Jessie Horn: Chapter 9 Quiz

Quiz

1. Why is there an asteroid belt?  Orbital resonances with Jupiter disrupted the orbits of planetesimals in the asteroid belt, preventing them from accreting into a terrestrial planet. Many were ejected, but some remained and make up the asteroid belt today. Most asteroids in other regions of of the inner solar system crashed into one of the planets.
2. How are meteorites related to asteroids? Most meteorites are pieces of asteroids. Primitive meteorites are essentially unchanged since the birth of the solar system. Processed meteorites are fragments of larger asteroids that underwent differentiation. 
3. How do comets get their tails? Comets are icy leftovers from the era of planet formation, and most orbit far from the Sun. If a comet approaches the Sun, its nucleus heats up and its ice sublimates into gas. The escaping gases carry along some dust, forming a coma and two tails: a plasma tail of ionized gas and a dust tail. Larger particles can also escape, causing meteor showers on Earth. 
4. Where do comets come from? Comets come from two reservoirs: the Kuiper belt and the Oort cloud. The Kuiper belt comets still reside in the region beyond Neptune in which they formed. The Oort cloud comets formed between the Jovian planets and were kicked out to a great distance by gravitational encounters with these planets. 
5. How big can a comet be? In the Kuiper belt, icy planetesimals were able to grow to hundreds or thousands of km in size. The recently discovered Eris is the largest known of these objects and Pluto is the second largest.
6. What are Pluto and other large objects of the Kuiper belt like? Like smaller comets, these objects are ice rich in composition. Thy orbit the Sun roughly between the orbit of Neptune and twice that distance from the Sun. Their orbits tend to be more elliptical and more inclined to the ecliptic plane than those of the terrestrial and Jovian planets. Many share orbital resonances with Neptune. A few have moons, including Pluto.
7. Have we ever witnessed a major impact? In 1994, we observed the fragmented Comet Shoemaker-Levy 9 impacting Jupiter, scarring its atmosphere for months.l In 2009, we saw the aftermath of another impact on Jupiter. 
8. Did an impact kill the dinosaurs? It may not have been the sole cause, but a major impact clearly coincided with the mass extinction in which the dinosaurs died out, about 65 million years ago. Sediments from this era contain iridum and other evidence of an impact, and an impact crater of the same age lies along the coast of Mexico. 
9. Is the impact threat a real danger or just media hype? Impacts certainly pose a threat, though the probability of a major impact in our lifetimes is fairly low. Impacts like the Tunguska event may occur every few hundred years and would be catastrophic if they struck populated areas. 
10. How do other planets affect impact rates and life on Earth? Impacts are always linked in at least some way to the gravitational influences of Jupiter and the other Jovian planets. These influences have shaped the asteroid belt, the Kuiper belt, and the Oon cloud and continue to determine when an object is flung our way.