A Little Quiz

List #1: Venus, Mars, Jupiter, Saturn. List #2: All the other planets.

Question: what theme differentiates the two lists?

First prize, for the first correct reply: a very small prize. Second prize, for the next correct reply: an even smaller prize. Third prize: a smug look of dismissal from the other two winners.

If needed, a barely-useful hint will be posted tomorrow.

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Okay, here's the hint: if you include the Sun and the Moon, they would both be on List No. 2. And now you really have no excuse for not getting this.