<p>There's basically no gravitational pull towards the barycenter.  The two objects are in free-fall around each other and objects in free-fall experience (almost) no gravity from the object they are in free-fall around.  Anyone standing on either planet would basically only feel the gravitation of that object alone, as if it were sitting still in space (though nothing actually "sits still" in space), everything in space is flying through it's local gravitational field.</p>

<p>There can be small variations to the local objects gravity, generated by any rotation.  Tidal locking might be common with a dual-planet system and Tidal locking is usually a relatively slow rotation unless the objects are very close, but while it's a slow rotation, it's still greater than zero, which creates a tiny tidal bulge and a very slight <a href="http://www.calctool.org/CALC/phys/newtonian/centrifugal.png" rel="nofollow noreferrer">centrifugal force</a> which would effectively lower the gravity.   This has nothing to do with the barycener, it is a product of the objects rotation.</p>

<p>As the objects get closer there is a tidal bulging which has some effect on gravity.   Parts of the planet that bulge outwards experience lower gravity and parts that are effectively stretched in closer to the center experience an increase in gravity.   This effect is pretty small and it's an indirect effect, caused by tidal forces from the other object, not caused by the barycenter.</p>

<p>At the <a href="https://en.wikipedia.org/wiki/Roche_limit#Explanation" rel="nofollow noreferrer">Roche Limit</a>, gravity is effectively cancelled out by the tidal force and objects can drift off the surface both on the near and far side of the smaller of the two tightly orbiting objects. </p>

<p>The amount of gravitational variation would be small, unless the orbit was very close.</p>

<p>I'd like to post a map of the change in gravity on Pluto's Moon Charon, or Jupiter's innermost Moon Io due to the tidal forces and tidal bulging, but I couldn't find any written results on that and I'm reluctant to try to do the math myself.  Even under very strong tidal forces like those two, the effect is likely still quite small, perhaps in the range of 1% or less.</p>

<p>Here's a <a href="https://space.stackexchange.com/questions/3977/would-it-be-possible-to-fall-off-phobos">question</a> where the tidal force and it's effect on Phobos' gravity is discussed.  You need very strong tidal forces before the gravity gets significantly effected.</p>

CC BY-SA 3.0
2017-05-22T14:33:56.710Z
So does the barycenter have any effect other than being the point the two bodies orbit around?
Ckam
CC BY-SA 3.0
2017-05-22T15:28:58.983Z
There's no gravitational effect towards the Barrycenter, outside of extreme situations, such as the objects might share atmosphere or have shared measurable relativistic effects where there's some natural resistance pulling them inwards, or not be tidally locked where there's some tugging on tidal bulges, which would be unlikely if they were close.  But nobody would be lifted off one planet towards the barycenter, even past the Roche limit where the planet starts to break apart, it would break apart into different orbits, it wouldn't break apart towards the barycenter.
userLTK
CC BY-SA 3.0
2017-05-22T07:06:49.673Z
2017-05-22T07:06:49.673Z
userLTK
<p>Assuming two similarly sized, tidally locked planets orbit a common barycenter, how would the gravity of the barycenter affect the surface gravity? For example, on the inner sides of the planets, what would be the effect of the multiple gravity centers (the planets' and the barycenter), especially to a being on the surface? </p>

<planet><gravity>
How would the barycenter of a double-planet system affect the two planets' surface gravity?
Ckam
# How would the barycenter of a double-planet system affect the two planets' surface gravity?

(Asked by: username_0 on 2017-05-22)

Assuming two similarly sized, tidally locked planets orbit a common barycenter, how would the gravity of the barycenter affect the surface gravity? For example, on the inner sides of the planets, what would be the effect of the multiple gravity centers (the planets' and the barycenter), especially to a being on the surface?

**Tags:** planet, gravity


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## 1 answers

### Answer by username_1 on 2017-05-22. Score: 2 | Accepted answer

There's basically no gravitational pull towards the barycenter. The two objects are in free-fall around each other and objects in free-fall experience (almost) no gravity from the object they are in free-fall around. Anyone standing on either planet would basically only feel the gravitation of that object alone, as if it were sitting still in space (though nothing actually "sits still" in space), everything in space is flying through it's local gravitational field.

There can be small variations to the local objects gravity, generated by any rotation. Tidal locking might be common with a dual-planet system and Tidal locking is usually a relatively slow rotation unless the objects are very close, but while it's a slow rotation, it's still greater than zero, which creates a tiny tidal bulge and a very slight [centrifugal force](http://www.calctool.org/CALC/phys/newtonian/centrifugal.png) which would effectively lower the gravity. This has nothing to do with the barycener, it is a product of the objects rotation.

As the objects get closer there is a tidal bulging which has some effect on gravity. Parts of the planet that bulge outwards experience lower gravity and parts that are effectively stretched in closer to the center experience an increase in gravity. This effect is pretty small and it's an indirect effect, caused by tidal forces from the other object, not caused by the barycenter.

At the [Roche Limit](https://en.wikipedia.org/wiki/Roche_limit#Explanation), gravity is effectively cancelled out by the tidal force and objects can drift off the surface both on the near and far side of the smaller of the two tightly orbiting objects.

The amount of gravitational variation would be small, unless the orbit was very close.

I'd like to post a map of the change in gravity on Pluto's Moon Charon, or Jupiter's innermost Moon Io due to the tidal forces and tidal bulging, but I couldn't find any written results on that and I'm reluctant to try to do the math myself. Even under very strong tidal forces like those two, the effect is likely still quite small, perhaps in the range of 1% or less.

Here's a [question](https://space.stackexchange.com/questions/3977/would-it-be-possible-to-fall-off-phobos) where the tidal force and it's effect on Phobos' gravity is discussed. You need very strong tidal forces before the gravity gets significantly effected.

> **Comments:**
> **username_0**: So does the barycenter have any effect other than being the point the two bodies orbit around?  
> **username_1**: There's no gravitational effect towards the Barrycenter, outside of extreme situations, such as the objects might share atmosphere or have shared measurable relativistic effects where there's some natural resistance pulling them inwards, or not be tidally locked where there's some tugging on tidal bulges, which would be unlikely if they were close.  But nobody would be lifted off one planet towards the barycenter, even past the Roche limit where the planet starts to break apart, it would break apart into different orbits, it wouldn't break apart towards the barycenter.  

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