structure of the solar system

Structure of the Solar System

Where and why it is what it is

Laws of motion

Planets move around SunNot always a given,

Anthropic Earth-centered Ptolomaic cosmology

Copernicus published his seminal work on his deathbed (1543)

A case of publish and perishDe revolutionibus orbium celestium

Conservation of angular momentumv1r1 = v2r2 = constant (for constant mass)

The two body problem

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

Titius-Bode Law

Distances of planets from Sun0.4, 0.7, 1.0, 1.6, 2.8, 5.2, …Can be formulated

R = 0.4 + 0.3kK = 0, 1, 2, 4, 8, 16, 320.4, 0.7, 1.0, 1.6, 2.8, 5.2, …

Titius 1729-1776, Bode 1747-1826

Titius-Bode Law

Planet missing between Mars and JupiterAt 2.8 au

Ceres discovered in 1801 at 2.77 auPallas, Juno, Vesta by 1804

Exploded planetNo common origin point

Failed planet

Titius-Bode Law

Okay for Uranus, not so good for Neptune (38 predicted vs 30 actual au)

No other correlation with planetary propertiesSecondary effect after formationRelated to stable resonances of orbital

periodsPlanets have moved

Asteroids

Total mass less than 5% of Moon1-2 Million asteroids with size > 1km

Asteroid beltGaps/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)

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Vesta, Ceres, Moon

Orbital resonances

Fractional orbital periods have greater orbital stability to perturbationConstructive or destructive

interferenceGaps or concentrations

1:1 2:1 3:2

Asteroids

Resonances and gaps







AsteroidsTrojan AsteroidsLagrange points

Gravitation = centripetal L4 and L5 ± 60°

Equal gravity to Jup & Sol



L1, L2, L3 unstable; L4,L5 stable

Asteroids

Several hundred thousand discovered26 > 200 kmSolid rock bodiesRubble piles

Visits by NEAR, HayabusaNEAR landed on ErosHayabusa landed on ItokawaPlus flybys of other missions on way to

Jupiter

Asteroid Spectral Classes

Definition Based on light reflectance (Albedo) Spectral features

Spectral shapeMineralogical 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)



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


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Mathilde

Spectral Class

S Class (17%)Moderately brightAlbedo 0.10-0.22Metallic Fe-Ni + magnesium silicateSpectrum has steep slope < 0.7µm

Absorption features around 1 and 2 µmLargest is 15 Eunomia (330 km diam)



Ida + Dactyl

Spectral Class

Spectral Class

M class (3rd abundant)Metallic Fe-NiModerately bright (0.10-0.18)Spectrum is flat to reddish

Absorption features at 0.55 and 0.75 µm16 Psyche (330 km)



16 Psyche

AsteroidsCompositional trends?

Igneous inside 2.8 au (S class)Metamorphic around 3.2 au (M class)Primitive outside 3.4 au (C class)



Origin of asteroid belt

Failed planetMeteorites

Iron meteorites from corePallasites show mantle olivineIgneous achondritesCrustal carbonaceous chondrites

But not from single bodyOxygen isotopes, chemistry



Origin of asteroid belt

Planetoids form in early SSCoalesce to form planets

Presence of JupiterPumped up the eccentricitiesLimits growthMany small bodies

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Near-Earth asteroids

Apollos, Atens and ArmorsFew thousand > 1km

107 10-100m1036 Ganymed, 433 ErosSource of meteorites?

Eros could survive 50-100 Myr5% chance of hitting Earth

Spectrophotometric Paradox

Most common meteorites are chondritesParent body apparently absent

3628 Boznemcová8km body with Ord-chondrite spectrum

Of 35 NEA, 6 have Ord-chondrite spectraPlus 10% of Main Belt asteroids of size ≈1km

Chondrites dominate meteorites,But not asteroids

Asteroids to Meteorites

Relative frequency of meteorites depends on efficiency of deliveryMeteorites unlikely to be sourced from

deep within asteroid beltAsteroids 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

Missing Olivine Meteorites

Iron MeteoritesCores

PallasitesCore-mantle

Achondrites, ChondritesCrust

Where’s the mantle olivine?

Individual asteroids

1 CeresLargest 933 km diameter 2.7 g/cm32.77 auC class9/13 largest asteroids similar



Individual asteroids4 VestaIrregular shape (460 km across)3.7 g/cm3Intact differentiated crust (basalt)Source of HED meteorites (4.560 Gyr)

460 km crater, 13 km deepTwo more

large craters (100 km+)




433 ErosS class2nd largest NEA33x13x13 kmDensity 2.5 ± 0.8 km

Coherent rather than rubble pile




NEAR Lands on Eros - 2001Boulders on surface from 250 m





5 m

Individual asteroids25143 Itokawa (1998)

S class500 m long2.0 g/cm3

Rubble pile









Hayabusa (Muses-C)


Visits to Mathilde, Gaspra, IdaIda has satellite (Dactyl)



NEAR Mission

Interplanetary dust

SourcesAsteroids (5 km/s)Comets (20-60 km/s)Interstellar grains?

10,000 tons/year to EarthFluffy grains can survive

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Moving Giant PlanetsJupiter moved sunwards depleting

asteroid belt beyond 4 auSaturn, Uranus, Neptune move out

Saturn now in 2:1 resonance with JupiterProduced by bombardment of centaurs

Centaurs

Between Saturn and Uranus2060 Chiron - 1977

182 kmDark-grey-black object (albedo 0.1)Similar in size and colour to Phoebe (Sat Moon)Orbit 8.5 - 19 auFits definition of comet

5145 Pholus - 1992185 km, red

Nessus, Asbolus, Chariklo





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



Moving Giant Planets

can throw KBO out to the Oort CloudOnly few % retained from JupiterRest lost5-10% from Saturn10-40% from Uranus40% from Neptune

Can throw out Rocky and Icy bodiesOort cloud primitive?

Throws objects inThe late heavy bombardment for inner SS

Solar System

DynamicMany time scales4 Vesta has survived 4.56 Gyr

But Exposure ages of HED meteorites 5-80 Myr

Survival time of some asteroids 50,000 years

Near Earth Asteroid Orbits

http://neo.jpl.nasa.gov/orbits/

structure of the solar system

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