SSC CPO 2025 PYQ — Question 50

Answer — Lack of gravity.

Explanation —

The primary reason for the absence of an atmosphere on the Moon is its low gravitational force. The Moon's mass is significantly smaller than that of Earth; consequently, its gravitational force is merely one-sixth (1/6) of Earth's gravity. Sufficient gravity is essential for any celestial body to retain an atmosphere. The escape velocity on the Moon is very low (approximately 2.38 km/s). Due to solar heating, the thermal motion of gas molecules exceeds this escape velocity, causing the gases to escape from the Moon's surface and drift into space.

Additional Points —

Solar Winds: Although Option 2 is indeed a contributing factor, the lack of gravity remains the primary cause. The Moon lacks an intrinsic magnetic field of its own; as a result, solar winds can easily strip away any residual gas molecules present there.

Temperature: The Moon experiences extreme temperature fluctuations between day and night (ranging from approximately -173°C to 127°C)—a phenomenon directly attributable to the absence of an atmosphere.

Comparison of Escape Velocities: Earth's escape velocity is 11.2 km/s, which is sufficient to retain heavier gases such as oxygen and nitrogen.

Potential Exam Questions and Answers —

Question: What is the value of the escape velocity on the Moon's surface?

Answer: Approximately 2.38 kilometers per second.

Question: How does the weight of an object on the Moon compare to its weight on Earth?

Answer: It is one-sixth (1/6) of its weight on Earth.