What type of chemical or molecule is most common in Earth’s atmosphere?

Why does Earth’s albedo change daily? Seasonally?

Why is Earth’s surface not riddled with craters as is that of the Moon?

List the layers of Earth’s atmosphere.

Describe the process of plate tectonics. Give specific examples of geographic features created by plate tectonics.

How do we know about Earth’s interior, given that the deepest wells and mines extend only a few kilometers into its crust?

What occurs on Earth when two tectonic plates of roughly equal density collide head-on?

What occurs when a higher-density tectonic plate collides head-on with a lower-density plate?

Describe the interior structure of Earth.

Why is the center of Earth not molten?

What are the Van Allen radiation belts?

Why do charged particles from the Sun (the solar wind) get trapped in the Van Allen radiation belts?

The Moon’s surface is best described as:

Explain why the maria appear darker than the lunar highlands.

Why are there so few craters on the maria?

Where on the Moon did the largest impact craters occur?

How do we know that the maria were formed after the lunar highlands?

Describe how the Moon creates ocean tides on Earth.

What is the difference between spring tides and neap tides? During which phase(s) of the Moon does each occur?

Why do most scientists support the collision-ejection theory for the Moon’s formation?

Why are nearly all of the craters on the Moon circular, even though many impacts there were not head-on?

Why hasn’t the water ice near the Moon’s poles been evaporated by sunlight?

Which pair of planets has atmospheres with the most similar chemical compositions?

Which planet is least likely to have water ice on or just under its surface?

Which object is most similar to Venus in mass and diameter?

Compare the surfaces of Mercury and our Moon. How are they similar? How are they different?

Compare the interiors of Mercury and Earth. How are they similar? How are they different?

On Mercury, when would you expect it to be coldest: noon, just before sunset, midnight, or just before sunrise? Explain your reasoning.

Why is Mercury more heavily cratered than Earth?

Astronomers often refer to Venus as Earth’s twin. What physical properties do the two planets have in common? In what ways are the two planets dissimilar?

Why is it hotter on Venus than on Mercury?

What evidence exists for active volcanoes on Venus?

Describe the Venusian surface. What kinds of geologic features would you see if you could travel around the planet?

Why is Mars red?

What is the greenhouse effect? What role does it play in the atmospheres of Venus and Earth?

What geologic features indicate that plate tectonic activity once occurred on Mars? What features created by tectonic activity on Earth are not found on Mars?

Why are volcanoes on Mars taller than those on Earth?

What evidence have astronomers accumulated that liquid water once existed in large quantities on Mars’s surface? What evidence is there that water still exists under its surface?

Explain how the outward flow of energy from Earth’s interior drives the process of plate tectonics.

Why are active volcanoes, such as Mount St. Helens, usually located in mountain ranges along the boundaries of tectonic plates?

Why is more lunar detail visible through a telescope when the Moon is near quarter phase than when it is at full phase?

Why are the Moon rocks retrieved by astronauts so much older than typical Earth rocks, even though both worlds formed at nearly the same time?

Apollo astronauts left seismometers on the Moon that radioed seismic data back to Earth. The data showed that moonquakes occur more frequently when the Moon is at perigee (closest to Earth) than at other locations along its orbit. Give an explanation for this finding.

Venus takes 440 days to move from greatest western elongation to greatest eastern elongation, but it needs only 144 days to go from greatest eastern elongation to greatest western elongation. With the aid of a diagram, explain why.

How might Venus’s cloud cover change if all of Venus’s volcanic activity suddenly stopped? How might these changes affect the overall Venusian environment?

Compare Venus’s continents with those on Earth. What do they have in common? How are they different?

Explain why Mars has the longest synodic period of all of the planets, although its sidereal period is only 687 days.

With carbon dioxide accounting for about 95% of the atmospheres of both Mars and Venus, why is there little greenhouse effect on Mars today?

Comment on the idea that without the Moon’s presence, life would have developed far more slowly.

Identify and compare the advantages and disadvantages of lunar exploration by astronauts as opposed to mobile, unmanned instrument packages and robots.

When was the last earthquake near your hometown? How far is your hometown from a plate boundary? What kinds of topography (for example, mountains, plains, seashore) dominate the geography of your hometown area? Does that topography and the frequency of earthquakes seem to be consistent with your hometown’s proximity to a plate boundary?

If you were planning a new Messenger mission to Mercury, what features and observations would be of particular interest to you and why?

If you were designing a space vehicle to land on Venus, what special features would be necessary? In what ways would this mission and landing craft differ from a spacecraft designed for a similar mission to Mercury?

Compare the scientific opportunities for long-term exploration offered by the Moon and Mars. What difficulties would there be in establishing a permanent base or colony on each of these two worlds?

Imagine you are an astronaut living at a base on Mars. Describe your day’s activities, what you see, the weather, the spacesuit you are wearing, and so on.

Will the Earth’s ozone layer, which has been depleted over decades, be naturally replenished? If so, how?

Since infrared radiation (heat) from the Sun does not enter a greenhouse, how do greenhouses get warm?

How can we tell by looking at the Moon that it rotates?

How were the craters on the Moon formed?

What gas in the atmosphere of Venus is primarily responsible for the greenhouse effect there?

Which of the following statements about life on Mars is correct?

What color does the surface of Venus have, as seen from that world, and why?

Which terrestrial planet has the coldest surface, and why?