1. Astronomy 340 Fall 2005
1 December 2005
Class #24

2. Kuiper/Edgeworth Belt
History  existence postulated since discovery of Pluto
Only really discovered since the 90s
Direct relics of the oldest solid bodies in the solar system
Questions
Orbits  what are they and how did they get like that?
Population  how many are there? What is their size and mass distribution?
Compostion  what are they made of?
Tracers  do they mark the edge of the solar disk?

3. Scales in the Outer Solar System
Saturn  10 AU
Uranus  20 AU
Neptune  30 AU
Pluto/Charon  AU
What else is out there besides Pluto?
Short period comets (P < 100 years)
Centaurs lie between J and S

4. Classical KBOs Most of the KBOs Reside outside of resonances
42 < a < 48 AU, e~0.1
Two gaussian distributions in inclination (2, 17)
Why the range of inclinations?

5. Classical KBOs Most of the KBOs Reside outside of resonances
42 < a < 48 AU, e~0.1
Two gaussian distributions in inclination (2, 17)
Why the range of inclinations?
Interactions with giants  should clear out low inclination orbits
Passing star?
Scattered by larger KBOs?

6. Resonant KBOs
4:3 (36.5 AU), 3:2 (39.5), 5:3 (42 AU), 2:1 (48 AU)  3:2 = “Plutinos”
Larger e, i than classical  mean inclination of ~ 10 degrees
3:2 resonance most heavily populated

7. Origin of Resonant KBOs
Migration of Neptune
N migrates outwards
Scatters objects & establishes new resonances
Model predicts equal numbers at all resonances but this isn’t observed

8. Migration Scattering Is it smooth? Start and stop? Back and forth?
Inward  planet gains angular mo and migrates outward
Outward  planet loses angular mo and migrates inward
Is it smooth? Start and stop? Back and forth?
How?
If local distribution of unaccreted objects is smooth  no migration
J very effective at scattering objects to escape velocity  loses angular momentum and migrates inwards

9. Populations Power law: Σ = 10α(R-R’) (R’ = 23.5 mag)
~100 KBOs per square degree at R = 28
Remember: Δm = -2.5 log (f1/f2)
KBOs are times fainter than Pluto!
Malmquist bias!!!
Size distribution
N(r) = kr-qdr (k = constant, q = slope)
N(r)dr = # with radius r in r+δr bin
3.6 < q < 4.8  N(r>1000 km) ~ 10  there are likely other Plutos (e.g. Sedna, Quaroar, UB313)
Integrate for total mass
Albedo ~ 4%
Density ~ g cm-3