[niccaluim]

Ditto the sun, the moon, the sky, the world, the universe, etc.

Seek ye not consistency in the rules of the English language; that way lies madness.

[Jedd]

Ask what planet people live on and they'll invariably tell you they live on the Earth.

Whereas in the speculative future, people are unlikely to say they live on the Mars (etc).

[DonHopkins]

Not necessarily. It's not my planet, monkey boy.

Ming the Merciless sidestepped the issue by labeling his buttons in capital letters. [1]

[1] http://3.bp.blogspot.com/-Z9E0myUALKw/UIRPUfNFiBI/AAAAAAAABE...