Astronomy Practice Exam

What is a common characteristic of terrestrial planets?

1. They are gaseous and lack solid surfaces

2. They possess a significant amount of water

3. They are rocky and dense

4. They orbit beyond the asteroid belt

The correct answer is: They are rocky and dense

Terrestrial planets, which include Mercury, Venus, Earth, and Mars, are known for their rocky and dense compositions. This characteristic arises from their formation in the inner solar system, where the temperatures were higher, allowing only metals and silicate minerals to condense and form solid surfaces. Their relatively small sizes, compared to gas giants, contribute to their density, indicating a greater proportion of solid material rather than gas. In addition to their rocky nature, terrestrial planets typically have solid surfaces that can support various geological processes, such as volcanism and tectonics. Their atmospheric compositions can vary widely among the planets, reflecting further differences in their geological and hydrological histories. The other choices reference characteristics that do not universally apply to terrestrial planets. For example, while some terrestrial planets may contain water, such as Earth, it is not a defining feature of all terrestrial planets. Similarly, terrestrial planets are not gaseous; this description aligns more with the characteristics of gas giants. Lastly, the reference to orbiting beyond the asteroid belt pertains to the positions of gas giants rather than terrestrial planets, which are located within the inner solar system.