The Outer Planets - Santa Monica...
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11/21/2010 1 The Outer Planets Bulk Properties of Uranus Summary 1. At an average distance of just over 19 AU, Uranus takes over 84 years to orbit the Sun 2. Uranus is smaller than Jupiter (4x the Earth) but much less massive (14.5x Earth). 3. Even though Uranus is smaller and less massive it has a similar density to Jupiter indicating that it probably contains more heavy elements 4. Uranus rotates more slowly than Jupiter in just over 17 hours 5. Uranus receives roughly 1/400 th of the radiation the Earth receives Bulk Properties of Neptune Summary 1. At an average distance of just over 30 AU, Neptune takes over 164 years to orbit the Sun 2. Neptune is similar in size and mass to Uranus (size 3.8x the Earth, mass 17.2x Earth). 3. Neptune also has a high density for its small size indicating that it also contains more heavy elements 4. Neptune rotates at a similar rate to Uranus in just over 16 hours 5. Neptune receives roughly 1/900 th of the radiation the Earth receives Uranus and Neptune are smaller than Jupiter and Saturn
Transcript of The Outer Planets - Santa Monica...
11/21/2010
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The Outer Planets
Bulk Properties of Uranus
Summary1. At an average distance of just over 19 AU,
Uranus takes over 84 years to orbit the Sun
2. Uranus is smaller than Jupiter (4x the Earth) but much less massive (14.5x Earth).
3. Even though Uranus is smaller and less massive it has a similar density to Jupiter indicating that
it probably contains more heavy elements
4. Uranus rotates more slowly than Jupiter in just over 17 hours
5. Uranus receives roughly 1/400th of the radiation the Earth receives
Bulk Properties of Neptune
Summary1. At an average distance of just over 30 AU, Neptune takes over 164 years to orbit the Sun
2. Neptune is similar in size and mass to Uranus (size 3.8x the Earth, mass 17.2x Earth).
3. Neptune also has a high density for its small size indicating that it also contains more heavy
elements
4. Neptune rotates at a similar rate to Uranus in just over 16 hours
5. Neptune receives roughly 1/900th of the radiation the Earth receives
Uranus and Neptune are smaller than Jupiter and Saturn
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Uranus from Earth Neptune from Earth
Uranus has a very large axis tilt - 98º!
Very extreme seasons!
Equatorial Bulges
Smaller than Jupiter or Saturn!
Why?
Slower rotations!
Uranus has a larger bulge even though it rotates slower!
Why?
It has a lower density!
Internal Heat
Neptune: energy emitted > energy received
Uranus: energy emitted < energy received
Uranus has no internal heat!
Why?
A collision may have “mixed up” its interior?
Voyager 2 at Uranus (1985)
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Image enhanced view of Uranus Voyager 2 at Neptune (1989)
The Great Dark Spot! Bright high-latitude clouds of methane (CH4)
Interiors of Uranus and NeptuneNo liquid metallic hydrogen!
Expect:
No magnetic fields!
Find:
Both have fields (50x Earth)!
Why?
Don’t know!
Charged particles in liquid ice layers?
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Magnetic axes are at large angles to rotational axes!
Stellar Occultation of Uranus
Observed Light Curve
Expected Light Curve
The rings of Uranus!
Shepherd Moons!
Uranus rings seen edge-on
2007
The rings of Neptune with Gaps
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Ring Arcs Hubble image of Neptune
Hubble image of Uranus
Uranus has 27 known moons
None are giant!
Many are named after characters in the plays by Shakespeare!
Miranda the smallest moon of Uranus
Chaotic surface: shattered by a collision?
Huge cliffs 2x height of Mt Everest!
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Neptune has 13 known moons
One giant moon called Triton
Neptune’s Moon Triton
Voyager 2 at Triton Triton is a slightly smaller than our moon
Triton’s Orbit
Triton orbits about Neptune in the opposite direction to planetary rotation (retrograde orbit) indicating that it
must have been captured
Very cold: 37 K – frozen nitrogen on surface!
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Triton is also tidally heated causing plumes of nitrogen gas to escape from beneath its surface
Cryovolcanism
Which blows dust up onto the surface forming streaks
Clouds above Triton’s South Pole The Mysterious “Cantaloupe Terrain” on Triton
Discovery of Pluto
Lowell Observatory (1930)
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Pluto – Roman god of the underworld
Bulk Properties of Pluto
Pluto is small!
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Pluto has a moon! Charon is not much smaller than Pluto!
Formation of Charon – collision-ejection? Pluto-Charon Double Synchronization
Pluto rotation = Charon rotation = orbital period = 6.4 daysSame side Charon faces Pluto and same side Pluto faces Charon
Pluto-Charon Eclipses 1982-1993 Two more recently discovered by Hubble!
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Is Pluto a planet?
One possible definition of a planet!
1. Orbits the Sun
2. Is reasonably large
How large is reasonable?
Only we can decide!
Recent discoveries of other large trans-Neptunian objects!
Quaoar! Quaoar is only slightly smaller than Pluto
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Quaoar’s orbit is similar to Pluto’s! Sedna
Sedna is a similar size to Pluto!Sedna has a highly elliptical orbit about the Sun at
an average distance of 90 AU!Orbital period 10,500 years!
Xena! Named after the Warrior Princess!
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Orbit of Xena
Xena is estimated to be 25% larger than Pluto!
Xena has a moon named Gabrielle! Named after Xena’s sidekick!
They have recently been assigned more dignified names by the International Astronomical Union
(IAU)!
Xena has recently been renamed Eris
Gabrielle has recently been renamed Dysnomia
Eris is the Greek god of discord and strife!
The Latin name for Eris is Discordia which just happens to be a character on the Xena show…
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There are several Pluto-sized objects beyond Neptune!
More to be discovered!
There are also many smaller objects!
The Kuiper Belt
If Pluto is not a planet what is it?
A dwarf planet!
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Protests at New Mexico State University
New IAU Definitions
Planets
1. Revolves around the Sun
2. Spherical in shape
3. Large enough to gravitationally dominate its surroundings
Examples: Mercury - Neptune
Dwarf Planets
1. Revolves around the Sun
2. Spherical in shape
Examples: Pluto, Eris, Ceres (largest asteroid)
Small Solar System Bodies
1. Revolve around the Sun
Examples: asteroids, comets and meteoroids
Plutons
The larger dwarf planets beyond the orbit of Neptune are also referred to as Plutons in honor of
their first member.
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New Horizons Mission to Pluto
Launched: Jan 2006, Arrive at Pluto: 2015
