29 NOVEMBER 2007 CLASS #25 Astronomy 340 Fall 2007
Slide 2
Review Pluto system Odd orbit, 3 moons Possible collision?
Triton Neptunes large moon Retrograde orbit likely gravitationally
captured
Slide 3
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 1 st KBO
is really Pluto!
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Slide 5
Bernstein et al 2004
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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
Slide 7
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
Slide 8
Distribution of TNOs
Slide 9
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?
Slide 10
Classical KBOs Mostly between 42 and 48 AU Formed via quiet
accretion
Slide 11
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
Explanation for Colors? Neptune migrates from 25 AU to 40 AU
Scatters objects Objects at 40 AU are relatively unperturbed
surfaces reflect methane ice
Slide 17
KBO colors
Slide 18
KBO Colors vs Dynamics
Slide 19
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
Slide 20
Centaurs Dynamical Evolution Dynamical lifetimes Orbital decay
rate N = N 0 e -t ( = 0.693/T 1/2 ) T 1/2 ~ 2-3 Myr scattered via
interaction with giant planets No correlation with color
Slide 21
Centaurs Dynamical Evolution Dynamical lifetimes Orbital decay
rate N = N 0 e -t ( = 0.693/T 1/2 ) T 1/2 ~ 2-3 Myr scattered via
interaction with giant planets No correlation with color Origin?
scattered TNOs scattered inward Hahn & Mulhatra
Slide 22
Sedna
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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
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Sedna
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Quaoar
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Quaor spectroscopy (Jewitt & Luu) Looks a bit like water
ice
Slide 28
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)
Slide 29
But are they really planets?
Slide 30
Eris - Spectroscopy Big circles = broadband colors Broad
absorption = solid methane Approximate diameter = Plutos Hey, the
thing has a moon.
