Saturn (& friends)

1. Composition & Structure

2. Rings

3. Diversity of Moons

Overview

Saturn & Friends 3

Saturn has a mean density of 0.687 g/cm3, meaning it would float on water.

Though it is rather large, like Jupiter, it is not nearly as dense, because it has less overall mass. (recall the issue of compressibility for gas/fluids...mass can be added w/o drastically changing size)

Saturn takes about 29.5 years to orbit the Sun and is >760 times the volume of Earth.

In addition to its striking rings, Saturn is remarkable for its diversity of moons.

Saturn has 62 moons (Titan is largest) and numerous additional moonlets (not all are named).

Titan is larger than Mercury and accounts for most of the total mass of Saturn’s moons and rings.

Saturn 4

The core of Saturn may consist of ice and silicate rock at such a high temperature that it may be in a liquid state. Saturn does not have a well-defined solid surface (i.e., it’s a gas giant).

The internal structure of Saturn is believed to be similar to that of Jupiter and the other gaseous planets. A thin outer envelope of clouds covers a thick layer of hydrogen, which increases in density downward. A significant boundary is believed to exist at a depth of 30,000 km, where molecular liquid hydrogen converts to metallic liquid hydrogen.

Saturn 5

The blue colors indicate a clear atmosphere down to a main cloud layer. Different shadings of blue indicate variations in the cloud particles, in size or chemical composition. The cloud particles are believed to be ammonia ice crystals. Most of the northern hemisphere that is visible above the rings is relatively clear. The dark region around the south pole at the bottom indicates a big hole in the main cloud layer.

The green and yellow colors indicate a haze above the main cloud layer. The haze is thin where the colors are green but thick where they are yellow. Most of the southern hemisphere (the lower part of Saturn) is quite hazy. These layers are aligned with latitude lines, due to Saturn's east-west winds.

Saturn 6

The red and orange colors indicate clouds reaching up high into the atmosphere. Red clouds are even higher than orange clouds. The densest regions of two storms near Saturn's equator appear white. On Earth, the storms with the highest clouds are also found in tropical latitudes. The smaller storm on the left is about as large as the Earth, and larger storms have been recorded on Saturn in 1990 and 1994.

The rings, made up of chunks of ice, are as white as images of ice taken in visible light. However, in the infrared, water absorption causes various colorations. The most obvious is the brown color of the innermost ring. The rings cast their shadow onto Saturn. The bright line seen within this shadow is sunlight shining through the Cassini Division, the separation between the two bright rings. It is best observed on the left side, just above the rings. This view is possible due to a rare geometry during the observation. An accurate investigation of the ring's shadow also shows sunlight shining through the Encke Gap, a thin division very close to the outer edge of the ring system.

Cassini @ Saturn 7

Cassini @ Saturn 8

Saturn: The Atmosphere 9

As on Jupiter, Saturn’s atmosphere exhibits complex banding patterns related to circulation in the atmosphere.

There are numerous storms and they can combine together to form larger storms, which ultimately disappear, but nothing as dramatic as the Great Red Spot on Jupiter.

Saturn: The Atmosphere 10

Unlike Jupiter, the banding in Saturn’s atmosphere is not very obvious at visible wavelengths of light.

False-color images based on infrared wavelengths often provide a clearer view of the atmospheric structure, as depicted here.

Note the storms (bright spots) in the atmosphere, similar to features observed on Jupiter.

Saturn: The Atmosphere 11

Atmospheric Changes on Saturn

Saturn: The Atmosphere 12

Saturn has a storm ‘season’ that occurs once about every orbit around the Sun (that is, every ~30 years).

Cassini imaged it in 2010-2011 and it lasted significantly longer (~200 days) than any previously recorded storm.

Storm eventually dissipated when the head came around the planet and intersected the tail.

Saturn: The Atmosphere 13

Saturn: The Rings 14

The brightest part of the rings, curving from the upper right to the lower left in the image, is the B ring. Color variations in Saturn's rings have previously been seen in Voyager and Hubble Space Telescope images. Cassini's images show that color variations in the rings are more pronounced in this viewing geometry than they are when seen from Earth.

Saturn's rings are made primarily of water ice. Because pure water ice is white, it is believed that different colors in the rings correspond to different amounts of contamination by other materials (e.g., dust, rock or carbon compounds).

Saturn: The Rings 15

This false-color image acquired by the IR spectrometer on Cassini depicts temperature variations in Saturn’s rings. This image represents the most detailed look to date at the ring temperatures.

Red represents temperatures of about 110 Kelvin (-261°F), and blue 70 Kelvin (-333°F). Green is equivalent to 90 Kelvin (-298°F). (Recall that water freezes at 273 Kelvin).

The data show that the opaque regions of the rings, like the outer A ring (on the far right) and the middle B ring, are cooler, while more transparent sections, like the Cassini Division (in red just inside the A ring) or the inner C ring (shown in yellow and red), are relatively warmer.

The temperature data were taken on July 1, 2004, of the unlit side of the rings. In order to show the full breadth of the rings, a strip of temperature data was mapped onto a picture of the lit side of the rings taken with the Cassini narrow angle camera on May 11, 2004. Saturn is overexposed and pure white in this picture.

Saturn: The Rings 16

Radio and stellar occultations of the rings also provide important information about ring structure, but only along a one-dimensional track through the rings. The radial resolution can be as fine as 50 meters (164 feet). An "image" is then constructed by assuming circular symmetry over the ring region of interest. Color is usually added to encode other information related to the observed structure.

This image compares structure of Saturn's rings observed by these two approaches. In the lower image,the upper half is a natural color mosaic of images by the Cassini narrow-angle camera (see above image). The bottom image was constructed from a radio occultation observation conducted on May 3, 2005. Color in the lower image is used to represent information about ring particle sizes.

Saturn: The Rings 17

The figure on the left represents the density of particles in Saturn’s rings. This image depicts the number and sizes of particles in a cube of ring material that is 3 m on each side (27 m3).

Even when the material in a 3-dimensional cube is represented in this 2-dimensional image, there is a significant amount of empty space. This highlights the low concentration of material in Saturn’s rings.

Saturn’s C ring is 19,000 km wide and displays a regular ordering of light and dark bands in this false color image. Its inner edge is sharp (on the left) and well defined, whereas the outer boundary (right) is less distinct. The general pattern is from "dirty" particles indicated by red in the C ring to cleaner ice particles shown in turquoise in the B ring.  The B ring begins a little more than halfway across the image.

Saturn: The Rings

Credit: NASA/JPL-Caltech/Space Science Institute

Ring structures are quite complex and some rings exhibit very fine banding (several hundred feet across).

Moon Daphnis has been observed to create ‘waves’ in the ring structure due to gravitational interaction with ring particles (shown at left).

Cassini @ Saturn 19

Mosaic of images acquired during ~3 hour period in 2006 when Saturn blocks the Sun from view.

Image is color-enhanced to show details.

20

Phoebe

21

Phoebe

Iapetus

24

Mimas

Mimas

26

Dione

27

Hyperion

28

Rhea

29

Pandora

30

Calypso Epimetheus

HeleneJanus