A Survey of the Solar System

Geocentric vs. Heliocentric

Planetary Orbits Pluto Neptune Uranus Saturn Jupiter Mars Earth Venus Mercury 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 3.4 o Exceptions: Mercury (7 o ) Pluto (17.2 o ) (Distances and times reproduced to scale)

Tipped over by more than 90 0 Mercury and Pluto: Unusually highly inclined orbits Planetary Orbits and Rotation

Two Kinds of Planets Planets 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 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.

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 1 st 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 Planets Much larger in mass and size than terrestrial planets Much lower average density All have rings (not only Saturn!) Mostly gas; no solid surface

Space Debris In addition to planets, small bodies orbit the sun: Asteroids, comets, meteoroids Asteroid Eros, imaged by the NEAR spacecraft

The Asteroid Belt Pluto Neptune Uranus Saturn Jupiter Mars (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.

1.384,000 km 2.1 AU 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