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

Icy bodies in orbit past Neptune

What is