1. 14b. Pluto, Kuiper Belt & Oort Cloud
Basic characteristics
Pluto’s moons
The Kuiper Belt
Resonant Kuiper Belt objects
Classical Kuiper Belt objects
The Oort Cloud

2. Pluto Data: Numbers Diameter: 2,290.km 0.18 . Earth
Mass: kg Earth
Density: water Earth
Orbit: km AU
Day: 6d.09h 17m 51s Earth
Year: years Earth

3. Pluto Data: Special Features
Pluto is the farthest planet from the Sun
Pluto is the smallest planet
Pluto has a very thin atmosphere
Pluto is much smaller than the Moon
Pluto has only ~ the mass of the Moon
Pluto has only ~ diameter of the Moon
Pluto’s interior likely consists of two layers
An “icy” mantle (~25% of Pluto’s mass)
A “rocky” core (~75% of Pluto’s mass)
Pluto is extremely difficult to observe from Earth
Pluto is extremely small & far from the Sun
Pluto’s moon Charon has ~ Pluto’s mass

4. Pluto Data (Table 14-5)

5. Pluto’s Amazing Discovery
The reason for a search
Apparent discrepancies in Neptune’s predicted orbit
Actually no unaccounted perturbations of Neptune
The actual search
Percival Lowell
Urged construction of a wide-field astronomical camera
Camera was completed in 1929
Clyde Tombaugh worked at Lowell Observatory
Discovered Planet X on 18 February 1930
Announced discovery on March
Some obvious problems
Much more dim & small than expected
More highly elliptical orbit than any other planet
More steeply inclined orbit than any other planet

6. Pluto & Charon Are Unique Objects
Planetary patterns
Terrestrial planets
H2 & He poor planets with solid surfaces
Satellites much smaller than parent planets
Jovian planets
H2 & He rich planets with no solid surfaces
Pluto’s patterns
Composition
Mixture of ices & rock with a solid surface
Satellite
Closest in mass & diameter of all Solar System pairs

7. The Discovery of Charon
U.S. Naval Observatory
James W. Christy 1978
Examined existing photographs of Pluto
Noted a bulge on one side
Examination of other photos confirmed a moon
Fundamental characteristics
Orbital period of ~ 6.4 days
< 5 % the Earth-Moon distance
Mutual synchronous axial rotation
One side of Charon always faces Pluto
One side of Pluto always faces Charon

8. Determining Surface Characteristics
An extremely rare alignment
Charon’s line of nodes points directly toward Earth
Throughout the years 1985 to 1990
Mutual eclipses of Pluto & Charon
Determined most accurate sizes of Pluto & Charon
Determined generalized brightness patterns of Pluto & Charon
The Hubble Space Telescope
Also helpful in determining surface brightness

9. Kuiper Belt Objects (KBO’s)
Hypothesized
Gerard Kuiper 1951
Proposed a source region for some comets
Discovered
David Jewitt & Jane Luu 1992
Found 1992 QB1 ~ 42 AU from the Sun
Spectrally very similar to Pluto & Charon
More than 1,000 KBO’s have been discovered
Quaoar discovered June 2002
Quaoar measured September 2002
~ 1,300 km in diameter & in a nearly circular orbit
Implications
Pluto & Charon may be the closest & largest KBO’s
Should we still consider Pluto a planet ? ? ?

10. Computer-Derived Views of Pluto

11. Kuiper Belt Objects (KBO’s)
Hypothesized
Gerard Kuiper 1951
Proposed as a source region for short-period comets
Discovered
David Jewitt & Jane Luu 1992
Found 1992 QB1 ~ 42 AU from the Sun
Spectrally very similar to Pluto & Charon
1,352 known KBO’s as of early 2008
Quaoar discovered 4 June 2002
Quaoar measured September 2002
Quaoar announced 7 October 2002
~ 1,300 km in diameter & in a nearly circular orbit
Implications
Pluto & Charon may be the closest large KBOs
I.A.U. no longer considers Pluto a [major] planet ! ! !

12. Resonant Kuiper Belt Objects
1:2 resonance Twotinos
14 confirmed members
2:3 resonance Plutinos
92 confirmed members Pluto is the naming member
104 possible members
2:5 resonance
6 confirmed members
3:5 resonance
10 confirmed members
4:7 resonance
5 confirmed members
Additional resonances are known
6 confirmed members in 6 resonances

13. Resonant TNO Orbits

14. Pluto In Color Pluto rotating
Pluto rotating

15. The Discovery of Hydra & Nix
Pluto's moons

16. The Largest Plutinos
ThePlutinos_Size_Albedo_Color2.svg/250px-ThePlutinos_Size_Albedo_Color2.svg.png

17. Trans-Neptunian Objects (TNO’s)
TheTransneptunians_73AU.svg/800px-TheTransneptunians_73AU.svg.png

18. 8 Largest Trans-Neptunian Objects

19. Still More Trans-Neptunian Objects
TheTransneptunians_Size_Albedo_Color.svg/600px-TheTransneptunians_Size_Albedo_Color.svg.png

20. The Outer Solar System KBO’s Scattered Disc Objects
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21. Classical Kuiper Belt Objects
Neptune’s influence negligible from 42 to 48 AU
Small-object orbits are essentially undisturbed
About two-thirds of all known KBO’s are here
Possible observational bias ⇒ Close enough to be seen
First discovered KBO was labeled QB1
Classical KBO’s are known as cubewanos “Q-B-1-os”
Two categories
Dynamically cold population
Orbital eccentricity < 0.1
Orbital inclination < 10°
Dynamically hot population
Orbital eccentricity > 0.1
Orbital inclination > 10° & < 30°

22. Eris Basic facts Largest known KBO One moon named Dysnomia
~ 1, km in diameter Highly uncertain
Ninth largest known object in orbit around the Sun
One moon named Dysnomia
Dysnomia
Eris

23. The Orbit of Eris

24. The Öpik-Oort Cloud Hypothesized by two astronomers
Ernst Öpik Estonian 1932
Comets originate in a distant spherical cloud
Jan Hendrik Oort Dutch 1950
Comets completely sublimate after a few orbits
Comets have survived to the present time
Basic characteristics
Spherical cloud of dormant long-period comets
~ 50 to 50,000 AU from the Sun
~ 1 light year
~ 25% the distance to Alpha Centauri, the nearest star

25. Features of the Öpik-Oort Cloud
Two segments
Inner cloud
Torus distribution
50 to 20,000 AU from the Sun
Source of Halley-type comets
Outer cloud
Spherical distribution
20,000 to 50,000 AU from the Sun
Source of long-period comets
Oort Cloud objects OCO’s
Only 4 candidates have been identified
2000 CR105
2003 Sedna
2006 SQ372
2008 KV42

26. The Kuiper Belt & Oort Cloud

27. Sedna Named after the Inuit goddess of the sea Orbital parameters
Discovered in 2003
Farthest presently known natural Solar System object
Maximum possible diameter is ~ 75% that of Pluto
Orbital parameters
AU Perihelion
Visible only when it is closest to the Sun
AU Aphelion

28. Sedna’s Orbit & the Oort Cloud
Oort_cloud_Sedna_orbit.svg/600px-Oort_cloud_Sedna_orbit.svg.png