<p><a href="https://en.wikipedia.org/wiki/Hot_Neptune" rel="nofollow noreferrer">Hot Neptunes</a> are known, beginning with an exoplanet orbiting the star Gliese 436. They may be formed either at greater distances from the star and then migrate inwards (ex-situ) or at close distances initially (in-situ).</p>
<p>Either way, these exoplanets would not be Earth-like. Their composition depends on how they are formed, but in general they must contain predominantly hydrogen and helium, overlying heavier ices or perhaps more refractory compounds:</p>
<blockquote>
<p>The first theoretical study of how hot Neptunes could form was carried out in 2004.[<a href="https://doi.org/10.1016/j.icarus.2005.02.015" rel="nofollow noreferrer">1</a>] If these planets formed ex situ, i.e., by migrating to their current locations while growing, they may contain large quantities of frozen volatiles and amorphous ices. Otherwise, if they formed in situ, their inventory of heavy elements should be made entirely of refractory materials.[<a href="https://doi.org/10.3847/0004-637X/828/1/33" rel="nofollow noreferrer">2</a>] Yet, regardless of the mode of formation, hot Neptunes should contain large fractions (by mass) of gases, primarily hydrogen and helium, which also account for most of their volume.[3][<a href="https://doi.org/10.1007/978-3-319-55333-7_140" rel="nofollow noreferrer">4</a>]</p>
</blockquote>
<p>On this basis a &quot;composition similar to Uranus&quot; would require an ex-situ formation process,csince Uranus itself has more ices than refractory material. With the hydrogen-helium gas overlay and a heat input similar to Earth the exoplanet would then look much like Uranus itself.</p>
<p><strong>Cited References</strong></p>
<ol>
<li><p>Adrián Brunini and Rodolfo G. Cionco (September 2005). &quot;The origin and nature of Neptune-like planets orbiting close to solar type stars&quot;. Icarus. 177 (1): 264–68. arXiv:astro-ph/0511051. Bibcode:2005Icar..177..264B. doi:10.1016/j.icarus.2005.02.015. S2CID 18979082.</p>
</li>
<li><p>D'Angelo, G.; Bodenheimer, P. (2016). &quot;In Situ and Ex Situ Formation Models of Kepler 11 Planets&quot;. The Astrophysical Journal. 828 (1): id. 33. arXiv:1606.08088. Bibcode:2016ApJ...828...33D. doi:10.3847/0004-637X/828/1/33. S2CID 119203398.</p>
</li>
<li><p>D'Angelo, G.; Durisen, R. H.; Lissauer, J. J. (2011). &quot;Giant Planet Formation&quot;. In S. Seager. (ed.). Exoplanets. University of Arizona Press, Tucson, AZ. pp. 319–346. arXiv:1006.5486.
Bibcode:2010exop.book..319D.</p>
</li>
<li><p>D'Angelo, G.; Lissauer, J. J. (2018). &quot;Formation of Giant Planets&quot;. In Deeg H., Belmonte J. (ed.). Handbook of Exoplanets. Springer International Publishing AG, part of Springer Nature. pp. 2319–2343. arXiv:1806.05649. Bibcode:2018haex.bookE.140D. doi:10.1007/978-3-319-55333-7_140. ISBN 978-3-319-55332-0. S2CID 116913980.</p>
</li>
</ol>

CC BY-SA 4.0
2023-06-23T23:56:29.777Z
So, to be clear, if Uranus, as it is composed, move into Earth's orbit, the thermal gain would not be sufficient for it to develop an atmosphere or melt?
Curious Gorge
CC BY-SA 4.0
2023-06-24T00:20:09.037Z
Probably not. Uranus is already hot in its interior, so solar heat gain would have little impact there. Uranus would be warmer at the surface, but likely not hot enough to give hydrogen loss given its large escape velocity.
Oscar Lanzi
CC BY-SA 4.0
2023-06-24T00:25:45.223Z
@curious You assume that uranus or neptune are frozen. They are not. The visible 'surface' is composed of gas, they have no (visible) surface. And the solid core is warm or hot as is any planet core as result of its formation by accretion.
planetmaker
CC BY-SA 4.0
2023-06-24T00:27:50.067Z
Yeah I was wondering why the asker referred to the planet melting. This on an astronomy board. Yeesh!
Oscar Lanzi
CC BY-SA 4.0
2023-06-24T00:30:00.693Z
Apologies for the layman's terms, but I appreciate the clarification.
Curious Gorge
CC BY-SA 4.0
2023-06-23T21:30:58.050Z
2023-06-23T22:27:35.350Z
2023-06-23T22:27:35.350Z
Oscar Lanzi
<p>In my recollection, until the late 1990s, all four outer planets, including Uranus and Neptune, were generally referred to (in lay media) as gas giants. They all have very deep atmospheres and may be wholly fluid, although pressures and temperatures are so high in the interior that scientists cannot be sure if the matter is crystalline and solid because the pressure is so high, or fluid because the temperature is so high. But none of them are known to have solid surfaces.</p>
<p>But Jupiter and Saturn are mostly hydrogen (with some helium), while Uranus and Neptune are mostly methane, ammonia, and water (with some hydrogen and helium). Astronomers call all of those substances &quot;ices&quot; when talking about the outer solar system, because that's the form they would normally take at those temperatures. So Uranus and Neptune are now called ice giants and the Wikipedia article says, for instance, that Uranus is mostly ice. But that does not mean that it is mostly frozen solid, just that it's mostly materials that would be liquid or gaseous on earth and would be frozen solid on a moon at that distance.</p>
<p>So, all of the above was just background. If you moved Uranus to Earth's orbit,  it would be very similar to the way it is now, just much warmer at the cloud tops.</p>
<p>Note that Oscar Lanczi's answer is much more detailed, and based on stronger knowledge, but I thought this would provide helpful background.</p>

CC BY-SA 4.0
2023-06-24T21:36:57.230Z
2023-06-24T21:36:57.230Z
Mark Foskey
<p>This is a hypothetical. If a gas giant with the approximate mass and density of Uranus existed within the goldilocks range to support life around a star, what would be the conditions on the service. Let's assume the same general composition as Uranus for a control. Would a gas giant still be mostly ice at this distance? And if there is a change in the state of the composition on the gas giant, how might this effect moons with water/liquid (i.e., would the tidal shifts be able to support like on land on a moon around such a planet?)</p>
<p>As a follow up, would different types of stars change this state, assuming stars ranging from Class A, F, G, or K?</p>

CC BY-SA 4.0
2023-06-23T19:58:19.877Z
What is your thought on it? What is the result of your research for an answer?
planetmaker
CC BY-SA 4.0
2023-06-23T23:51:20.187Z
I am attempted to build to a book series that is conceptually possible in the universe as we know it. Additionally, this will drive flora and fauna and minor adaptive/evolutionary changes in the humans there. For the record, I am attempting validate if a planet could have an annual/frequent eclipse lasting 2-3 days, either by means of it being a moon to a much larger planet (i.e. the Uranus question) or some other means.
Curious Gorge
CC BY-SA 4.0
2023-06-23T23:51:35.230Z
I'm also considering a multi-"star" system with two massive brown dwarf twins orbiting each other countered by a Class G or K star, orbital times as such that the brown dwarves would block the light/heat from the star to a tidally locked (to the barycenter of the system) goldilocks planet periodically.
Curious Gorge
CC BY-SA 4.0
2023-06-24T02:49:31.563Z
You can check WorldBuilding.SE for hypothetical questions.
Nilay Ghosh
CC BY-SA 4.0
2023-06-24T07:33:59.127Z
I don't see your brown dwarf system possible. Or it is a close triple system of start and brown dwarfs and the planet so far out that it definitely is not habitable
planetmaker
CC BY-SA 4.0
2023-06-24T16:26:14.627Z
Thank you both. @planetmaker Yes to the close triple of the brown dwarves and Class G/K star system. Are you saying that a habitable planet wouldn't be possible in such a system? I know brown dwarves are rarely seen in systems with stars. I'm just trying to check my theocraticals before I get started. I apologize to the masses if this wasn't the appropriate place to start, but there is a remarkable knowledge base here I could not replicate even remotely. Thank you again.
Curious Gorge
CC BY-SA 4.0
2023-06-24T17:29:07.750Z
@CuriousGorge systems with two brown dwarfs and a "normal" star, and planets orbiting all three are certainly possible (maybe even known). But any planet in a stable orbit would be either FAR out from the triple system which would orbit rather close. Or the planet would have to orbit the star directly - and the two brown dwarves would have to be far out (gut feeling: like Uranus distance or more); then it wouldn't look much different than here on Earth, just with a faint self-irradiating object instead one of our gas- or ice giants in our solar system
planetmaker
CC BY-SA 4.0
2023-06-24T18:20:00.360Z
@planetmaker this is great, thank you. Plausibility is sufficient for this exercise.
Curious Gorge
<star><tidal-forces><gas-giants><habitable-zone><hypothetical>
What would a gas giant, such as Uranus, look like if it were orbiting a sun like star at an Earthlike orbit?
Curious Gorge
# What would a gas giant, such as Uranus, look like if it were orbiting a sun like star at an Earthlike orbit?

(Asked by: username_0 on 2023-06-23)

This is a hypothetical. If a gas giant with the approximate mass and density of Uranus existed within the goldilocks range to support life around a star, what would be the conditions on the service. Let's assume the same general composition as Uranus for a control. Would a gas giant still be mostly ice at this distance? And if there is a change in the state of the composition on the gas giant, how might this effect moons with water/liquid (i.e., would the tidal shifts be able to support like on land on a moon around such a planet?)

As a follow up, would different types of stars change this state, assuming stars ranging from Class A, F, G, or K?

**Tags:** star, tidal-forces, gas-giants, habitable-zone, hypothetical

> **Comments:**
> **username_1**: What is your thought on it? What is the result of your research for an answer?  
> **username_0**: I am attempted to build to a book series that is conceptually possible in the universe as we know it. Additionally, this will drive flora and fauna and minor adaptive/evolutionary changes in the humans there. For the record, I am attempting validate if a planet could have an annual/frequent eclipse lasting 2-3 days, either by means of it being a moon to a much larger planet (i.e. the Uranus question) or some other means.  
> **username_0**: I'm also considering a multi-"star" system with two massive brown dwarf twins orbiting each other countered by a Class G or K star, orbital times as such that the brown dwarves would block the light/heat from the star to a tidally locked (to the barycenter of the system) goldilocks planet periodically.  
> **username_2**: You can check WorldBuilding.SE for hypothetical questions.  
> **username_1**: I don't see your brown dwarf system possible. Or it is a close triple system of start and brown dwarfs and the planet so far out that it definitely is not habitable  
> **username_0**: Thank you both. @username_1 Yes to the close triple of the brown dwarves and Class G/K star system. Are you saying that a habitable planet wouldn't be possible in such a system? I know brown dwarves are rarely seen in systems with stars. I'm just trying to check my theocraticals before I get started. I apologize to the masses if this wasn't the appropriate place to start, but there is a remarkable knowledge base here I could not replicate even remotely. Thank you again.  
> **username_1**: @username_0 systems with two brown dwarfs and a "normal" star, and planets orbiting all three are certainly possible (maybe even known). But any planet in a stable orbit would be either FAR out from the triple system which would orbit rather close. Or the planet would have to orbit the star directly - and the two brown dwarves would have to be far out (gut feeling: like Uranus distance or more); then it wouldn't look much different than here on Earth, just with a faint self-irradiating object instead one of our gas- or ice giants in our solar system  
> **username_0**: @username_1 this is great, thank you. Plausibility is sufficient for this exercise.  

---

## 2 answers

### Answer by username_3 on 2023-06-23. Score: 3

[Hot Neptunes](https://en.wikipedia.org/wiki/Hot_Neptune) are known, beginning with an exoplanet orbiting the star Gliese 436. They may be formed either at greater distances from the star and then migrate inwards (ex-situ) or at close distances initially (in-situ).

Either way, these exoplanets would not be Earth-like. Their composition depends on how they are formed, but in general they must contain predominantly hydrogen and helium, overlying heavier ices or perhaps more refractory compounds:

> The first theoretical study of how hot Neptunes could form was carried out in 2004.[[1](https://doi.org/10.1016/j.icarus.2005.02.015)] If these planets formed ex situ, i.e., by migrating to their current locations while growing, they may contain large quantities of frozen volatiles and amorphous ices. Otherwise, if they formed in situ, their inventory of heavy elements should be made entirely of refractory materials.[[2](https://doi.org/10.3847/0004-637X/828/1/33)] Yet, regardless of the mode of formation, hot Neptunes should contain large fractions (by mass) of gases, primarily hydrogen and helium, which also account for most of their volume.[3][[4](https://doi.org/10.1007/978-3-319-55333-7_140)]

On this basis a "composition similar to Uranus" would require an ex-situ formation process,csince Uranus itself has more ices than refractory material. With the hydrogen-helium gas overlay and a heat input similar to Earth the exoplanet would then look much like Uranus itself.

**Cited References**

1. Adrián Brunini and Rodolfo G. Cionco (September 2005). "The origin and nature of Neptune-like planets orbiting close to solar type stars". Icarus. 177 (1): 264–68. arXiv:astro-ph/0511051. Bibcode:2005Icar..177..264B. doi:10.1016/j.icarus.2005.02.015. S2CID 18979082.
2. D'Angelo, G.; Bodenheimer, P. (2016). "In Situ and Ex Situ Formation Models of Kepler 11 Planets". The Astrophysical Journal. 828 (1): id. 33. arXiv:1606.08088. Bibcode:2016ApJ...828...33D. doi:10.3847/0004-637X/828/1/33. S2CID 119203398.
3. D'Angelo, G.; Durisen, R. H.; Lissauer, J. J. (2011). "Giant Planet Formation". In S. Seager. (ed.). Exoplanets. University of Arizona Press, Tucson, AZ. pp. 319–346. arXiv:1006.5486.
   Bibcode:2010exop.book..319D.
4. D'Angelo, G.; Lissauer, J. J. (2018). "Formation of Giant Planets". In Deeg H., Belmonte J. (ed.). Handbook of Exoplanets. Springer International Publishing AG, part of Springer Nature. pp. 2319–2343. arXiv:1806.05649. Bibcode:2018haex.bookE.140D. doi:10.1007/978-3-319-55333-7\_140. ISBN 978-3-319-55332-0. S2CID 116913980.

> **Comments:**
> **username_0**: So, to be clear, if Uranus, as it is composed, move into Earth's orbit, the thermal gain would not be sufficient for it to develop an atmosphere or melt?  
> **username_3**: Probably not. Uranus is already hot in its interior, so solar heat gain would have little impact there. Uranus would be warmer at the surface, but likely not hot enough to give hydrogen loss given its large escape velocity.  
> **username_1**: @username_0 You assume that uranus or neptune are frozen. They are not. The visible 'surface' is composed of gas, they have no (visible) surface. And the solid core is warm or hot as is any planet core as result of its formation by accretion.  
> **username_3**: Yeah I was wondering why the asker referred to the planet melting. This on an astronomy board. Yeesh!  
> **username_0**: Apologies for the layman's terms, but I appreciate the clarification.  

---

### Answer by username_4 on 2023-06-24. Score: 0

In my recollection, until the late 1990s, all four outer planets, including Uranus and Neptune, were generally referred to (in lay media) as gas giants. They all have very deep atmospheres and may be wholly fluid, although pressures and temperatures are so high in the interior that scientists cannot be sure if the matter is crystalline and solid because the pressure is so high, or fluid because the temperature is so high. But none of them are known to have solid surfaces.

But Jupiter and Saturn are mostly hydrogen (with some helium), while Uranus and Neptune are mostly methane, ammonia, and water (with some hydrogen and helium). Astronomers call all of those substances "ices" when talking about the outer solar system, because that's the form they would normally take at those temperatures. So Uranus and Neptune are now called ice giants and the Wikipedia article says, for instance, that Uranus is mostly ice. But that does not mean that it is mostly frozen solid, just that it's mostly materials that would be liquid or gaseous on earth and would be frozen solid on a moon at that distance.

So, all of the above was just background. If you moved Uranus to Earth's orbit, it would be very similar to the way it is now, just much warmer at the cloud tops.

Note that username_3 Lanczi's answer is much more detailed, and based on stronger knowledge, but I thought this would provide helpful background.


---

