<p>The <a href="https://en.wikipedia.org/wiki/Kepler-20" rel="nofollow noreferrer">Kepler-20</a> system has planets with masses in the following order, going outwards from the star:</p>

<ul>
<li>Kepler 20b:  <span class="math-container">$\approx 10 M_\oplus$</span></li>
<li>Kepler 20e:  <span class="math-container">$\approx M_\oplus$</span></li>
<li>Kepler 20c:  <span class="math-container">$\approx 16 M_\oplus$</span></li>
<li>Kepler 20f:  <span class="math-container">$\approx 1.5 M_\oplus$</span></li>
<li>Kepler 20g:  <span class="math-container">$\approx 20 M_\oplus$</span></li>
<li>Kepler 20d:  <span class="math-container">$&lt; 20 M_\oplus$</span></li>
</ul>

<p>If Wikipedia is to be believed, Kepler 20b may be a rocky world;  but at the very least, Kepler 20c is a hot Neptune and has a rocky planet (Kepler 20f) outside its orbit.</p>

CC BY-SA 4.0
2020-06-17T16:18:24.923Z
20c has f outside of its orbit, but I can understand how that could sporadically happen. Here the system is still weighted on the outside. I'm wondering whether there's an alternative formation pathway that produces a consistent relationship for all of the planets.
Axion
CC BY-SA 4.0
2020-06-14T19:35:50.703Z
2020-06-14T19:35:50.703Z
Michael Seifert
<p>I understand that formation theories for gas giants suggest they should be born further away where there is more gas for them to monopolize vs the sun, and then to form Hot Jupiters they need to migrate inwards, which would disrupt the orbits of rocky planets.</p>

<p>Are there any quibbles with this? Out of all the extrasolar systems is there even one where you have hot or warm gas giants and then cold Earth or Super-Earth sized terrestrials? Bodies like we have in the Kuiper belt lie beyond our gas giants but they are mostly made of ices and represent a small leftover fraction of the system mass, so they don't really count here.</p>

CC BY-SA 4.0
2020-06-17T16:15:02.523Z
Neptune-like planets are usually considered ice giants.
Axion
<astrophysics><exoplanet><planetary-formation><gas-giants><terrestrial-planets>
Are there other planetary systems where gas giants are on the inside to rocky planet orbits?
Axion
# Are there other planetary systems where gas giants are on the inside to rocky planet orbits?

(Asked by: username_0 on 2020-06-14)

I understand that formation theories for gas giants suggest they should be born further away where there is more gas for them to monopolize vs the sun, and then to form Hot Jupiters they need to migrate inwards, which would disrupt the orbits of rocky planets.

Are there any quibbles with this? Out of all the extrasolar systems is there even one where you have hot or warm gas giants and then cold Earth or Super-Earth sized terrestrials? Bodies like we have in the Kuiper belt lie beyond our gas giants but they are mostly made of ices and represent a small leftover fraction of the system mass, so they don't really count here.

**Tags:** astrophysics, exoplanet, planetary-formation, gas-giants, terrestrial-planets

> **Comments:**
> **username_0**: Neptune-like planets are usually considered ice giants.  

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## 1 answers

### Answer by username_1 on 2020-06-14. Score: 4 | Accepted answer

The [Kepler-20](https://en.wikipedia.org/wiki/Kepler-20) system has planets with masses in the following order, going outwards from the star:

* Kepler 20b: $\approx 10 M\_\oplus$
* Kepler 20e: $\approx M\_\oplus$
* Kepler 20c: $\approx 16 M\_\oplus$
* Kepler 20f: $\approx 1.5 M\_\oplus$
* Kepler 20g: $\approx 20 M\_\oplus$
* Kepler 20d: $< 20 M\_\oplus$

If Wikipedia is to be believed, Kepler 20b may be a rocky world; but at the very least, Kepler 20c is a hot Neptune and has a rocky planet (Kepler 20f) outside its orbit.

> **Comments:**
> **username_0**: 20c has f outside of its orbit, but I can understand how that could sporadically happen. Here the system is still weighted on the outside. I'm wondering whether there's an alternative formation pathway that produces a consistent relationship for all of the planets.  

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