Asteroids, Comets, and Pluto

1
Asteroids, Comets, and Pluto

• (Most of) The Rest of the Solar System

2
Is there another planet?

• After Uranus discovery, many astronomers thought
  there must be a planet between Mars and Jupiter
• New object discovered b/w Mars and Jupiter (1801)
• Second object discovered b/w Mars and Jupiter
  (1802)
• Third object discovered (1804)

3
The Asteroid Belt

• 50,000 asteroids discovered
• Most orbit between Mars and Jupiter
• Why wouldnt they combine to form a planet?
  Hint Saturns rings

4
Asteroids

• Range from 500 miles across to sand grains
• All add up to less than half the Moons mass /
  size
• Made of stone, metal, or both

5
Comets

• Seen occasionally throughout history
• Halley noticed that one could be seen every 76y
• It last appeared in 1986 when will it be back?
• Originate very, very far away from the Sun
• Why then do some comets have short periods?

6
Comets Cont.

• Small nucleus - Dirty Snowball
• Tail material vaporized by Suns heat
• If material is vaporized each time a comet passes
  close to the Sun, what happens to the comet after
  a long time?

7
Discovery of Pluto

• Search for Planet X b/c
• Discovered on photos (1930)
• Large moon, Charon, discovered (1978)
• Charon is half Plutos size!
• Diameter 1,440 mi
• Density 1.8 g/cm3
• Likely mixture of ice and rock

8
Pluto vs. Outer Planets

• Much smaller than the outer planets
• Pluto has no hydrogen or helium
• Gas Giant except no gas or giant

9
Pluto vs. Inner Planets

• Density 1.8 g/cm3 vs. 5 g/cm3
• Must have a different composition more ice, less
  rock
• Size less than ½ diameter of Mercury
• Distance from Sun Whys an inner planet out
  there?

10
Pluto vs. All Planets

• Orbit tilted 17 to ours
• Very eccentric orbit
• (1979-1999) Pluto was closer to the Sun than
  Neptune!
• Because of its size, composition, and unusual
  orbit, Pluto has never really fit in as a planet

11
Is there more beyond Neptune?

• Computer simulations of Nebular Theory predicted
  a disk of debris beyond Neptune
• New object discovered beyond Neptune (1992)
• Second object discovered beyond Neptune (1993)
• Third object discovered
• Does this story sound vaguely familiar?

12
The Kuiper Belt

• Like asteroid belt, contains many small bodies
  made of ice and rock
• Several large bodies discovered
• Quaoar (2002)
• Sedna (2003)
• Eris (Xena) (2005)
• Eris is larger than Pluto!
• Why might that be significant?

13
Dwarf Planets

• Either Eris is a planet, or Pluto isnt!
• IAU voted to define planets as an object that has
  cleared the neighborhood around its orbit (Aug
  2006)
• Why would this disqualify Pluto?
• Any object that has not cleared its neighborhood
  but is large enough to be round is a Dwarf planet
• Currently, 3 objects likely, more will follow
  soon

14
The New Solar System