The History of Pluto
- People started looking for a 9th planet because of unexplained tugs on Neptune's orbit.
- Implied that this planet was 3 to 10x mass of Earth.
- When Pluto was discovered in 1930, it fit expectations because:
- It was in the right part of the sky.
- It was 'bright'.
- However, an object can be bright because:
- It is low albedo (% of light reflected) and large.
- It has high albedo and small.
- Most Solar System objects are low albedo - The Moon reflects only ~7% of sunlight.
- So, people thought Pluto was big.
- However, as time went on, more and more stellar occultations did not happen.
- Pluto was smaller than they thought.
- It was not until Pluto's satellites was discovered that people knew how small Pluto is.
- 0.002 X Mass of Earth.
Artist conception.
From Hubble Space Telescope
