Transcript GEOL 3045: Planetary Geology

GEOL 3045: Planetary Geology
Lysa Chizmadia
Edgeworth-Kuiper Belt
Introduction
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Discovered in 1992 by David Jewitt & Jane Luu
Estimated >70,000 objects >100km
Estimated mass: 0.06-0.3 x 
Source for short-period comets
– Period < 200 years
HST image
Images from: http://www.nineplanets.org/kboc.html
Image from:Malhotra & Williams (1997)
Structure of the Kuiper Belt
 EKB from 30-55 AU
– Main body from 3:2 at 39.5Au to 1:2 at 48AU
 Thick: up to 10 outside ecliptic
– More diffuse distribution extends further
Image from: http://en.wikipedia.org/wiki/Kuiper_belt
Kuiper Belt Objects
 NH3, CH4 & H2O ices
 Quaoar:
– Xline H2O, not amorph
– resurfaced
Sedna
Quaoar
Images from: http://en.wikipedia.org/wiki/Kuiper_belt
Types of KBOs
 Name is controversial
 AKA Trans-Neptunian Objects (TNOs)
– Includes KBOs but also all other objects orbiting
Sun at the edge of the solar system
 Three main groups:
– Classical objects
– Resonant objects
– Scattered objects
Images from: http://en.wikipedia.org/wiki/Kuiper_belt
Classical Objects
 AKA cubiwanos (Q-B-1-os)
– 42-47 AU
– No resonances w/ Neptune
 Two populations:
– Dynamically cold:
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Nearly circular orbits (e<0.1)
Low inclinations <10
Image from: Jewitt & Luu (1995)
Redder compositions
Formed + in position, may have migrated w/ Neptune
– Dynamically hot:
 Nearly circular orbits (e<0.1)
 Higher inclinations <30
 Thought to have formed near Jupiter & the ejected
Resonant Objects
 Locked in mean motion
resonances with Neptune
 2:3 ~ Pluto “Plutinos”
– Semi major axis ~ 39.4 AU
– ~200 objects
 1:2 called “twotinos”
– Semi major axis ~47.7 AU
– Sparesely populated
Image from: Jewitt et al. (1998)
 Minor resonances:
– 3:4, 3:5, 4:7, 2:5
 >50 AU “Kuiper Cliff ”
Image from: http://en.wikipedia.org/wiki/Kuiper_belt
Scattered Objects
 High eccentricities
– 0.59
 High inclinations
– ~24°
 Origin of Jupiter-family
comets
Image from: Duncan & Levison (1997)
Image from: http://en.wikipedia.org/wiki/Kuiper_belt
Pluto System
 Barycenter between Pluto & Charon
 At least 3 moons
– Charon (double object)
– Nix (in same plane as Charon)
– Hydra (~1:6 res w/ Charon)
 Atmosphere:
– N2, CH4, CO
 Structure: (=1.8-2.1 g/cm3)
– 1) Frozen N2
– 2) H2O ice
– 3) Silicate & H2O ice
Image from: http://en.wikipedia.org/wiki/Pluto_%28astronomy%29
Images from: http://en.wikipedia.org/wiki/Charon_(moon)
Pluto As A Planet
 Pro:
 Con:
– Hydrostatic equilibrium
(spherical shape)
– Primarily orbits Sun
– Larger than 1000 km
– Largest object in general
vicinity (has cleared its
neighborhood)
– High inclination
– High eccentricity
– Orbits barycenter w/
Charon
– Not largest object in KB
(has not cleared its
neighborhood)
Images from: http://en.wikipedia.org/wiki/2006_definition_of_planet
Centaur Comets
 Orbit between Jupiter & Neptune
– Orbits not stable
 At least 3 display cometary
comas
 Probably from KB
 Reflectance spectra:
– Amorphous carbon
– Hydrocarbons
– Methanol ice
Image from: Stern & Campins (1996)
Formation Theories
 The classical & resonant KBOs probably not
primordial
– Inclinations & eccentricities too high
– Three formation theories:
 Long-term effects of planetary perturbations
 Resonant sweeping due to planetary migration
 Massive scatterers resulting in impacts & gravitational perturbations
 As of 2006, 9 other star systems have KB-like disks
Images from: http://en.wikipedia.org/wiki/Kuiper_belt
New Horizons
Summary
 From 33-50 AU
 Composed of NH3, CH4 &
H2O ices
 Quaoar has crystalline H2O
ice on surface
– Evidence for resurfacing
 Three types of objects:
– Classical
– Resonant
– Scattered
 Pluto’s status as a
planet
– Hydrostatic equilibrium
– Primarily orbits sun
– Has cleaned up
neighborhood?
 Centaur comets similar
compositions
– Probably originated in KB
Image from: http://en.wikipedia.org/wiki/Kuiper_belt