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L11. Asteroid belt
Lecture 11 in Astro 150 UW
27
Astronomy
Undergraduate 2
05/06/2011

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Term
Why did astronomers think to look at the space 2.8AU in the solar system for planets?
Definition
There is a large gap between Mars and Jupiter that holds the astroid belt.
Term
Asteroid belt
Definition
~250,000 asteroids orbiting the sun between Mars and Jupiter
Term
Are there more small or large asteroids?
Definition
Many more small
Term
What did the NEAR satellite find when it visited the asteroid Eros
Definition
It looked like the surface of the moon
2the R-Plot showed that there are very few small craters.
3 small asteroids spin slowly
Term
Why do asteroids lack small impact craters?
Definition
When they are impacted they shake and the craters get filled in with dust
Term
Why are only large asteroids spherical?
Definition
When they get big enough th pressure from gravity crushes the rock at the center and it collapses into a sphere.
Term
Do different materials collaps into spheres at different pressures?
Definition
No. It doesnt matter what material it is, at about 500km the asteroid will collapse into a sphere.
Term
What happens to asteroids when you hit them with small objects?
Definition
You get impact craters
Term
What happens when you hit asteroids with large objects?
Definition
They break apart completely.
Term
Rubble pile asteroids.
Definition
Layered Asteroids that get broken apart and then pulled back together. They are essentially a ball of rubble
Term
Why do asteroids not rotate fast?
Definition
They are rubble piles, the pieces are not held together well, if they rotated fast they would fall apart.
Term
What are the 2 ways that we know that the asteroid belt did not start as a single planet that was broken apart into pieces?
Definition
1. Carbonaceous Chondrite meteorites are primitive, meaning they come from unaltered, small asteroids that have ALWAYS been small and unaltered!!!
2. The asteroids all have very different oxygen isotope ratios
Term
Oxygen isotope ratios
Definition
Oxygen isotopes are different forms of oxygen.
Every planet has specific ratios that act as finger prints
Term
What two objects mark the boundaries of the asteroid belt?
Definition
The sun and Jupiter
Term
Lagrange Points
Definition
Two stable points between Jupiter and the sun where material can rest and not get pulled tword either one
Term
Whay do asteroids reside in the orbit of Jupiter?
Definition
They are in the Lagrange points. Where it is stable and they are not negatively effected by jupiter's gravitational pull
Term
Are asteroids evenly distributed in the asteroid belt?
Definition
No there are places in the asteroid belt where the orbital speed of the asteroids would resonate with the orbital speed of Jupiter and the asteroids would get bumped out of orbit.
Term
Resonance
Definition
When the orbits of asteroids in the asteroid belt line up with the orbit of Jupiter. I.e. In one orbit of Jupiter the asteroid makes a curtain number of complete orbits.
Term
What happens to asteroids that get into resonance with Jupiter?
Definition
Jupiters gravity pushes theem so that they wobble in their orbits until they eventually get flicked out of the asteroid belt and into the inner solar system where they collide with the sun, earth, mars, mercury, or venus.
Term
Where did the K/T meteor (that killed the dinosaurs) come from?
Definition
Two asteroids collided in the asteroid belt shattering both and sending pieces into resonance with Jupiter. Those pieces were then bumped into the inner solar system where one collided with Earth.
Term
Primitive asteroids are located where in the asteroid belt?
Definition
Further from the sun
Term
Geologically active / differentiated asteroids are located where?
Definition
Closer to the sun.
Term
Frost line / snow line
Definition
the distance from the sun where it is cold enough that water freezes.
After this point ice can be used as a building block for Planets and whatnot.
Planets and satellites are made of rock and ice and are often much larger then the inner solar system planets.
Term
Why are the outer solar system planets so much larger then the inner solar system planets?
Definition
They are past the snow line.
There is so much ice to use in making planets that they are very large.
Term
Why didn't the asteroid belt ever accrete into a planet like the rest of the material floating inn our solar system?
Definition
The gravitational pull of Jupiter keeps the asteroids apart and continuously crashes them together breaking them into small pieces.
Term
Do asteroids have atmospheres?
Definition
No they are too small.
Term
True or false: if you were to fly through the astroid belt you would have to dodge between them as you went.
Definition
False.
The asteroids are so spread out that were you standing on one you would not even be able to see another one.
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