Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-28
Course Announcements
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How is the sunset/sunrise observing going?
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SW-chapter 7 posted: due Fri. Oct. 30
SW-chapter 8 posted: due Wed. Nov. 4
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Exam-3 Wed. Nov. 4: Ch. 6, 7, 8
I will collect the L-T books on Monday, Nov. 23
Take more astronomy!
Registration for the Spring semester starts soon so think
about taking more astronomy.
ASTR-1010/1011: Planetary Astro & lab (Tell your friends)
ASTR-1020/1021: Stellar Astronomy & lab (Reg. + Honors)
ASTR-2020: Problems in Stellar Astronomy
ASTR-3010: History of Astronomy
ASTR-3040: Intro. To AstroBiology
PHYS-2468: Intro. To Physics Research
ASTR-3030/3031: Instrumentation & Techniques
Radioactive Dating
 Some elements can decay from one to another (e.g.,
uranium to thorium).
 These changes take place at known rates.
 Parent element declines, daughter element
accumulates.
 Ratio of parent to daughter abundance gives the age of
the rock.
 Age = time since rock was last molten.
CONNECTIONS 8.1
 Rock layers are
formed through
sedimentation.
 To find the ages of
rock in these layers
(or from Mars),
scientists use
radiometric dating.
 Parent particles
decay into stable
daughter particles at
a steady rate.
MATH TOOLS 8.1
 A radioactive isotope
decays to half its
original amount in a
half-life.
 We model the
Earth’s interior
by studying
earthquakes.
 Seismic waves
travel differently
through different
materials.
 Some waves
are surface
waves; others
travel through.
 Primary waves
travel through
solids and
liquids; they are
longitudinal
waves.
 Secondary
waves go
through solids
only; they are
transverse
waves.
 Earth has a
crust, mantle,
and core (dense
materials).
 Produced by
differentiation
in the early
Earth: Dense
materials sink,
low-density
materials rise.
 Current prevailing
theory: Moon formed
in large collision
between Earth +
Mars-sized
protoplanet.
 The material
collected to form the
Moon.
 The composition of
the Moon is like that
of Earth’s crust.
PROCESS OF SCIENCE
 Sometimes
multiple
hypotheses
must be
considered,
though one
might fit the
data better
than others.
 The Moon and the other
terrestrial planets have
interiors similar to Earth.
 Deeper in a planet means
hotter and more pressure.
 Formation energy and
radioactive material help to
heat the interior.
 Smaller planets lose heat
faster; large ones more
slowly.
MATH TOOLS 8.2
 Large planets cool off more slowly than
small planets.
 If we assumed planets all began with the
same amount of radioactive material and
that the successive decay produced all the
internal heat, then the rate of energy loss is
dictated by how much energy there is
(volume = 4/3 π R3) and where the planet
loses the energy (surface area = 4 π R2) .
 The amount of energy that could be lost
divided by the area of loss is proportional to
R/3, where R is the radius of the planet.
 Earth’s magnetic field acts like a giant bar
magnet.
 It originates from processes deep in the
interior that are not understood fully.
 Iron-bearing minerals tell us the orientation
changes over time.
 Earth and Mercury are the only terrestrial
planets with a substantial magnetic field.
 It is a puzzle why Venus and Mars do not
have one.
 The Moon had one long ago.
Concept Quiz
Internal Heat
What should be true about Earth’s internal
heat?
A. It is produced by the magnetic field.
B. It would have been greater long ago
when Earth was young.
C. It currently is produced by differentiation.
 Tectonism is the deformation of Earth’s crust.
 Earth’s crust is broken into lithospheric plates.
 Continental drift and plate tectonics describe
the movement of those plates.
 Crustal plates are moved around by
convection—the rising and falling of hot/cold
material.
 Earth has seven major plates and six smaller
ones.
 Plates can separate or collide.
 Because of these motions, most volcanoes and
earthquakes occur along plate boundaries.
 Only Earth has its
crust broken into
plates.
 All terrestrial
planets have seen
some form of
deformation,
though.
 Mercury’s surface
shrank after it
cooled, leaving
cliffs.
 Mars has experienced extensive tectonism,
and boasts the massive chasm Valles
Marineris.
 Venus may have a different form of
tectonism, with melting and overturning of the
crust.