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Discussion
What causes the helmet shaped structures in the
corona? Why isnt the corona spread out
uniformly around the Sun?
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Coronal Mass Ejection
Giant magnetic bubbles that can hurl 5 to 50
billion tons of matter at speeds of 400 km/sec.
70 of coronal mass ejections are associated
with, or followed by, erupting prominences.
While 40 are accompanied by solar flares that
occur at about the same time and place.
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The Sun-Earth connection
Coronal mass ejections and solar flares can be
directed at Earth. Luckily for us, Earth has a
magnetic field and an atmosphere to protect us.
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Aurora
When high speed particles from the Sun collide
with atoms in Earths upper atmosphere. The
electrons are knocked into higher energy
orbitals and emit light when returning to the
ground state.
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Solar Wind
Although the Suns surface gravity is much higher
than the Earths, it is not able to contain
particles with a temperature on over a million K.
Thus the hot corona spews matter constantly (not
just during flares, CME, and explosive
prominences) into space at a rate of about 1
million tons per second.
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Terrestrial Planets
All the terrestrial planets are more or less
differentiated, i.e. the densest materials have
sunk to the core and the lighter materials have
floated to the surface. The terrestrial
planets were all completely molten at some time
in the past.
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Discussion
Why do you think all the terrestrial planets were
so hot in the past? Isnt space rather cold?
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Terrestrial planets interior structure
Core highest density material, mostly iron and
nickel Mantle high density silicate
rocks Crust lower density silicate rocks,
granite and basalt.
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Discussion
Whats a silicate? Give and example of a
silicate.
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Earths internal structure

• Solid crust 5 km thick under the oceans, made
  of basalt silicates of aluminum, magnesium and
  iron with a density of about 3.5 g/cm3. Under
  the continents the crust is 35 to 70 km thick and
  is made mostly of granite silicates of aluminum,
  sodium and potassium with a density of 3.0 g/cm3.
  The continents float on the basalt.

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2. Mantle solid, but top layer is plastic
called the asthenosphere. Is about 2800 km thick
and made of compounds rich in iron and magnesium.
Density increases from 3.5 g/cm3 at top to 5.5
g/cm3 near the bottom.
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3. Outer core liquid. Is about 2200 km thick
and is made of iron, nickel and sulfur. 4.
Inner core solid. Is about 1300 km thick and
is composed of nearly pure crystalline iron with
a density of 13 g/cm3.
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Why is inner core solid while outer core is
liquid?
Isnt the inner core hotter than the outer core?
The melting point of substance depends on both
temperature and pressure. In general, the
melting point goes up with pressure. The inner
core is hotter than the outer core but is under a
greater pressure and thus has a higher melting
temperature.
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Earthquakes

• Earthquakes produce three types of waves that
  travel through the Earth.
• Surface waves
• Primary waves, or P waves
• Secondary waves, of S waves

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Wave speed
The speed of seismic waves depends primarily on
the density of the material through which they
travel. If the density changes, the waves will
be refracted, just as light is refracted in a
glass lens.
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Discussion
Which type a wave do you think will travel better
through a liquid and why?
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Discussion
How do we know that the Earths inner core is
solid?
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Discussion
Study of seismic waves on Earth indicate that the
inner solid core is rotating faster than the rest
of the Earth. How do we know the core is
rotating faster?
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Discussion
What do you suspect would be the result of this
difference in rotation rate between the solid and
liquid cores?
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Planetary seismic data?
We know the internal structure of the Moon
because astronauts placed nuclear powered seismic
stations at the Apollo landing sites. But this
information is not available for any of the other
planets.
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Planets internal structure

• Two tools without seismic data
• Mean density
• Gravitational mapping mascons

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Density
Mass of the planet divided by the volume of the
planet. Higher density implies a larger
percentage of high density materials, such as
iron and nickel, lower density implies more
silicates.
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Mapping the gravitational field
By carefully tracking an orbiting space probe,
concentrations of denser materials below the
surface can be mapped. Space probes are
accelerated more toward higher density regions.
Also important for human exploration.
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Discussion
What do you think caused the terrestrial planets
to be completely molten in the past?
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How the planets got hot

• Heat of accretion
• Heat of differentiation
• Heat from radioactive decay

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Heat and planets
All the terrestrial planets started out hot and
have been losing heat over time by radiating it
into space from their surfaces.
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2nd law of Astronomy 201
Larger planets lose heat more slowly than do
smaller planets.
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Discussion
Dont larger planets have larger surface areas,
and with a larger surface area shouldnt larger
planets be able to radiate more energy into
space? So shouldnt larger planets cool faster?
Why doesnt this work?
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Geologic activity
Internal heat drives geologic activity on the
planets surfaces.
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Discussion
How does the heat from the interior of the planet
get to the surface?
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Lithosphere
The convective cells in the planets do not make
it to the surface as on the Sun, but are stopped
at the base of the lithosphere. The lithosphere
includes the crust and the upper mantel region of
cooler, stronger rock which does not flow as
easily as the warmer, lower mantel rock.
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Geologic processes

• Impact cratering
• Volcanism
• Tectonics
• Erosion

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3rd law of astronomy 201
The more impact craters on a surface, the older
that surface is.
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Discussion
Which area on the Moon is older, the light region
to the left or the dark region in the center of
the picture?
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Why?
All the terrestrial planets probably receive
about the same number and size distribution of
impacts. All the other geologic processes
(volcanism, tectonics, and erosion) tend to erase
impact craters on the surface.
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Discussion
Rank the terrestrial planets (include the Moon)
in terms of the age of their surfaces from
youngest to oldest to try and predict which
planets will have the most craters.
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• Earth
• Venus
• Mars
• Mercury
• Moon
• Smaller planets retain less heat and therefore
  have less geologic activity.