[quote=thewizardguy]
What he summoned wasn't Optimus's body, it was his soul. Which had been fused with the Matrix, if I recall. Then, he put together a body for him.
[/quote]
Okay, that's the Hasbro magic (trademark of Hasbro)
[quote=thewizardguy]
Unicron is a planet. He can't be 'on earth' or his mere gravity would rip it to pieces.
[/quote]

He could be near earth ... but event then it'd be risky