1. 1/11/2017
What is Saturn’s Largest moon?

2. Uranus, Neptune, and Pluto

3. Outline I. Uranus A. The Discovery of Uranus B. The Motion of Uranus
C. The Atmosphere of Uranus
D. The Interior of Uranus
E. The Rings of Uranus
F. The Moons of Uranus
G. A History of Uranus
II. Neptune
A. The Discovery of Neptune
B. The Atmosphere and Interior of Neptune
C. The Rings of Neptune
D. The Moons of Neptune
E. The History of Neptune

4. Outline (continued) III. Pluto A. The Discovery of Pluto
B. Pluto as a Planet
C. The Origin of Pluto and Charon

5. Uranus Chance discovery by William Herschel in 1781,
while scanning the sky for nearby objects with measurable parallax: discovered Uranus as slightly extended object, ~ 3.7 arc seconds in diameter.

6. The Motion of Uranus
Very unusual orientation of rotation axis: Almost in the orbital plane.
97.9o
19.18 AU
Possibly result of impact of a large planetesimal during the phase of planet formation.
Large portions of the planet exposed to “eternal” sunlight for many years, then complete darkness for many years!

7. The Atmosphere of Uranus
Like other gas giants: No surface.
Gradual transition from gas phase to fluid interior.
83 % H; 15 % He, 2 % Methane, trace ammonia and water vapor.
Optical view from Earth: Blue color due to methane, absorbing longer wavelengths
Cloud structures only visible after artificial computer enhancement of optical images taken from Voyager spacecraft.

8. The Structure of Uranus’ Atmosphere
Only one layer of Methane clouds (in contrast to 3 cloud layers on Jupiter and Saturn).
3 cloud layers in Jupiter and Saturn form at relatively high temperatures that occur only very deep in Uranus’ atmosphere.
Uranus’ cloud layer difficult to see because of thick atmosphere above it.
Also shows belt-zone structure
 Belt-zone cloud structure must be dominated by planet’s rotation, not by incidence angle of sun light!

9. Cloud Structure of Uranus
Hubble Space Telescope image of Uranus shows cloud structures not present during Voyager’s passage in 1986.
 Possibly due to seasonal changes of the cloud structures.

10. Ices of water, methane, and ammonia, mixed with hydrogen and silicates
The Interior of Uranus
Average density ≈ 1.29 g/cm3  larger portion of rock and ice than Jupiter and Saturn.
Ices of water, methane, and ammonia, mixed with hydrogen and silicates

11. The Magnetic Field of Uranus
No metallic core  no magnetic field was expected.
But actually, magnetic field of ~ 75 % of Earth’s magnetic field strength was discovered:
Offset from center: ~ 30 % of planet’s radius!
Inclined by ~ 60o against axis of rotation.
Possibly due to dynamo in liquid-water/ammonia/methane solution in Uranus’ interior.
Magnetosphere with weak radiation belts; allows determination of rotation period: hr.

12. The Magnetosphere of Uranus
Rapid rotation and large inclination deform magnetosphere into a corkscrew shape.
UV images
During Voyager 2 flyby: South pole pointed towards sun; direct interaction of solar wind with magnetosphere  Bright aurorae!

13. Apparent motion of star behind Uranus and rings
The Rings of Uranus
Rings of Uranus and Neptune are similar to Jupiter’s rings.
Confined by shepherd moons; consist of dark material.
Apparent motion of star behind Uranus and rings
Rings of Uranus were discovered through occultations of a background star

14. The Rings of Neptune Interrupted between denser segments (arcs)
Ring material must be regularly re-supplied by dust from meteorite impacts on the moons.
Interrupted between denser segments (arcs)
Made of dark material, visible in forward-scattered light.
Focused by small shepherd moons embedded in the ring structure.

15. 1/12/2017
What is special about Uranus’s Rotation

16. The Moons of Uranus 5 largest moons visible from Earth.
10 more discovered by Voyager 2; more are still being found.
Dark surfaces, probably ice darkened by dust from meteorite impacts.
5 largest moons all tidally locked to Uranus.

17. Interiors of Uranus’s Moons
Large rock cores surrounded by icy mantles.

18. The Surfaces of Uranus’s Moons (1)
Oberon
Titania
Old, inactive, cratered surface,
Largest moon
but probably active past.
Heavily cratered surface, but no very large craters.
Long fault across the surface.
Dirty water may have flooded floors of some craters.
Active phase with internal melting might have flooded craters.

19. The Surfaces of Uranus’s Moons (2)
Umbriel
Ariel
Dark, cratered surface
Brightest surface of 5 largest moons
Clear signs of geological activity
No faults or other signs of surface activity
Crossed by faults over 10 km deep
Possibly heated by tidal interactions with Miranda and Umbriel.

20. Uranus’s Moon Miranda Most unusual of the 5 moons detected from Earth
Ovoids: Oval groove patterns, probably associated with convection currents in the mantle, but not with impacts.
20 km high cliff near the equator
Surface features are old; Miranda is no longer geologically active.

21. Neptune
Discovered in 1846 at position predicted from gravitational disturbances on Uranus’s orbit by J. C. Adams and U. J. Leverrier.
Blue-green color from methane in the atmosphere
4 times Earth’s diameter; 4 % smaller than Uranus

22. The Atmosphere of Neptune
The “Great Dark Spot”
Cloud-belt structure with high-velocity winds; origin not well understood.
Darker cyclonic disturbances, similar to Great Red Spot on Jupiter, but not long-lived.
White cloud features of methane ice crystals

23. The Moons of Neptune Unusual orbits:
Two moons (Triton and Nereid) visible from Earth; 6 more discovered by Voyager 2
Triton: Only satellite in the solar system orbiting clockwise, i.e. “backward”.
Nereid: Highly eccentric orbit; very long orbital period (359.4 d).

24. The Surface of Triton
Very low temperature (34.5 K)
 Triton can hold a tenuous atmosphere of nitrogen and some methane; 105 times less dense than Earth’s atmosphere.
Surface composed of ices: nitrogen, methane, carbon monoxide, carbon dioxide.
Possibly cyclic nitrogen ice deposition and re-vaporizing on Triton’s south pole, similar to CO2 ice polar cap cycles on Mars.
Dark smudges on the nitrogen ice surface, probably due to methane rising from below surface, forming carbon-rich deposits when exposed to sun light.

25. The Surface of Triton (2)
Ongoing surface activity: Surface features probably not more than 100 million years old.
Large basins might have been flooded multiple times by liquids from the interior.
Ice equivalent of greenhouse effect may be one of the heat sources for Triton’s geological activity.

26. Discovered 1930 by C. Tombaugh.
Pluto
Discovered 1930 by C. Tombaugh.
Existence predicted from orbital disturbances of Neptune, but Pluto is actually too small to cause those disturbances.

27. Pluto as a Dwarf Planet
Virtually no surface features visible from Earth.
~ 65 % of size of Earth’s Moon.
Highly elliptical orbit; coming occasionally closer to the sun than Neptune.
Orbit highly inclined (17o) against other planets’ orbits
 Neptune and Pluto will never collide.
Surface covered with nitrogen ice; traces of frozen methane and carbon monoxide.
Daytime temperature (50 K) enough to vaporize some N and CO to form a very tenuous atmosphere.

28. Pluto’s Moon Charon
Discovered in 1978; about half the size and 1/12 the mass of Pluto itself.
Tidally locked to Pluto.
Hubble Space Telescope image

29. Pluto and Charon Orbit highly inclined against orbital plane.
From separation and orbital period:
Mpluto ~ 0.2 Earth masses.
Density ≈ 2 g/cm3
(both Pluto and Charon)
 ~ 35 % ice and 65 % rock.
Large orbital inclinations  Large seasonal changes on Pluto and Charon.

30. The Origin of Pluto and Charon
Probably very different history than neighboring Jovian planets.
Older theory:
Pluto and Charon formed as moons of Neptune, ejected by interaction with massive planetesimal.
Mostly abandoned today since such interactions are unlikely.
Modern theory: Pluto and Charon members of Kuiper belt of small, icy objects.
Collision between Pluto and Charon may have caused the peculiar orbital patterns and large inclination of Pluto’s rotation axis.

31. Recent Pluto Pictures

32. Is Pluto a Planet? Answer these questions:
Does pluto have moons?
What is the size of pluto?
What is the density of Pluto?
How long is Pluto’s day/year?
What is the Temperature on pluto?
Does Pluto have an atmosphere?
Does pluto have a Magnetic Field?
What is pluto composed of?
State which qualities should be used to describe a planet and which ones shouldn’t using other planets as examples. At the end, state whether or not Pluto should be a planet based on these qualities.

33. 1/13 Which of these is a Binary Compound? Ammonium Sulfide
Sodium Chloride Sodium Chlorite

34. 1/13/2017
What is the trait that scientist used to reclassify pluto as a dwarf planet?

35. Example
Pluto has no moons. Other planets, like Mercury and Venus, have no moons which is why it is not a good quality to define planets.
(Take note, pluto does have moons, this is an example)