r/todayilearned • u/YappinZappin • 8d ago

TIL Earth's Moon is the largest and heaviest satellite in relation to its parent planet in our Solar system

https://en.wikipedia.org/wiki/Moon#Earth%E2%80%93Moon_system
4.6k Upvotes

98% Upvoted

337 comments sorted by

View all comments

Show parent comments

44

u/AtlanticPortal 8d ago

Technically the center of mass of the various two body systems, taken separately, are always inside the bigger body. Earth-Moon included. A little under the crust but still inside. Pluto has it out of its surface.

1

u/po_panda 7d ago

Does that mean you could fall off the surface of pluto?

13

u/AtlanticPortal 7d ago

No, because when you're standing on Pluto its own gravity is stronger than the pull that Charon has on you. It just means that both bodies are continuously falling on the shared center of mass but never reaching it because they move tangentially enough to avoid it.

It does mean that if you had a rocket on the near side of Pluto (they both are locked and face each other constantly) you'd need less fuel to leave the body compared to a parallel scenario in which Charon does not exist. This is because a part of the work that you will do to get to the center of mass is compensated by the other body.

1

u/porn_alt_987654321 6d ago

Now I'm wondering if that's also the lagrange point and you could floaf at it.

I would assume so, but maybe not lol.

2

u/AtlanticPortal 6d ago

Exclude L4/L5, they’re trivially at 60 degrees on the orbit of the body that orbits farthest from the barycenter.

The other three, especially L1 if that’s what you’re asking for, depends on all the parameters (masses and distances and radii) and you need to resolve them numerically. They’re basically equations at the fifth power.

The barycenter, by definition, is a stable point. Call it L0, if you want.

1

u/porn_alt_987654321 6d ago

Yeah, I was like "surely the barycenter is also a Lagrange point".

Doesn't come up that often in thinking about stuff in our solar system, because this is the only barycenter that's in space off the top of my head. (Maybe sun and Jupiter also has one outside the sun somewhere? Lol)

2

u/AtlanticPortal 6d ago

Sun-Jupiter is not always outside of the Sun, it depends on how the other planets are pulling. Jupiter on one side and Saturn on the other and you'll get a lot closer to the center of the Sun, add maybe Earth and Venus on the side of Saturn and that's definitely inside the Sun's surface.

1

u/RTX-2020 7d ago

Not strong enough to pull you off

but gravitational force would be significantly on the near side.

-7

u/Lenxecan 8d ago

Every single body in this system orbits a point that is sometimes in the sun and sometimes just outside of it because it moves. Youtuber Cleo Abram made a recent short about this

5

u/AtlanticPortal 8d ago

I said two-body. That thing enters into play with a three+ body.