As you can see above, the stamp screenshot that was released seems to showcase player icons. Looks like Mario, Peach, Toad and Luigi's player icons fit perfectly into the stamp collection lineup, but what about that other icon that looks quite similar? Hit the jump to see some speculation.
Could these icons represent a playable Rosalina? We know that the Comet Observatory from Super Mario Galaxy appears in the game somehow, but we don't know the details behind it. With that said, the icons above certainly seem to correspond to Rosalina. There's even one with two Lumas surrounding it!