Category Archives: Cassini

Saturn’s Rings

saturnrings
The rings of Saturn. Credit: NASA/JPL-Caltech/Space Science Institute

 

Cassini captured this image of the Saturn rings and the little moon Prometheus. I got to thinking about the early drawings, in particular the famous 1666 drawing by Robert Hooke showing the shadows from the planet and rings.

saturnhooke

As an aside, Robert Hooke is probably one of the most famous scientists many school kids have never heard of.

From NASA’s Groovy:

From afar, Saturn’s rings look like a solid, homogenous disk of material. But upon closer examination from Cassini, we see that there are varied structures in the rings at almost every scale imaginable.

Structures in the rings can be caused by many things, but often times Saturn’s many moons are the culprits. The dark gaps near the left edge of the A ring (the broad, outermost ring here) are caused by the moons (Pan and Daphnis) embedded in the gaps, while the wider Cassini division (dark area between the B ring and A ring here) is created by a resonance with the medium-sized moon Mimas (which orbits well outside the rings). Prometheus is seen orbiting just outside the A ring in the lower left quadrant of this image; the F ring can be faintly seen to the left of Prometheus.

This view looks toward the sunlit side of the rings from about 15 degrees above the ringplane. The image was taken in red light with the Cassini spacecraft wide-angle camera on Jan. 8, 2015.

The view was obtained at a distance of approximately 566,000 miles (911,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 37 degrees. Image scale is 34 miles (54 kilometers) per pixel.

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Iapetus

The Saturn moon Iapetus from Cassini
The Saturn moon Iapetus from Cassini

Here’s an image of the Saturn moon Iapetus from the Cassini spacecraft. It is the third largest moon of Saturn with a diameter of 1,417 km / 914 miles or about 40 percent of our moon . Iapetus has density of 1.1 so we know it is made largely of ices.

It’s a strange moon. Take note of the dark spot, that’s not a shadow. Iapetus has a dark side to it that has nothing to do whether or not it is facing the Sun. What causes the asymmetry? There are a few theories, the latest (and my new favorite) is due to ice migration in what is known as the Thermal Runaway Model.

Check out our Iapetus page for more images and more about the moon including physical details.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

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Cubist Saturn

Cassini art from Saturn.  Click. Image Credit: NASA/JPL-Caltech/Space Science Institute
Cassini art from Saturn. Click. Image Credit: NASA/JPL-Caltech/Space Science Institute

Cubism is an artistic movement that featured surfaces of geometrical planes in France beginning in the early 1900’s.

Cassini got into the act back in December 2014 with this image. Usually I find cubist art pretty straightforward,  this one is a little confusing so here is the description from JPL:

Sometimes at Saturn you can see things almost as if from every angle at once, the way a Cubist might imagine things. For example, in this image, we’re seeing Saturn’s A ring in the lower part of the image and the limb of Saturn in the upper. In addition, the rings cast their shadows onto the portion of the planet imaged here, creating alternating patterns of light and dark. This pattern is visible even through the A ring, which, unlike the core of the nearby B ring, is not completely opaque.
The ring shadows on Saturn often appear to cross the surface at confusing angles in close-ups like this one. The visual combination of Saturn’s oblateness, the varying opacity of its rings and the shadows cast by those rings sometimes creates elaborate and complicated patterns from Cassini’s perspective.
This view looks toward the sunlit side of the rings from about 19 degrees above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 5, 2014.
The view was obtained at a distance of approximately 1.2 million miles (2 million kilometers) from Saturn. Image scale is 7 miles (11 kilometers) per pixel.

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Battered Mimas

A view of the north polar region of the moon Mimas. Image Credit:NASA/JPL-Caltech/Space Science Institute
A view of the north polar region of the moon Mimas. Image Credit:NASA/JPL-Caltech/Space Science Institute

Cassini took this image of Mimas from just 50,000 km / 31,000 miles on 05 June 2012. North is up and rotated four degrees to the left.

Mimas shows a surface with numerous impact craters. Generally the more craters there are, the older the terrain is. As always there are other factors like surface renewal processes which can erase craters on a few moons. In most cases the rule of thumb prevails.

See the image and JPL caption at the Cassini webpage.

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High Phase Geometry

Not the usual bright gem of a planet Saturn tends to be thanks to the “high phase” geometric positioning of Sun, Saturn, and Cassini in this image.

A dark looking Saturn. Image credit: NASA/JPL-Caltech/Space Science Institute
A dark looking Saturn. Image credit: NASA/JPL-Caltech/Space Science Institute

From the Cassini web page:

Saturn’s main rings, seen here on their “lit” face, appear much darker than normal. That’s because they tend to scatter light back toward its source — in this case, the Sun.

Usually, when taking images of the rings in geometries like this, exposures times are increased to make the rings more visible. Here, the requirement to not over-expose Saturn’s lit crescent reveals just how dark the rings actually become. Scientists are interested in images in this sunward-facing (“high phase”) geometry because the way that the rings scatter sunlight can tell us much about the ring particles’ physical make-up.

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Jupiter From Below

A Cassini view of Jupiter's southern hemisphere. Credit: NASA/JPL/Space Science Institute
A Cassini view of Jupiter’s southern hemisphere. Credit: NASA/JPL/Space Science Institute

Instead of Saturn, this Cassini image shows us Jupiter from a completely different perspective.  Yes there is a view from the north too it’s linked below.

No polar vortex is evident from this image.

From ESA’s Space in Images:

This Cassini image shows Jupiter from an unusual perspective. If you were to float just beneath the giant planet and look directly up, you would be greeted with this striking sight: red, bronze and white bands encircling a hazy south pole. The multicoloured concentric layers are broken in places by prominent weather systems such as Jupiter’s famous Great Red Spot, visible towards the upper left, chaotic patches of cloud and pale white dots. Many of these lighter patches contain lightning-filled thunderstorms.

Jupiter has very dramatic weather – the planet’s axis is not as tilted (towards or away from the Sun) as much as Earth’s so it does not have significant seasonal changes, but it does have a thick and tumultuous atmosphere filled with raging storms and chaotic cloud systems.
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Moon Pairing

Cassini spies a pair of Saturn moons. Image Credit: NASA/JPL-Caltech/Space Science Institute
Cassini spies a pair of Saturn moons. Image Credit: NASA/JPL-Caltech/Space Science Institute

A very nice Cassini image of the Saturn moons Rhea and Tethys. The orientation of the pair is such that we can see what looks like large matching craters on each moon.  I believe the crater on Rhea (the moon in front) is Tirawa.  The crater is 360 km / 220 mile wide and makes up the Tirawa impact basin. The crater on Tethys is even larger, a true giant considering it is has a diameter 400 km / 249 miles or about 40 percent of the moons diameter.

From the Cassini site:

Tethys appears to be peeking out from behind Rhea, watching the watcher.

Scientists believe that Tethys’ surprisingly high albedo is due to the water ice jets emerging from its neighbor, Enceladus. The fresh water ice becomes the E ring and can eventually arrive at Tethys, giving it a fresh surface layer of clean ice.

Lit terrain seen here is on the anti-Saturn side of Rhea. North on Rhea is up. The image was taken in red light with the Cassini spacecraft narrow-angle camera on April 20, 2012.

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Enceladus

Enceladus seen against Saturn. Image Credit: NASA/JPL-Caltech/Space Science Institute
Enceladus seen against Saturn. Image Credit: NASA/JPL-Caltech/Space Science Institute

A nice image of the moon Enceladus seen with the back drop of the planet Saturn. This is the same sort of alignment Cassini was in to get the image of Tethys and Mimas posted here a last week (see Ring Shadows).

Enceladus is 504 km / 313 miles across and Cassini was 948,000 km / 589,000 miles away (about twice the Earth – Moon distance) so we can see how massive Saturn is.  Learn more about Enceladus here,

Aside from Enceladus, the image shows wonderful detail in Saturn’s atmosphere. In particular the two dark round spots (center and upper right) and the interesting cloud feature about half way between Enceladus and the larger round spot. The cloud features look like they are rising vertically from the planet but probably are not. The round spots are disturbances in the atmosphere, much like Jupiter’s Great Red Spot only smaller.

Click the image to get a larger version and it scales pretty well so if you download it you can make it larger yet. You can get a full-res version and more details at the “Mighty Little Dot“.

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Ring Shadows

Ring Shadows on Saturn. Image Credit: NASA/JPL-Caltech/Space Science Institute
Ring Shadows on Saturn. Image Credit: NASA/JPL-Caltech/Space Science Institute

The Cassini – Saturn – Sun angles were just right for Cassini to capture this unusual picture. The rings of Saturn are edge on and their shadows are projected onto the planet.

From the NASA caption:

This view looks toward the sunlit side of the rings from slightly above the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 14, 2014.

The view was obtained at a distance of approximately 1.1 million miles (1.7 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 23 degrees. Image scale is 63 miles (102 kilometers) per pixel.

There are two moons in the image: the most obvious one is Tethys, seen at the lower right below the rings. The other is Mimas. Can you spot it? You may need to click the image to see the large version. Funny how it sticks right out once you find it. Give it a try.

If you give up ckck the “More” link below to narrow you search.
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Saturn Swirls

Atmospheric swirls on Saturn. Credit: NASA/JPL-Caltech/Space Science Institute
Atmospheric swirls on Saturn. Credit: NASA/JPL-Caltech/Space Science Institute

Originally meant to publish yesterday: Cassini took this image of the Saturn swirling atmosphere. Planetary atmospheres (including our own) are a study in fluid dynamics and that is clearly evident here.

The image was taken on 23 August 2014 in red light from about 1.8 million km / 1.1 million miles with the narrow-angle camera.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. 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 and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

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