<p>The loss of the Martian atmosphere can be mostly attributed to its mass. The reason why Earth still has an atmosphere made of lighter elements is because with larger mass comes larger <a href="http://en.wikipedia.org/wiki/Escape_velocity" rel="noreferrer">escape velocity</a>, which is the speed at which an atom's kinetic energy overcomes the gravitational potential energy of its planet.</p>

<p>The distribution of speeds of most gasses can be described by the <a href="http://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution" rel="noreferrer">Maxwell–Boltzmann distribution</a>.</p>

<p><img src="https://i.sstatic.net/7LPXz.png" alt="Maxwell-Boltzmann"></p>

<p>This curve represents the probability of finding a particle with a given speed at a given temperature. Holding temperature constant, the above chart illustrates that lighter molecules will have higher probabilities of being found with higher speeds. 
$$P(\epsilon) = \frac{2}{\sqrt{\pi}k_{B}T} \left( \frac{\epsilon}{k_{B}T}  \right)^{1/2} \exp{-\left(\frac{\epsilon}{k_{B}T}\right)} $$
where $\epsilon$ is the energy of the particle, $\frac{p^{2}}{2m}$ in the absence of a gravitational field (see <a href="https://www.google.com/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=2&amp;cad=rja&amp;ved=0CC8QFjAB&amp;url=http://highenergy.phys.ttu.edu/~slee/2402/2010_Fall/F10_2402_Lecture23.pdf&amp;ei=bVluUob8E-ih4APN9IC4Cg&amp;usg=AFQjCNFIhCzaBMVzBeTEHPu56JLMz_GZfw" rel="noreferrer">this lecture</a> for information regarding how to include the gravitational term).</p>

<p>Integrated over time, the lighter gasses tend to exceed the escape velocity more often than their heavier counterparts. This is why the larger planets like Jupiter and Saturn still have atmospheres dominated by hydrogen and helium.   </p>

CC BY-SA 3.0
2013-10-20T01:35:32.220Z
2013-10-28T12:41:45.033Z
2013-10-28T12:41:45.033Z
astromax
<p>If the atmosphere on Mars was once much thicker, how was it likely lost?  Was it due to interaction with the solar wind, the small size of the planet, both, or something else, and approximately how long did it take to reach its current thickness?</p>

<planetary-atmosphere><mars>
Loss of atmosphere on Mars
Becky Ericson
# Loss of atmosphere on Mars

(Asked by: username_0 on 2013-10-19)

If the atmosphere on Mars was once much thicker, how was it likely lost? Was it due to interaction with the solar wind, the small size of the planet, both, or something else, and approximately how long did it take to reach its current thickness?

**Tags:** planetary-atmosphere, mars

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## 1 answers

### Answer by username_1 on 2013-10-20. Score: 11 | Accepted answer

The loss of the Martian atmosphere can be mostly attributed to its mass. The reason why Earth still has an atmosphere made of lighter elements is because with larger mass comes larger [escape velocity](http://en.wikipedia.org/wiki/Escape_velocity), which is the speed at which an atom's kinetic energy overcomes the gravitational potential energy of its planet.

The distribution of speeds of most gasses can be described by the [Maxwell–Boltzmann distribution](http://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution).

![Maxwell-Boltzmann](https://i.sstatic.net/7LPXz.png)

This curve represents the probability of finding a particle with a given speed at a given temperature. Holding temperature constant, the above chart illustrates that lighter molecules will have higher probabilities of being found with higher speeds.
$$P(\epsilon) = \frac{2}{\sqrt{\pi}k\_{B}T} \left( \frac{\epsilon}{k\_{B}T} \right)^{1/2} \exp{-\left(\frac{\epsilon}{k\_{B}T}\right)} $$
where $\epsilon$ is the energy of the particle, $\frac{p^{2}}{2m}$ in the absence of a gravitational field (see [this lecture](https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&ved=0CC8QFjAB&url=http://highenergy.phys.ttu.edu/~slee/2402/2010_Fall/F10_2402_Lecture23.pdf&ei=bVluUob8E-ih4APN9IC4Cg&usg=AFQjCNFIhCzaBMVzBeTEHPu56JLMz_GZfw) for information regarding how to include the gravitational term).

Integrated over time, the lighter gasses tend to exceed the escape velocity more often than their heavier counterparts. This is why the larger planets like Jupiter and Saturn still have atmospheres dominated by hydrogen and helium.


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