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Chapter

Chapter Twelve Review: Saturn

8 Pages
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Department
Astronomy
Course Code
ASTA01H3
Professor
Brian Wilson

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Nov. 2nd, 2010
ASTA01H
Intro to Astronomy and Astrology Part I
Chapter 12: Saturn
Orbital and Physical Properties
Overall Properties
Less than a third of the size of Jupiter
Composed primarily of hydrogen and helium like Jupiter
oSaturns lower mass, however, results in lower interior pressure, so these
gases are less compressed than in Jupiters case
Rotation Rate
Also rotates very rapidly and exhibits differential rotation
The planets core rotational period is 10 hours and 46 minutes
Because of Saturns lower density, its rapid rotation makes it even more flattened
than Jupiter
Rings
The rings are very thin, a few tens of meters, even though they are over 200,000 km
in diameter
Saturns Atmosphere
Much less colourful than Jupiter
oIe. Bands and storms do exist but colour changes that would distinguish them
on Jupiter a largely absent on Saturn
Composition and Colouration
Astronomers believe that Saturns relative lack of atmospheric helium, compared to
Jupiter, is a result of this heavier element sinking towards the planets core
www.notesolution.com
In many respects, Saturns atmosphere is quite similar to Jupiters, except that the
temperature is a little lower because of Saturns greater distance from the Sun and
because Saturns clouds are somewhat thicker (due to Saturns weaker gravity)
Saturns Atmospheric Layers:
oSince it lacks a solid surface we take the top of the troposphere as our
reference point and set it to 0 km
oAbove the clouds lies a layer of haze formed by the action of sunlight on
Saturns upper atmosphere
oAs on Jupiter, the clouds are arranged into three distinct layers, composed (in
order of increasing depth) of ammonia ice, ammonium hydrosulfide, and
water ice
oThe total thickness of the cloud layers being 200 km
Weather
Like Jupiters
Has lightning storms like those on Earth, however they are much more intense
oThought to be powered by convection and precipitation (both water and
ammonia rain)
Saturns Interior and Magnetosphere
Has the same basic internal parts as Jupiter, but their relative proportions are
somewhat different; Saturns metallic hydrogen layer is thinner and its core is larger
Internal Heating
Radiates more energy than it absorbs from the Sun, like Jupiter
oHowever, the source of this excess energy is different than in Jupiters case
oAt the temperatures and high pressures found in Jupiters interior, liquid
helium dissolves into liquid hydrogen; whereas on Saturn where the internal
temperature is lower, the helium tends to form droplets instead
oSaturn probably started out with a fairly uniform solution of helium dissolved
in hydrogen, much as water vapour condenses out of Earths atmosphere to
form a mist
www.notesolution.com
The amount of helium condensation was greatest in the planets cool
outer layers, where the mist turned to rain about 2 billion years ago
A light shower of liquid helium has been falling through Saturns
interior ever since
oThis helium precipitation is responsible for this excess heat, as well as
depleting the outer layers of their helium content (accounting for Saturns
relatively low amount of atmospheric helium compared with hydrogen
As the helium sinks toward the center, the planets gravitational field
compresses is and heats it up
The gravitational energy thus released is the source of
Saturns internal heat
Saturns Ring System
The View from Earth
Cassini Division: An apparent gap between ring bands (appearing as a black strip
in the more colourful sequence), with some ring material there, lies between the A
and B rings
Careful observation from earth show that the inner ring is in reality also composed
of two rings
oFrom the outside in, the three rings are known as the A, B, and C rings
oAnother gap in the sequence, the Encke gap, some 300 km wide, is found in
the outer part of the A ring
What Are Saturns Rings?
By the middle of the 19
th century, various dynamic and thermodynamic arguments
had conclusively proved that the rings could not be solid, liquid or gas
After showing in 1857, that a solid ring would become unstable and break up, a
Scottish physicist suggested that the rings are composed of a great number of small
particles, all independently orbiting Saturn
The objects that the rings are composed of it ice
The Roche Limit
www.notesolution.com

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Description
Nov. 2 , 2010 ASTA01H Intro to Astronomy and Astrology Part I Chapter 12: Saturn Orbital and Physical Properties Overall Properties Less than a third of the size of Jupiter Composed primarily of hydrogen and helium like Jupiter o Saturns lower mass, however, results in lower interior pressure, so these gases are less compressed than in Jupiters case Rotation Rate Also rotates very rapidly and exhibits differential rotation The planets core rotational period is 10 hours and 46 minutes Because of Saturns lower density, its rapid rotation makes it even more flattened than Jupiter Rings The rings are very thin, a few tens of meters, even though they are over 200,000 km in diameter Saturns Atmosphere Much less colourful than Jupiter o Ie. Bands and storms do exist but colour changes that would distinguish them on Jupiter a largely absent on Saturn Composition and Colouration Astronomers believe that Saturns relative lack of atmospheric helium, compared to Jupiter, is a result of this heavier element sinking towards the planets core www.notesolution.com
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