ORIGIN OF THE

SOLAR SYSTEM

ORIGIN OF THE SOLAR

SYSTEM

ORIGIN OF THE SOLAR SYSTEMOur solar system began forming about 5 billion years ago,

when a cloud of gas and dust between the stars in our Milky

Way Galaxy began contracting. A nearby supernova—an

exploding star—may have started the contraction, but most

astronomers believe a random change in density in the cloud

caused the contraction.

Once the cloud—known as the solar nebula—began to

contract, the contraction occurred faster and faster. The

gravitational energy caused by this contraction heated the

solar nebula.

This spin kept the nebula from forming a sphere; instead, it

settled into a disk of gas and dust.

HOW DID THE SOLAR SYSTEM FORMED?

Astronomers think that the solar system may have come from a swirling cloud of gas and dust. First a star, our Sun, formed from a clump in the cloud. It began as a spinning ball of gas at the center of the cloud. Then the planets, their moons, and the other objects in the solar system formed from the leftover gas and dust.

Formation of the Solar System

s

Evidence for Ongoing Planet

Formation

Many young stars in the Orion Nebula are

surrounded by dust disks:

Probably sites of planet formation

right now!

PLANETS AND ITS SATELLITES

Two Kinds of Planets

Terrestrial (earthlike) planets: Mercury, Venus,

Earth, Mars

Jovian (Jupiter-like) planets: Jupiter, Saturn,

Uranus, Neptune

Terrestrial Planets

Four inner planets of the solar system

Relatively small in size and mass (Earth is the

largest and most massive)

Rocky surface

Surface of Venus can not be seen directly from Earth because of its

dense cloud cover.

The Jovian PlanetsMuch larger in mass

and size than terrestrial planets

Much lower average density

All have rings (not only Saturn!)

Mostly gas; no solid surface

SUN

SUN

The Sun provides

Earth with huge

amounts of energy in the form of heat

and light. Without the Sun, life on Earth would

not be possible.

MERCURY

MERCURY

Mercury is the planet closest to the Sun. It

is dry, hot, and nearly airless.

VENUS

VENUS

Days on Venus seem endless. Venus is the

second planet from the Sun. One day on Venus is as long as 243 days

on Earth.

EARTH

EARTH

EARTH HAS 1satellite.

cc

MOON

MARS

MARSIts surface is

like a very cold desert. There is ice, but no liquid water.

Mars has reddish-brown rocks and soil. We often call Mars the red

planet because from Earth, it looks bright red in the night sky.

This animation traces a system of canyons on Mars.

The Pathfinder mission, which visited Mars in 1997, did many tests of the planet’s soil and rocks. It also sent back lots of photos,

like this one.

Scientists believe that Mars once had

water on its surface, based on evidence like the

channels shown in this photo.

Olympus Mons is not only the biggest mountain on Mars, it’s the biggest in the whole solar

system!

MARS HAS 2 satellites.

Deimos, lower left, and Phobos, lower right. An asteroid called Gaspra, top, is

shown for comparison.

JUPITER

JUPITER

Jupiter is the fifth planet from the Sun and the biggest planet in our solar system. More than 1,300 planets the size of Earth could fit inside Jupiter.

The impact of Comet Shoemaker-Levy. The comet was torn apart by Jupiter’s gravitational field as it approached the planet.

JUPITER HAS 69 satellites.

CALLISTO

Callisto is Jupiter’s second largest moon. Its surface is covered by many large

craters.

EUROPA

The surface of Jupiter’s

moon Europa is covered with ice.

Astronomers think the ice

may lie on top of huge

oceans of liquid or

slushy water.

GANYMEDE

Ganymede, Jupiter’s

largest moon, is also the

biggest moon in the solar

system!

Io

Jupiter’s moon Io has the

most active volcanoes in the solar

system.

SATURN

SATURN

Saturn’s rings are pretty

thin. In places they are only

16 feet (5 meters) thick. The rings are

made of dust, pieces

of rock, frozen gases,

and ice.

SATURN HAS 63

satellites.

TitanThe largest

moon of Saturn is

Titan. Titan is larger than the planets Pluto and Mercury. It

has an atmosphere

made of nitrogen gas.

RHEA

DIONE

MIMAS

TETHYS

JANUS

HYPERION

ENCELADUSSaturn's moon

Enceladus is the brightest moon

in the solar system. The cold, distant world reflects

over 90 percent of the sunlight it receives, giving

its surface about the same reflectivity as

new-fallen snow.

PHOEBE

IapetusSaturn's third largest

moon, Iapetus, has two sharply contrasting

types of terrain.

URANUS

uranus

Uranus is covered with

a kind of smog. Smog on Earth is

pollution that comes

mostly from cars that

burn gasoline. Sunlight changes

fumes from the cars to

smog.

URANUS HAS27

SATELLITES.

titania

Ariel

Astronomers think Ariel is made of ice and rock.

Oberon

umbriel

Miranda

NEPTUNE

Neptune

Neptune has the fastest

winds in the solar system.

Neptune wobbles as it

orbits the Sun.

NEPTUNE HAS 13 SATELLITES.

Triton

Triton is largest of Neptune’s moons. It has few

craters, but many

cracks in its surface.

Nereid

PLUTO

Pluto

PlutoScientists are not sure what Pluto is made of. They think it’s made of rock and ice. They know

that Pluto is very cold because

it is so far from the Sun.

Pluto has 3 SATELLITES.

Charon

Planetary Orbits

Plut

oNe

ptun

eUran

usSaturn

Jupi

terM

ars

Earth

VenusMercury

All planets in almost circular (elliptical)

orbits around the sun, in approx. the same

plane (ecliptic).

Sense of revolution: counter-clockwise

(Distances and times reproduced to scale)

HOW SMALL

AREWE ?

WATCHEARTH

SHRINK!

I THANK THEE.