Titan is the only moon in the solar system with a thick atmosphere, and the only world besides Earth known to have lakes and seas on its surface. However, with a frigid surface temperature of around -290° F (94 K), the rain falling on Titan isn’t water. It’s liquid methane and ethane, compounds that are gases at room temperature on Earth.
Most of Saturn’s moons display their ancient faces pockmarked by thousands of craters. Titan, Saturn’s largest moon, looks younger than it really is because its craters are being eroded. Radar observations by the Cassini spacecraft show that dunes of hydrocarbon sand are filling in the craters.
This image taken with the Cassini radar shows two craters on Titan. On the left is crater Sinlap which is a relatively ‘fresh’ crater, with a depth-to-diameter ratio similar to is found on other large moons in the solar system such as Ganymede. One the right is Soi, an extremely eroded crater with a very small depth compared to similar craters on Ganymede. These craters are both about 80 km (almost 50 miles) in diameter.
This snapshot was taken by the Cassini spacecraft. The small moon that seems to be hovering over Saturn’s rings is Janus. It’s only about 180 km across. The larger moon is Rhea, which is around 1500 km across. Saturn’s thin outer F ring is visible in front of Rhea, and the top of the moon is visible between the larger A and B rings.
Well, you are if you’re over 15 years old. Back in 2006, the Cassini spacecraft orbiting Saturn drifted in giant planet’s shadow and looked back toward the eclipsed Sun. Saturn’s rings lit up so much that new rings were discovered, although they are hard to see in this image. Saturn’s E ring, the ring created by the newly discovered ice-fountains of the moon Enceladus and the outermost ring visible above, does show up in vivid detail. Far in the distance, at about 10 o’clock on the left, just above the bright main rings, is the almost ignorable pale blue dot of Earth. You may have to click on the image to embiggen it in order to see the Earth.
The Cassini spacecraft snapped this picture of the moon Dione orbiting Saturn. At 1122 km in diameter, Dione is the 15th largest moon in the Solar System. Its interior is probably a combination of equal masses of silicate rock and water ice.
Shape and gravity observations collected by Cassini suggest the moon has a core of around 400 km of rock surrounded by a roughly 160 km envelope of water, probably in the form of ice. However, some models suggest the lowermost part of this layer could be in the form of an internal liquid salt water ocean.
These two natural color images taken by the Cassini spacecraft show how Saturn’s north polar region has changed between 2012 and 2016. The color change is thought to be an effect of Saturn’s seasons. It’s believed that the change from a bluish color to a more golden hue is caused by the increased production of smog in the atmosphere as the north pole approached the summer solstice due in May, 2017.
The hexagon, Saturn’s six-sided jetstream, seems to act as a barrier preventing haze particles produced outside it from entering. If that’s the case, the polar atmosphere becomes clear of aerosols produced by photochemical reactions, reactions caused by sunlight, during the winter darkness. After Saturn’s northern spring equinox, the north pole polar is in continuous sunshine, and smog aerosols can be produced inside the hexagon, making the polar atmosphere appear hazy.
This picture is a mosaic of nine images taken by the Cassini spacecraft four years ago, just days before in was do-orbited into Saturn’s atmosphere. We won’t be able to view Saturn’s night side again until we again get another spacecraft to the planet’s far side.
This is the Earth-Moon system as seen by the Cassini spacecraft orbiting Saturn in the outer Solar System. Earth is the larger of the two spots near the center; the Moon is to its lower left. This raw, unprocessed image shows several streaks that are not stars. They are cosmic rays that struck the digital camera while it was taking the picture.
In 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.
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.
Hyperion 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.
On 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.
Saturn’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.
At 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.
Enceladus 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.
This 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.
This beautiful picture of Saturn from the Cassini mission was taken several years ago during winter in Saturn’s northern hemisphere. The tilt of the planet’s axis causes the Sun to cast shadows on the winter hemisphere.
Although 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.”
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.
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.
Pan is the innermost moon of Saturn that has been given a name. It’s walnut-shaped, approximately 35 km across and 23 km wide. It’s orbit is in the Encke Gap of Saturn’s A Ring. Pan is one of the rings’ shepherd moon, and it sweeps the Encke Gap free of ring particles.
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.
The Cassini spacecraft did a flyby of Jupiter on its way to Saturn. During that pass by the gas giant, it took this picture of the moon Io. The planet and the moon appear deceptively close in this image, but Io is orbiting 217,000 miles above the planet.
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.