Download Dwarf Planets

Dwarf Planets
Pluto
• Neptune’s orbit also didn’t quite match Kepler’s laws.
• In the late 1800’s Lowell predicted a ninth planet.
• It was discovered in 1929 as a faint star that moved
slightly each day.
• Pluto’s orbit is sometimes inside Neptune’s.
Neptune
Sun
Pluto
Pluto
• No spacecraft has yet visited Pluto.
• Adaptive optics have imaged part of Pluto’s surface.
Ice Ball
•
•
•
•
Pluto is small (seven moons are larger).
Pluto has low density.
60% stony core.
40% frozen gas: nitrogen, carbon monoxide, methane, and
water.
• Some ice can vaporize when Pluto is at its closest point to
the sun. This forms a thin atmosphere.
Charon
• Pluto’s moon Charon is almost as big as Pluto.
• The pair can be viewed as a double planet and they are
tidally locked to each other.
• Charon has more water ice on the surface than Pluto.
Classifying Pluto
• The inner planets (Mercury, Venus, Earth, Mars) are
rocky.
• The outer planets (Jupiter, Saturn, Uranus, Neptune) are
gas giants.
• Pluto doesn’t fit in; it’s icy mixed with rock and carbon.
Kuiper Belt
• Gerard Kuiper suggested
in the 1940’s that there
was a ring of icy objects
from the early solar
system beyond the orbit of
Pluto.
– Confirmed in 1992
– Many times the mass of
the asteroid belt
Pluto
Neptune’s orbit
Kuiper Belt
Kuiper Belt Objects
• Hundreds of Kuiper Belt
Objects (KBOs) have been
found.
– Sizes from 50 to 2400
km across.
– Eris is the largest KBO
• Astronomers estimate
100,000 KBOs larger than
100 km.
Planets Redefined
• The discovery of Eris forced astronomers to create a better
definition of a planet (2006).
– In orbit around the Sun
– Sufficient mass to assume a nearly round shape
– Cleared the neighborhood around its orbit
• A dwarf planet was defined as a new category.
– Not cleared the neighborhood around its orbit
– Not a satellite of a planet
History of Planets
Scientific American