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The Universe
Video Outline
Episode Title: The Outer Planets
Length:
:44
General Characteristics
Pluto
Always considered “different”
Largest moon to planet ratio
Most inclined orbit - highly elliptical
Percival Lowell searched for “Planet X” to
explain orbital perturbations of Uranus
and Neptune
Clyde Tombaugh discovered Pluto in 1930 at
age 24
Originally thought to be Mars-sized - actually
smaller than the Moon
2.6 billion miles from Sun (closest approach)
Diameter half width of US
Revolution - 248 years, Rotation - 6.4 Earth
days
Clearly has dark and light surface features
Light areas are ices composed of carbon
monoxide, nitrogen, methane
Dark areas likely silicate rock
Very little sunlight reaches surface
One of coldest bodies in solar system
Average temperature -388oF
Very low gravity
Believed to consist of primordial material
from early solar system - no tectonics,
etc . believed to be present
Likely heavily cratered
So little solar energy strikes surface, most
frozen gases remain instead of
vaporizing
Pluto Planetary Debate
Eris - discovered in 2005 -larger than Pluto
plus a moon
Eris forced issue of formal planetary
classification
Kuiper Belt
Confirmed in 1992
3.5 billion mile wide belt of debris at outer
reaches of solar system
Contains hundreds of thousands of objects
including Pluto
2006 definition of planet included object
clearing out all other debris in same
orbital plane - Pluto failed this
requirement
Reclassified as “dwarf planet”
Largest asteroid in asteroid belt (Ceres) also
reclassified as dwarf planet in 2006
New Horizons
First spacecraft to go to Pluto
Launched in 2006
Rendezvous in 2015
Must reach Pluto on schedule or miss
opportunity to examine thin atmosphere atmosphere freezes in Pluto winter
Fastest spacecraft ever launched
Uranus
Almost featureless surface
1.5 billion miles from Sun
4x Earth diameter
Revolution 84 years, Rotation 17 hours
Planet tilted 98o
Hemispheres stay in light/darkness for ~40
years through single revolution
Blue color is due to methane - absorbs
red/oranges
Fuzzy appearance is due to reaction with
sunlight (photochemical reactions)
Believe to have formed from similar processes
to Neptune
Likely contains higher amount of ices than
Jupiter/Saturn
Sometimes nicknamed “Ice Giants”
Weather Patterns
No apparent internal heating source
Very calm weather patterns
First planet discovered by telescope (William
Herschel 1781)
Ring System
Rings discovered in 1977 by occultation of
background star - second known planet with
rings
5 planetary rings discovered
Second set discovered by HST in 2005
Composed of very small dust particles
Moon System
~27 moons
13 small and in very close orbit
Some orbital periods 12-24 hours
Collisions may have supplied material for
rings
Some collisions between moons likely within
1-2 million years (Cupid/Belinda)
Neptune
~3 billion miles from Sun
4x diameter of Earth
Revolution - 165 years, Rotation - 16 hours
Rotates very quickly like other outer planets
1000+mph winds - highest in solar system
Mechanism that creates winds this high is not
known
Not enough energy from Sun to explain winds
Believed to possess additional energy source
from planet’s interior
Radiates 2x energy than it receives from the
Sun - highest ration of any planet
Theory suggests planet is still “forming” - as
gases compress into center, friction is
created
Shows banding like Jupiter/Saturn
Great Dark Spot
Voyager II - 1989 photographed “Great Dark
Spot” - giant anticyclonic storm in
southern hemisphere
Disappeared in 1994
Another appeared but in northern hemisphere
Size changed considerably over several
days and path was erratic
Moon System
~13 known
Most are likely captured debris from outer solar
system
Triton
Largest moon
Coldest object in solar system
Highly reflective, ice covered surface prohibits
absorption of solar energy
Volcanic plumes of liquid nitrogen, methane
and ammonia observed
Geologic activity brings into question
subsurface heating and possibility of
water and life
Future Exploration
No current plans for additional missions due to
orbital difficulties