1. Journal 11/7/16 Objective Tonight’s Homework
Tell me everything you know about asteroids.
Objective Tonight’s Homework
To learn about some of the other, smaller objects in the solar system.
p 358: review 5, 7, 9, 18

3. Notes on Pluto and the Asteroid Belt
It’s only very recently that we sent a mission to Pluto and got to see it up close for the first time. We expected to find a simple frozen ball of ice with no surface features. What we’ve found instead is quite different and very mysterious.
To start, the mountains seen in the picture below are about 11,000 feet high. How did they get there? We don’t know.

4. Notes on Pluto and the Asteroid Belt
Pluto has a large, heart shaped area that’s also very interesting because it’s smooth. We care because smooth means there’s been recent geological activity that erased craters. Pluto is way too small to have tectonics Everything should be frozen!

5. Notes on Pluto and the Asteroid Belt
Pluto also has a very tilted orbit that’s very elliptical. When Pluto is at its farthest, it gets so cold that its atmosphere freezes and snows onto the surface, leaving Pluto with no atmosphere for a while.

6. Notes on Pluto and the Asteroid Belt
Pluto’s biggest moon, Charon is also very mysterious. Charon has a canyon that goes so deep you could fit all of Mount Everest inside!
Other than that, Pluto and Charon remain mostly a mystery.
We still have a lot of data to go through to uncover more secrets.

8. Notes on Pluto and the Asteroid Belt
There’s more stuff floating around the solar system than just planets. The previous slide showed comet 67P. This comet is still far from the sun, so right now it’s just a dirty ice ball. The whole thing is about as big as L.A.
The European Space Agency actually landed on this comet and is taking data for the next several years.

9. Notes on Pluto and the Asteroid Belt
Why do we care about comets? Most comets are literally left over chunks of ice and rock from the beginning of the solar system. We care about them because samples from them can tell us what the solar system was like right when it formed.
One thing we’ve already learned is that the ice comets are made from is chemically different from the water on Earth. This means Earth couldn’t have gotten its oceans from a bunch of comets hitting it, which is what our current theory proposed.

10. Notes on Pluto and the Asteroid Belt
Comets are interesting because they also have very elliptical orbits. As a comet gets closer to the sun, the ice heats up and starts to melt. This is a pretty violent process, causing tons of water and gas to stream off the comet in a direction opposite the sun.
Each time a comet goes around the sun it loses a bit more material. Eventually a comet will get “used up” and disappear.

11. Notes on Pluto and the Asteroid Belt
In 1994, a comet got caught by Jupiter’s gravity, broke apart, and slammed into Jupiter in about 20 pieces. Each piece hitting released way more energy than a nuclear bomb and left scars that stayed on Jupiter for months.

12. Notes on Pluto and the Asteroid Belt
The last major thing is the asteroid belt. This is a large collection of asteroids orbiting the sun between Mars and Jupiter.

13. Notes on Pluto and the Asteroid Belt
We originally thought that the asteroid belt was the remains of a planet that got ripped apart or maybe never formed, but there’s just not enough stuff.
If we gather up all the material in the asteroid belt into one big ball, its still not even as big as the Moon.
In fact, stuff here is so spread out that you’d have trouble seeing one asteroid if you were standing on the surface of another. They’re just too small and far apart.

14. Notes on Pluto and the Asteroid Belt
The two largest asteroids - Ceres and Vesta – were once considered planets, but are now dwarf planets like Pluto. Ceres is even big enough to form into a sphere.

15. Notes on Pluto and the Asteroid Belt
A number of years back, we sent a lander to an asteroid named 433 Eros. For scale, this asteroid would cover about 1/3 of Denver. Even though it’s small, it still has enough gravity for craters to form.

16. Notes on Pluto and the Asteroid Belt
Asteroids come in 3 types – C, S, and M.
C (carbon) asteroids are mostly made of ice, carbon, and some organic compounds like tar. There’s a lot of gravel and rock here, too.
S (silicon) asteroids are mostly made of metals like nickel and silicon. This makes them the most rocky of the asteroids. A lot of their surface is covered in dust and gravel.
M (metal) asteroids are mostly made of pure nickel and iron. These are usually smaller but more dense.

17. Exit Question
Why do comets emit gas and dust as they get near the sun?
a) They start moving fast enough to break apart
b) Their unstable orbit causes them to shake apart
c) Because the sun’s heat is causing them to evaporate
d) We don’t know why
e) Because God loves gassy comets.