Astronomy 340 Fall 2007
description
Transcript of Astronomy 340 Fall 2007
29 NOVEMBER 2007CLASS #25
Astronomy 340Fall 2007
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 massesTotal number unknown
> 1500 detected via surveysColors (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 between42 and 48 AU
Formed via “quiet accretion”
Orbital PopulationsReflect 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 - orbitsTrujillo, Jewitt, Luu 2000 ApJ 529 L103
Populations (Hahn & Malhotra 2005)
Explanation for Colors?
Neptune migrates from 25 AU to 40 AUScatters objectsObjects at 40 AU are relatively unperturbed
surfaces reflect methane ice
KBO colors
KBO Colors vs Dynamics
Centaurs (Horner, Evans, Bailey 2004)
Eccentricity e = 0.2-0.6Perihelia
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 inwardHahn & Mulhatra
Sedna
SednaHow 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….