A Survey of the Solar System

Geocentric vs. Heliocentric

Planetary Orbits

Plu

toN

eptu

neUra

nus

Saturn

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

Sense of rotation: counter-clockwise (with exception of Venus, Uranus,

and Pluto)

Orbits generally inclined by no more than 3.4o

Exceptions:

Mercury (7o)

Pluto (17.2o)

(Distances and times reproduced to scale)

Tipped over by more than 900

Mercury and Pluto: Unusually highly inclined orbits

Planetary Orbits and Rotation

Two Kinds of PlanetsPlanets of our solar system can be divided

into two very different kinds:

Terrestrial (earthlike) planets: Mercury, Venus, Earth, Mars

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

Size of Terrestrial Planets Compared to Jovian Planets

Terrestrial PlanetsFour 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.

• Earth began forming ~ 4.6 bya

• For a few hundred million years Earth was very hot and constantly bombarded from space

• At this point there was no liquid water, life was impossible

• About 3,900,000,000 yrs ago, Earth was solidified enough and cool enough for liquid water

Early Earth

Conditions on Early Earth

• Oldest existing earth materials: 4.1 billion years old • Oldest rocks: 3.9 billion years old

• 1st atmosphere – N2, H2, CO and CO2 – no O2 or ozone, high UV radiation and winds (present oxygen is created by life)

• Faint Early Sun: perhaps 30 per cent less bright

• Transition to atmosphere containing oxygen between 3.5 – 1.5 billion years ago

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

Space DebrisIn addition to planets, small bodies orbit the sun:

Asteroids, comets, meteoroids

Asteroid Eros,

imaged by the NEAR spacecraft

The Asteroid Belt

Plu

toN

eptu

neUra

nus

Saturn

Jupi

terM

ars

(Distances and times reproduced to scale)

Most asteroids orbit the sun in a

wide zone between the

orbits of Mars and Jupiter.

Comets

Mostly objects in highly elliptical orbits, occasionally coming close to the sun.

Icy nucleus, which evaporates and gets blown into space by

solar wind pressure.

Meteoroids

Small (m – mm sized) dust grains throughout

the solar system

If they collide with Earth, they evaporate in the

atmosphere.

Visible as streaks of light (“shooting stars”):

meteors.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

41 42 43 44 45 46 47 48 49 50

1. 384,000 km

2. 1 AU

3. 100 AU

4. 1 light year

5. 75,000 light years

What is (approximately) the size of the solar system?

Remember:

1 AU = distance Sun – Earth = 150 million km