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GEOL 3045: Planetary Geology Lysa Chizmadia Edgeworth-Kuiper Belt Introduction 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: 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