There is no atmosphere on the moon because

Options

A. it is closer to the earth
B. it revolves round the earth
C. it gets light from the sun
D. the escape velocity of gas molecules is lesser then their mean square velocity here

Answer

To answer the question "There is no atmosphere on the moon because...", we need to analyze the factors that contribute to the presence or absence of an atmosphere on celestial bodies. Here’s a step-by-step solution:

### Step 1: Understand the concept of atmosphere
An atmosphere is a layer of gases surrounding a planet or moon, held in place by gravity. For a celestial body to retain an atmosphere, it must have sufficient gravitational pull to keep gas molecules from escaping into space.

**Hint:** Remember that gravity plays a crucial role in retaining gases.

### Step 2: Consider the size and mass of the moon
The moon is relatively small and has a lower mass compared to Earth. This means it has a weaker gravitational pull. The gravitational force is directly related to the mass of the celestial body; smaller bodies have less gravity.

**Hint:** Think about how mass affects gravitational strength.

### Step 3: Define escape velocity
Escape velocity is the minimum speed needed for an object to break free from the gravitational attraction of a celestial body. For the moon, the escape velocity is lower than that of Earth due to its smaller mass.

**Hint:** Recall that escape velocity depends on both the mass and radius of the celestial body.

### Step 4: Compare root mean square velocity of gas molecules
The root mean square velocity of gas molecules is a measure of the average speed of gas particles. If this speed is greater than the escape velocity of the moon, the gas particles will have enough energy to escape into space.

**Hint:** Consider the relationship between temperature and the speed of gas molecules.

### Step 5: Conclusion
Since the root mean square velocity of gas molecules on the moon is greater than the escape velocity, gas particles can easily escape the moon's gravitational pull. This is the primary reason the moon does not have a significant atmosphere.

**Final Answer:** There is no atmosphere on the moon because the root mean square velocity of gas molecules is greater than the escape velocity, allowing these particles to escape into space.