Astronomy Homework – Question and Answers

Astronomy Homework – Question and Answers
#1.What is comparative planetology? What is its basic premise? What are its basic primary goals?
Comparative planetology is an approach to the study of different worlds in a solar system. The basic premise of it is that all bodies in our solar system are formed at about the same time from the same cloud of interstellar gas and dust, and in accord with the same physical laws. Therefore, we can study the word by comparing them with one another. By studying comparative planetology, we can begin to understand much more about the modern theory of formation that explains much of what we see.

#8. Distinguish between metals, rocks, hydrogen compounds, and light gases in terms of condensation temperatures and relative abundances in the solar nebula.

Metals include iron, nickel, aluminium, and other metals that are found on Earth. They are the least commen material, making up about .2%, and the typical condensation is between 1000-1600 K. Rocks are the materials usually found on the surface of the Earth, mostly silicon based minerals. Rocks typically melt and vaporize between 500-1300 K, and make up about .4% of the nebula’s mass. Hydrogen compounds are molecules including methane, ammonia, and water that are solidified into ices below 150 K. Hydrogen compounds make up a considerably larger mass of the nebula, about 1.4%. Light gases such as Hydrogen and Helium never condense under solar temperatures, and make up the remaining 98% of the nebula’s mass.

#15. What clues suggest that a planetary satellite was captured instead of forming with its planet?

Several unusual moon’s including Phobos and Deimos, are said to be captured asteroids instead of moons that formed when the planet did. Several reasons why is because they have ‘unusual’ orbits- they orbit opposite the rotation of their planet. Also, they do resemble asteroids, and are darker and lower in density then Mars.


#4. A solar system has 12 planets that all orbit the star in the same direction and in nearly the same plane. The 15 largest moons in this solar system orbit their planets in nearly the same plane as well. However, several smaller moons have highly inclined orbits around their planets.

This would not be an uncommon solar system to find except for one fact. Most planets and moons do indeed lie in the same plane, and orbit in the same direction. However, It would be highly unusual to find moons with a high inclination of their orbits- all moons always lie on the same plane as the other moons.

#9. Explain in terms a friend or roommate would understandable why the jovian planets are lower in density then the terrestrial planets even though they all formed from the same cloud.

The reason that the Jovian planets are less dense is that they are made from less dense materials- the light gases and hydrogen compounds that make up the nebula. The other materials, Rocks and metals, make up the smaller terran planets, and because solids are denser then gases, the terrestrial planets are more dense. All planets are formed from the same cloud, but the four different materials in it do not have to be present in all the same amounts.