Saturn

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Saturn

In 1977, two spacecraft were launched on a journey that would take them to the outer reaches of the solar system. Voyager 1 and 2 were designed to

make studies of Jupiter and Saturn, their satellites, magnetospheres, and the interplanetary medium.

Three years later, Voyager 1 arrived at Saturn, sending back detailed images of the planet and its mysterious moons. This was followed a year later

by the equally prolific Voyager 2.

Much of what is known about the planet is due to these two venerable spacecraft.

Voyager 1 image of Saturn and

three of its moons taken from a

distance of 106 million km.

Saturn is 74,000 miles in diameter.

Enceladus

Dione

Tethys

Like the inner planets and Jupiter, Saturn is clearly visible in the night sky.  

While it is not nearly as bright as Jupiter, it is easy to identify as a planet because it

doesn't "twinkle" like the stars do.

The rings and the larger satellites are visible with a

small astronomical telescope

Mercury

Venus

EarthMars

Jupiter

Saturn

Uranus

Neptune

The Solar System

The Saturn we know is an intriguing planet for many

reasons. It is the sixth planet from the Sun and is the second

largest in the solar system.

It was the most distant planet known to man before the

development of the telescope, and is known to have over 30

satellites.

It has a similar visible appearance to Jupiter, with

alternating light and dark cloud bands, known as zones and

belts respectively.

Vital statistics

Diameter (equatorial) 75,000 miles

Diameter (polar) 67,000 miles

Mass 95 times that of Earth

Volume 764 times that of Earth

Surface Gravity 1.2 times that of Earth

Temperature at cloud tops -180 oC

Saturn was formed four billion years ago and is made up mainly of gas.

It is also the only known planet that is less dense than water, meaning that if it could be placed inside a

giant ocean, it would float.

Saturn is visibly flattened at the poles when viewed through a small

telescope.

Its equatorial and polar diameters vary by almost 10%. This is the

result of its rapid rotation and fluid state.

The other gas planets are also oblate, but not as much.

Its day is 10 hours, 39 minutes long, and it takes 29.5 Earth years to

revolve about the Sun.    

But what sets Saturn apart from the rest of the planets in the solar system

are its picturesque rings. There are hundreds of these rings, believed to be pieces of shattered comets, asteroids or moons that broke apart before they

reached the planet.

‘B’ Ring

‘A’ Ring

Cassini Division

Saturn’s Main Rings

While the dramatic appearance of Saturn stems mainly from the spectacular rings, the atmosphere looks much less dramatic.

It is primarily composed of hydrogen with small amounts of helium and methane.

Contrast is also muted by an overlying haze layer. The white clouds are composed of ammonia particles, and the other colours are generated through dynamical and photochemical reactions in the atmosphere

High Altitude Clouds

Saturn's atmosphere

. Saturn's atmosphere is just as fierce as that of Jupiter.

The wind blows at high speeds mostly in an easterly

direction, and reaches velocities of 1,100 miles an

hour near the equator.

The clouds of Saturn are contain sulphur which adds to

Saturn's overall yellow appearance.

Probably the most dramatic features witnessed in the atmosphere are the great

white spots which break out at roughly 30 year intervals, and

were last seen in 1990.

Mysterious Brown Cloud

Other stable clouds of various colours have been

observed in the atmosphere, reminiscent of the great red

spot on Jupiter.

This unique red oval cloud feature is visible in Saturn's

southern hemisphere.

The difference in color between the red oval and

surrounding bluish clouds indicates that material within

the oval contains a substance that absorbs more blue and violet light than the

bluish clouds.

The white clouds are ammonia ice crystals that form when an upward flow of warmer gases

shoves its way through Saturn's frigid cloud tops.

Storm on Saturn

This image shows a rare storm that appears as a white arrowhead-shaped feature near the planet's

equator.

The east-west extent of this storm is equal to the

diameter of the Earth.

The storm's motion and size have changed little

since its discovery in 1994.

Hydrogen gas

Liquid hydrogen

Metallic hydrogen

Water, methane

and ammonia iceRocky ice

Saturn’s

Interior

The atmosphere of Saturn is only a narrow region compared to its vast interior, illustrated in this diagram. The outer layer is primarily composed of molecular hydrogen, which liquefies as we go deeper. As the pressure increases, hydrogen changes into a new metallic state, resembling a molten metal. Below this is a soupy layer of water, methane, and ammonia

under high temperatures and pressures. Finally at the center is a rocky-ice core, about the size of the Earth. The core is very hot, about 12,000oC, and the planet radiates more energy

Solar Wind

BowShock

Magnetosheath

Magnetopause

Neutral sheath

Trapping region

Lobes

Cusp

Motions in the interior of Saturn contribute to the development of the powerful and extensive magnetosphere. This is the magnetic field surrounding the planet,

containing charged particles.

The magnetosphere represents an obstacle to the solar wind, which is forced to flow around it, compressing the upstream side while dragging the downwind side

into an extended tail.

Aurorae

Aurorae are produced when

charged particles in the magnetosphere collide with gases in

the upper atmosphere

Saturn's magnetosphere produces beautiful aurora, as well as strong radio signals and other waves, known as whistler waves. This Hubble image is the first ever taken of bright aurorae at

Saturn's northern and southern poles.

The aurora is produced as trapped charged particles precipitating from the magnetosphere collide with atmospheric gases. As a result of the bombardment, Saturn's gases glow at far-ultraviolet

wavelengths. Here we see a circular band centered on the north pole, where an enormous auroral curtain rises as far as 1,200 miles above the cloud tops. This curtain changed rapidly in brightness

and extent over the two hour period of Hubble observations

For centuries, Saturn and its rings puzzled

observers, in particular, Italian

astronomer Galileo Galilei.

The first to use a telescope to explore the wonders of the heavens, Galileo

couldn't understand why Saturn looked

different in the night sky at varying times -

a phenomenon that we now know is caused by the shifting of our

view of the ring plane.

1996

1997

1998

1999

2000

The changing face of Saturn

The Hubble Space Telescope captured Saturn on May 22,

1995 as the planet's magnificent ring system

turned edge-on. This ring-plane crossing

occurs approximately every 15 years when the Earth

passes through Saturn's ring plane.

Disappearing Rings

Saturn's rings are extraordinarily thin: though they're 150,000 miles or more in diameter, they are less than one mile thick. When the rings face Earth edge-on they are virtually invisible. They seem to reappear months later when our angle of view

changes.

Close up of Saturn's rings.

Saturn's ring system makes the planet one of the most beautiful

objects in the solar system.

Saturn's rings, unlike the rings of the other planets, are very

bright.

Though they look continuous from the Earth, the rings are

actually composed of innumerable small particles each

in an independent orbit.

They range in size from a centimeter or so to several

meters. A few mile -sized objects are also likely.

A Ring

B Ring

C Ring

F Ring

(barely visible)

Cassini Division

(separates the A and B rings)

Encke Division(splits the A ring in two)

The rings are split into a number of different parts,

which include the bright outer A and B rings and a fainter

inner C ring. .

The ring system has various gaps. The most notable gap, separating the A and B rings,

is the Cassini Division, discovered by another Italian astronomer, Giovanni Cassini

in 1675.

The ‘C’ ring

Here we take a closer look at the inner C ring. Despite its impressive

appearance, there's really very little material in the rings.

If all the rings were compressed into a single round body it would be no

more than 50 miles across.

The ring particles seem to be composed primarily of water ice, but they may also include rocky particles

with icy coatings

The B ring was observed by amateur astronomers to contain radial, spoke-like features. The

features are believed to be composed of fine, dust-size particles.

The spokes were observed to form and dissipate in the time-lapse images taken by the Voyagers. While the spokes may be dust particles raised

above the ring by electrostatic charges, the exact cause of their formation is unknown.

The ‘B’ ring

The‘A’

ringThis is a view of Saturn’s broad outer

A ring, and the narrow Encke Gap that divides this ring into two parts.

The origin of Saturn’s rings is obscure.

It is thought that the rings may have been formed from larger moons that were shattered by impacts of comets

and meteoroids.

Saturn's outermost ring, the F-ring, is a complex structure made up of several smaller rings along which "knots" are

visible. Scientists speculate that the knots may be clumps of ring material, or mini moons. Much of the elaborate structure

of some of the rings is due to the gravitational effects of nearby satellites.

This phenomenon is demonstrated by the relationship between the F-ring and two

small moons that shepherd the ring material

The ‘F’ ring

Saturn and some of its satellites

Titan

DoineRhea

Enceladus

Mimas

Iapetus

Saturn has 18 named satellites and more than a

dozen newly reported satellites that have been

given provisional designations until they are

verified and named.

Mimas

Enceladus

Thethys

Dione

Rhea

Titan

Iapetus

Major moons of Saturn

showing size and position

Some are icy moons and resemble the three outer Galilean satellites. The others are small

moons and resemble large rocks in space. The moon Titan is one of the few moons in the solar

system with a significant atmosphere.

Other unusual moons of Saturn include the "Death Star" shaped Mima, the half-black, half-white

Iapetus, and the garbage-can shaped Hyperion.

We will now take a closer look at some of these interesting objects, starting with the closer ones

then moving outwards.

Mimas

Mimas, the innermost of Saturn’s larger moons, was nearly shattered by a cataclysmic impact.

From observing Mimas' crater Herschel,

scientists speculate that the inner satellites of the

outer planets have, in fact, been shattered and

gravitationally reassembled many

times in their geologic history

Some regions of Enceladus show impact craters up to 22 miles in diameter, whereas other areas are smooth and

uncratered.

Linear sets of grooves tens of kilometers long traverse

the surface and are probably faults resulting from

deformation of the crust.

The uncratered regions are geologically young and

suggest that Enceladus has experienced a period of relatively recent internal

melting.

Enceladus

Tethys' surface is composed of densely cratered regions and a lightly cratered, dark belt that extends across the

satellite. Light cratering indicates that

the region was once internally active early in

Tethys' history and resurfaced part of the older

terrain. Ithaca Chasma, an enormous trench that is 40 miles wide

and several miles deep, runs parallel to the terminator at

the right.

Thethys

Dione

This image of Dione shows the Saturn-

facing hemisphere. The darker trailing

hemisphere is located toward the right limb,

with wispy white streaks crisscrossing the surface. The plains terrain is located along

the terminator.

Rhea

The heavily cratered surface attests to the satellite's ancient age.

The craters and landscape resemble those on the Moon and Mercury, and are

unlike the flattened crater forms that have collapsed in the soft icy crusts of

the Jupiter’s moons.

Scientists believe that Rhea froze and became rigid, behaving like a rocky

surface, very early in its history.

Titan

Titan is the largest moon of Saturn and the second largest moon in the solar system, rivaled only by Jupiter's moon Ganymede. It has a planet-like atmosphere which is

more dense than those of Mercury, Earth, and Mars.

Titan's air is predominantly made up of nitrogen with other hydrocarbon elements which give Titan its orange hue. These hydrocarbon rich elements are the building

blocks for amino acids necessary for the formation of life.

Scientists believe lakes of ethane exist that contain dissolved methane. Titan's methane, when combined with nitrogen, forms hydrogen cyanide, an important

building block of amino acids.

Visible CompositeInfra-red

The leading hemisphere of Iapetus

is covered by extremely dark material, whereas the trailing hemisphere is covered with bright material. Two models

have been proposed to explain this. The first proposes that dark

material from Phoebe, a dark exterior moon,

falls onto Iapetus from orbit. The second

model says that the dark material erupted

from the interior of Iapetus into a low area

in the leading hemisphere.

Iapetus

Pan

This image shows the small

moonlet Pan located within Saturn's Encke

gap.

Nearest moon

Pandora

Prometheus

Shepherd MoonsPrometheus is located on the inner edge of Saturn's F Ring.

The moon is extremely elongated about 90 by 53 by 39

miles in diameter.

Pandora is located on the outer side of the F Ring, and is

more heavily cratered than  Prometheus,

Prometheus and Pandora act as shepherd satellites for the inner edge of the F Ring, preventing it

from dispersing.

The inner moon moves faster and speeds up any slow

particles that may fall inwards, while the outer moon moves more slowly, and drags any

escaping particles back into the ring.

Minor moons Atlas

Calypso

Hyperion

Telesto

Phoebe

Janus

Epimetheus

Helene

Atlas, the second nearest of Saturn's known satellites, orbits near the outer edge of the A-ring and is probably a shepherd satellite for this ring. It is about 25 by 15 miles in size.

Telesto and Calypso are called the Tethys Trojans because they circle Saturn in the same orbit as Tethys, about 60 degrees ahead of and behind that body. Telesto is the leading

Trojan and Calypso is the trailing Trojan. Epimetheus is the fifth satellite of Saturn , with an irregular shape about 90 miles in diameter.

In 1997, the Cassini spacecraft was launched for a rendezvous with Saturn in

June 2004.

Cassini- Huygens Spacecraft

The spacecraft completed a four-year tour of the ringed

planet, its mysterious moons, the stunning rings, and its complex magnetic

environment.

On December 25, 2004, the Huygens probe separated from the orbiter and made a

descent into Titan's atmosphere, and downwards to

the surface, This was the first landing ever accomplished

in the outer solar system.

Huygen's eventual landing site was in the large dark area below, just right of the center.

This relatively featureless, dark, sandy basin appears to

be surrounded by light colored hills to the right and a landscape fractured by streambeds and

canyons above. 

Recent evidence indicates that Titan's lakebeds and

streambeds are usually dry but sometimes filled with a

flashflood of liquid methane from rare

torrents of methane rain.  

Last view of Saturn

Gerry Barrow

Two days after its encounter with Saturn, Voyager 1 looked back on the planet from a distance of more than 3 million

miles. This view of Saturn has never been seen by an earth based telescope, since the earth is so close to the Sun that

only its sunlit face is ever seen.