If It's Sunday, It's Ask Snug!

I heard that Pluto isn't a planet anymore? How many planets are there?
- Neil deGrasse Tyson (Astrophysicist, Director of Hayden Planetarium at AMNH, and Lilly's cousin)



(Photo: Lilly in her "planets" onesie and Cousin Neil in his "planets" tie.)


This is a great question, Cousin Neil. Yes, it's true -- Pluto is no longer a planet, so now there are only 8 planets in our solar system. Pluto was demoted to a "dwarf planet." According to the International Astronomical Union, a planet must satisfy the following three criteria:

1. It must be in an orbit around the sun. (Pluto does orbit the sun.)
2. It must be spherical -- in other words, the planet has to be massive enough, have enough gravity, to pull itself into a sphere. (Pluto is, indeed, spherical.)
3. It must be massive enough to knock all other objects out of it's orbit around the sun. (Unfortunately, it turns out that Pluto can't do that.)

Thus, Pluto does NOT satisfy criterion #3. So, now we say that Pluto is a "dwarf planet." Time to change your dioramas, Cousin Neil.

- Lillian (aka AstroSnug)