Yes. Everyone now can play on the Moon, even if you just bought the game. And I don't know where they're going to go after the solar system. Maybe other galaxies? I know Keita Takahashi wants to keep this going as long as possible.
I see.
I don't think you'll have to worry about what comes after the solar system just yet though. The moon is very,
very close to earth, so if they continue to use real-life distances then it'll be months until the solar system is completed. (Unless the game becomes hugely popular and thousands are playing it all the time
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)