What factors determine the composition of a planet's atmosphere?

In summary, the mass of a body affects the type of atmosphere it can hold. Planets like Saturn and Jupiter have been able to retain hydrogen and helium due to their high mass, while Earth tends to lose its lighter gases over time. The escape velocity, which is higher for planets with heavier mass, also plays a role in retaining gases in the atmosphere. Additionally, non-thermal losses, such as solar and stellar winds, can also affect a planet's ability to hold onto gases. This information is further explained in a Wikipedia article that includes a chart plotting escape velocity versus temperature for different gases.
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Drakkith
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I'm curious as to how the mass of a body affects the kind of atmosphere it can hold. I know that Earth tends to lose its lightest gases over time, which is one reason why helium doesn't build up in the atmosphere, whereas planets like Saturn and Jupiter have held on to lots and lots of hydrogen and helium. However, I haven't read much on how other gases are affected. Does anyone have any good information on this?
 
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I don't have a good source, but ## \bar{v}=\sqrt{\frac{8 kT}{\pi m}} ##. This means with sufficiently high temperatures, atoms of lighter masses are going to be able to thermally acquire the necessary escape velocity more readily. The escape velocity, with ## \frac{1}{2}(m)v^2=\frac{GM}{r}(m) ##, (the ## m's ## cancel) , will be higher for a planet of heavier mass ## M ## . Thereby a cold planet with a heavy mass favors being able to contain the lighter atoms in its atmosphere.
 
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That matches with what I was thinking, but I hadn't seen any real information on the subject before. Makes me wonder if all those hot Jupiter's are slowly losing mass.
 
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This wikipedia article deals with the issue. It includes a useful overview of the importance of non-thermal losses (especially solar/stellar winds) in some circumstances. There is a useful chart plotting escape velocity versus temperature for some of the more important gases.
 
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Ophiolite said:
This wikipedia article deals with the issue. It includes a useful overview of the importance of non-thermal losses (especially solar/stellar winds) in some circumstances. There is a useful chart plotting escape velocity versus temperature for some of the more important gases.

Thanks! Just what I was looking for!
 

1. What is the relationship between planetary mass and atmosphere?

The relationship between planetary mass and atmosphere is a complex one. Generally, a higher mass planet tends to have a thicker atmosphere due to its stronger gravitational pull. However, other factors such as distance from the sun, composition of the atmosphere, and presence of a magnetic field also play a role in determining the thickness and composition of a planet's atmosphere.

2. Can a planet have a thick atmosphere with a low mass?

Yes, it is possible for a planet to have a thick atmosphere with a low mass. This is because other factors such as distance from the sun, chemical composition, and magnetic field can also influence the thickness and composition of a planet's atmosphere.

3. How does a planet's atmosphere affect its mass?

A planet's atmosphere does not significantly affect its mass. While the atmosphere does have a slight mass, it is relatively small compared to the overall mass of the planet. The majority of a planet's mass comes from its solid core and mantle.

4. What types of gases make up a planet's atmosphere?

The composition of a planet's atmosphere varies depending on the planet's distance from the sun, its size and mass, and its geological activity. However, the most common gases found in planetary atmospheres are nitrogen, oxygen, and carbon dioxide. Other gases such as methane, ammonia, and water vapor can also be present in smaller amounts.

5. How does the atmosphere protect a planet?

The atmosphere provides protection for a planet in several ways. It helps regulate the planet's temperature by trapping heat from the sun, preventing extreme temperature fluctuations. It also shields the planet from harmful solar radiation and space debris, which can pose a threat to life on the planet's surface. Additionally, the atmosphere plays a crucial role in the water cycle and helps maintain a habitable environment for living organisms.

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