system
Given the following post, respond as if you're commenting on Reddit:
human
Could an Earth sized object orbit Jupiter?

Some moons of Jupiter are quite large. Is there a limit to how big of a moon could naturally form around a planet? Could Jupiter have an Earth sized moon in a stable orbit? 

I know our moon is quite high ratio wise compared to us, leading to the preferred theory it was the result of an already existing large body colliding with a pre-Earth body.
gpt
Regarding orbital mechanics, nothing prevents a large moon from orbiting a planet. It could even be equal in mass and size to the planet itself and the orbit could still be stable. Double planets have been theorized but are yet to be discovered.

Regarding co-accretion, it happens with double stars, so nothing prevents it from being possible with planets.

The giant impact hypothesis about the origin of the Moon is not only due to the size, but also to the similarity in composition and to the lack of an iron core. That suggests the Moon was formed from material ejected from the proto-Earth's surface during the impact.