<p>Orbital eccentricities and inclinations are damped to zero during the protoplanetary disc phase. This is because the gaseous parts of the protoplanetary disc are a great sink for excess angular momentum.</p>
<p>After the gas disc dissipates, the formed planets start to interact dynamically as they do not necessarily form in stable configurations. This can lead to the exchange of angular momentum. A giant planet with small initial eccentricity can hereby pump a lot of eccentricity into less massive planets, as the angular momentum <span class="math-container">$L=rmv$</span> is conserved.<br />
So 'classical' thinking involves the exchange of angular momentum between planets after the gas disc dissipates as the origin of exoplanetary eccentricities.</p>
<p>A modern caveat to this is that there are mechanisms to incline parts of the inner gas disc during the planet formation phase w.r.t. the rest of the disc. As eccentricity and inclination are intrinsically linked, those inclined sub-discs may form inclined planets, which later lead to strong eccentricity pumping.</p>

CC BY-SA 4.0
2021-02-08T16:59:01.197Z
2021-02-08T16:59:01.197Z
AtmosphericPrisonEscape
<p>The field of <a href="https://astronomy.stackexchange.com/questions/tagged/astrobiology">astrobiology</a> specifically discovering other planets that revolve around the sun-like star (also known as Exoplanets) has risen since 1990, but certain orbits of exoplanets are observed to have a much wider range in eccentricity than exhibited by the planets in our solar system. What's the reason behind this?</p>

CC BY-SA 4.0
2021-02-05T12:36:25.267Z
Welcome to astronomy SE! I found https://physics.stackexchange.com/questions/160893/calculating-the-eccentricity-of-an-exoplanet and https://www.pnas.org/content/112/1/20 which you might find interesting.
B--rian
CC BY-SA 4.0
2021-02-05T12:36:56.890Z
Related question: https://astronomy.stackexchange.com/questions/32018/what-maintains-the-high-orbital-eccentricity-of-many-exo-planets-near-their-sun which does not yet have an answer
B--rian
<observational-astronomy><astrophysics><exoplanet><observable-universe><astrobiology>
Eccentricity of Exoplanets
Autodidact
# Eccentricity of Exoplanets

(Asked by: username_0 on 2021-02-05)

The field of [astrobiology](https://astronomy.stackexchange.com/questions/tagged/astrobiology) specifically discovering other planets that revolve around the sun-like star (also known as Exoplanets) has risen since 1990, but certain orbits of exoplanets are observed to have a much wider range in eccentricity than exhibited by the planets in our solar system. What's the reason behind this?

**Tags:** observational-astronomy, astrophysics, exoplanet, observable-universe, astrobiology

> **Comments:**
> **username_1**: Welcome to astronomy SE! I found https://physics.stackexchange.com/questions/160893/calculating-the-eccentricity-of-an-exoplanet and https://www.pnas.org/content/112/1/20 which you might find interesting.  
> **username_1**: Related question: https://astronomy.stackexchange.com/questions/32018/what-maintains-the-high-orbital-eccentricity-of-many-exo-planets-near-their-sun which does not yet have an answer  

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## 1 answers

### Answer by username_2 on 2021-02-08. Score: 2 | Accepted answer

Orbital eccentricities and inclinations are damped to zero during the protoplanetary disc phase. This is because the gaseous parts of the protoplanetary disc are a great sink for excess angular momentum.

After the gas disc dissipates, the formed planets start to interact dynamically as they do not necessarily form in stable configurations. This can lead to the exchange of angular momentum. A giant planet with small initial eccentricity can hereby pump a lot of eccentricity into less massive planets, as the angular momentum $L=rmv$ is conserved.  
So 'classical' thinking involves the exchange of angular momentum between planets after the gas disc dissipates as the origin of exoplanetary eccentricities.

A modern caveat to this is that there are mechanisms to incline parts of the inner gas disc during the planet formation phase w.r.t. the rest of the disc. As eccentricity and inclination are intrinsically linked, those inclined sub-discs may form inclined planets, which later lead to strong eccentricity pumping.


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