<p>There is no good &quot;one answer fits all&quot; answer, given the huge differences in how you can or cannot even well define a surface.</p>
<p>For terrestrial planets with a clearly defined solid surface, the usual answer to &quot;what is the boundary&quot; is usually just that: the solid surface. But of course that doesn't mean that the atmosphere doesn't belong to the planet nor that even the entire magnetosphere doesn't belong to the planet, or its gravitational well - what is useful depends on the questions you want to ask.</p>
<p>For gas planets like Jupiter, Saturn... one usually defines the &quot;surface&quot; often where the optical depth is one (thus the 'layer' which we see most prominently).</p>

CC BY-SA 4.0
2024-12-23T12:08:01.060Z
I am not trying to define a physical surface of a planet per se, but more as what constitutes a planetary system.  Does the boundary of a definition of a planet end at its gravity well or its sphere of magnetic influence?
ksinkar
CC BY-SA 4.0
2024-12-23T12:09:02.140Z
This is interesting from both a legal and scientific perspective. It helps you define certain processes that happen to a planet as endogenic or exogenic.
ksinkar
CC BY-SA 4.0
2024-12-23T19:13:31.083Z
@ksinkar If you didn't notice, even defining *if* something is a planet is still a problem.
Mithoron
CC BY-SA 4.0
2024-12-20T21:00:39.653Z
2024-12-20T21:00:39.653Z
planetmaker
<p>A planet is dynamic system of of rocks. A planet has a petrological cycle however slow. This petrological cycle gives rise to various other parts of the planet e.g. a magnetosphere.</p>
<p>A planet could also have an atmosphere and fluvial flow on its lithosphere.</p>
<ul>
<li>What is the official boundary of a planet?</li>
<li>Which spheres are considered intrinsic to a planet?</li>
</ul>
<h5>Why do we need know the definition of the boundary of a planet?</h5>
<p>A clear definition of the systemic boundary of a planet is required for scientific and legal purposes.</p>
<h6>Scientific</h6>
<p>To define which processes that happen on the planet are</p>
<ul>
<li>endogenic</li>
<li>exogenic</li>
</ul>
<p>e.g.</p>
<ul>
<li>Is fluvial flow on the surface of a planet endogenic or exogenic?</li>
<li>Are atmospheric weather erosions endogenic or exogenic?</li>
</ul>
<h6>Legal</h6>
<p>To define the jurisdictional boundary of a planetary government for taxation, resource management and conflict resolution purposes</p>
<p>e.g.</p>
<ul>
<li>Is the electricity generated using the tides of the ocean classified as endogenic or exogenic? The cause of the tides is exogenic, but the tides themselves are endogenic IMHO.</li>
</ul>

CC BY-SA 4.0
2024-12-20T22:54:12.700Z
And the third question... why does it matter?
James K
CC BY-SA 4.0
2024-12-21T02:13:23.477Z
See: https://earthscience.stackexchange.com/questions/13888/is-the-atmosphere-a-part-of-earth
Nilay Ghosh
CC BY-SA 4.0
2024-12-21T02:30:31.310Z
Also related: https://astronomy.stackexchange.com/questions/36684/where-do-we-define-the-surface-of-a-gas-planet
Nilay Ghosh
CC BY-SA 4.0
2024-12-21T02:37:17.400Z
https://www.physicsforums.com/threads/why-jupiter-saturn-and-the-sun-have-a-distinctive-and-sharp-boundary.976172/
Nilay Ghosh
CC BY-SA 4.0
2024-12-22T00:22:20.790Z
What do you mean by "endemic".  It is used of diseases (Malaria is endemic to much of Africa), and it is used about plants/animals (kangaroos are endemic to Australia). You don't use "endemic" to talk about "spheres" like lithosphere or atmosphere.  That's not the right word.
James K
CC BY-SA 4.0
2024-12-22T00:23:20.773Z
So your two questions are unanswerable. There is no official boundary.  And "endemic" doesn't apply to spheres.
James K
CC BY-SA 4.0
2024-12-23T11:52:45.710Z
@JamesK The reason why it matters is to better define endogenic and exogenic processes on a planet. Whether a process on a planet could be defined either way, IMHO one needs to be clear about what is an "endemic" part of a planet and what is not.
ksinkar
CC BY-SA 4.0
2024-12-23T13:33:28.680Z
I don't see any difficulty in the definition of endogenic and exogenic, but perhaps you could clarify the issue in the question.  What is an example of a process that would change classification based on whether the atmosphere is considered part of the planet or not.  The word "endemic"  still doesn't apply here. The classification into endemic and exogenic is a convenience and there are processes which are driven partially from with and partially from without.
James K
CC BY-SA 4.0
2024-12-23T14:03:24.543Z
Is the magnetic field around a magnet an integral part of the magnet?  Is the dust cloud around Linus part of Linus?
eshaya
CC BY-SA 4.0
2024-12-26T11:49:25.510Z
The legal issues are irrelevant to astronomy, but the Outer Space Treaty applies.  Whether tides are ex or endo is irrelevant to who can extract energy from them. The scientific issues of exogenic and endogenic are perhaps of minor interest to Earth Sciences (not everything has to be classified as one or the other, the classification is only to simplify discussion, it doesn't reflect a fundamental truth). It's not relevant to Astronomy. I vote to close this question as off topic on that basis.
James K
CC BY-SA 4.0
2024-12-26T19:35:18.747Z
@JamesK Classification is a matter of taxonomy. Taxonomy is an important part of the scientific process. Your comment above is equivalent to saying that whether Pluto is classified as a planet or not, is irrelevant to astronomy!  The legal example is simply given to highlight the significance of the definition to exist in the first place.
ksinkar
CC BY-SA 4.0
2024-12-26T22:59:07.337Z
The question of whether rivers are exo or endo is irrelevant to astronomy. It is of minor interest to Earth Science (The question of whether Pluto has cleared its neighbourhood is of minor interest to astronomy. The question of what the definition of "planet" should be is entirely bureaucratic, an not relevant to science at all)
James K
CC BY-SA 4.0
2024-12-26T23:01:54.843Z
The answer to the E.S. questions is "fluvial flows: mostly powered by the sun, so exogenic"  Weather: mostly powered by the sun,  exogenic.  Tides.  A vaguely interesting edge case. The source of the energy in tides is mostly the kinetic energy in the rotation of the Earth.  Thus they are neither typical exogenic nor endogenic, and probably belong in a category of their own.  But that is again a matter for bureaucracy not science.
James K
CC BY-SA 4.0
2024-12-27T00:08:26.783Z
@ksinkar: "A planet is dynamic system of of rocks". Incorrect. Only small planets are dynamic systems of rocks. There are other classes of planets which are made up of significant amounts of gas, which are very frequent in the universe (or at least, the local galaxy). Your question title asks about gas, but the body of your question asks about many other, albeit different things. Maybe you want to straighten that out.
AtmosphericPrisonEscape
CC BY-SA 4.0
2024-12-30T18:07:14.970Z
@ksinkar I'm not sure I follow the argument about the scientific merit. What question exactly would be easier to answer if we define "atmosphere not part of a planet" (or whatever arbitrary definition we choose)? Nature doesn't care about that. To me that sounds like creating problems where there wouldn't be any with a problem-specific definition and in the absence of any such strict boundary. Care to give a few questions which will get easier *iff* one has a clear-cut definition instead of the usual problem-specific ones for boundaries? I don't understand it for fluvial flows nor erosion.
planetmaker
CC BY-SA 4.0
2024-12-30T20:20:13.603Z
https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line
Mithoron
<planet><planetary-atmosphere><planetary-science>
Is the atmosphere of a planet considered an integral part of the planet?
ksinkar
# Is the atmosphere of a planet considered an integral part of the planet?

(Asked by: username_0 on 2024-12-20)

A planet is dynamic system of of rocks. A planet has a petrological cycle however slow. This petrological cycle gives rise to various other parts of the planet e.g. a magnetosphere.

A planet could also have an atmosphere and fluvial flow on its lithosphere.

* What is the official boundary of a planet?
* Which spheres are considered intrinsic to a planet?

##### Why do we need know the definition of the boundary of a planet?

A clear definition of the systemic boundary of a planet is required for scientific and legal purposes.

###### Scientific

To define which processes that happen on the planet are

* endogenic
* exogenic

e.g.

* Is fluvial flow on the surface of a planet endogenic or exogenic?
* Are atmospheric weather erosions endogenic or exogenic?

###### Legal

To define the jurisdictional boundary of a planetary government for taxation, resource management and conflict resolution purposes

e.g.

* Is the electricity generated using the tides of the ocean classified as endogenic or exogenic? The cause of the tides is exogenic, but the tides themselves are endogenic IMHO.

**Tags:** planet, planetary-atmosphere, planetary-science
> **Comments:**
> **username_1**: And the third question... why does it matter?  
> **username_2**: See: https://earthscience.stackexchange.com/questions/13888/is-the-atmosphere-a-part-of-earth  
> **username_2**: Also related: https://astronomy.stackexchange.com/questions/36684/where-do-we-define-the-surface-of-a-gas-planet  
> **username_2**: https://www.physicsforums.com/threads/why-jupiter-saturn-and-the-sun-have-a-distinctive-and-sharp-boundary.976172/  
> **username_1**: What do you mean by "endemic".  It is used of diseases (Malaria is endemic to much of Africa), and it is used about plants/animals (kangaroos are endemic to Australia). You don't use "endemic" to talk about "spheres" like lithosphere or atmosphere.  That's not the right word.  
> **username_1**: So your two questions are unanswerable. There is no official boundary.  And "endemic" doesn't apply to spheres.  
> **username_0**: @JamesK The reason why it matters is to better define endogenic and exogenic processes on a planet. Whether a process on a planet could be defined either way, IMHO one needs to be clear about what is an "endemic" part of a planet and what is not.  
> **username_1**: I don't see any difficulty in the definition of endogenic and exogenic, but perhaps you could clarify the issue in the question.  What is an example of a process that would change classification based on whether the atmosphere is considered part of the planet or not.  The word "endemic"  still doesn't apply here. The classification into endemic and exogenic is a convenience and there are processes which are driven partially from with and partially from without.  
> **username_3**: Is the magnetic field around a magnet an integral part of the magnet?  Is the dust cloud around Linus part of Linus?  
> **username_1**: The legal issues are irrelevant to astronomy, but the Outer Space Treaty applies.  Whether tides are ex or endo is irrelevant to who can extract energy from them. The scientific issues of exogenic and endogenic are perhaps of minor interest to Earth Sciences (not everything has to be classified as one or the other, the classification is only to simplify discussion, it doesn't reflect a fundamental truth). It's not relevant to Astronomy. I vote to close this question as off topic on that basis.  
> **username_0**: @JamesK Classification is a matter of taxonomy. Taxonomy is an important part of the scientific process. Your comment above is equivalent to saying that whether Pluto is classified as a planet or not, is irrelevant to astronomy!  The legal example is simply given to highlight the significance of the definition to exist in the first place.  
> **username_1**: The question of whether rivers are exo or endo is irrelevant to astronomy. It is of minor interest to Earth Science (The question of whether Pluto has cleared its neighbourhood is of minor interest to astronomy. The question of what the definition of "planet" should be is entirely bureaucratic, an not relevant to science at all)  
> **username_1**: The answer to the E.S. questions is "fluvial flows: mostly powered by the sun, so exogenic"  Weather: mostly powered by the sun,  exogenic.  Tides.  A vaguely interesting edge case. The source of the energy in tides is mostly the kinetic energy in the rotation of the Earth.  Thus they are neither typical exogenic nor endogenic, and probably belong in a category of their own.  But that is again a matter for bureaucracy not science.  
> **username_4**: @ksinkar: "A planet is dynamic system of of rocks". Incorrect. Only small planets are dynamic systems of rocks. There are other classes of planets which are made up of significant amounts of gas, which are very frequent in the universe (or at least, the local galaxy). Your question title asks about gas, but the body of your question asks about many other, albeit different things. Maybe you want to straighten that out.  
> **username_5**: @ksinkar I'm not sure I follow the argument about the scientific merit. What question exactly would be easier to answer if we define "atmosphere not part of a planet" (or whatever arbitrary definition we choose)? Nature doesn't care about that. To me that sounds like creating problems where there wouldn't be any with a problem-specific definition and in the absence of any such strict boundary. Care to give a few questions which will get easier *iff* one has a clear-cut definition instead of the usual problem-specific ones for boundaries? I don't understand it for fluvial flows nor erosion.  
> **username_6**: https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line  

---

## 1 answers

### Answer by username_5 on 2024-12-20. Score: 7

There is no good "one answer fits all" answer, given the huge differences in how you can or cannot even well define a surface.

For terrestrial planets with a clearly defined solid surface, the usual answer to "what is the boundary" is usually just that: the solid surface. But of course that doesn't mean that the atmosphere doesn't belong to the planet nor that even the entire magnetosphere doesn't belong to the planet, or its gravitational well - what is useful depends on the questions you want to ask.

For gas planets like Jupiter, Saturn... one usually defines the "surface" often where the optical depth is one (thus the 'layer' which we see most prominently).

> **Comments:**
> **username_0**: I am not trying to define a physical surface of a planet per se, but more as what constitutes a planetary system.  Does the boundary of a definition of a planet end at its gravity well or its sphere of magnetic influence?  
> **username_0**: This is interesting from both a legal and scientific perspective. It helps you define certain processes that happen to a planet as endogenic or exogenic.  
> **username_6**: @ksinkar If you didn't notice, even defining *if* something is a planet is still a problem.  

---

