Transcript Other solar system objects

Asteroids, Comets, and Pluto
(Most of) The Rest of the Solar
System
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) …
The Asteroid Belt
• ~50,000 asteroids
discovered
• Most orbit between
Mars and Jupiter
– Why wouldn’t they
combine to form a
planet? Hint: Saturn’s
rings
Asteroids
• Range from 500 miles
across to “sand grains”
• All add up to less than
half the Moon’s mass /
size
• Made of stone, metal,
or both
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?
Comets Cont.
• Small nucleus - “Dirty
Snowball”
• Tail – material
vaporized by Sun’s
heat
– If material is vaporized
each time a comet
passes close to the
Sun, what happens to
the comet after a long
time?
Discovery of Pluto
• Search for “Planet X”
b/c
• Discovered on photos
(1930)
• Large moon, Charon,
discovered (1978)
– Charon is half Pluto’s
size!
• Diameter = 1,440 mi
• Density = 1.8 g/cm3
– Likely mixture of ice and
rock
Pluto vs. Outer Planets
• Much smaller than the outer planets
• Pluto has no hydrogen or helium
• “Gas Giant” – except no gas or giant
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: Why’s an inner planet out
there?
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
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?
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?
Dwarf Planets
• Either Eris is a planet, or Pluto isn’t!
• 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
The “New” Solar System