Solar System and Sun: Formation, Planets, and Solar Activity

Sun's Mass

The Sun contains 99.8% of the solar system's mass

Inner Terrestrial Planets

Small rocky planets close to the Sun (Mercury, Venus, Earth, Mars)

Outer Jovian Planets

Large gas/ice giants far from the Sun (Jupiter, Saturn, Uranus, Neptune)

Asteroid Belt

Region between Mars and Jupiter filled with rocky bodies

Kuiper Belt

Region beyond Neptune containing small icy bodies and dwarf planets

Oort Cloud

Distant spherical shell of icy objects surrounding the solar system

Patterns of Motion

Planets orbit in same direction, same plane, nearly circular orbits

Two Planet Types

Terrestrial (small, rocky) and Jovian (large, gas/ice)

Solar System Exceptions

Uranus tilt, Venus retrograde rotation, Earth's large Moon

Origin of Exceptions

Likely caused by giant impacts in early solar system

Nebular Theory

Solar system formed from the gravitational collapse of a gas/dust cloud

Conservation of Energy

As gas collapses it heats up; important in star formation

Conservation of Angular Momentum

As nebula shrinks it spins faster and flattens into a disk

Hydrogen & Helium Fate

Most H/He gas never condenses; becomes massive atmospheres of Jovian planets

Frost Line

Boundary where temperatures are low enough for ices to condense; divides rocky from icy planet formation

Terrestrial vs Jovian Formation

Rocky planets form inside frost line; icy/giant planets form outside and collect gas

Moon Origin Theory

Giant impact between young Earth and Mars-sized body formed the Moon

Photosphere

Visible surface of the Sun; shows granulation and sunspots

Granulation

Rising hot gas and falling cool gas on Sun's surface

Sunspots

Cooler, darker magnetic regions on the Sun

Solar Flares

Sudden magnetic energy releases causing radiation bursts

Sunspot Cycle

11-year cycle of magnetic activity and sunspot numbers

Chromosphere

Middle layer of solar atmosphere; reddish color

Corona

Hot outer layer; source of solar wind

Solar Wind

Stream of charged particles flowing outward from the corona

Solar Activity Effects on Earth

Can impact satellites, auroras, and communications

Internal Heat Sources

Accretion, differentiation, and radioactive decay heat terrestrial planets

Planet Size & Heat Loss

Larger planets cool slower; smaller planets cool faster

Volume-Surface Ratio

Larger volume vs smaller surface area means slower cooling

Cratering Age

More craters = older surface; fewer craters = younger surface

Three Internal Layers

Core, mantle, crust

Lithosphere

Rigid outer layer including crust and upper mantle

Convection

Hot material rises, cool sinks; drives geology

Planetary Magnetic Field Origin

Caused by rotating, convecting, electrically conducting interior

Geological Processes

Impact cratering, volcanism, tectonics, erosion shape surfaces

Atmosphere Function

Protects planets, traps heat (greenhouse effect)

Factors Affecting Planet Temperature

Distance from Sun, reflectivity (albedo), greenhouse strength

No-Greenhouse Temperature

Temperature based only on sunlight and albedo (Math Insight 10.1)

Earth vs Venus Differences

Similar size/mass but Venus has runaway greenhouse because it lost its water

Fate of Water on Venus

Water vapor broke apart; hydrogen escaped; left dense CO₂ atmosphere

Fate of CO₂ on Earth

CO₂ removed by oceans and rock cycle (carbonates)

Key Development Removing CO₂

Life + oceans forming carbon-locking rocks

Origin of Oxygen in Earth's Atmosphere

Photosynthesis from early life

CO₂ Cycle

Regulates temperature by weathering, ocean absorption, and volcanoes returning CO₂

Plate Tectonics & Outgassing

Moves seafloor rocks, releasing CO₂ locked inside

Natural Greenhouse Effect

Atmosphere traps heat and keeps Earth warm enough for life

Anthropogenic Greenhouse Effect

Human-driven increase in CO₂ causing warming

Major Greenhouse Gases

CO₂, methane, water vapor

Evidence for Anthropogenic Warming

Rising CO₂ levels and global temperature data

Climate Models

Show link between greenhouse gas increases and warming trends

Long-Term Implications of Warming

Sea level rise, extreme weather, ecosystem changes