Download What happened to the leftovers?

October 26 and 28:
Chapter 9 - Planetary Geology
8.4 Evolution of the Solar System
of Earth and the other Terrestrial Worlds
• Our goals for learning
– What happened to the leftovers?
– Where
Wh did asteroids
t id andd comets
t come
from?
– How do we explain “exceptions”?
– How do we explain Earth’s moon?
– How “typical” is our solar system?
Time to start looking at www.sci.angelo.edu/phys1302/termexam3.pdf
What happened
to the leftovers?
Asteroids, Comets & KBOs
•
•
•
•
Leftovers from the accretion process
Rocky asteroids inside frost line
Primordial KBOs outside the Frost Line and away from
strong gravity of jovian planets
Icy interstellar debris (comets) beyond in Oort Cloud
Heavy Bombardment
• Leftover
planetesimals
bombard other
objects
j
in late
stages of solar
system formation
–
–
–
–
Earth
Mars
Uranus
Venus?
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Late Heavy Bombardment
Origin of Earth’s Water?
Some H2O released from
hydrated rocks
• Shouldn’t be here!
• Water must have come
to Earth by way of icy
planetesimals from
outer solar system
Primordial CO2
atmosphere
300 million year delay. Why?
Differentiation
• Gravity attracts high
mass (high-density)
material to center
• Lower-density
material is displaced
p
to surface
Too hot at time of
heavy bombardment
DRY!
Major Impacts
• Surfaces must be cooled and solidified to leave
a trace of major impacts → differentiation
• e.g. Mars
M C
Crustal
t l Dichotomy
Di h t
– Atmospheric gases
– Silicate rocks
– Nickel/Iron core
• Material ends up
segregated by
density
Mars Crustal Dichotomy
Like Earth & Venus, initially
dense CO2 atmosphere
Origin of Earth’s Magnetic Field
• Differentiation must be essentially complete
• Molten convecting Nickel/Iron core
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Captured Moons
Earth’s
Moon?
•Apollo and Luna samples
prove Earth and Moon
are chemically related
Phobos & Demios @ Mars
•
• So why didn’t they form
as one larger planet
during accretion period?
Unusual moons of
some planets are likely
captured planetesimals
or actual KBOs
Triton @ Neptune
Giant Impact Hypothesis
• Answer: The Moon was
created later as part of
a heavy bombardment
event.
Most interesting?
Mars--sized impact on early Earth
Mars
Stripped matter goes in to orbit
Then accreted into Moon
8.5 Age of the Solar System
• Entire Uranian
system (planet,
rings & moons)
are all knocked on
their
h i sides
id
• Likely from a
megaimpact
before the
planetesimal
period
• Venus flipped
almost 180°
Radiation
• Our goals for learning
– How does radioactivity reveal an
object’s
bj
age?
– Ultimate Question: When did the
planets form?
• ergo…How long have they been evolving?
• An exact definition of the meaning of this word…
• ra‫ڄ‬di‫ڄ‬a‫ڄ‬tion [rey-dee-ey-shuhn] –noun
– the complete process in which energy is emitted by one
body, transmitted through an intervening medium or
space, and absorbed by another body.
• All “light” is radiation. The key is “what’s the λ”?
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Radioactive Materials
are ubiquitous
• The concept of Metastability
• Very heavy elements are unstable – they decay.
• The decay process generates radiation.
– e.g. radioactive elements
• The decay process happens at a very specific rate.
– e.g. there is a “clock” in the rocks
Background
Radiation
295 natural background
+63 anthropogenic
~265 mRems
-vs.Standard medical
X-ray <200 mRems
Most natural radon is
from radioactive decay
of igneous rocks
Radioactive Decay
Radioactive
Decay
Count the
number of
parent and
daughter atoms
What are the results?
• Many isotopes
decay into other
nuclei
• A half-life
h lf lif is
i the
h
time for half of
the parent atoms
in a substance to
decay into a
daughter product
The Stardust Mission
• Radiometric dating tells us that oldest Earth rocks are
4.4 billion years old
• Radiometric dating tells us that oldest Moon rocks are
4 4 billion years old
4.4
• Radiometric dating tells us that oldest meteorites are
4.55 billion years old (younger ones are mostly SNCs
from Mars).
• Radiometric dating tells us that cometary material is
up to 4.6 billion years old
• Planets probably formed 4.5 billion years ago
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Not to hot, not too
cold, not too new
and not too old…
• If our solar system
is a book,
book that is
the story.
• What are the
questions?
How “typical”? See Fig. 8.13
• Formation of planets
in solar nebula seems
inevitable
• Physics should be
universal
i
l
• Major variables are:




http://www.lpi.usra.edu/education/timeline/
Total mass of cloud
Composition of cloud
Angular Momentum
Random interactions
within solar system
http://www.sci.angelo.edu/phys1302/universe_timeline.pdf
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