Chapter 3: Our Solar System

Intro to Our Solar System

Our Solar System • Most of the planets in our solar system

can be seen without a telescope.

• Uranus and Neptune are the only two too far to see.

• The largest planet is about 10 times larger than Earth across.

Our Solar System

Distances• Astronomers use astronomical units, or

AUs, to measure distance in space.

• 1 AU = distance from Sun to Earth; about 150 million km.

• The first four (inner) planets are relatively close to one another; the outer planets are much more spaced out.

Orbits • More than 99% of the Mass in our

Solar System is the Sun.

• This results in a strong gravitational pull on everything else.

• Each planet (and other objects) orbits the Sun in an elliptical, or oval, shape.

Orbits • All planets orbit in the same direction, and

most other objects do, also.

• Scientists think this is a clue – the solar system formed from a huge cloud of gases and dust; most mass = Sun, the rest clumped together to form planets.

• Not all of them were large enough to planets; resulting in asteroids, comets, and moons.

Chapter 3: Our Solar System

The Inner Planets

Inner Planets • Mercury, Venus, Earth, and Mars

• Called terrestrial planets

• Rocky crust, dense mantles and cores

Processes and Surface Features • They all have layers; the heaviest materials

sank to the center in their collisions and the lightest rose to become crust.

• Four main processes shaped the crust:• Tectonics• Volcanism• Weathering and erosion• Impact cratering

Tectonics • Earth’s crust has tectonic plates that are moved

by convection in the mantle.

• As the plates move, different features (mountains, valleys) are formed.

• The other planets do not have plates, but still are able to move with the mantle.

• Tectonics: process of change in the crust due to motion of material in the mantle.

Volcanism • Occurs when molten rock moves from

the interior to the surface.

• Volcanoes are on Earth, Venus, and Mars.

• When the inside of a planet cools enough, no more molten rock reaches the surface.

Weathering and Erosion• Water and wind are important factors

on Earth.

• Planets without wind still have weathering due to heating and cooling of the surface.

Impact Cratering • When small objects hit a larger object

and leave a resulting indentation.

• Harder to find on Earth

• Easily found on other planets due to less weathering/erosion.

Atmospheres • Mainly formed from volcanic gases.

• Venus, Earth, and Mars have enough gravity to hold in gases like CO2, but lighter gases escaped.

• Earth is mostly nitrogen.

• Can make a planet warmer due to loss of energy

Mercury • Believed to shrink from original size,

creating cliffs. • Large areas of cooled lava. • Several impact craters, suggesting the

surface has not changed much. • Longest cycle of day and night – 3 months

of daylight, 3 months of darkness. • Can get 800+ F during day, and -170 F

during night.

Mercury

Venus • Slightly smaller than Earth. • 8 months to turn once; retrograde

rotation (opposite way than orbit) creates 2 months of daylight and 2 months of darkness.

• Very dense, mostly CO2. • Temp = about 470 F. • Sulfuric acid in atmosphere form thick

clouds.

Mars • About half the size of Earth• Two moons – Deimos and Phobos • Red because of iron/rust • Large valley – Valles Marineris • Large areas of cooled lava; several

volcanoes • Winds up to 300 mph; sand dunes. • Several craters

Mars • Mostly CO2 in atmosphere, but very

low air pressure. • Temps vary from about 60 F in day to -

130 F at night. • Polar caps, mostly made of dry ice. • No liquid water on surface, but there

is frozen water in ground.

Chapter 3: Our Solar System

The Outer Planets

Outer Planets • Jupiter, Saturn, Uranus, and Neptune –

gas giants : mostly made of H, He, and other gases.

• The atmosphere is very thick, almost like a liquid in some places.

• They are all believed to have a large, solid core.

Jupiter • Largest planet • 5.2 AU from Sun• 1 year = 12 Earth years• Fast rotation = fast wind and storms • White clouds made of ammonia; lower

clouds are brown/red and made of chemicals

• Storms form between winds; the largest is the Great Red Spot (100+ years old).

Saturn • Gas particles spread out more,

forming layers of clouds. • Rings: wide, flat zone of small

particles that orbit a planet. • Bright rings made out of water ice

chunks, with moons mixed in. • Axis is tilted at 27 degrees; rings

appear to change b/c of this. • 1 year = almost 30 Earth years.

Uranus and Neptune • Mostly methane, ammonia, and water. • Uranus = blue/green; Neptune = dark

blue – colors are from methane.

Uranus• 1 year = 84 Earth years• Rings and moons around equator • Seems to spin on its side • Scientists think the unusual rotation

was caused from a collision.

Neptune • Sometimes looks white due to

methane clouds• Severe storms, such as the Great Dark

Spot, can be seen in darker shades of blue.

• This storm moved toward the equator, where it is thought that the winds broke up the storm.

Chapter 3: Our Solar System

Other Objects

Pluto • Was once a planet.• Discovered in 1930 • No spacecraft has been close to it. • Has a moon, Charon – they orbit each

other; sometimes called a “double planet”.

• More oval-shaped orbit • 1 year = 248 Earth years

Asteroids • Small, solid, rocky bodies that orbit close to Sun. • Most have irregular shapes• Most between Mars and Jupiter – The Asteroid

Belt • Craters, broken rock, and dust cover them; most

have no atmosphere and no layers, so surfaces don’t change.

• Can hit Earth – 65 mya, a 6 mi asteroid hit Earth and sent dust into the air, most likely changing the temps of Earth and killing off any living organisms.

Comets • Have oval orbits• Have a coma (cloud of material) and a

tail (gets longer closer to the Sun). • Small, icy rock is hard to see without

the parts above. • The tail always points away from the

Sun. • Halley’s Comet – orbits approx. every

75 years; expected to return in 2061.

Meteors & Meteorites • Meteors: Brief streaks of light caused

by hot particles/air in the upper atmosphere. • Usually can see a few/hour in the night

sky. • Usually very quick, only a few seconds.

• Meteorites: space object that reaches Earth’s surface• Usually smooth on the outside from

melting; inside can still be icy.