Category Archives: Cassini

Mother and Daughter


From the Cassini page:

In Greek mythology, Dione was the daughter of Tethys, so we should perhaps not be surprised to see the two eponymous moons together.

In reality, the moons Tethys (660 miles or 1062 kilometers across) and Dione (698 miles or 1123 kilometers across) are not mother and daughter in any sense. They are perhaps more like sisters since scientists believe that they formed out of the same disk around an early Saturn.

Dione in this image is the upper moon, while Tethys is the lower.

This view looks toward the anti-Saturn side of Dione. North on Dione is up. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 4, 2015.

The view was obtained at a distance of approximately 1.5 million miles (2.4 million kilometers) from Dione. Image scale is 9 miles (14 kilometers) per pixel.

Credit: NASA/JPL-Caltech/Space Science Institute

Pluto Seen from Cassini


As New Horizons made its close approach, the Cassini spacecraft in orbit around Saturn was able to take this image showing Pluto.  Hard to tell which is Pluto?  Yes I agree, it is just about centered in the frame, click the image for an annotated version.

The distance to Pluto at the time was 3.9 billion km / 2.4 billion miles and the resolution of the image is too low to be able to see other members of the Pluto family.

You will note in the annotated version there are four stars labeled too. Those stars have a magnitude of between 11 and 12.

New Pluto pictures starting later today.

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

Titan and Saturn

While we wait for data from New Horizons, here is a lovely Cassini image of Saturn and Titan. This image was acquired from 1.5 million km / 930,000 miles looking toward the anti-Saturn hemisphere of Titan.


The image gives us a nice sense of scale, Titan at 5,150 km / 3,200 miles across (and the second largest moon in our solar system) has a diameter 23 times smaller than its parent planet Saturn.

Things are much different in the Plutonian system, Charon is just over half the diameter of Pluto and many people think of the pair as binary planets.

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



This image from Cassini has to be one of the best shots of Prometheus and the interaction between it and the F ring. Check out the bump in the bottom third of the image.

Very nice.

JPL/NASA’s description:

Saturn’s moon Prometheus, seen here looking suspiciously blade-like, is captured near some of its sculpting in the F ring.
Prometheus’ (53 miles or 86 kilometers across) orbit sometimes takes it into the F ring. When it enters the ring, it leaves a gore where its gravitational influence clears out some of the smaller ring particles. Below Prometheus, the dark lanes interior to the F ring’s bright core provide examples of previous ring-moon interactions.
This view looks toward the unilluminated side of the rings from about 7 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 15, 2015.
The view was obtained at a distance of approximately 286,000 miles (461,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 115 degrees. Image scale is 1.7 miles (2.8 kilometers) per pixel.

Credit: NASA/JPL-Caltech/Space Science Institute

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

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

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

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



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

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.