Tethys Takes a Look at Saturn

Tethys and SaturnIn this picture taken by the Cassini spacecraft the two large craters on Tethys near the line where day fades to night seem to be looking at Saturn. (Click the image to embiggen it.)

The shadowing on the craters caused by being near Tethys’ terminator throws their topography into sharp relief. The larger, southernmost of the two shows a more complex structure. Its central peak is  probably the result of the surface reacting to the violent post-impact excavation of the crater. The northern crater doesn’t have a similar feature. The impact was likely too small to form a central peak, or the composition of the material in the immediate vicinity couldn’t support the formation of a central peak.

Image Credit: NASA


Mimas is one of Saturns moons. It’s about 130 km in diameter, one of the smallest bodies in the Solar System with sufficient gravity to pull itself into a spherical shape. This picture was taken in 2010 by the Cassini spacecraft.

The Gentle Reader may make his own moon-not-a-space-station or AT&T-naming-rights jokes.

Image Credit: NASA


HyperionHyperion is one of Saturn’s moons. It is named for one of the Titans who was the Greek god of watchfulness and observation and the older brother of Cronus. Saturn was the analog of Cronus in Roman mythology.

Hyperion is one of the largest irregularly shaped bodies in the Solar System, and it rotates chaotically, tumbling unpredictably as it orbits Saturn. That made it  challenging to target a specific region of the moon’s surface for observation by the Cassini spacecraft, and most of Cassini‘s approaches saw the same side of the craggy moon. The view above is from a closest encounter in 2005.

BTW, the first time I saw this picture, I was reminded of a wasps’ nest.

Image Credit: NASA

B and C in False Color UV

RingsInUVOn 1 July, 2004, the Cassini spacecraft arrived at Saturn, marking the end of the spacecraft’s nearly seven-year journey through the solar system and the beginning of its tour of Saturn and the planet’s rings and moons.

This picture was taken in ultraviolet on 30 June, 2004 during Cassini’s orbital insertion maneuver. It shows, from left to right, the outer portion of the C ring and inner portion of the B ring which begins a little more than halfway across the image. The “dirty” particles are indicated by red, and “cleaner: ice particles shown in turquoise.

Saturn’s ring system is labeled from the inside out with the D, C, B and A rings followed by the F, G and E rings.

Image Credit: NASA

That’s No Space Station. It’s a Moon.

TethysSaturn’s moon Tethys’s trailing side shows two terrains that tell a story of a rough past. To the north (up in this picture) is older, rougher terrain, while to the south is new material dubbed “smooth plains” by scientists. The smooth plains are roughly antipodal to the large impact crater Odysseus. Odysseus, which is on the far side of Tethys, is out of view. The leading theory is that the impact that created Odysseus also created the smooth plains, although exactly how this happened is not yet clear.

Image Credit: NASA

A Speck in the Corner

Saturn & TethysAt 116,500 km across, Saturn is roughly 10 times the diameter of Earth. The planet is much larger in relation to its moons than our Earth to its Moon. Saturn’s moon Tethys (which is a bit more than 1,000 km in diameter and could be counted as a dwarf planet it orbited the Sun by itself) can be seen as a speck in the lower right of the picture.

Image Credit: NASA

A Lunar Lineup

Enceladus_Tethys_bullseyEnceladus and Tethys line up almost perfectly in this shot from the Cassini spacecraft. Since the two moons are not only aligned, but also at nearly the same distance from Cassini, their apparent sizes are a reasonable approximation of their relative sizes. Enceladus is 504 km across, and Tethys is 1,062 km in diameter.

Image Credit: NASA

You Can’t See This From Here

South Pole via CassiniThis view of Jupiter as seen from space above its south pole was constructed from images taken during the Cassini spacecraft’s flyby on the way to Saturn. When I first published this image in 2014, it was a rare view of Jupiter. Since then, the Juno spacecraft has been orbiting Jupiter and sending back views from almost every possible angle.

Image Credit: NASA

A Pair of Moons

Dione_EnceladusAlthough Saturn’s moons Dione (in the foreground) and Enceladus are made of more or less the same stuff, Enceladus has a considerably higher reflectivity than Dione. Therefore, it appears brighter against the blackness of space.

Enceladus has a constant rain of ice grains from its south polar jets which cover its surface with a bright snow. Dione’s older, weathered surface has slowly gathered dust and radiation damage, darkening through a process known as “space weathering.”

Image Credit: NASA

Look Closely, You’re In This Picture

Click the image to embiggen it. No, really, do it, and click on the new image a second time. You can use your BACK button to return.saturn_full_annotated

On 19 July, 2013,  the Cassini spacecraft slipped into Saturn’s shadow and turned to image the planet, seven of its moons, its inner rings,and—in the background—Earth.

With the Sun eclipsed by Saturn, Cassini‘s cameras were able to take advantage of this unusual viewing geometry. A panoramic mosaic of the Saturn system was taken that allows details in the rings backlit by the sun to be seen. This event was the third time Earth was imaged from the outer solar system.

Cassini captured 323 images in just over four hours. This final mosaic uses 141 of them. Images taken using the red, green, and blue spectral filters of the wide-angle camera were combined to create this natural-color view. This image spans a bit more than 650,000 km.

Make sure you embiggen it and scroll around.

Image Credit: NASA

Titan and Tethys

converted PNM fileSaturn’s moon Tethys with its prominent Odysseus Crater seems to lurk behind Saturn’s largest moon Titan in this image taken by the Cassini spacecraft in 2014.

The Titans were the pre-Olympian gods in Greek mythology. Tethys was a Titan daughter of Uranus and Gaia, sister and wife of the Titan Oceanus, and mother of the river gods and the Oceanids

Image Credit: NASA

Crescent Saturn

On Earth we never see Saturn in a crescent phase because it is farther from the Sun than Earth, and it is always fully illuminated from our point of view. The Cassini spacecraft’s orbits around the planet allowed its cameras to see Saturn in ways not possible from Earth.

Image Credit: NASA

Io and Jupiter

In Greek mythology Io was a priestess of Hera (Zeus’ wife) and a nymph who was seduced by Zeus. He changed her into a heifer to escape detection. Io is also the name of the innermost of the four Galilean moons of the planet Jupiter. The most volcanic body in the Solar System, Io is 3,600 kilometers in diameter, about the size of planet Earth’s moon.

While cruising past Jupiter at the turn of the millennium, the Cassini spacecraft captured this view of Io with Jupiter as a backdrop–offering an impressive demonstration of the ruling planet’s relative size. (An astronomer from another star system would probably describe our solar system as having one main planet and assorted debris.) Although Io appears to be located just in front of the swirling Jovian clouds, Io is about 350,000 km above Jupiter’s cloud tops. That’s roughly the same as the distance between Earth and Moon. The Cassini spacecraft itself was about 10 million km from Jupiter when this picture was taken.

Image Credit: NASA

Herschel Crater

Herschel Crater is 130 km wide, covering a large portion of Saturn’s moon Mimas. The moon itself is only 396 km wide.

The dayside terrain seen here is on leading hemisphere of Mimas. North on Mimas is up and rotated 1 degree to the left in this image which was taken in visible light by the Cassini spacecraft in 2010.

Image Credit: NASA

You Can’t See It From Here

Crescent SaturnThis is a view of Saturn partially lit in crescent phase, a view that can only be seen when the object is between the observer and the Sun. From the Earth, we can only see Mercury and Venus in varying crescent phases and Mars and the other outer planets fully lit. Because the Moon can be either between the Earth and the Sun or farther away, we see it go through all the phases from New to Full to New again.

This picture of Saturn was made by the Cassini spacecraft.

As the data download from New Horizons proceeds, we should soon have pictures from an similar point of view of the Kuiper Belt Object Ultima Thule.

Image Credit: NASA

Moar Science from Cassini

As the Cassini spacecraft was running out of fuel for the thrusters used to maintain control of its attitude so that it could point it instruments at the desired targets and its antenna toward Earth so send back data, it was placed in a series of Grand Finale orbits that took it between Saturn’s rings and the planet’s upper atmosphere. Eventually, an orbit was low enough that the spacecraft burned up in the upper atmosphere. It will take years to go through all the data, but papers are beginning to be published with findings from the Grand Finale. Interesting findings include an electric current that flows between the rings and the upper atmosphere and organic compounds falling as “rain” from the rings. There’s more interesting stuff here. Go take a look.

Image Credit: NASA

The Dust Storms of Titan

Analysis of data taken by the Cassini spacecraft appears to show giant dust storms on Saturn’s moon Titan. Titian is the second largest moon in the Solar System (Jupiter’s moon Ganymede is slightly bigger.); it’s even lager than the planets Mercury and Pluto (Pluto is still a planet in the Hogewash! universe.). Titan is the only other body in the Solar System beside Earth that has stable surface liquid, hydrocarbons rather than water. If the dust storms are really occurring, it would join Earth and Mars as the only known bodies in the Solar System with dust storms.

The animation above is based on images captured by Cassini mission during several Titan flybys in 2009 and 2010. The bright spots that have been interpreted as evidence of the dust storms.

There’s more information about this at the NASA website.

Image Credit: NASA