Which statement accurately describes the atmospheres of the inner planets? 1 Mars has no atmosphere. 2 Mercury has a thick atmosphere. 3 Mars and Venus have similar atmospheres. 4 Earth and Venus have similar atmospheres.
The Correct Answer and Explanation is:
The correct answer is 4. Earth and Venus have similar atmospheres.
Explanation:
The atmospheres of the inner planets—Mercury, Venus, Earth, and Mars—are vastly different in terms of composition, density, and the role they play in supporting life. Let’s break down each statement to understand why option 4 is correct.
- Mars has no atmosphere.
- This statement is incorrect. While Mars does have a very thin atmosphere, it is not absent. The Martian atmosphere is primarily composed of carbon dioxide (CO₂), with traces of nitrogen and argon. However, it is extremely thin, with a pressure less than 1% of Earth’s atmosphere, which is why it doesn’t support life in the same way Earth does.
- Mercury has a thick atmosphere.
- This is also incorrect. Mercury has an extremely thin atmosphere, often called an exosphere, consisting mainly of oxygen, sodium, hydrogen, helium, and potassium. Because Mercury is so close to the Sun, its weak gravity cannot retain a substantial atmosphere. The temperatures on Mercury also fluctuate dramatically, making it inhospitable.
- Mars and Venus have similar atmospheres.
- This statement is false. While both planets have a primarily carbon dioxide atmosphere, their atmospheric conditions are vastly different. Venus has a thick, dense atmosphere, resulting in a runaway greenhouse effect that causes extremely high surface temperatures, around 900°F (475°C). In contrast, Mars has a very thin atmosphere, and while it has a weak greenhouse effect, it is not strong enough to support liquid water at the surface or regulate temperature in the same way Venus does.
- Earth and Venus have similar atmospheres.
- This is the correct answer. Earth and Venus share some similarities in their atmospheric composition. Both planets have atmospheres composed primarily of carbon dioxide, nitrogen, and traces of other gases. However, the critical difference lies in the abundance of carbon dioxide. Venus has a far greater concentration of CO₂, leading to its extreme greenhouse effect, whereas Earth has a balanced carbon cycle, allowing for the presence of liquid water and life. Despite these differences, the overall structure and composition of the atmospheres of Venus and Earth are more similar than those of any other inner planets.
In conclusion, Earth’s atmosphere is the most hospitable for life, with a balanced composition that supports liquid water and a mild climate. Venus’s atmosphere, while similar in composition, results in an inhospitable environment due to the extreme greenhouse effect.