Why Isn’t Pluto a Planet Anymore?
Dec 31, 2015
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