Near-Earth Space:
The Van Allen Belts
Nature of the Belts
• Discovered early in the
space age with a Geiger
counter.
• Energetic charged particles
are trapped in the Earth’s
magnetic field.
• The inner belt contains
protons, and the outer
contains electrons.
• The inner belt begins at
only 100 km or so above
ground.
Aurorae
Space Aurora
Aurora Borealis from
Yellowknife in Canada
Aurorae
• Solar wind particles are generally repelled
by the magnetosphere, but some “sneak”
into the atmosphere by running along
magnetic field lines toward the poles.
(Outer belt)
• Earth atmospheric particles sneak into the
belts as well. (Inner belt)
• At ~100km altitude, solar wind particles
collide with atmosphere particles to
produce an auroral light display.
Comparison of
Planetary Magnetic Fields
Equatorial Field
(Gauss)
Mercury
0.002
Venus
<0.0003
Earth
0.305
Mars
(0.0004)
Jupiter
4.2
Saturn
0.20
Uranus
0.23
Neptune
0.06-1.2
The space around the Earth is not
exactly crowded, but there is a
great deal of “space debris” in
orbit around Earth.
Cosmic Rays: The penetration of energetic particles from
space into the Earth’s atmosphere
The Earth at Night (light pollution)
Sky Appearance
Understanding Sky Color
Sky Color from Two Places
Structure of the Earth’s Atmosphere
The Ozone Layer Component
Antarctic Ozone Hole
Ozone Layer
Ozone molecule = O3
O3 protects use from harmful solar UV radiation
An efficient O3 destruction mechanism involves
chlorofluorocarbons (CFC’s – Cl, F, C):
<chemistry> …
Catalyst
A single Cl atom can be used 1000’s of times to break up
ozone molecules!
Ozone Trends
North Pole
South Pole
Energy Budget of the Earth
Global Warming: Trends and Effects
• The topic of global warming is complicated. The question is
not whether warming exists, but its origin.
• Increased greenhouse gases (carbon dioxide, methane, etc)
act like a blanket to block the escape of infrared “heat” light.
• The Earth has also undergone cycles in the past.
• The main concern is the impact and control of warming.
Climate Regulation
Share Question
The Earth's surface absorbs energy from sunlight and
then radiates about as much energy back into space. The
best proof you can offer for this fact is that the average
surface temperature on Earth is
a) warming slowly.
b) not warming rapidly.
c) half light and half dark.
d) warmer at the core than on the surface.
Weather
Primarily driven by solar radiation.
Other significant influences include:
1. Land mass and oceans
2. Planet rotation
3. Atmospheric composition
o Ozone
o Greenhouse effect
4. Volcanic activity
The Hadley Cell: Fundamental circulation pattern
because of the fact that planets are round.
Coriolis Deflection: Planet rotation causes north-south
weather circulation to deflect east-west.
The Coriolis Force
Hadley Cells on the Earth
Volcanoes and Resurfacing
• Magma is less dense than rock, and so
rises from the interior
• This breaks through, giving a volcano
• Products
– New rocks (esp. basalts)
– Ash ( ~1mm )
– Cinders (~ 1cm )
• The key point is that volcanoes lead to
resurfacing and are evidence of an active
planetary interior
Mount St. Helens
Tungurahua (Andes)
Rock Types
Igneous (“ignus”=fire) Sedimentary - formed by
deposition of small
form from crystallization
particles which become
of molten rock
cemented (e.g.,
– Magma - molten inside
sandstone, shales)
earth
– Lava - molten on
Metamorphic - changed by
surface
heat, pressure, and/or
* Of planetary interest:
chemistry (e.g., marble)
– Basalt - fast cooling
– Granite - slow cooling
Crustal Plates and Tectonic Activity
• Earth’s surface (or crust) is not a single
solid piece, but consists of large and small
“plates”
• These plates slowly drift around
• At points of convergence, get volcanoes,
mountain ranges, and earthquakes
Crustal Plates
Long Term Plate Drifting
Plate Motion
Volcanic Activity on Earth
and Relation to Motion of
Plates
Recycling process and resurfacing
effects
Interior Structure of the Earth
Detail of Earth Interior
Seismology
Study of the Earth’s interior from how it carries
vibrations
• Types of vibrations
– P-waves: pressure waves that travel like sound
– S-waves: shear waves, like on a rope
• Terminology:
– Focus: point at which the earthquake originates
– Epicenter: surface point above the focus
– Seismometer: a device to measure P & S waves and
the strength of earthquakes
Earthquake
Wave Forms
Refraction of traveling sound waves
in the Earth reveals its components
Shuddering of the Earth
Share Question
Earthquakes are an important tool for scientists because
their vibrations
a)
b)
c)
d)
influence the Earth's orbit about the Sun
allow the study of the Earth's internal structure
inform us of the mass of the Earth
are used to predict the future of plate tectonics
Earth’s Magnetic Field
• Lines of force are somewhat like a bar magnet.
• Its origin and maintenance comes from dynamo
activity in the core:
Circulation of conducting fluid (e.g., molten
metals) generates magnetic fields.
So, planetary magnetic fields act like probes of
unseen planetary interiors
Earth Dynamo
Share Question
The Earth's magnetic dynamo is caused by a combination
of convection in its molten core and
a)
b)
c)
d)
the Earth's orbit around the Sun
the Earth's rotation
lunar tidal action
the aurora borealis