Chapter 28 Notes

Our Solar System

Our Solar System

The Inner Planets (and Pluto)

All the Planets (and Pluto)

The Planets and the Sun (and Pluto)

Formation of the Solar System

• Nebular Theory:a)Interstellar cloud

contracts and spinsb)Dense center begins

nuclear fusion (sun)c) Remaining material

forms planetesimals and then planets

Historical Solar System Models

• Geocentric (Earth-centered) model– One problem was how to explain

retrograde motion

• Copernicus’ heliocentric model– 1543, Polish scientist– Planets (including Earth) orbit the

Sun in circular orbits– Supporting evidence collected by

Tycho Brahe

Kepler’s laws of planetary motion

• Johannes Kepler inherited Tycho’s data after his unexpected death.

Galileo

• First person to use a telescope to observe the sky

• Discovered moons orbiting Jupiter• Also observed sun spots, phases of Venus, and

Moon craters

Newton and Gravity

• Newton’s discovery of the law of universal gravitation provided an explanation for the heliocentric model of the solar system

Zone 1: Inner Planets

• Terrestrial: “Earth-like”• Small • Composed of rock (high density)• Close to the Sun• Few or no moons• No rings

Mercury

• Smallest• Closest to the Sun • No moons • No atmosphere• Cratered like the Moon• 1 orbit = 1.5 rotations (2 years = 3 days)

Venus

• No moons• Earth’s “twin” in size• Rotates backwards• 1 day = 243 Earth days• Very high CO2 concentration in the atmosphere

causes super greenhouse effect• Surface temperature of 464C!!• Can be seen as a bright morning or evening “star”

Earth

• One moon• Tectonically active• O2 in atmosphere

• Water exists in all 3 phases• Mild greenhouse effect to

keep the planet warm enough for life

Mars

• The red planet• CO2 atmosphere

• 2 moons (Phobos and Deimos)• Has seasons like Earth, but a year is twice as

long• Largest volcano in the solar system: Olympus

Mons• Once had liquid water, has polar CO2 ice caps

Outer Planets

• Gas giants or “Jovian”: Jupiter-like• Large• Low density • Lots of moons• All have ring systems• Far from the Sun

Jupiter

• Largest planet• Banded appearance• Great red spot• Faint ring system• 4 large moons, more than 60 total• Rapid rotation (10 hours = 1 day); shortest day

of all the planets

Saturn

• Famous for ring system• More than 55 moons• Density lower than water• Largest moon, Titan, has an atmosphere of

nitrogen and methane• Another moon, Enceladus, shows evidence of

geologic activity

Uranus

• Discovered in 1781• Rotational axis is 98• At least 27 moons• Rings are dark and nearly

invisible• Appears blue because of

the way it reflects light

Neptune

• Discovered 1846• 13 moons• Distinctive clouds and belts• Predicted before it was discovered• 6 rings composed of dust particles• Largest moon, Triton, orbits backwards

Other Solar System Objects

• Dwarf planets• Asteroids• Kuiper belt objects (KBOs)• Comets (the Oort cloud)