1. The Solar System Chapter 13
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2. Planets, moons and other bodies
Solar System
Sun
8 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
Dwarf Planet
Pluto
Orbits the sun, nearly spherical, has not cleared matter from its orbital zone, and is not a satellite

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
No moon

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. Earth’s Moon Lunar highlands Maria Craters No water, atmosphere
Light colored mountainous regions
Breccias - rock fragments compacted from meteorite impact
Formed ~4 billion years ago
Maria
Smooth dark areas formed from floods of lava
Basalt - similar to rock formed from cooling lava on earth
Formed about 3.1 – 3.8 billion years ago
Craters
No water, atmosphere
Surface
3 meters grey dust containing microscopic glass beads formed by bombardment of meteorites

7. Stages in Formation of the Moon
Origin Stage
Moon formed from impact of earth with very large object
Molten Surface Stage
First 200 million years
Lunar surface melted due to rock impact
Fewer bombardments, moon surface solidified
Craters: result of meteorite impact after formation of crust
Molten Interior Stage
3.8 billion years ago
Interior melted due to heat generated by radioactivity
Cold and Quiet Stage
3.1 billion years ago
Last lava solidified
Surface change little

8. 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

9. Spirit and Opportunity Mars Exploration Rovers
Found that Mars made of basalt rock and groundwater that is dilute sulfuric acid
Confirmed sufficient amounts of water have been present in the past

10. Jupiter ~ 5 AU from Sun Most massive planet
318 times Earth’s mass
Mostly H and He with iron-silicate core
Dynamic atmosphere
H2, He, ammonia, methane, water, …
Great Red Spot
64 satellites

11. Saturn 9.5 AU from Sun Rings of particles Density = 0.7 that of water
Surface similar to Jupiter’s
62 satellites
Titan: only moon with substantial atmosphere

12. Uranus and Neptune Uranus (~19 AU) and Neptune: (~30 AU)
Outermost giant planets
Similar internal structures

13. Planet summary

14. 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)

15. Comet origins Oort cloud Kuiper belt
Origin of long-period comets (>200 years)
30 AU to light-year away
Kuiper belt
Origin of short-period comets (<200 years)
Disk-shaped region AU from Sun
Gravitational nudges deflect objects toward Sun

16. Comet structure Small, solid objects “Dirty snowball” model Comet head
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

17. 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

18. Meteors and meteorites
Meteoroids
Remnants of comets and asteroids
Meteor
Meteoroid encountering Earth’s atmosphere
Meteor showers: Earth passing through comet’s tail
Meteorite
Meteoroid surviving to strike Earth’s surface
Iron, stony (chondrites and achondrites) or stony-iron

19. 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

20. 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

21. 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