<p>This is certainly possible! As long as the objects are orbiting each other fast enough, they won't collapse into a single sphere.</p>
<p>However, for some reason brown dwarves tend to form binaries less frequently than stars in the Milky Way (e.g. <a href="https://arxiv.org/abs/1806.08737" rel="nofollow noreferrer">arxiv.org/abs/1806.08737</a>), so if that trend continues, gas giant binaries could be rare.</p>
<p>It's not super clear how this would work for terrestrial planets, but it's worth noting that Pluto/Charon are relatively close to being contact binaries, and are often considered a &quot;double dwarf planet system&quot;. We also often see asteroids joined together, as you've described, but they often have low enough mass that they wouldn't collapse into a sphere anytime soon, even if they weren't rotating.</p>
<p>Answering the question in the comments: Because of the rapid rotation needed to keep such a planet stable, Earth-like conditions are pretty much impossible. Any atmosphere would likely be flung away, and even if it were present, the winds would be bizarre and very strong (see Jupiter for an example of what winds on a rapidly rotating planet can be like).</p>
<p>Gravity would be the weakest at the point of contact, but depends a lot on the actual shape, density, etc.</p>
<p>For more on the conditions and gravity of contact binary terrestrial planet, check out <a href="https://worldbuilding.stackexchange.com/questions/100607/gravity-ecosystem-on-a-peanut-shaped-planet">this question</a>.</p>

CC BY-SA 4.0
2024-08-04T16:14:09.647Z
Stars and planets most likely form due to (predominantly) different mechanisms as hinted to by the so-called 'Brown Dwarf desert'. As such, the answer 'certainly' does necessarily follow without more argument than from inference from the abundance of multiplicity of stars. The stability of orbits also has to consider the lifetime of these due to tides which might (or might not) reduce the planets orbit quickly enough that they won't survive in close-in orbits for an extended time. this will need more careful mathematical analysis to come up with a number.
planetmaker
CC BY-SA 4.0
2024-08-04T15:47:11.213Z
2024-08-04T15:47:11.213Z
Sub 6 Resources
<p>Objects such as asteroids and comets can orbit close enough in binaries that their surfaces overlap and form what a single object. The same process can happen with binary stars. Both of these objects are relatively stable. However I cannot find much on the possibility of contact binary terrestrial or gas giant planets. Are such objects, that consist of two planetary mass objects with overlapping/touching surfaces, possible? And if not, why are contact binary stars possible? What about brown dwarfs if not? The closest I can find to a planetary mass contact binary is the 600 km wide trans-neptunian object <a href="https://en.m.wikipedia.org/wiki/19521_Chaos" rel="noreferrer">19521 Chaos</a>, which occulted a star and revealed a two-lobed shape, which suggests either a close binary or contact binary object.</p>

CC BY-SA 4.0
2024-08-04T03:28:58.120Z
I think this is certainly possible! So long as the objects are orbiting each other fast enough, they won't collapse into a single sphere. However, for some reason brown dwarves tend to form binaries less frequently than stars in the Milky Way (e.g. https://arxiv.org/abs/1806.08737), so if that trend continues gas giant binaries could be rare. Not sure about rocky planets, although Pluto/Charon are relatively close to being contact binaries, and are often considered a "double dwarf planet system".
Sub 6 Resources
CC BY-SA 4.0
2024-08-04T04:29:18.217Z
There's some ambiguity with the word "stable" here; it might refer to [Hydrostatic equilibrium](https://en.wikipedia.org/wiki/Hydrostatic_equilibrium) proper, or simply "doesn't seem to change shape much over a a period of a few years of observing".
uhoh
CC BY-SA 4.0
2024-08-04T12:36:15.127Z
@Sub6Resources put that as an answer so you can get some points!
ArchiveOfStars
CC BY-SA 4.0
2024-08-04T12:38:05.267Z
@Sub6Resources also I have a question, do you think that under the right circumstances, could a contact binary terrestrial planet support earth-like conditions? Also how would the gravity work at the point of contact?
ArchiveOfStars
<contact-binaries>
Can stable contact binary planets exist
ArchiveOfStars
# Can stable contact binary planets exist

(Asked by: username_0 on 2024-08-02)

Objects such as asteroids and comets can orbit close enough in binaries that their surfaces overlap and form what a single object. The same process can happen with binary stars. Both of these objects are relatively stable. However I cannot find much on the possibility of contact binary terrestrial or gas giant planets. Are such objects, that consist of two planetary mass objects with overlapping/touching surfaces, possible? And if not, why are contact binary stars possible? What about brown dwarfs if not? The closest I can find to a planetary mass contact binary is the 600 km wide trans-neptunian object [19521 Chaos](https://en.m.wikipedia.org/wiki/19521_Chaos), which occulted a star and revealed a two-lobed shape, which suggests either a close binary or contact binary object.

**Tags:** contact-binaries

> **Comments:**
> **username_1**: I think this is certainly possible! So long as the objects are orbiting each other fast enough, they won't collapse into a single sphere. However, for some reason brown dwarves tend to form binaries less frequently than stars in the Milky Way (e.g. https://arxiv.org/abs/1806.08737), so if that trend continues gas giant binaries could be rare. Not sure about rocky planets, although Pluto/Charon are relatively close to being contact binaries, and are often considered a "double dwarf planet system".  
> **username_2**: There's some ambiguity with the word "stable" here; it might refer to [Hydrostatic equilibrium](https://en.wikipedia.org/wiki/Hydrostatic_equilibrium) proper, or simply "doesn't seem to change shape much over a a period of a few years of observing".  
> **username_0**: @username_1 put that as an answer so you can get some points!  
> **username_0**: @username_1 also I have a question, do you think that under the right circumstances, could a contact binary terrestrial planet support earth-like conditions? Also how would the gravity work at the point of contact?  

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## 1 answers

### Answer by username_1 on 2024-08-04. Score: 2

This is certainly possible! As long as the objects are orbiting each other fast enough, they won't collapse into a single sphere.

However, for some reason brown dwarves tend to form binaries less frequently than stars in the Milky Way (e.g. [arxiv.org/abs/1806.08737](https://arxiv.org/abs/1806.08737)), so if that trend continues, gas giant binaries could be rare.

It's not super clear how this would work for terrestrial planets, but it's worth noting that Pluto/Charon are relatively close to being contact binaries, and are often considered a "double dwarf planet system". We also often see asteroids joined together, as you've described, but they often have low enough mass that they wouldn't collapse into a sphere anytime soon, even if they weren't rotating.

Answering the question in the comments: Because of the rapid rotation needed to keep such a planet stable, Earth-like conditions are pretty much impossible. Any atmosphere would likely be flung away, and even if it were present, the winds would be bizarre and very strong (see Jupiter for an example of what winds on a rapidly rotating planet can be like).

Gravity would be the weakest at the point of contact, but depends a lot on the actual shape, density, etc.

For more on the conditions and gravity of contact binary terrestrial planet, check out [this question](https://worldbuilding.stackexchange.com/questions/100607/gravity-ecosystem-on-a-peanut-shaped-planet).

> **Comments:**
> **username_3**: Stars and planets most likely form due to (predominantly) different mechanisms as hinted to by the so-called 'Brown Dwarf desert'. As such, the answer 'certainly' does necessarily follow without more argument than from inference from the abundance of multiplicity of stars. The stability of orbits also has to consider the lifetime of these due to tides which might (or might not) reduce the planets orbit quickly enough that they won't survive in close-in orbits for an extended time. this will need more careful mathematical analysis to come up with a number.  

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