<p>It's certainly possible such a system could be stable in the long term. Barring the consideration of what exactly we're talking about (in terms of planets and stars) what you're describing is referred to as a <a href="https://en.wikipedia.org/wiki/Star_system#Hierarchical_systems" rel="noreferrer">hierarchical system</a>. Effectively you have two bodies orbiting quite close to each other (in your case, two planets of similar Earth-comparable masses). Then they're both orbiting a star far enough from it that, from the perspective of the Sun, the binary planet system can be considered a single object of the combined mass of the two planets.</p>
<p>There are certainly star systems that have this same configuration (one potential example is <a href="https://en.wikipedia.org/wiki/HR_6819" rel="noreferrer">HR 6819</a>). The only difference is that you're dramatically reducing the mass of two of the &quot;stars&quot; so that they're now planets.</p>
<p>I will say that the real question is how did such a system form in the first place. You'd need a mechanism that allows these two planets to become gravitationally bound without accreting into a single planet. It's not impossible, but statistically unlikely.</p>

CC BY-SA 4.0
2021-12-20T20:53:26.063Z
2021-12-20T20:53:26.063Z
zephyr
<p>Earth and Venus and very close to each other in mass and would both orbit around a point in space positioned almost perfectly in between the two.</p>
<p>Assume that this system is 1 AU from the Sun and the distance between Earth and Venus is the same as the distance between the Earth and the Moon. <em><strong>Would this system be stable in the long-term?</strong></em></p>
<p>Both planets would very likely be tidally locked to each other, but I'm not sure if that would have any impact on stability.</p>
<p>PSA: I only used Venus and Earth because they're very close to each other in mass. What I'm really curious about is if a double planet consisting of 2 components very similar in mass can be stable in the long-term.</p>

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2021-12-21T00:01:10.490Z
FWIW, using 384399 km for the semi-major axis, and grav params of Venus & Earth from Horizons, the orbital period of the Venus-Earth binary system (ignoring the Sun) is
1760541.5 seconds = 20.37664 days =
20 d, 09 h 02 m 21.5 s. The distances from the barycentre are 211790.3 km & 172608.7 km.
PM 2Ring
<orbit><earth><orbital-mechanics><venus>
Would a system consisting of Earth and Venus orbiting around a common center be stable in the long-term?
user177107
# Would a system consisting of Earth and Venus orbiting around a common center be stable in the long-term?

(Asked by: username_0 on 2021-12-20)

Earth and Venus and very close to each other in mass and would both orbit around a point in space positioned almost perfectly in between the two.

Assume that this system is 1 AU from the Sun and the distance between Earth and Venus is the same as the distance between the Earth and the Moon. ***Would this system be stable in the long-term?***

Both planets would very likely be tidally locked to each other, but I'm not sure if that would have any impact on stability.

PSA: I only used Venus and Earth because they're very close to each other in mass. What I'm really curious about is if a double planet consisting of 2 components very similar in mass can be stable in the long-term.

**Tags:** orbit, earth, orbital-mechanics, venus

> **Comments:**
> **username_1**: FWIW, using 384399 km for the semi-major axis, and grav params of Venus & Earth from Horizons, the orbital period of the Venus-Earth binary system (ignoring the Sun) is 1760541.5 seconds = 20.37664 days = 20 d, 09 h 02 m 21.5 s. The distances from the barycentre are 211790.3 km & 172608.7 km.  

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## 1 answers

### Answer by username_2 on 2021-12-20. Score: 5 | Accepted answer

It's certainly possible such a system could be stable in the long term. Barring the consideration of what exactly we're talking about (in terms of planets and stars) what you're describing is referred to as a [hierarchical system](https://en.wikipedia.org/wiki/Star_system#Hierarchical_systems). Effectively you have two bodies orbiting quite close to each other (in your case, two planets of similar Earth-comparable masses). Then they're both orbiting a star far enough from it that, from the perspective of the Sun, the binary planet system can be considered a single object of the combined mass of the two planets.

There are certainly star systems that have this same configuration (one potential example is [HR 6819](https://en.wikipedia.org/wiki/HR_6819)). The only difference is that you're dramatically reducing the mass of two of the "stars" so that they're now planets.

I will say that the real question is how did such a system form in the first place. You'd need a mechanism that allows these two planets to become gravitationally bound without accreting into a single planet. It's not impossible, but statistically unlikely.


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