29 NOVEMBER 2007 CLASS #25 Astronomy 340 Fall 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 1 st 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 )  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 = 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 = N 0 e -λt (λ = 0.693/T 1/2 )  T 1/2 ~ 2-3 Myr  scattered via interaction with giant planets  No correlation with color

Centaurs – Dynamical Evolution Dynamical lifetimes  Orbital decay rate  N = N 0 e -λt (λ = 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

Sedna

How do you measure the diameter? Best fit orbit  R = AU  a = 480 AU  e = 0.84  i =  Perihelion ~ 76 AU in 2075

Sedna

Quaoar

Quaor spectroscopy (Jewitt & Luu) Looks a bit like water ice

2003 UB years worth of data Orbital properties  a = 67.9 AU, e = , i =  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….