scatter light in roughly the original direction it was traveling. This is called “forward scattering.” Because of forward scattering, rings like the F ring, which encircles the outer edge of the main rings, appear to glow brightly at this large viewing angle.

Two moons hover above the rings from this perspective — Enceladus (313 miles or 504 kilometers across), at left, and Janus (111 miles or 179 kilometers across), at right.

This view looks toward the unilluminated side of the rings from about 0.5 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 21, 2015.

The view was acquired at a distance of approximately 750,000 miles (1.2 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 136 degrees. Janus’ brightness was enhanced by a factor of two to improve its visibility in this image.

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



Helorus is a crater on the Saturn moon Dione.

From Cassini:
Cassini captures a crater duo on Saturn’s moon Dione that is superimposed on older, linear features. The upper of the pair, named Italus, is overprinted on a grouping of ancient troughs called Petelia Fossae. The lower crater, Caieta, sits atop a feature named Helorus Fossa.

Scientists are confident that Helorus and features like it are very old, both because there are many old craters on top of it and because of the way that material has apparently filled in the shallow valley, giving its edges a softer appearance. Fossae on Dione (698 miles or 1,123 kilometers across) like Helorus are believed to be tectonic features, formed when the area between tectonic faults drops down into trough-like structures.

This view is centered on terrain at 22 degrees south latitude, 73 degrees west longitude. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 30, 2015.

The view was obtained at a distance of approximately 25,000 miles (41,000 kilometers) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 64 degrees. Image scale is 804 feet (245 meters) per pixel.

Credit: NASA/JPL-Caltech/Space Science Institute

Saturnian Sisters


I liked the NASA title so I kept it. For comparison to the numbers below our moon averages 384,400 km / 238,855 miles from Earth.

From NASA:
Similar in many ways, Saturn’s moons Tethys and Rhea (left and right, respectively) even share a discoverer: Giovanni Cassini, namesake of the NASA spacecraft that captured this view.

The moons are named for sisters — two Titans of Greek mythology. Although somewhat different in size, Rhea (949 miles or 1,527 kilometers across) and Tethys (660 miles or 1,062 kilometers across) are medium-sized moons that are large enough to have pulled themselves into round shapes. They are both composed largely of ices and are generally thought to be geologically inactive today.

The view looks toward the anti-Saturn sides of Tethys and Rhea. North on both moons is up. The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on Oct. 11, 2015.

The two moons appear close together here, but Tethys was about 220,000 miles (360,000 kilometers) farther away from Cassini when the image was captured — nearly the distance from Earth to our moon. Thus, the view does not accurately reflect the bodies’ relative sizes.

The image was obtained at a distance of approximately 708,000 miles (1.14 million kilometers) from Rhea. Image scale on Rhea is 4 miles (7 kilometers) per pixel. Tethys was 930,000 miles (1.5 million kilometers) away during this observation and has a pixel scale of 6 miles (9 kilometers) per pixel.

Credit: NASA/JPL-Caltech/Space Science Institute