Why Isnt Pluto a Planet Anymore Do they

Why Isn’t Pluto a Planet Anymore?

Do they have something against Yellow Dogs or something? • Maybe he’s just a little too friendly?

Fault of Mike Brown • One of most important planetary astronomers • Published book: How I Killed Pluto, and Why it Had it Coming. • Things came to a head at International Astronomical Union Meeting (IAU) in 2006 • Meeting had heated arguments and shouting matches – His young daughter didn’t like it either

Why was this such a big Deal? • This is where you guys try to answer (not all at once, please!)

We always knew something wasn’t quite right with Pluto. . . • Very small, (two thirds the size of Mercury) • Very far out • Orbit is much more elliptical – And not in the plane of the eight other planets • Not always the ninth planet – it was inside the orbit of Neptune for about 20 years (1979 to 1999)

Lots of objects far out, comparable to Pluto

And their orbits are different:

If Pluto was going to be a planet, it was going to have a lot of company • Asteroid Ceres • Pluto’s own moon Charon • Eris (formerly Xena), Greek God of Discord, was the final straw, because it was actually bigger than Pluto • Would have meant between 3 and 20 new planets, possibly up to 200 later.

How was our solar system formed?

So What’s a Planet? • In 2006, astronomers voted on a planet’s definition: A. Is in orbit around the Sun B. Has enough mass so that it assumes a nearly round shape C. Has cleared its orbit (of space objects)

So What’s Pluto? Dwarf Planet: A. Is in orbit around the Sun B. Has enough mass so that it assumes a nearly round shape C. Has NOT cleared its orbit (of space objects) D. Is not a satellite

is t ha W Icy bodies in orbit past Neptune