Structure of the Solar System

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
Keplers 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
Vesta, Ceres, Moon

• Total mass less than 5 of Moon
• 1-2 Million asteroids with size gt 1km
• Asteroid belt
• Gaps/concentrations due to resonances with
  Jupiter (Kirkwood Gaps)
• Gaps at 21 (3.28 au) and 31 (2.50 au)
• Concs at 11 32 (3.97 au) 43 (4.2 au)

8
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 gt 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
Spectral Class
Mathilde

• 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
Ida Dactyl

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

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 gt 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 31(2.50 au)
• Source of H-Chondrites IIE Irons

22
Missing Olivine Meteorites

• Iron Meteorites
• Cores
• Pallasites
• Core-mantle
• Achondrites, Chondrites
• Crust
• Wheres 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 21 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 32 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/