Is Pluto a planet?

Question 1

Who first classified Pluto as a planet?

Answer 1

Clyde Tombaugh in 1930

Question 2

How did he discover Pluto?

Answer 2

Compared photographic plates of the sky on two different nights and noticed a tiny dot that drifted back and forth against the backdrop of the stars

Question 3

How big is Pluto?

Answer 3

Diameter = 2,390 km
70% diameter of the Moon
20% diameter of Earth

Question 4

What are the moons of Pluto?

Answer 4

There are five: Styx, Nix, Kerberos, Hydra, Cheron

Question 5

What happened in 1992?

Answer 5

First Kuiper Belt objects found.
More bodies were found comprising a belt of frozen entities.
Pluto remained the largest.

Question 6

What is the Kuiper Belt?

Answer 6

A ring of icy bodies just outside of Neptune’s orbit

Question 7

Pluto’s place in the Kuiper Belt

Answer 7

Pluto is the largest body in the Kuiper Belt. It’s reflectivity is 60% making it the brightest in the belt

Question 8

Pluto’s rotation

Answer 8

Pluto is locked in an orbital dance with Neptune – meaning Pluto orbits around the Sun twice for every three orbits of Neptune

Question 9

What happened in 2005?

Answer 9

Eris was discovered!

Question 10

What is the criteria for a planet?

Answer 10

1) Must orbit the Sun (so cannot be a satellite like the Moon).
2) Must be round or mostly round (so not an oddly-shaped asteroid) having reached hydrostatic equilibrium.
3) Must be able to clear the neighborhood around its orbit.

Question 11

What is a dwarf planet?

Answer 11

Dwarf planets satisfy the first two categories but not the third, and small solar system bodies only meet the first criterion.

Question 12

What happened in 2006?

Answer 12

The IAU voted to reclassify Pluto.