Earth and Other Planets
3 November 2015
Chapter 16
Great Idea:
Earth, one of the planets that orbit the Sun, formed
4.5 billion years ago from a great cloud of dust.
1
Chapter Outline
• The Formation of the Solar System
• Exploring the Solar System
• The Earth
2
The Formation of the
Solar System
3
Clues to the Origin
of the Solar System
• Solar system
– Objects gravitationally bound to Sun
• Deduction of origin
– Observations
• Earth
• Space
4
Clue #1: Planetary Orbits
• Features of solar system
– All planets orbit in same direction
– Orbits in same plane
– Most rotate in direction of orbit
5
Clue #2: Distribution of Mass
• Most material within Sun
• Two types of planets
– Terrestrial planets
– Jovian planets
• Other objects
– Moons, asteroids, comets
6
The Nebular Hypothesis
• Nebular
Hypothesis
– Cloud of dust and
gas
– 99% H and He
• Collapse of
nebula
– Planetary orbits
– Clumping of
matter
– Planetesimals
– Temperature
7
Basic Planet Categories
• Terrestrial planets
–
–
–
–
Mercury
Venus
Earth
Mars
• Jovian planets
–
–
–
–
Jupiter
Saturn
Uranus
Neptune
8
Some Conclusions
• Planets formed at same time as Sun
• Planetary and satellite/ring systems are
similar to remnants of dusty disks such
as that seen about stars being born
• Planet composition dependent upon
where it formed in solar system
9
Nebular Condensation
(protoplanet) Model
• Most remnant heat from collapse
retained near center
• After sun ignites, remaining dust
reaches an equilibrium temperature
• Different densities of the planets are
explained by condensation temperatures
• Nebular dust temperature increases to
center of nebula
10
Nebular Condensation Physics
• Energy absorbed per unit area from Sun =
energy emitted as thermal radiator
• Solar Flux = Lum (Sun) / 4 x distance2
• Flux emitted = constant x T4 [Stefan-Boltzmann]
• Concluding from above yields
T = constant / distance0.5
11
Nebular Condensation Chemistry
Molecule
H2
H2O
CH4
NH3
FeSO4
SiO4
Freezing Point Distance from
Center
10 K
>100 AU
273 K
>10 AU
35 K
>35 AU
190 K
>8 AU
700 K
>1 AU
1000 K
>0.5 AU
12
Nebular Condensation Summary
• Solid Particles collide, stick together, sink
toward center
– Terrestrials -> rocky
– Jovians -> rocky core + ices + light gases
• Coolest, most massive collect H and He
• More collisions -> heating and differentiating
of interior
• Remnants flushed by solar wind
• Evolution of atmospheres
13
Pictorial View of Origins
14
Pictorial View Continued
15
HST Pictorial Evidence
16
HST Pictorial Evidence
17
The Formation of Earth
• Planetesimals
– Combined (accretion)
to form earth
• Great bombardment
– Meteors
– Growth of planet
• 20 metric tons per day
18
Differentiation
• Differentiation
– Heat from collisions
– Dense material sank to
center
– Lighter material rose to
surface
• Structure
– Core
– Mantle
– Crust
19
Crust and Us
20
Earth’s Interior How We Know It
21
The Formation of the Moon
• Large object (asteroid close to size of
Mars) impacted earth
• Parts of mantle blown into orbit
• Moon formed from this material
22
Planetary Idiosyncracies
• Cratering
– Mercury, Mars, Moon
– Few on Earth
• weathering
• Rotation
– Venus
– Earth’s axis
– Uranus
23
The Evolution of
Planetary Atmospheres
• Earth’s atmosphere
– Early
– Outgassing
• Atmosphere was N2, CO2, H2, & H2O
– Gravitational escape
– Living organisms
24
Exploring the Solar System
The Inner Solar System
• Mercury, Venus, Mars
– Mercury and Venus too hot for life
• Mars Exploration
– Multiple missions
– Found evidence of water
26
The Outer Solar System
• Jupiter, Saturn, Uranus,
Neptune
– Layered structure
– No solid surface
• Jupiter
– Comet Shoemaker-Levy
– Galileo spacecraft
• Saturn
– Cassini spacecraft
27
Outer Solar System II
28
• Jupiter’s Moons
– Io, Europa, Ganymede, Callisto and 63 others known
• Saturn’s Moons
– Titan, Mimas, Hyperion and about 59 (61?) others
• Rings
Moons
and
Rings
– Ice and rock - more ice in Saturn’s rings
29
Dwarf
Planet
Pluto
Surprises
• It has moons
• Original moon discovered 1978
– Charon (KAIR’ en)
• Now more
– 2005 discovery of 2 additional
moons
– Named Nix and Hydra
– 2011 #4 is P4 (Kerberos)
– July 7, 2012 #5 is P5 (Styx)
30
Pluto’s Interior to Surface
Old -> New Model
• Model 1
– partially hydrated rock
core
– water ice layer II
– predominant water ice
layer I
• Model 2
– partially hydrated rock
core
– organics layer
– predominantly water ice
layer
31
The Launch of New Horizons Pluto Mission
17 Jan 2006
http://www.youtube.com/watch?v=KNJNaIoa5Hk
32
Io’s Volcanoes from New Horizons
33
34
Pluto
35
Pluto’s Methane (frozen)
36
Charon
37
Pluto
38
Pluto Atmosphere Detection
39
Pluto and Charon
40
Carbon Monoxide (Frozen)
41
Solar Wind at Pluto
42
Pluto “Heart” Region
43
Pluto
Mountain
Range
44
Nix and Hydra
45
Pluto, True Color
46
Asteroids, Comets,
and Meteors
• Asteroids
– Small rocky bodies
– Orbit sun
– Most in belt between Mars and Jupiter
• Comets
– Dirty snowballs
• Orbit outside Pluto
• Oort cloud
• Kuiper belt
– Halley’s Comet
– Stardust and Deep Impact missions
• Meteoroids, Meteors, and Meteorites
– Meteor showers
– Original solar system material
51
Planetary Summary
Mass
(Earth=1)
Density
(g/cm3)
Major
Constituents
Mercury
Venus
Earth
Mars
0.06
0.82
1.00
0.11
5.4
5.2
5.5
3.9
Rock, Iron
Rock, Iron
Rock, Iron
Rock, Iron
Jupiter
Saturn
318
95
1.3
0.7
H, He
H, He
Uranus
Neptune
14
17
1.3
1.7
Ices, H, He
Ices, H, He
Planet
52