<blockquote>
<p>The Gas Giant should have a hill sphere of 0.15627750286244 Astronomical Units. But that seems very large.</p>
</blockquote>
<p>Your planet is 12 Jupiter masses in size... it <em>is</em> very large! It probably counts as a small <a href="https://en.wikipedia.org/wiki/Brown_dwarf" rel="nofollow noreferrer">brown dwarf</a>... <a href="https://en.wikipedia.org/wiki/GU_Piscium" rel="nofollow noreferrer">GU Piscium</a> has a similar mass, for example. Your &quot;planet&quot; masses about as much as the whole of the solar system excluding the Sun.</p>
<p>Anyway, I get the same Hill radius that you did, so your calculation is probably correct.</p>
<blockquote>
<p>And if i place a body in 0.1 AU Distance of the Planet, it will quickly leave its orbit.</p>
</blockquote>
<p><a href="https://en.wikipedia.org/wiki/Hill_sphere#Regions_of_stability" rel="nofollow noreferrer">The wikipedia article on the subject</a> says &quot;<em>Detailed numerical calculations show that orbits at or just within the Hill sphere are not stable in the long term; it appears that stable satellite orbits exist only inside 1/2 to 1/3 of the Hill radius</em>&quot;.</p>
<p>Try placing the body at .5 AU instead.</p>

CC BY-SA 4.0
2024-04-25T03:04:51.993Z
Good advice.  I was thinking that a distance of 0.666 of the Hill Sphere was too far from the planet.
M. A. Golding
CC BY-SA 4.0
2024-04-24T21:08:09.110Z
2024-04-24T21:08:09.110Z
Starfish Prime
<p>So according to this calculation here including:</p>
<ul>
<li>A Gas Giant of 12 Jupiter Masses</li>
<li>A Sun like Star of <strong>1047.57 Jupiter Masses</strong></li>
<li>and a semi major axis of the Planet of 1 AU</li>
</ul>
<p><a href="https://i.sstatic.net/vTXQrxfo.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/vTXQrxfo.png" alt="enter image description here" /></a></p>
<p>The Gas Giant should have a hill sphere of 0.15627750286244 Astronomical Units. But that seems very large. And if i place a body in 0.1 AU Distance of the Planet, it will quickly leave its orbit.</p>
<p>What am i missing here?</p>

<gravity>
Universe Sandbox and Hillsphere calculation (Updated)
Zadai.Fehbiab
# Universe Sandbox and Hillsphere calculation (Updated)

(Asked by: username_0 on 2024-04-24)

So according to this calculation here including:

* A Gas Giant of 12 Jupiter Masses
* A Sun like Star of **1047.57 Jupiter Masses**
* and a semi major axis of the Planet of 1 AU

[![enter image description here](https://i.sstatic.net/vTXQrxfo.png)](https://i.sstatic.net/vTXQrxfo.png)

The Gas Giant should have a hill sphere of 0.15627750286244 Astronomical Units. But that seems very large. And if i place a body in 0.1 AU Distance of the Planet, it will quickly leave its orbit.

What am i missing here?

**Tags:** gravity

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## 1 answers

### Answer by username_1 on 2024-04-24. Score: 2

> The Gas Giant should have a hill sphere of 0.15627750286244 Astronomical Units. But that seems very large.

Your planet is 12 Jupiter masses in size... it *is* very large! It probably counts as a small [brown dwarf](https://en.wikipedia.org/wiki/Brown_dwarf)... [GU Piscium](https://en.wikipedia.org/wiki/GU_Piscium) has a similar mass, for example. Your "planet" masses about as much as the whole of the solar system excluding the Sun.

Anyway, I get the same Hill radius that you did, so your calculation is probably correct.

> And if i place a body in 0.1 AU Distance of the Planet, it will quickly leave its orbit.

[The wikipedia article on the subject](https://en.wikipedia.org/wiki/Hill_sphere#Regions_of_stability) says "*Detailed numerical calculations show that orbits at or just within the Hill sphere are not stable in the long term; it appears that stable satellite orbits exist only inside 1/2 to 1/3 of the Hill radius*".

Try placing the body at .5 AU instead.

> **Comments:**
> **username_2**: Good advice.  I was thinking that a distance of 0.666 of the Hill Sphere was too far from the planet.  

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