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The Nature of the Solar System

Chapter 15 Lecture

Natalie Bursztyn

Utah State University

Foundations of Earth Science

Eighth Edition

Explain the geocentric view of the solar system.

Describe how it differs from the heliocentric view.

Focus Questions 15.1

Ancient Greeks

Used philosophical arguments to explain natural phenomena

Also used observational data

Most held a geocentric view of the universe

“Earth-centered” view

Earth as a motionless sphere at the center of the universe

Stars on the celestial sphere

Transparent, hollow sphere

Celestial sphere turns daily around Earth

Aristarchus first to propose heliocentric (sun-centered) universe

Ancient Astronomy

Ptolemaic system

a.d. 141

Geocentric model

To explain retrograde motion, Ptolemy used two motions for the planets

– Large orbital circles, called deferents, and

– Small circles, called epicycles

Ancient Astronomy

List and describe the contributions to modern astronomy of Nicolaus Copernicus, Tycho Brahe, Johannes Kepler, Galileo Galilei, and Isaac Newton.

Focus Question 15.2

Nicolaus Copernicus (1473–1543)

Concluded Earth was a planet

Constructed a model of the solar system that put the Sun at the center, but he used circular orbits for the planets

Ushered out old astronomy

The Birth of Modern Astronomy

Tycho Brahe (1546–1601)

Precise observer

Tried to find stellar parallax

The apparent shift in a star’s position due to the revolution of Earth

Did not believe in the Copernican system because he was unable to observe stellar parallax

The Birth of Modern Astronomy

Johannes Kepler (1571–1630)

Ushered in new astronomy

Planets revolve around the Sun

Three laws of planetary motion

Orbits of the planets are elliptical

Planets revolve around the Sun at varying speeds

There is a proportional relation between a planet’s orbital period and its distance to the Sun (measured in astronomical units (AU’s)— One AU averages about 150 million kilometers, or 93 million miles)

The Birth of Modern Astronomy

Galileo Galilei (1564–1642)

Supported Copernican theory

Used experimental data

Constructed an astronomical telescope in 1609

Four large moons of Jupiter

Planets appeared as disks

Phases of Venus

Features on the Moon

Sunspots

The Birth of Modern Astronomy

Sir Isaac Newton (1643–1727)

Law of universal gravitation

Proved that the force of gravity, combined with the tendency of a planet to remain in straight-line motion, results in the elliptical orbits discovered by Kepler

The Birth of Modern Astronomy

Describe the formation of the solar system according to the nebular theory.

Compare and contrast the terrestrial and Jovian planets.

Focus Questions 15.3

Nebular theory

Planets formed ~ 5 billion years ago

Solar system condensed from a solar nebula

Most material collected at center as the hot protosun

Other material formed a flattened rotating disc

Matter in the disc cooled and collided forming planetesimals

Our Solar System: An Overview

As the protoplanets formed, the materials that compose them separated

Dense metallic elements (iron and nickel) sank toward their centers

Lighter elements (silicate minerals, oxygen, hydrogen) migrated toward their surfaces

Process called chemical differentiation

Due to their surface gravities, Venus and Earth retained atmospheric gases

Due to frigid temperatures, the Jovian planets contain a high percentage of ices

Our Solar System: An Overview

Two groups of planets occur in the solar system

Terrestrial (Earth-like) inner planets

Mercury, Venus, Earth, Mars

Small, dense, rocky

Low escape velocities

Jovian (Jupiter-like) outer planets

Jupiter, Saturn, Uranus, Neptune

Large, low density, gaseous—gas giants

Massive

Thick atmospheres composed of hydrogen, helium, methane, and ammonia

High escape velocities

Our Solar System: An Overview

Planetary Impacts

Occurred throughout history of solar system

Bodies that have little or no atmosphere

No air resistance to prevent impact

Smallest pieces of debris reach the surface

At high velocities, debris produces microscopic cavities on individual mineral grains!

Large impact craters result from collisions with massive bodies, such as asteroids and comets

Our Solar System: An Overview

List and describe the major features of Earth’s Moon.

Explain how maria basins were formed.

Focus Questions 15.4

General characteristics

Diameter of 3475 km (2150 mi)

Unusually large compared to its parent planet

Density

3.3 times that of water

Comparable to Earth’s crustal rocks

Perhaps Moon has a small iron core

Gravitational attraction is one-sixth of Earth

No atmosphere

Tectonics no longer active

Surface bombarded by micrometeorites

Gradually make the landscape smooth

Earth’s Moon: A Chip Off the Old Block

Consensus is that the Moon formed as a result of a collision

Mars-sized body collided with semimolten Earth

~4.5 billion years ago

Some ejected debris thrown into orbit coalesced to form the Moon

Impact model

Consistent with Moon having

Proportionately smaller core than Earth’s

Lower density than Earth

Earth’s Moon: A Chip Off the Old Block

Lunar surface

Two types of terrain:

Maria (singular, mare), Latin for “sea”

Dark regions

Fairly smooth lowlands

Originated from asteroid impacts and lava flooding

Highlands

Bright, densely cratered regions

Make up most of the Moon

Make up all of the “back” side of the Moon

Older than maria

Earth’s Moon: A Chip Off the Old Block

Lunar surface

Craters

Most obvious features of the lunar surface

Ejecta

Occasional rays

Associated with younger craters

Earth’s Moon: A Chip Off the Old Block

Lunar surface

Lunar regolith

Covers all lunar terrains

Gray, unconsolidated debris

Composed of:

Igneous rocks

Breccia

Glass beads

Fine lunar dust

Earth’s Moon: A Chip Off the Old Block

Outline the principal characteristics of Mercury, Venus, and Mars.

Describe their similarities to and differences from Earth.

Focus Questions 15.5

Mercury: The Innermost Planet

Smallest planet

Revolves around the Sun quickly (88 days)

Rotates slowly on its axis

Mercury’s day–night cycle lasts 176 Earth-days

Greatest temperature extremes: 173°C to 427°C

Resembles Earth’s Moon in that it has very low reflectivity, no sustained atmosphere, numerous volcanic features, and a heavily cratered terrain

Terrestrial Planets

Venus: The Veiled Planet

Orbits in a near perfect circle every 225 Earth-days

Rotates in the opposite direction of other planets

Rotates slowly: 1 Venus day is 243 Earth-days

Has the densest atmosphere of the terrestrial planets

97% carbon dioxide

Extreme greenhouse effect

Surface temperature averages about 450°C day and night

Surface is completely hidden by a thick cloud layer of tiny sulfuric acid droplets

Terrestrial Planets

Composition probably similar to Earth’s

Weak magnetic field means internal dynamics must be very different from Earth’s

More than 1000 volcanoes >20 km wide identified

Terrestrial Planets

Mars: The Red Planet

Fourth planet from the Sun

Half the diameter of Earth

Revolves around the Sun in 687 Earth-days

Surface temps range from lows of 140°C at the poles in winter to highs of 68°C at the equator in summer

Very thin atmosphere: 1% as dense as Earth’s

Consists of 95% carbon dioxide

Small amounts of nitrogen, oxygen, and water vapor

Terrestrial Planets

Two-third of Mars’ surface is cratered highlands

If Mars had abundant water, it would flow north, forming an ocean

Mars has some of the largest volcanoes in the solar system, including Olympus Mons

The dominant force of erosion is wind

Poleward of 30°, water ice is found within 1 m of surface

Terrestrial Planets

Summarize and compare the features of Jupiter, Saturn, Uranus, and Neptune, including their ring systems.

Focus Question 15.6

Jupiter: Lord of the Heavens

Largest planet—very massive

2.5 more massive than combined mass of planets, satellites, and asteroids

Orbits the sun once ever 12 Earth years

Rapid rotation—slightly less than 10 hours

Banded appearance

Multicolored

Bands are aligned parallel to Jupiter’s equator

Generated by wind system’s rapid rotation

Great Red Spot

In planet’s Southern Hemisphere

Counterclockwise rotating cyclonic storm

Jovian Planets

Three main cloud layers:

Warmest, lowest layer

Mainly water ice

Appears blue-gray

Cooler middle layer

Ammonium hydrosulfide droplets

Brown to orange-brown

Upper layer

Ammonia ice

White, wispy

Jovian Planets

At least 67 moons

Four largest moons discovered by Galileo

Callisto—Outermost Galilean moon

Europa—Smallest Galilean moon

Ganymede—Largest Jovian satellite

Io—Innermost Galilean moon and volcanically active

Jovian Planets

Saturn: The Elegant Planet

29 Earth years for one revolution around the Sun

Similar to Jupiter in

Atmosphere

Composition

Internal structure

Most striking feature is ring system

Discovered by Galileo in 1610

Ring nature determined by Christiaan Huygens 50 years later

Jovian Planets

Other features of Saturn

Dynamic atmosphere

93% hydrogen and 3% helium by volume

Clouds composed mainly of ammonia, ammonium hydrosulfide, and water

Segregated by temperature

Large cyclonic storms similar to Jupiter’s Great Red Spot

Emits roughly twice as much energy as it receives

Must have an internal heat source

Jovian Planets

Saturn’s Moons

62 known moons; 53 named moons

Vary significantly in size, shape, surface age, and origin

23 “original” satellites formed in tandem with parent planet

Titan

Largest Saturnian moon

Second largest moon in the solar system

Has a substantial atmosphere

Enceladus

Cryovolcanism – eruption of magmas derived from partial melting of ice

Jovian Planets

Saturn’s Rings

Composed of small particles (mainly water ice, lesser amounts of rocky debris) that orbit the planet

Most fall into one of two categories of particle density

Thought to be debris ejected from moons

Origin is still being debated

Jovian Planets

Uranus and Neptune: Twins

Uranus: The Sideways Planet

84 Earth years for one revolution

Rotates “on its side”

Rings

Large moons have varied terrains

Neptune: The Windy Planet

165 Earth years for one revolution

Dynamic atmosphere

One of the windiest places in the solar system

Great Dark Spot

White cirrus-like clouds above the main cloud deck

Jovian Planets

Uranus’s Moons

Uranus’s five largest moons have varied terrains

Innermost was recently geologically active

Uranus’s Rings

Discovered in 1977 that Uranus had five rings

More recent observations indicate that Uranus has atleast 10 rings

Jovian Planets

Neptune’s Moons

14 known satellites

Triton

Largest Neptune moon

Cryovolcanism

Icy magma is a mixture of water ice, methane, and probably ammonia

Generate outpourings of ice lavas great distances across the surface

Occasionally produce explosive eruptions

Ice equivalent of volcanic ash

Neptune’s Rings

Neptune has five named rings

Two broad and three narrow

Jovian Planets

List and describe the principal characteristics of the small bodies that inhabit the solar system.

Focus Question 15.7

Other solar system objects classified into two broad categories:

Small solar system bodies—including asteroids, comets, and meteoroids

Dwarf planets

Small Solar System Bodies

Asteroids: Leftover Planetesimals

Small bodies that remain from the formation of the solar system

Most in asteroid belt between Mars and Jupiter

Some have very eccentric orbits

Many recent impacts on the Moon and Earth were collisions with asteroids

Irregular shapes

Small Solar System Bodies

Comets: Dirty Snowballs

Loose collections of rocky material, dust, water ice, and frozen gases (ammonia, methane, and carbon dioxide)

Nucleus—small central body

1 to 10 km diameter

Frozen gases vaporize when near the Sun

Produces a glowing head called the coma

Some may develop a tail that points away from Sun

Originate in Kuiper belt or Oort cloud

Small Solar System Bodies

Meteors, Meteoroids, and Meteorites

Called meteors when they enter Earth’s atmosphere

A meteor shower occurs when Earth encounters a swarm of meteoroids associated with a comet’s path

Called meteorites when they are found on Earth

Types classified by composition

Irons

Mostly iron, 5–20% nickel

Stony

Silicate minerals with inclusions of other minerals

Stony irons

Mixtures

Small Solar System Bodies

Dwarf Planets

Orbit the sun

Essentially spherical due to their own gravity

Not large enough to sweep their orbits clear of other debris

Pluto’s diameter: 2370 km (1470 mi)

~1/5 Earth’s diameter

<1/2 Mercury’s diameter

Eris (Kuiper belt object)

Ceres (largest-known asteroid)

Small Solar System Bodies