Now Pluto did come with the kit, but I didn't add him. Why? Because he's not a planet anymore, based on the new definition by the International Astronomical Union (IAU).
Luca asked the same question, and I had to think for a minute how I could explain this to him. There are a few main components of what makes up a planet (simplified):
- Orbit: All planets orbit a star.
- Shape: Each planet is nearly round.
- Neighborhood: Each planet has cleared its orbital neighborhood of other stuff.
So I told Luca, "Pluto isn't a planet because he didn't clean up his room."
By the way, here are some new, spectacular images of Earth:
The New Blue Marble West
The New Blue Marble East