Calculating the aphelion distance of Halley's comet from the sun.

Halley's comet has a perihelion distance of 0.6 A.U. and an orbital period of 76 years. What is its aphelion distance from the Sun?

Moon and its seismic activity in comparison to Earth.

In view of the preservation of ancient craters and the lack of folded mountain ranges on the Moon, would you predict the Moon to have more or less seismic activity than the Earth? Why?

Comparing the ages of the Earth and Moon.

If the ages of the Earth and Moon are nearly identical, as believed, why are most rocks found on the Moon so much older than earth rocks?

Understanding why carbon dioxide is a major constituent of the atmosphere of Venus.

Venus and Earth are about the same size and mass, and degassing volcanoes on each probably produced both CO2 and H20 gas. Why is CO2 a major constituent of the atmosphere only on Venus, while H20 is not a major constituent of the atmosphere on either planet? (Please cite all references and supply urls)

Comparing planet composition.

Two large planets have the same size and mass but different orbits. a. Which would you expect to have more hydrogen? Why? b. If they have had different amounts of volcanism, which would you expect to have more carbon dioxide? Why?