Chapter 5: Problem 5

In the most general terms, why do the Moon and the planet Mercury not have atmospheres?

Short Answer

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The Moon and Mercury lack atmospheres primarily due to their weak gravitational fields, high temperatures, and lack of protective magnetic fields. The weaker gravity makes it difficult for these bodies to retain gas particles, while high temperatures cause gas particles to move faster, increasing the chance of them escaping. Additionally, the absence of significant magnetic fields makes them more susceptible to the erosive effects of solar radiation, which can strip away any potential atmosphere.

Step by step solution

Gravity and Atmosphere Retention

The Moon and Mercury not having atmospheres can be partly attributed to their smaller masses, which translate to weaker gravitational fields. For a celestial body to retain an atmosphere, its gravity must be strong enough to hold the gas particles from escaping into space. The weaker a planet or moon's gravity, the more difficult it is for the body to hold on to the gas particles making up the atmosphere.

Escape Velocity and Gas Particle Speeds

It is essential to understand the concept of escape velocity in relation to atmospheric retention. Escape velocity refers to the minimum velocity required for an object to overcome the gravitational pull of a celestial body. For a gas particle to remain in an atmosphere, its average thermal speed should be much less than the escape velocity. Lighter gas particles move faster and, if their speeds are greater than the escape velocity, they can escape into space.

The Role of Temperature

The temperature of a celestial body directly affects the speed of gas particles in its atmosphere. The higher the temperature, the faster the gas particles move. Both the Moon and Mercury have high temperatures due to their proximity to the Sun, causing gas particles to move faster than they would in colder environments. Thus, it becomes increasingly difficult for these bodies to retain an atmosphere.

Absence of Magnetic Field

Another factor that may contribute to the lack of atmospheres on the Moon and Mercury is the absence of significant magnetic fields. Earth's magnetic field, for example, helps protect the atmosphere from being stripped away by solar winds. The Moon and Mercury, having weak or nonexistent magnetic fields, are more susceptible to the erosive effects of solar radiation. In conclusion, the absence of atmospheres on the Moon and Mercury can be mainly attributed to their weak gravitational fields, high temperatures, and lack of protective magnetic fields. These factors make it difficult for these celestial bodies to retain and maintain an atmosphere.

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In the most general terms, why do the Moon and the planet Mercury not have atmospheres?

Short Answer

Step by step solution

Gravity and Atmosphere Retention

Escape Velocity and Gas Particle Speeds

The Role of Temperature

Absence of Magnetic Field

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