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Transcript 
Astronomy 340
Fall 2007
29 NOVEMBER 2007
CLASS #25
Review
 Pluto system
 Odd orbit, 3 moons
 Possible collision?
 Triton
 Neptune’s large moon
 Retrograde orbit  likely
gravitationally captured
A Little History
 Gerard Kuiper and Kenneth Edgeworth “predicted”
a distribution of small bodies in the outer solar
system – 1940s
 Real surveys began in early ’90s



70,000 KBOs w/ d > 100 km (estimated)
30 AU < a < 50 AU
Range of inclination/eccentricity
 1st KBO is really Pluto!
Bernstein et al 2004
Properties of TNOs
 Green stars  scattered
population
 Red squares  classical
KBOs
 Lines are different
power law fits
 Surface density best fit
by two power laws
Basic Orbital Properties
 “Classical”
 Low eccentricity, low inclination
 40 AU < a < 47 AU
 “Resonant”
 Occupying various resonances with Neptune  3:2, 4:3, 2:1 etc
 a ~ 40 AU
 “Scattered”
 High eccentricity, high inclination
Distribution of TNOs
Population
 Total mass ~ 0.5 Earth masses
 Total number  unknown
 > 1500 detected via surveys
 Colors (Tegler et al 2003 ApJ 599 L49)
 ~100 KBOs with photometry
 “classical” KBOs are “red” (B-R > 1.5)
 “scattered” KBOs are “grey”
Largely colorless (flat spectrum)
 Primordial?

Classical KBOs
Mostly between
42 and 48 AU
Formed via
“quiet accretion”
Orbital Populations
 Reflect dynamical
history of the outer
solar system

Hahn & Malhotra (2005
AJ 130 2392)
N-body simulation
 Neptune migration 
previously heated disk
 Populates the 5:2
resonance with Neptune


“scattered” KBOs largely
affected by planet
migration
Orbital Populations
Hahn & Mulhatra
Scattered KBOs - orbits
Trujillo, Jewitt, Luu 2000 ApJ 529 L103
Populations (Hahn & Malhotra 2005)
Explanation for Colors?
 Neptune migrates from 25 AU to 40 AU
 Scatters objects
 Objects at 40 AU are relatively unperturbed 
surfaces reflect methane ice
KBO colors
KBO Colors vs Dynamics
Centaurs (Horner, Evans, Bailey 2004)
 Eccentricity  e = 0.2-0.6
 Perihelia
 4 < q < 6.6 AU
 6.6 < q < 12.0 AU
 12.0 < q < 22.5 AU
 Aphelia
 6.6  60 AU
 Mean diameters ~ few hundred km
Centaurs – Dynamical Evolution
 Dynamical lifetimes
 Orbital decay rate  N = N0 e-λt (λ = 0.693/T1/2)
 T1/2 ~ 2-3 Myr  scattered via interaction with giant planets
 No correlation with color
Centaurs – Dynamical Evolution
 Dynamical lifetimes
 Orbital decay rate  N =
N0 e-λt (λ = 0.693/T1/2)
 T1/2 ~ 2-3 Myr  scattered
via interaction with giant
planets
 No correlation with color
 Origin?
 “scattered” TNOs 
scattered inward
Hahn & Mulhatra
Sedna
Sedna
 How do you measure
the diameter?
 Best fit orbit





R = 90.32 AU
a = 480 AU
e = 0.84
i = 11.927
Perihelion ~ 76 AU in
2075
Sedna
Quaoar
Quaoar
Quaor spectroscopy (Jewitt & Luu)
Looks a bit like water ice
2003 UB313
 16 years worth of data
 Orbital properties
 a = 67.9 AU, e = 0.4378, i = 43.99
 Aphelion at 97.5 AU, perihelion at 38.2 AU (2257)
But are they really planets?
Eris - Spectroscopy
 Big circles = broadband
colors
 Broad absorption =
solid methane
 Approximate diameter
= Pluto’s
 Hey, the thing has a
moon….
Moons, moons everywhere….
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