Chapter 9 Quiz: Olivia Ward

1. Why is there an asteroid belt?
   
   There is an asteroid belt due to orbital resonance. Orbital resonance with Jupiter disrupted the orbits of planetesimals, located in the asteroid belt, which prevented them from forming into a terrestrial planet. Many planetesimals were ejected, but some remained. These make up the asteroid belt today. Most of the asteroids, which were located in other areas of the inner solar system, have crashed into one of the planets.
   
2. How are meteorites related to asteroids?
   
   Most meteorites are pieces of asteroids. Primitive meteorites have no experienced changes since the birth of the solar system. Processed meteorites are fragments of larger asteroids that have gone through differentiation.
   
3. How do comets get their tails?
   Comets get their tails from sublimation. Comets are the icy leftovers of planet formation. If a comet comes near the Sun, the nucleus heats up and its ice undergoes sublimation. The escaping gases carry along with dust. This forms a coma and two tails: a plasma tail of ionized gas, and a dust tail.
   
4. Where do comets come from?
   
   Comets come from either the Kuiper Belt or the Oort Cloud. The Kuiper Belt comets are still located in a region beyond Neptune, where they formed. The Oort Cloud comets formed between the jovian planets and were kicked out by gravitational encounters with these planets.
   
5. How big can a comet be?
   
   Icy planetesimals in the Kuiper Belt were able to grow up to thousands of km in size. Eris is the largest known of these objects. Pluto is the second largest.
   
   
6. What are Pluto and other large objects of the Kuiper belt like?
   
   Pluto and other large objects of the Kuiper Belt are ice-rich. They orbit the Sun between the orbit of Neptune and twice that distance from the Sun. Their orbits tend to be elliptical and more inclined than those of terrestrial and jovian planets.
   
7. Have we ever witnessed a major impact?
   
   In 1994, fragmented Comet Shoemaker-Levy 9 impacted Jupiter which scarred its atmosphere for months. In 2009, there was another impact on Jupiter.
   
   
8. Did an impact kill the dinosaurs?
   
   A major impact may not have been the only cause for extinction of dinosaurs, but mass extinction coincides with the major impact. This occurred 65 million years ago. Sediments from this time contain Iridium. An impact crater of the same age is located along the coast of Mexico.
   
9. Is the impact threat a real danger or just media hype?
   
   Impacts are a threat, but the probability of a major impact happening in our lifetimes is low. It's not a matter of if a major impact will happen, it's a matter of when. Major impacts may occur every few hundred years.
   
10. How do other planets affect impact rates and life on Earth?
    
    Impacts are always linked to the gravitational influence of Jupiter and other jovian planets. These influences have shaped the asteroid belt, the Kuiper belt, and the Oort Cloud. The influences also continue to determine when objects are flung in our direction.