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Chapter

Chapter Eleven Review: Jupiter


Department
Astronomy
Course Code
ASTA01H3
Professor
Brian Wilson

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October 26th, 2010
ASTA01H
Intro to Astronomy and Astrology Part I
Chapter Eleven: Jupiter
Orbital and Physical Properties
The View from Earth
Third brightest object in the night sky
In contrast to the terrestrial planets, Jupiter has many moons that vary
greatly in size and other properties
oThe four largest are known as the Galilean Moons, discovered in 1610
On Jupiter’s surface, there are alternating light and dark bands that cross the
planet parallel to its equator
oThese atmospheric features are unlike anything found on the inner
planets
Mass and Radius
Mass is   ξ€‚ξ€„ξ€…ξ€†ξ€‡ξ€ˆ or 318 Earth masses
oTwice the mass of all the other planets combined
As massive as Jupiter is it is still only 1/1000 the mass of the Sun
Its radius is 71,500 km or 11.2 Earth radii
Rotation Rate
Originally hard to determine since its β€œsurface features” are clouds in the
upper atmosphere, that are not attached to a solid surface and therefore
move independently of one another
Jupiter thus exhibits differential rotation – the rotation rate is not constant from
one location to another
oDifferential rotation is, therefore, obviously not possible in solid objects
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Charged particles that come into contact with Jupiter’s magnetic field rotate
at 9 hours and 55 minutes
oWe assume that this measurement matches the rotation of the planet’s
interior, where the magnetic field arises
This is a fast rotation period for such a large object
oThis rapid spin has altered Jupiter’s shape
This spin creates a bulge at the planet’s equatorial plane
This equatorial bulge tells us something important about the planet’s deep
interior:
oIf Jupiter’s core was composed of hydrogen and helium alone it would
be more flattened, therefore we must assume that it has a dense,
compact core, probably of rocky composition
The Atmosphere of Jupiter
Two dominant surface features:
oEver-changing atmospheric bands
oAn oval atmospheric blob called the Great Red Spot
Atmospheric Composition
Molecular hydrogen is the most abundant gas (86.1%)
Followed by helium (13.8%)
Small amounts of atmospheric methane, ammonia and water vapour
The abundance of Hydrogen and Helium is a direct consequence of Jupiter’s
strong gravity
oAs a result of gravity, not as much of these light-weight gases were
able to escape into space as is the case on the smaller terrestrial
planets
Atmospheric Bands
Described as a series of bright zones and dark belts crossing the planet
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oThese variations appear to be the result of convection motion deeper in
Jupiter’s atmosphere
The light-coloured zones lie above the upward-moving convection currents,
the dark belts are regions representing the other parts of the convection
cycle, during which material is generally sinking downward
oTherefore, the zones are high pressure regions; the belts, conversely,
are low pressure regions
The belts and zones are Jupiter’s equivalents of familiar high and low pressure
systems that cause our weather on Earth
oThe major difference being that Jupiter’s rapid rotation has caused
these systems to wrap all the way around the planet instead of forming
localized circulating storms
Underlying the bands, is an apparently very stable pattern of eastward and
westward wind flow, known as Jupiter’s zonal flow
The difference in altitude between the belts and zones (and therefore the
difference in temperature) are the reasons for the different colours of these
Jovian features
Atmospheric Structure and Colour
The colours of the clouds are the result of complex chemical processes
occurring in the planet’s turbulent upper atmosphere
oWhen we observe Jupiter’s different colours, we are actually looking
down to many different depths in the planet’s atmosphere
Since the planet lacks a solid surface to use as a reference level for
measuring altitude, the tops of the troposphere is conventionally taken to lie
at 0 km
Weather is the result of convection in the troposphere – weather layer in a
planet’s atmosphere – as is the case on all planets
Just above the troposphere lies a thin, faint layer of haze created by
photochemical reactions (reactions involving sunlight similar to those that
cause smog on Earth)
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