AST101H1 Lecture Notes - Lecture 13: Decay Product, Uranium-235, Giant Planet

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Week 7 – Lecture 13 Tues. Oct.
nebular theory – created by the collapse of a dense region (molecular cloud)
dust in the gas (in between the stars) it keeps us from seeing the rest of the galaxy
inner is warmer - warmed by compression of the gas on its way to the sun and from the
light of the newborn sun
frost line – where ice can exist
most of the mass is the gas (hydrogen and helium)
terrestrial planet formation
frost line – inside the orbit of jupiter (outside of jupiter is ice)
dust stick to other dust (even rocks stick together) – if you put dust grains outside to
float they will eventually stick to the size of a pebble
run away growth – growing from small to large – mountain sized rocks have gravity
strong enough that it starts to pull
when a rock is big enough gravity pulls it into a sphere (spherical rocks are larger than
bulgy ones)
first phase – many small rocks and their orbits intersect with one another
second phase – clearing their zones by colliding with one another (mutual gravity helps to
pull them together)
third phase - all the collisions (billion of years) – system of planets that go around in the
same orbit so that their orbit don't cross one another, orbit is stable
jovian planet formation
uranus and neptune - cores are smaller and process took longer = icy core
left-over icy planetesimals - able to remain icy for billion of years and become the
comets are the reason why planets have water
clicker quiz: if the sun were smaller and dimmer, the solar nebula would have been cooler.
What effect would this have on planet formation?
A. jovian planets should have formed closer to the sun
frost line is based on temperature
when did all this happen?
Use of radioactive isotopes
potassium 40 – radioactive atom that forms into argon 40
at 1.25 (purple) it has a 50/50 chance of being potassium
1/4 left of potassium at 2.5 billion years
uranium 235 (less of a half life)
daughter product is lead 207
moon has two places on its surface
highlands – crater regions
maria – lower darker section of surface
rocks in those two places (maria is younger than highlands)
sun formed the same time as the oldest meteorites (4.5 billion years) (half age of the
galaxy, 1/3 of the age of the universe)
moon forming event
our moon is large because of colliding planets
young earth was struct by a planet like mars
the moon has a smaller core compared to others
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