Saturn and Some of Its Moons


The animation shows the orbits of Saturn’s visible moons Tethys, Janus, Mimas, Enceladus, and Rhea over the observing run in June, 2019 (with elapsed time bar).

Video Credits: NASA / ESA / A. Simon (Goddard Space Flight Center) / M.H. Wong (University of California, Berkeley) / J. DePasquale (STScI)

Odysseus


Don’t worry. It’s a moon, not a space station.

It’s Saturn’s icy moon Tethys. The enormous impact created the crater is named Odysseus. The crater is about 450 km across surrounded by a ring of steep cliffs and and has a rang of mountains rising from its center. Tethys is only a bit over 1070 km in diameter.

This picture is a composite assembled from images taken in visible light with the Cassini spacecraft in 2015 when is was roughly 44,500 km from the moon.

Image Credit: NASA

Saturn, Rings, and Moons


Cassini snapped this picture with its narrow-angle camera. It shows Saturn and its rings seen here nearly edge on. The image also shows the moons Mimas (above the rings), tiny Janus (apparently almost in the rings), and Tethys (below the rings). “Above” and “below” the rings is a matter of perspective. All three moons and the rings orbit Saturn in roughly the same plane.

Image Credit: NASA

Saturn and Tethys


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

Bullseye


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

Tethys Eyes Saturn


Tethys and SaturnIn this picture taken by the Cassini spacecraft last April, 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

Odysseus


Tethys with craterOdysseus is the name of the huge crater on Saturn’s moon Tethys. Tethys is a bit more than 1000 km in diameter, and the crater is roughy 450 km across. To put that into scale, a crater that covered the same percentage of the Earth’s surface would be about the size of Africa.

Image Credit: NASA

Three Moons


3MoonsThe Cassini spacecraft has sent us this family photo of three of Saturn’s moons that are different from each other. The largest of the three, Tethys is round and has a variety of terrains across its surface. Hyperion (to the upper-left of Tethys) is the “wild one” with a chaotic spin, and Prometheus (lower-left) is a tiny moon that busies itself shepherding the F ring.

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

Tiny Tethys


Tiny_TethysSaturn’s rings appear to dwarf Tethys (1,062 km or 660 mi across), which appears as a small dot at the upper left edge of the picture, although astronomers believe the moon is probably many times more massive than the entire ring system combined. This view looks toward the unilluminated side of the rings from about 18 degrees below the ringplane. The image was taken in green light with the Cassini spacecraft wide-angle camera in August, 2012. The view was acquired at a distance of approximately 2.4 million km (1.5 million mi) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 63 degrees. If you click on the image to embiggen it, the scale is 138 km (86 mi) per pixel.

Image Credit: NASA

Tethys and the Rings


We have no idea how old Saturn’s rings are. One possibility is that the rings were formed relatively recently in our Solar System’s history. It could be that only 100 million or so years ago a moon-sized object broke up near Saturn. One bit of evidence for young rings is the fact that the rings are so bright and relatively unaffected by numerous small dark spots caused by meteor strikes. However, a recent discovery raises the possibility that some of Saturn’s rings could be billions of years old—almost as old as Saturn itself. Inspection of images taken by the Saturn-orbiting Cassini spacecraft indicates that some of Saturn’s ring particles temporarily bunch and collide, effectively refinishing the surfaces of the ring particles by uncovering fresh bright ices. This picture taken by Cassini shows Saturn’s rings in their true colors. Tethys, one of Saturn moons, is visible in front of the darker rings.

Image Credit: NASA

Titan and Tethys


The Cassini spacecraft snapped this picture of a pair of Saturn’s moons, giant Titan beyond smaller Tethys. This view looks toward the Saturn-facing sides of the moons. Titan is about 5,150 km in diameter,  and Tethys is roughly 1,060 km across.

This picture was taken in visible green light with the spacecraft’s narrow-angle camera on in October, 2010. Titan is about 2.5 million km (2.5 Gm) from Titan. Tethys is only about1.5 million km away. If you click on the picture to embiggen the image, the scale is 15 km per pixel on Titan and 9 km per pixel on Tethys.

Image Credit: NASA