* The Moon: This is Earth's natural satellite and the closest celestial body to our planet. It's often called Earth's companion.
* A hypothetical second moon: Some theories suggest Earth may have once had a second moon, but this is highly speculative and not confirmed.
* A hypothetical planet in Earth's orbit: Some theories suggest there might be a planet sharing Earth's orbit, but no evidence of such a planet has been found.
To clarify what you mean by "Earth companion," please provide more context.
