Category Archives: Cassini

Triple Crescents

his beautiful image from the Cassini spacecraft showing three of Saturn’s moons as crescents is too good to pass up.


The largest moon in the image is Titan (also Saturn’s largest moon), notice how the crescent seems to wrap much around the moon more than the other two. Titan has an atmosphere that refracts light around the moon than it would otherwise would.

Rhea is in the upper left shows more cratering, especially if you click the image to see a larger version.  I believe we may be able to see the Tirawa impact basin in the image.

Mimas is the bottom moon in the image. Of the three Mimas is probably my favorite. It has a HUGE impact crater called Herschel – almost a full third of the moons diameter!

Physical charachterisitics and images
for each of the moons can be found at the links to each below.

Spacecraft to moon distances:
To Titan – 2 million km / 1.2 million miles
To Rhea – 3.5 million km / 2.2 million miles  (see the Tirawa impact basin)
To Mimas – 3.1 million km / 1.9 million miles  (check out Herschel)

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

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Saturn and Dione


A Cassini image of Saturn with moons Dione in the foreground and Enceladus just above the rings seen to the right hand side.

The iamge was taken in visible light with Cassini’s wide angle camera from a distance of 77,000 km / 44,000 miles to Dione.

Click the image for a larger version. One of those images that would make a great framed poster.

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

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Tethys and Saturn


A nice image from the Cassini spacecraft of the moon Tethys and Saturn.

The configuration shows two large craters on Tethys facing Saturn in sharp relief. The larger crater is the southern crater with a central peak indicating a violent impact. The northern crater does not seem to have a central peak so the impact wasn’t quite as violent or the surface composition did not support the central peak formation.

The moon is much closer to the spacecraft, Saturn is in the background. The distance to Tethys is about 120,000 km / 75,000 miles.

Today Cassini is doing a rather distant flyby of a few of Saturn’s smaller moons including: Polydeuces, Methone, Pan, Atlas and Telesto. We don’t get to see these very often so I hope they are close enough for images.

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

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Crater Odysseus


We can see by this Cassini image of the Saturn moon Tethys is is covered in craters and then there is the crater called Odysseus seen on here on the right hand side on the moon.

Odysseus is colossal in scale. The moon Tethys is 1,062 km / 660 miles in diameter and the crater Odysseus is 450 km / 280 miles in diameter. The impact created a crater covering 18 percent of the moon’s surface! The image here washes out the crater a bit and it’s hard to get a good look. I made some adjustments to the image and if you click it you can get a enhanced version showing the internal detail a little better.

The image was acquired by Cassini from a distance of 190,000 km / 118,000 miles. The view has the north pole of the moon rotated 42 degrees to the right and looking at the anti-Saturn side of the moon on 11 April 2015.

Check out our Tethys page.

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

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The Cassini spacecraft just completed a flyby of one of my favorite moons Hyperion. Here’s a couple of images from the flyby of 31 May 2015. Click the one above to get the next and closer version.

These are raw images so they were not processed by JPL, I however did tweak them a little to bring out some of the detail. And there is plenty of detail to be seen. I believe these images will be processed by the imaging team sometime next year.

Hyperion is small, only 286 km / 177 miles in diameter, that’s an average it’s more of a potato shaped spongy looking thing. Amazingly enough it was discovered in 1848 by William Cranch Bond, his son George Phillips Bond and William Lassell.

The moon appears to be mostly ice and has lots of empty space it has a density of only 0.544 grams/cm^3 (compare to water ice at 1 gram/cm^3).

The moon was likely a fragment of a larger body created by an impact. Check out our Hyperion page for a more data on the moon.
Image Credit: NASA/JPL-Caltech/Space Science Institute

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Rhea’s Horizon


Seeing the icy moon Rhea up close is always a treat. This Cassini image shows us a very battered surface.

Being a moon of Saturn this is a very cold place, the surface temperature  ranges from about -220 C to -174 C on a warm day (-364 F to -281 F).  It will be fun to compare this to Pluto and its moons which we think is about -229 C (-380 C).

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

From the Cassini imaging team:

Gazing off toward the horizon is thought-provoking no matter what body’s horizon it is. Rhea’s horizon is slightly irregular and battered by craters, so thoughts inevitably turn towards the forces that shape these icy worlds.

The surface of Rhea (949 miles or 1527 kilometers across) has been sculpted largely by impact cratering, each crater a reminder of a collision sometime in the moon’s history. On more geologically active worlds like Earth, the craters would be erased by erosion, volcanoes or tectonics. But on quieter worlds like Rhea, the craters remain until they are disrupted or covered up by the ejecta of a subsequent impact.

Lit terrain seen here is on the trailing hemisphere of Rhea. North on Rhea is up and rotated 12 degrees to the right. In this view, Cassini was at a subspacecraft latitude of 9 degrees North. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 10, 2015.

The view was obtained at a distance of approximately 35,000 miles (56,000 kilometers) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 76 degrees. Image scale is 1,100 feet (330 meters) per pixel.

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Serene Saturn


NASA’s title for the image was so good I had to use it. Looks can be a little deceiving because the atmosphere we are looking at is moving at 1,800 kmh / 1,100 mph.

Winds are driving storms you can see (click the image) that probably would be anything but serene, except for the fact the lack of a solid surface. The lack of a solid surface means no drag to slow down the winds which contribute to the speed. Saturn like Jupiter actually generates more heat internally than it receives from the Sun and this also contributes to the wind speed and convection to feed the storms.

You can see a moon in is image too, Mimas can be seen at about the one o’clock position just above the planet. Mimas was brightened by a factor of 2 so it would show up aside the brightness of Saturn.

Cassini to Saturn distance was about 2.5 million km / 1.6 million miles.
Image Credit: NASA/JPL-Caltech/Space Science Institute

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Saturn Weather



Saturn’s atmosphere is very active and the storms are much less noticeable than Jupiter but they are no less interesting.

From NASA:
Saturn’s surface is painted with swirls and shadows. Each swirl here is a weather system, reminding us of how dynamic Saturn’s atmosphere is.

Images taken in the near-infrared (like this one) permit us to peer through Saturn’s methane haze layer to the clouds below. Scientists track the clouds and weather systems in the hopes of better understanding Saturn’s complex atmosphere – and thus Earth’s as well.

This view looks toward the sunlit side of the rings from about 17 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on Feb. 8, 2015 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers.

The view was obtained at a distance of approximately 794,000 miles (1.3 million kilometers) from Saturn. Image scale is 47 miles (76 kilometers) per pixel.

If you click the image you will get a larger version. There is an odd feature in the dark spot towards the upper part of the planet. Is it a part of the cloud wall? An updraft of some sort?


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The Cassini spacecraft took this image of Iapetus on 27 March from a distance of about a million km (621,000 miles). This is the second-closet approach to the moon in this mission phase. The closest was in 2011.

The image was taken with the narrow angle camera and gives a good view of the bright terrain in the north polar region.

Iapetus is 1,471 km / 914 miles in diameter. Iapetus is two-toned so the color shading isn’t shadow. The color is pretty close to natural color thanks to RGB filters, the image was brightened to bring out the darker features.

NASA’s description of the features:
The large basin at lower right, within the dark terrain, is named Turgis. The slightly smaller crater at the nine o’clock position is Falsaron. The two prominent craters just above image center are Roland and Turpin. At the limb around the three o’clock position is the darkened rim of the crater Naimon.

The image was produced by Tilmann Denk at Freie Universität in Berlin. Image Credit: NASA/JPL-Caltech/Space Science Institute

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Wakonda Crater

A look at the crater Wakonda.  Click. Image Credit: NASA/JPL-Caltech/Space Science Institute
A look at the crater Wakonda. Click. Image Credit: NASA/JPL-Caltech/Space Science Institute

The Cassini spacecraft made a close flyby of Rhea on 9 February 2015 and returned one of the highest resolution color views of the Saturn moon Rhea so far.

From NASA:
Images taken using clear, green, infrared and ultraviolet spectral filters were combined to create these enhanced color views, which offer an expanded range of the colors visible to human eyes in order to highlight subtle color differences across Rhea’s surface. The moon’s surface is fairly uniform in natural color.

The largest crater in the view above is 123 km / 76 miles in diameter and is named Wakonda.

The names of surface features follow a naming convention adopted by the International Astronomical Union. In the case of craters on Rhea names are from People and places from creation myths. In this case Wakonda is a term used by Native Americans of the Omaha people when praying, and also applied by them to objects or phenomena regarded as sacred or mysterious.

The image was produced by Heike Rosenberg and Tilmann Denk at Freie Universität in Berlin, Germany.

Want the large versions? You can find them here.

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