Earth Science 101 The Solar System Chapter 23 Instructor : Pete Kozich.

Earth Science 101

The Solar SystemChapter 23

Instructor : Pete Kozich

Overview of the solar system

Solar system includes • Sun• Eight planets and their satellites (moons)• Asteroids• Comets• Meteoroids

The solar system

Figure 22.1


A planet’s orbit lies in an orbital plane • Similar to a flat sheet of paper or a disc• The orbital planes of the planets are inclined

• Planes of seven planets lie within 4 degrees of the Sun's equator

• Mercury's is inclined 7 degrees

• Pluto's is inclined 17 degrees


Two groups of planets occur in the solar system • Terrestrial (Earth-like) planets, the 4 inner planets

• Mercury, Venus, Earth, and Mars

• Small, dense, and rocky

• Low escape velocities (Earth is 7 miles/second or 25,200 mph)

• Rockets have to reach this to escape Earth’s gravitational pull

Overview of the solar system Two groups of planets occur in the solar

system • Jovian (Jupiter-like) planets or the gas giants

• Jupiter, Saturn, Uranus, and Neptune• Large, low density, and gaseous• Massive (Jupiter is 317 times more massive than Earth)• Thick atmospheres composed of hydrogen and helium

(Jupiter and Saturn) and methane and ammonia (Uranus and Neptune)

• High escape velocities (14-40 miles/second or 50,400-144,000 mph)

• Pluto is not included in either group• One of the largest Kuiper objects

The planets drawn to scale

Figure 22.2

Overview of the solar system Planets are composed of

• Gases• Hydrogen• Helium

• Rocks• Silicate minerals• Metallic iron

• Ices• Ammonia (NH3)

• Methane (CH4)

• Carbon dioxide (CO2)

• Water (H2O)

Evolution of the planets

Nebular hypothesis • Planets formed about 4.6 billion years ago• Solar system condensed from a gaseous nebula

• Nebula – a cloud of interstellar gas and dust

As the planets 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• Processes responsible called chemical differentiation

and mass sorting

Evolution of the planets

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

Due to frigid temperatures, the Jovian planets contain a high percentage of ices, especially smaller and colder Uranus and Neptune

Earth's Moon General characteristics

• Diameter of 3475 kilometers (2150 miles) is unusually large compared to its parent planet (1/4 the size of the Earth)

• Density • 3.3 times that of water

• Comparable to Earth's crustal rocks and mantle

• Perhaps the Moon has a small iron core

• Gravitational attraction is one-sixth of Earth's

• No atmosphere

• Tectonics no longer active

• Surface is bombarded by micrometeorites from space which gradually makes the landscape smooth

Major topographic features on the lunar surface

Figure 22.6

Earth's Moon

Lunar surface• Two types of terrain

• Maria (singular, mare), Latin for "sea"

• Dark regions

• Fairly smooth lowlands

• Originated from asteroid impacts and lava flooding the surface

• 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

Lunar surface• Craters

• Most obvious features of the lunar surface

• Most are produced by an impact from a meteoroid which produces

• Ejecta

• Occasional rays (associated with younger craters)

A 20-kilometer-wide crater on the Moon

Figure 22.5

Earth's Moon

Lunar surface• Lunar regolith

• Covers all lunar terrains

• Gray, unconsolidated debris

• Composed of

• Igneous rocks

• Glass beads

• Fine lunar dust

• "Soil-like" layer produced by meteoric bombardment

Earth's Moon

Lunar history• Hypothesis suggests that a Mars-sized object

collided with Earth to produce the Moon • Older areas have a higher density

• Younger areas are smoother

• Moon evolved in three phases • I. Original crust (highlands)

• As Moon formed, its outer shell melted, cooled, solidified, and became the highlands

• About 4.5 billion years ago, just after collision

Earth's Moon

Lunar history• Moon evolved in three phases

• II. Formation of maria basins

• Younger than highlands

• Between 3.2 and 3.8 billion years old

• III. Formation of rayed craters

• Material ejected from craters is still visible

• e.g., Copernicus (a rayed crater)

Planets: a brief tour

Mercury• Innermost planet, not too different from the moon• Smallest planet, if one excludes Pluto• No atmosphere (too small and warm)• Cratered highlands• Vast, smooth terrains• Dense (large iron core)• Revolves quickly• Rotates slowly (night side is frigid)• Absorbs most light that hits it, reflects only 6%

Photomosaic of Mercury

Figure 22.8


Venus • Second to the Moon in brilliance • Similar to Earth in

• Size• Density• Location in the solar system

• Shrouded in thick clouds • Impenetrable by visible light• Atmosphere is 97% carbon dioxide, 900 deg sfc T• Surface atmospheric pressure is 90 times that of

Earth's


Venus • Surface

• Mapped by radar

• Features

• 80% of surface is subdued plains that are mantled by volcanic flows

• Low density of impact craters

• Tectonic deformation must have been active during the recent geologic past

• Thousands of volcanic structures

Computer generated view of Venus

Figure 22.9


Mars • Called the "Red Planet"• Atmosphere

• 1% as dense as Earth's, most lost to space

• Primarily carbon dioxide

• Cold polar temperatures (-193ºF)

• Polar caps of water ice, covered by a thin layer of frozen carbon dioxide

• Extensive dust storms with winds up to 270 kilometers (170 miles) per hour


Mars • Surface

• Numerous large volcanoes – largest is Olympus Mons

• Northern portion may have been covered by oceans or seas billions of years ago

• Less-abundant impact craters

• Tectonically dead

• Several canyons• Valles Marineras – the largest canyon

Olympus Mons, an inactive shield volcano on Mars

Figure 22.11

The Valles Marineris canyon system on Mars

Figure 22.12

Planets: a brief tour Mars

• Surface• "Stream drainage" patterns

• Found in some valleys

• No bodies of surface water on the planet remain

• Possible origins

• Past rainfall

• Surface material collapses as the subsurface ice melts

• Old ocean that has evaporated away into space

• Moons• Two moons (both are tiny)

• Phobos

• Deimos

• Captured asteroids


Jupiter • Largest planet, usually second brightest• Very massive

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

• If it had been seventy-five times more massive, it would have been a small star (brown dwarf)

• Rapid rotation • Slightly less than 10 hours

• Bulges at equator

Comparisonof Earth and

Jupiter

Planets: a brief tour Jupiter

• Banded appearance • Multicolored

• Bands are aligned parallel to Jupiter's equator

• Generated by wind systems and rapid rotation of planet

• Great Red Spot • In planet's southern hemisphere

• Counterclockwise rotating cyclonic storm

• Structure • Surface thought to be a gigantic ocean of liquid hydrogen

• Halfway into the interior, pressure causes liquid hydrogen to turn into liquid metallic hydrogen

• Rocky and metallic material probably exists in a central core

Planets: a brief tour Jupiter

• Moons• 50 moons + (like Saturn)• Four largest moons

• Discovered by Galileo, called Galilean satellites• Callisto - outermost Galilean moon, old surface• Ganymede - largest moon in solar system,

between Mercury and Mars in size • Europa - smallest Galilean moon (liquid water

probably underneath thick ice surface)• Io - innermost Galilean moon and is also

volcanically active• The interiors of Io and Europa are warmed by

stresses from Jupiter’s gravity (“tidal forces”)

A volcanic eruption on

Io

Planets: a brief tour Saturn

• Similar to Jupiter in its • Atmosphere

• Composition

• Internal structure (less dense and more oblique, though)

• Rings• Most prominent feature

• Discovered by Galileo in 1610

• Complex • Composed of small particles (moonlets) that orbit the planet

• Most rings fall into one of two categories based on particle density

• Thought to be debris ejected from moons or bits of a moon that was destroyed ~100 million years ago

The ring system of Saturn

Figure 22.18


Saturn • Other features

• Dynamic atmosphere, windiest of the planets

• Large cyclonic storms similar to Jupiter's Great Red Spot

• Titan – the largest Saturnian moon • Second largest moon (Jupiter's Ganymede is

larger) in the solar system

• Has a substantial atmosphere (80% Nitrogen) that is thicker than Earth’s

• Liquid hydrocarbon lakes on surface


Uranus• Uranus and Neptune are nearly twins, both with

several icy satellites• Uranus rotates "on its side”• Atmosphere currently rather bland in terms of

striking cloud features• Rings second most prominent of the gas giants• Large moons have varied terrains

Planets: a brief tour Neptune

• Dynamic atmosphere • One of the windiest places in the solar system

• Great Dark Spot (like Jupiter’s Red Spot)

• White cirrus-like clouds above the main cloud deck

• Triton – largest Neptune moon • Orbit is retrograde, captured Kuiper object?

• Low surface temperature (-391ºF) • Atmosphere of mostly nitrogen, along with methane

• Volcanic-like activity

• Composed largely of water ice, covered with layers of solid nitrogen and methane

• Furthest out of the seven big solar system moons (Earth’s moon, 4 Galilean satellites, and Saturn’s Titan)


Pluto (no longer a planet?)• Not visible with the unaided eye (like Neptune)• Discovered in 1930• Highly elongated orbit causes it to occasionally

travel inside the orbit of Neptune, where it resided from 1979 thru 1999

• Moon (Charon) discovered in 1978, but now it is considered a dwarf planet like Pluto.

• Average temperature is -210ºC

Pluto and its moon Charon as compared to the size of Earth

Figure 22.18

Minor members of the solar system

Asteroids• Most lie between Mars and Jupiter• Small bodies – largest (Ceres) is about 620 miles

in diameter• Some have very eccentric orbits• Many of the recent impacts on the Moon and

Earth were collisions with asteroids• Irregular shapes except largest half dozen or

so, which are spherical• A few visible to naked eye when brightest

The orbits of most asteroids lie between Mars and Jupiter

Image of asteroid 951 (Gaspra)

What determines a planet?New criteria adopted for describing a planet:

• Must be massive enough to pull themselves into a sphere due to their own gravity (good criterion)

• Must have enough mass to “clear their orbit” -- This is a more questionable assertion

-- Neptune, while much more massive than inner

planets, has a huge orbit that it cannot clear

-- This is why Pluto was not called an official

planet. Neptune has problems with this point, too,

but it seems to be ignored.

-- This is a bad criterion and may be fixed later.

Minor members of the solar system Comets

• Often compared to large, "dirty snowballs”• Now found to be more rock, with some ice• Composition

• Rocky and metallic materials• Frozen gases

• Frozen gases vaporize when near the Sun • Produces a glowing head called the coma• Some may develop a tail that points away from Sun due

to • Radiation pressure • Solar wind

Orientation of a comet’s tail as it orbits the Sun

Figure 22.25

Gas (ion) tail always points directly away from sun due to solar wind. Dust tail is often broader and is affected by orbital motion as well as the solar wind.


Comets• Origin

• Many form at great distance from the Sun

• Bright comets are usually long period • Most famous short-period (< 200 years) comet

is Halley's comet • 76 year orbital period

• Potato-shaped nucleus (16 km by 8 km)

• Responsible for two meteor showers (Eta Aquarids in May and Orionids in October)

Comet Hale-Bopp

Figure 22.26


Meteoroids• Called meteors when they enter Earth's

atmosphere• A meteor shower occurs when Earth encounters

a swarm of meteoroids associated with a comet's or asteroid’s path

• Meteoroids are referred to as meteorites when they are found on Earth, must be large enough to not completely burn up, as vast majority do

Minor members of the solar system Types of meteorites classified by their composition --Give an idea as to the composition of Earth’s core --Help provide an age of the solar system, little changed

• Irons• Mostly iron, dense• 5-20% nickel

• Stony• Silicate minerals with• Inclusions of other minerals

• Stony-irons – mixtures• Carbonaceous chondrites

• Rare• Composition – organic material, simple amino acids?


Meteorites• Good percentage of meteorites large enough to

make it through the Earth’s atmosphere originated in the asteroid belt

• Collide with other asteroids and deflected toward the Earth

• As meteors enter the atmosphere friction caused by the air produces large amounts of heat that produce light

• Meteor Crater Arizona – believed to occur in the last 20,000 years

• The cavity is ¾ mile wide and 560 ft deep

Earth’s tectonic activity erases most craters

A Taurid fireball (very bright meteor)

The Taurids are one of many meteor showers.

This particular shower is characterized by slow and, in some years, very bright meteors.

End of Chapter 23

Earth Science 101 The Solar System Chapter 23 Instructor : Pete Kozich.

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