Earth and Other Planets

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.

Chapter Outline

• The Formation of the Solar System• Exploring the Solar System

The Formation of the Solar System

Clues to the Origin of the Solar System

• Solar system–Objects gravitationally bound to Sun

• Deduction of origin–Observations

• Earth• Space

Clue #1: Planetary Orbits

• Features of solar system–All planets orbit in same direction–Orbits in same plane–Most rotate in direction of orbit

Clue #2: Distribution of Mass• Most material within Sun• Two types of planets

– Terrestrial planets– Jovian planets

• Other objects– Moons, asteroids, comets

The Nebular Hypothesis

• Nebular Hypothesis– Cloud of dust

and gas– 99% H and He

• Collapse of nebula– Planetary orbits– Clumping of

matter– Planetesimals– Temperature

Basic Planet Categories

• Terrestrial planets– Mercury– Venus– Earth– Mars

• Jovian planets– Jupiter– Saturn– Uranus– Neptune

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

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

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

Nebular Condensation Chemistry

Molecule Freezing Point Distance fromCenter

H2 10 K >100 AUH2O 273 K >10 AUCH4 35 K >35 AUNH3 190 K >8 AU

FeSO4 700 K >1 AUSiO4 1000 K >0.5 AU

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

iClicker Question

The most abundant chemical element in the solar nebula

A UraniumB IronC HydrogenD HeliumE Lithium

Pictorial View of Origins

Pictorial View Continued

HST Pictorial Evidence

HST Pictorial Evidence

iClicker Question

As a planetary system and its star forms the temperature in the core of the nebula

A Decreases in timeB Increases in timeC Remains the same over timeD Cannot be determined

iClicker Question

As a planetary system and its star forms the rate of rotation of the nebula

A Decreases in timeB Increases in timeC Remains the same over timeD Cannot be determined

The Formation of Earth

• Planetesimals–Combined

(accretion) to form earth

• Great bombardment–Meteors–Growth of planet

• 20 metric tons per day

Differentiation

• Differentiation– Heat from collisions– Dense material sank to

center– Lighter material rose to

surface

• Structure– Core– Mantle– Crust

Crust and Us

Earth’s Interior -How We Know It

iClicker Question

Which of the diagram represents the mantle of the Earth?

ABCDE None of the

above.

iClicker Question

Which of the diagram represents the outer core of the Earth?

ABCDE None of the

above.

iClicker Question

Energy transport from one region to another by the movement of material as in the mantle of the Earth is known as

A chaos.B radiance.C conduction.D differentiation.E convection.

iClicker Question

The existence of earthquake shadow zones indicates that there is an abrupt change between the properties of the mantle and those of the core. Specifically, the transverse wave shadow zone shows that the outer core must be

A solid.B liquid or semi-liquid.C gaseous.D similar to crustal material.E impossible to determine.

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

Planetary Idiosyncracies

• Cratering–Mercury, Mars, Moon–Few on Earth

• weathering

• Rotation–Venus –Earth’s axis–Uranus

The Evolution of Planetary Atmospheres

• Earth’s atmosphere–Early–Outgassing

• Atmosphere was N2, CO2, H2, & H2O

–Gravitational escape–Living organisms

iClicker Question

• All our observations of the Sun and planets have been made from the surface of the Earth.

– A True– B False

iClicker Question

• All planets and most of their moons orbit in the same direction around the Sun

– A True– B False

iClicker Question

• Almost all planets and moons rotate on their axes in the same direction as the planets orbit the Sun.

– A True– B False

iClicker Question

• What is the shape of our solar system?

– A spherical (like a ball)– B flat (like a dish)– C tubular (like a hot dog)

iClicker Question

• The mass in our solar system is evenly distributed.

– A True– B False

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

The Outer Solar System

• Jupiter, Saturn, Uranus, Neptune– Layered structure– No solid surface

• Jupiter– Comet Shoemaker-Levy– Galileo spacecraft

• Saturn– Cassini spacecraft

Moons and Rings• Jupiter’s Moons

– Io, Europa, Ganymede, Callisto and about 60 others• Saturn’s Moons

– Titan, Mimas, Hyperion and about 60 others• Rings

– Ice and rock - more ice in Saturn’s rings

Pluto

• Pluto–Outermost planet– .3% of earth’s mass–Three moons

• Charon, Nix, Hydra

–Formation• Captured comet or asteroid

– What about density?

• Still open to question

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

Planetary Summary

Planet 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

iClicker Question

• Mercury, Venus, Earth, and Mars are called:

– A galaxial objects– B standard planetoids– C Jovian planets– D terrestrial planets

iClicker Question

• Jupiter, Saturn, Uranus, and Neptune are called:

– A galaxial objects– B standard planetoids– C Jovian planets– D terrestrial planets

iClicker Question

• The asteroid belt is located:– A between the Sun and Mercury– B between Mercury and Venus– C between Mars and Jupiter– D outside of our solar system

iClicker Question

• Distinctive features of the solar system such as the rotation of the Sun, orbits of the planets, and the distribution of mass into one large central object and lots of much smaller orbiting bodies is explained by:

– A the Hubble theory– B the nebular hypothesis– C the Trefil and Hazen gambit– D the relativity theory

iClicker Question

• What are the Jovian planets composed of?

– A hydrogen and helium– B rocky substances– C element 119 (Jo)– D iron (Fe)

iClicker Question

• Scientists estimated that the mass of the Earth has grown by about what mass each day?

– A 20 kg– B 20,000 kg– C 2 million kg– D it is not growing at all

iClicker Question

• Which elements is the mantle rich in?

– A H, O and C– B P, S, Mn and Cl– C O, Si, Mg and Fe– D transuranic elements such as Np

and Pu

iClicker Question

• Outgassing and gravitation escapeare processes by which:

– A planets form an atmosphere– B space travel may become possible– C solar systems form planets– D string theory can be applied

iClicker Question

• Have you ever seen a meteor or meteorite?

– A yes– B no– C don’t know what these are

iClicker Question

• Should future missions to the planets carry people or should they only carry machines?

– A yes– B no