<p>Astronomers are not still completely sure that these satellites are captured asteroids (see for example <a href="https://ui.adsabs.harvard.edu/abs/2011A%26ARv..19...44R/abstract" rel="nofollow noreferrer">this paper</a>). However, in case they are, it's true that their eccentricity should be much higher. There are several theories that provide scenarios for the circularization of the orbits (the most recent I found is <a href="https://www.sciencedirect.com/science/article/abs/pii/S0019103519305950" rel="nofollow noreferrer">this one</a>, which invokes impacts on the moons causing them to start tumbling and exciting the spin), but more data is needed to test these hypothesis (see <a href="https://www.nature.com/articles/s41586-019-1202-7" rel="nofollow noreferrer">this last paper</a> for a review of this).</p>

CC BY-SA 4.0
2020-08-07T09:55:33.867Z
2020-08-07T09:55:33.867Z
Pablo Lemos
<p>The satellites of Mars might be captured asteroids. But Phobos has an eccentricity of <span class="math-container">$0.015$</span>, and Deimos of <span class="math-container">$3\times10^{-4}$</span>. If they were captured, they likely were captured with rather eccentric orbits. How did their orbits circularize?</p>

<mars><natural-satellites><phobos><deimos>
How did the orbits of Phobos and Deimos circularize?
usernumber
# How did the orbits of Phobos and Deimos circularize?

(Asked by: username_0 on 2020-08-07)

The satellites of Mars might be captured asteroids. But Phobos has an eccentricity of $0.015$, and Deimos of $3\times10^{-4}$. If they were captured, they likely were captured with rather eccentric orbits. How did their orbits circularize?

**Tags:** mars, natural-satellites, phobos, deimos

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## 1 answers

### Answer by username_1 on 2020-08-07. Score: 1 | Accepted answer

Astronomers are not still completely sure that these satellites are captured asteroids (see for example [this paper](https://ui.adsabs.harvard.edu/abs/2011A%26ARv..19...44R/abstract)). However, in case they are, it's true that their eccentricity should be much higher. There are several theories that provide scenarios for the circularization of the orbits (the most recent I found is [this one](https://www.sciencedirect.com/science/article/abs/pii/S0019103519305950), which invokes impacts on the moons causing them to start tumbling and exciting the spin), but more data is needed to test these hypothesis (see [this last paper](https://www.nature.com/articles/s41586-019-1202-7) for a review of this).


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