Chapter 23: Touring Our Solar System

23.1: The Solar System

Text pp 644-648

The sun is a hub of a huge rotating

system of eight planets, their

satellites and other small bodies.

About 99.85% of the mass of

our solar system is contained

within the sun.

Most of the remaining 0.15% of

the mass is contained by the

planets.

(Although Pluto is now a dwarf

planet, it is large enough for us to

study it separately.)

Fast Facts on the Solar System

• Each planet moves in an elliptical orbit.

• All planets travel in the same direction.

• The planet closest to the Sun is

Mercury, and it has the fastest orbital

speed of all planets as well as the

shortest period of revolution.

• The (dwarf) planet furthest from the

Sun is Pluto. It has the slowest orbital

speed as well as the longest period of

revolution.

The Planets in order, from

closest to furthest from the sun :

• Mercury

• Venus

• Earth

• Mars

• Jupiter

• Saturn

• Uranus

• Neptune

• Pluto (recently reassigned as a “dwarf planet.”)

The Planets: An Overview

• Terrestrial Planets• Terrestrial =

Earthlike

• AKA “Rocky Planets, Inner Planets”

• Mercury, Venus, Earth, Mars

• Small and rocky.

• Dense, solid.

• Jovian Planets• Jovian = Jupiter-like

• AKA “Gas Giants, Outer Planets”

• Jupiter, Saturn, Uranus, Neptune.

• Huge and gaseous.

• Not dense, made ofgas.

Key Concepts

• Size is the most obvious difference

between the Terrestrial and the Jovian

planets.

• Density, chemical makeup, and the rate

of rotation are other ways in which the

two groups differ.

Planet Interiors

• Terrestrial planetsare dense. They

consist of mostly of

rocky and metallic

substances, and

only small amounts

of gasses and

liquids.

• Jovian planets contain

mostly gases (hydrogen

and helium) and ices

(mostly water, ammonia

and methane.) This

explains their low

densities. What solids

they have are

concentrated in their

cores.

Atmospheres of the Planets

• Terrestrial Planets

• Lower surface

gravity means…

• Low escape velocity

(the speed a gas

molecule needs to

escape Earth’s gravity

& go into space.

Therefore…

• Thin atmospheres

• Jovian Planets

• High surface gravity

means…

• High escape velocity.

Therefore…

• Thick, heavy

atmospheres of

hydrogen, helium,

methane & ammonia.

23.2: The Terrestrial Planets

Text pp 649-653

Mercury- The Innermost Planet

• The innermost and smallest planet.

• Has cratered highlands, like Earth’s moon.

• VERY dense - iron core?

• One full day cycle = about 88 earth hours.

• One full orbit cycle = 59 earth days.

• Three months of day/ three months of night.

Mercury has the greatest temperature

extremes of any planet.

Day temperatures are high

enough to melt lead: +425 C.

Night temperatures can

drop down to -173°C.

The chances of life as we

know it living on Mercury is

practically nonexistent.

Venus – The Veiled Planet

Venus orbits the sun

every 244 earth-days.

It rotates on its axis

about every 225

earth-hours.

Neither Mercury nor Venus

have natural satellites.

Venus has been called “Earth’s

Twin,” because it is so similar

to Earth in size, density, mass

and location in the Solar

System.

Volcanism and tectonic activity have shaped

Venus’ surface. This is also like earth.

Venus is covered with a thick

atmosphere of mostly carbon

dioxide, a greenhouse gas.

It traps solar heat, making

Venus the hottest planet in

the Solar System, over 475 C,

hot enough to melt lead.

Mars – The Red Planet

Mars is called the Red

Planet for its reddish

appearance when viewed

through a telescope.

Mars has some dark regions

that change intensity during

the Martian year. It also has

brilliant white polar caps.

Mars has two natural satellites –

Phobos and Deimos, only discovered in 1977.

The Martian Atmosphere

The atmosphere of Mars

has only 1% the density of

Earth’s atmosphere. It is

made up of mostly carbon

dioxide and tiny amounts

of water vapor.

Mars’ polar ice caps seem

to be made mostly of

frozen carbon dioxide.

Although the atmosphere of Mars is very thin, extensive

dust storms occur and may cause the color changes

observed from Earth. Hurricane-force winds up to 270 kph

can go on for weeks.

Surface Features of Mars

Much of the Martian surface strongly resembles some of

Earth’s desert areas, including dust storms.

Its surface holds numerous large volcanoes; the largest,

Olympus Mons, is the size of Ohio and 23 kilometers high!

There are also several canyons, much larger that Earth’s

Grand Canyon.

Most of Martian surface

features are old by Earth’s

standards. The “newest”

may be more than one

billion years old.

Water on Mars

This is a photograph taken

of a frozen water “puddle”

on the surface of Mars.

There are many

indicators that in the

VERY distant past,

Mars had streams

and islands in large

bodies of water.

Many of its rocks

could not have

formed without water,

as well.

This is an artist’s rendition on how frozen water could be

trapped underneath Mars’ dusty & dry surface.

Most scientists believe

that most surface water

on Mars seeped out

from pockets of

underground ice.

Although there are stream

channels on its surface, most

of Mars’ water has either

evaporated away or re-frozen

in underground pockets.

The Outer Planets

Text pp 654-659

Jupiter: Giant Among Planets

Jupiter has a mass that is 2 ½ times greater than

all the other planets combined.

Had Jupiter been 10 times

larger, it would have

evolved into a small star.

Jupiter completes one rotation

in just less than 10 earth hours –

the fasted rotating planet in the

Solar System.

Jupiter appears to be covered in bands of multicolored

clouds that run parallel to its equator. These are driven

by a constant wind system and the rotation of the planet.

•Jupiter gives off twice as much heat as it absorbs from

the sun. The convection currents produced by this heat

drives the winds at Jupiter’s surface.

Notice how the cloud bands move in opposite directions.

This is because the convection currents underneath

the clouds are rising and sinking.

Jupiter’s most striking feature is the Great Red Spot in its

southern hemisphere. This appears to be a huge cyclone

which has been raging for at least the past 400 years.

At least two earths could fit

into the Great Red Spot.

Here is a video of The Great Red Spot’s wind currents.

Structure of Jupiter

• Jupiter’s atmosphere is mostly

hydrogen and helium.

• Beneath its gaseous surface, Jupiter

may be a ball of liquid hydrogen

underneath its atmosphere because of

its enormous internal pressure.

Jupiter’s Moons

Jupiter has at least 60

moons.

The four largest are

(1)Callisto;

(2) Ganymede;

(3) Io and

(4) Europa.

Each moon is its own

unique geological world.

(4)

(3)

(2)

(1)

Jupiter’s Rings

Jupiter’s rings were one of the most unexpected

discoveries by Voyager I.

Saturn: The Elegant Planet

Saturn Fast Facts

• Saturn takes almost 30 Earth-years to

make one revolution.

• It is very similar to Jupiter in

composition and atmosphere, but only

half its size.

• The most prominent feature of Saturn

is its system of rings.

Features of Saturn

Saturn’s atmosphere

is very active, with

winds up to 1500 km

per hour.

Saturn has large

“cyclone” storms similar

to Jupiter’s Great Red

Spot, just not as large.

Saturn has at least 31

moons. Titan is the

largest moon, and is

larger than Mercury.

Saturn’s density

is so light that it

could float in a

tub of water!

Saturn’s Rings

All of the Jovian planets

have ring systems.

They all consist of

multiple concentric rings

separated by gaps in

various widths.

Saturn’s rings are very dense and wide, but they

are only about 100 meters from top to bottom.

Uranus: The Sideways Planet

Uranus is unique in that it rotates “on its

side.” Its axis of rotation is lies nearly

parallel with the plane of its orbit.

Uranus, like all Jovian

planets, has a ring system

that is perpendicular to its

axis.

Uranus has at least five moons.

Neptune: The Windy Planet

Winds exceeding 1000 km per hour encircle Neptune,

making it one of the windiest places in the solar system.

Neptune has a layer of white, whispy clouds of

frozen methane about 50 kms above its surface.

It also has at least 13 moons.

Neptune has a

“Great Dark

Spot” similar to

Jupiter’s Great

Red Spot.

Scientists believe

that it is also a

cyclone, about

the size of the

earth.

Pluto: Planet X

Pluto was downgraded to a “dwarf planet”

in 2005. It is still a controversial decision.

Pluto lies at the edge of the Solar

System, more than 40 times

farther from the sun than Earth.

Pluto takes about 248 earth-years to orbit the sun.

Pluto’s orbit is highly eccentric,

and the planet sometimes travels

inside the orbit of Neptune.

Pluto is cold enough to freeze most gases that might be

present. It could be described as a dirty ice ball.