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….