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Structure of the Solar System - PowerPoint PPT Presentation

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Structure of the Solar System

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  1. Structure of the Solar System Where and why it is what it is

  2. Laws of motion • Planets move around Sun • Not always a given, • Anthropic Earth-centered Ptolomaic cosmology • Copernicus published his seminal work on his deathbed (1543) • A case of publish and perish • De revolutionibus orbium celestium • Conservation of angular momentum • v1r1 = v2r2 = constant (for constant mass) • The two body problem

  3. Kepler’s Laws • Planets move around the Sun in elliptical orbits, with Sun as one of the foci • A radius vector sweeps out equal area in equal time • Squares of the periods of the revolutionof the planets are proportional to the cubes of their distance from the Sun

  4. Titius-Bode Law • Distances of planets from Sun • 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, … • Can be formulated • R = 0.4 + 0.3k • K = 0, 1, 2, 4, 8, 16, 32 • 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, … • Titius 1729-1776, Bode 1747-1826

  5. Titius-Bode Law Planet missing between Mars and Jupiter • At 2.8 au • Ceres discovered in 1801 at 2.77 au • Pallas, Juno, Vesta by 1804 • Exploded planet • No common origin point • Failed planet

  6. Titius-Bode Law • Okay for Uranus, not so good for Neptune (38 predicted vs 30 actual au) • No other correlation with planetary properties • Secondary effect after formation • Related to stable resonances of orbital periods • Planets have moved

  7. Asteroids • Total mass less than 5% of Moon • 1-2 Million asteroids with size > 1km • Asteroid belt • Gaps/concentrations due to resonances with Jupiter (Kirkwood Gaps) • Gaps at 2:1 (3.28 au) and 3:1 (2.50 au) • Concs at 1:1 3:2 (3.97 au) 4:3 (4.2 au) Vesta, Ceres, Moon

  8. 3:2 1:1 2:1 Orbital resonances • Fractional orbital periods have greater orbital stability to perturbation • Constructive or destructive interference • Gaps or concentrations

  9. Asteroids • Resonances and gaps

  10. Asteroids • Trojan Asteroids • Lagrange points • Gravitation = centripetal • L4 and L5 ± 60° • Equal gravity to Jup & Sol L1, L2, L3 unstable; L4,L5 stable

  11. Asteroids • Several hundred thousand discovered • 26 > 200 km • Solid rock bodies • Rubble piles • Visits by NEAR, Hayabusa • NEAR landed on Eros • Hayabusa landed on Itokawa • Plus flybys of other missions on way to Jupiter

  12. Asteroid Spectral Classes • Definition • Based on light reflectance (Albedo) • Spectral features • Spectral shape • Mineralogical features • e.g. olivine, pyroxene, water, … • Chapman 1975 • 3 types (C-carbonaceous, S-stony, and U) • Tholen 1984 • used spectra 0.31-1.06 µm • Types A-X (23)

  13. Mathilde Spectral Class • C-type (Most abundant 75 %) • Low albedo (0.03-0.10) • Strong UV absorption below 0.4 µm • Longer wavelengths featureless • Reddish • Water feature at 3 µm • Type 10-Hygeia • 4th largest asteroid

  14. Spectral Class • S Class (17%) • Moderately bright • Albedo 0.10-0.22 • Metallic Fe-Ni + magnesium silicate • Spectrum has steep slope < 0.7µm • Absorption features around 1 and 2 µm • Largest is 15 Eunomia (330 km diam) Ida + Dactyl

  15. Spectral Class • M class (3rd abundant) • Metallic Fe-Ni • Moderately bright (0.10-0.18) • Spectrum is flat to reddish • Absorption features at 0.55 and 0.75 µm • 16 Psyche (330 km) 16 Psyche

  16. Asteroids • Compositional trends? • Igneous inside 2.8 au (S class) • Metamorphic around 3.2 au (M class) • Primitive outside 3.4 au (C class)

  17. Origin of asteroid belt • Failed planet • Meteorites • Iron meteorites from core • Pallasites show mantle olivine • Igneous achondrites • Crustal carbonaceous chondrites • But not from single body • Oxygen isotopes, chemistry

  18. Origin of asteroid belt • Planetoids form in early SS • Coalesce to form planets • Presence of Jupiter • Pumped up the eccentricities • Limits growth • Many small bodies • No planet at 2.8 au

  19. Near-Earth asteroids • Apollos, Atens and Armors • Few thousand > 1km • 107 10-100m • 1036 Ganymed, 433 Eros • Source of meteorites? • Eros could survive 50-100 Myr • 5% chance of hitting Earth

  20. Spectrophotometric Paradox • Most common meteorites are chondrites • Parent body apparently absent • 3628 Boznemcová • 8km body with Ord-chondrite spectrum • Of 35 NEA, 6 have Ord-chondrite spectra • Plus 10% of Main Belt asteroids of size ≈1km • Chondrites dominate meteorites, • But not asteroids

  21. Asteroids to Meteorites • Relative frequency of meteorites depends on efficiency of delivery • Meteorites unlikely to be sourced from deep within asteroid belt • Asteroids must be close to resonances to supply meteorites into Earth-crossing orbit • 6 Hebe near 3:1(2.50 au) • Source of H-Chondrites + IIE Irons

  22. Missing Olivine Meteorites • Iron Meteorites • Cores • Pallasites • Core-mantle • Achondrites, Chondrites • Crust • Where’s the mantle olivine?

  23. Individual asteroids • 1 Ceres • Largest 933 km diameter • 2.7 g/cm3 • 2.77 au • C class • 9/13 largest asteroids similar

  24. Individual asteroids • 4 Vesta • Irregular shape (460 km across) • 3.7 g/cm3 • Intact differentiated crust (basalt) • Source of HED meteorites (4.560 Gyr) • 460 km crater, 13 km deep • Two more large craters (100 km+)

  25. Individual asteroids • 433 Eros • S class • 2nd largest NEA • 33x13x13 km • Density 2.5 ± 0.8 km • Coherent rather than rubble pile

  26. Individual asteroids • NEAR Lands on Eros - 2001 • Boulders on surface from 250 m 5 m

  27. Individual asteroids • 25143 Itokawa (1998) • S class • 500 m long • 2.0 g/cm3 • Rubble pile Hayabusa (Muses-C)

  28. Individual asteroids • Visits to Mathilde, Gaspra, Ida • Ida has satellite (Dactyl) NEAR Mission

  29. Interplanetary dust • Sources • Asteroids (5 km/s) • Comets (20-60 km/s) • Interstellar grains? • 10,000 tons/year to Earth • Fluffy grains can survive atmospheric entry • Many carbonaceous

  30. Moving Giant Planets • Jupiter moved sunwards depleting asteroid belt beyond 4 au • Saturn, Uranus, Neptune move out • Saturn now in 2:1 resonance with Jupiter • Produced by bombardment of centaurs

  31. Centaurs • Between Saturn and Uranus • 2060 Chiron - 1977 • 182 km • Dark-grey-black object (albedo 0.1) • Similar in size and colour to Phoebe (Sat Moon) • Orbit 8.5 - 19 au • Fits definition of comet • 5145 Pholus - 1992 • 185 km, red • Nessus, Asbolus, Chariklo

  32. Moving Giant Planets • Neptune plows into and depletes inner zone of Kuiper Belt (30-35 au) • Pluto swept into a 3:2 orbital resonance at high eccentricity and inclination

  33. Moving Giant Planets • can throw KBO out to the Oort Cloud • Only few % retained from Jupiter • Rest lost • 5-10% from Saturn • 10-40% from Uranus • 40% from Neptune • Can throw out Rocky and Icy bodies • Oort cloud primitive? • Throws objects in • The late heavy bombardment for inner SS

  34. Solar System • Dynamic • Many time scales • 4 Vesta has survived 4.56 Gyr • But Exposure ages of HED meteorites 5-80 Myr • Survival time of some asteroids • 50,000 years

  35. Near Earth Asteroid Orbits • http://neo.jpl.nasa.gov/orbits/