The Solar System

1
The Solar System

• Chapter 15

2
Planets, moons and other bodies

• Solar System
• Sun
• 9 planets
• 100 moons
• Thousands of asteroids, millions of icy bodies,
  comets,
  
• Astronomical unit (AU)
• Average Earth-Sun distance
• 1.5x108 km
• Planet classification size, density and
  atmosphere

• Terrestrial planets
• Mercury, Venus, Earth and Mars
• Mostly rocky materials, metallic nickel and iron
• Giant planets
• Jupiter, Saturn, Uranus and Neptune
• Mostly hydrogen, helium and methane
• Pluto
• In a class by itself
• True planet?

3
The order of the planets
4
Mercury

• Innermost planet
• Highly elliptical orbit
• Average distance 0.4 AU
• Orbital period 3 months
• Rotational period 59 days
• Visible shortly after sunset or before sunrise
• Highly cratered no atmosphere

5
Venus

• Orbital distance 0.7 AU
• Morning and evening star
• Exhibits phases, like the Moon
• Rotational motion opposite orbital motion
• Venusian day longer than Venusian year
• Visited by numerous probes
• Mostly CO2 atmosphere, high temperature and
  pressure
  
• Surface mostly flat but varied

6
Mars

• Orbital distance 1.5 AU
• Geologically active regions
• Inactive volcanoes
• Canyons
• Terraced plateaus near poles
• Flat regions pitted with craters
• Thin atmosphere, mostly CO2
• Strong evidence for liquid water in past
• Numerous space probes

7
Jupiter

• 5 AU from Sun
• Most massive planet
• 318 times Earths mass
• Mostly H and He with iron-silicate core
• Dynamic atmosphere
• H2, He, ammonia, methane, water,
• Great Red Spot
• 39 widely varying satellites

8
Saturn

• 9.5 AU from Sun
• Rings of particles
• Density 0.7 that of water
• Surface similar to Jupiters
• 30 satellites
• Titan only moon with substantial atmosphere

9
Uranus, Neptune and Pluto

• Uranus (19 AU) and Neptune (30 AU)
• Outermost giant planets
• Similar internal structures
• Pluto
• Smaller than the Moon
• 70 rock 30 water ice tenuous, thin atmosphere
  
  
• Unusual orbit
• Tilted 17o from ecliptic
• Crosses Neptunes

10
Planet summary
11
Smaller bodies of the Solar System

• Comets, asteroids, meteorites
• Leftover from solar and planetary formation
• Mass of smaller bodies may be 2/3 of total Solar
  System mass
  
• Bombard larger objects
• Comet Shoemaker-Levy 9 fragments (bottom)
• and strikes Jupiter (July 1994)

12
Comet origins

• Oort cloud
• Origin of long-period comets (200 years)
• 30 AU to light-year away
• Kuiper belt
• Origin of short-period comets (
• Disk-shaped region 30-100 AU from Sun
• Gravitational nudges deflect objects toward Sun

13
Comet structure

• Small, solid objects
• Dirty snowball model
• Frozen water, CO2, ammonia, and methane
• Dusty and rocky bits
• Comet head
• Solid nucleus and coma of gas
• Two types of tails
• Ionized gases
• Dust
• Tail points away from Sun

14
Asteroids

• Located in belt between Mars and Jupiter
• Sizes up to 1,000 km
• Varied composition
• Inner belt stony
• Outer belt dark with carbon
• Others iron and nickel
• Formed from original solar nebula
• Prevented from clumping by Jupiter nearby

15
Meteors and meteorites

• Meteoroids
• Remnants of comets and asteroids
• Meteor
• Meteoroid encountering Earths atmosphere
• Meteor showers Earth passing through comets
  tail
  
• Meteorite
• Meteoroid surviving to strike Earths surface
• Iron, stony (chondrites and achondrites) or
  stony-iron

16
Origin of the Solar System

• Protoplanet nebular model
• Stage A
• Formation of heavy elements in many earlier stars
  and supernovas
  
• Concentration in one region of space as dust, gas
  and chemical compounds

17
Origin of the Solar System

• Stage B
• Formation of large, rotating nebula
• Gravitational contraction, spin rate increases
• Most mass concentrates in central protostar
• Remaining material forms accretion disk
• Material in accretion disk begins clumping

18
Origin of the Solar System

• Stage C
• Protosun becomes a star
• Solar ignition flare-up may have blown away
  hydrogen and helium atmospheres of inner planets
  
• Protoplanets heated, separating heavy and light
  minerals
  
• Larger bodies cooled slower, with heavy materials
  settling over longer times into central cores