1. The Solar System
Chapter 21

2. 21.1 Structure of the Solar System
The sun is the center of our solar system
The sun and 9 planets make up our solar system
Planets “wander” or orbit around the sun at different distances
Sometimes when we view stars, we actually see planets that appear to be stars
Venus is the closest planet to Earth and is easily seen most nights
Stars are much farther away than planets so appear as tiny specks of light

3. Objects in the Solar System
Sun: largest star in the solar system-makes up 99%, 10x larger than Jupiter, made of gases (hydrogen)
The sun produces energy through nuclear fusion and applies gravity to all planets
Planets: reflect sunlight, spherical shaped object that orbits sun, classified/grouped as inner, outer, dwarf
Asteroids: small rocky objects orbiting sun between Mars & Jupiter (belt), range in size
Comets: Gas, dust, and ice orbiting sun and producing a glowing tail (melting), trillions in space

4. Planets
Inner: terrestrial/rocky: Mercury, Venus, Earth, Mars; smaller than outer planets
Outer: gas giants: Jupiter, Saturn, Uranus, Neptune; larger than inner planets
Dwarf: tiny mass, made of rock and ice: Pluto, Ceres, Eris, Makemake

5. Measuring Space
AU-astronomical unit is used to measure distance in space
It is the average distance from Earth to the sun
About 150 million kilometers
Each planet’s AU increases as it gets farther from the sun
See Chart p. 764

6. Motion of Planets
Sun’s gravitational pull on each planet prevents planets from drifting apart and keeps each planet on a curved path around the sun
Revolution/revolve-is the time it takes a planet to travel once around the sun (year)
Rotation/spinning on axis-is the time it takes planet to spin once on the axis (day)
Copernicus proposed the idea that Earth and other planets orbit the sun (heliocentric model) instead of Earth being in the center (geocentric model) in 1500’s
Kepler discovered in 1600’s that planet’s orbit is an ellipse and not a perfect circle and speed increases near the sun

7. 21.2 Inner Planets
Terrestrial planets are closest to the sun and made of rock/metal; have solid outer layers
Different sizes, atmospheres, and surfaces
See p. 769

8. Mercury Smallest and closest to the sun
No atmosphere/wind, extreme changes in temps, many craters due to no erosion, solidified lava, cliffs
Very little change over time
Core, mantle, and crust
Largest impact crater in solar system: Caloris Basin 1550 km across formed billions of years ago
P. 770 See Red Table

9. Venus
Second closest to sun, hottest, about same size as Earth, many probes and landers visited
Dense atmosphere of CO2 & thick acidic clouds cover the planet
Greenhouse effect traps energy
80% is covered with solidified lava
A day is longer than a year due to slow rotation; rotates east to west
Core, mantle, and crust p. 771 See Red Table

10. Earth “third rock from the sun”
Third planet from the sun; has a moon
Protective atmosphere provides water and temps to support life
Greenhouse effect traps energy
Only planet with liquid water on the surface
Core, mantle, crust
Crust is broken into pieces/ plates that constantly move to create and destroy more crust
P. 772 See Red Table

11. Mars
Fourth from the sun; reddish color due to iron oxide (rust) in the soil; many probes have visited
No water or life; polar ice caps hint to water once being available
Thin atmosphere of CO2, extreme temps, Covered with craters and solidified lava; large & long lasting dust storms
Valles Marineris- largecanyon; larger that the U.S.
Martian Olympus volacano- largest mountain in solar system; wide as Arizona and higher than Everest
P. 773 See Red Table

12. 21.3 Outer Planets
Gas giants with liquid interiors-hydrogen and helium
Small solid cores
Strong gravitational pull due to large mass/size
All have a rings

13. Jupiter
5th planet, largest-twice the mass of all other planets combined, thick atmosphere of clouds
Rotates faster than any other planet causing dense, colorful clouds to stretch out and appear as rings
Solid core surrounded by liquid hydrogen- mostly made of hydrogen & helium
63+ moons (more than any other planet), discovered by Galileo so the 4 largest are Galilean moons
Io, Europa, Ganymede, and Callisto are all made of rock and ice
P. 778 See Red Tables

14. Saturn
6th planet, considered the ringed planet due to 7 bands of rings of chunky ice and stretched clouds
Least dense planet
Solid core with layer of liquid hydrogen and gas outer layer - mostly made of hydrogen and helium
60+ moons; largest is Titan and it is the only moon in the solar system with an atmosphere
P. 779 See Red Table

15. Uranus
7th planet, seems to orbit the sun like a rolling ball due to sideways tilt
So far away, only 1 space probe (Voyager 2) explored it in 1986
Thick atmosphere with thick, slushy layer of water and ammonia - mostly made of hydrogen & helium and methane gas
We assume it has a core surrounded by water, ice and gases
27+ moons
P. 780 See Red Table

16. Neptune
8th planet with not as much knowledge due to lack of exploration
Voyager 2 explored it in 1989 (took 3 years to travel from Uranus to Neptune)
Huge storm (dark spot) was detected in 1989 but gone 5 years later
Atmosphere made of hydrogen, helium and methane gas
13+ moons
P. 781 See Red Table

17. 21.4 Other Space Objects
Dwarf planets are objects that orbit the sun, has enough mass & gravity to form a sphere and has other similar objects orbiting near it-new classification in 2006
Pluto, Ceres (smallest), Eris, (largest) MakeMake, and Haumea are dwarf planets
All are smaller than our moon
Pluto is ⅔ size of our moon, very cold (frozen), 3 moons, and takes 248 years to revolve around the sun
Explored by the Hubble Telescope

18. Asteroids & Comets
Most asteroids are located in the asteroid belt & orbit the sun; made of chunks of rock and ice tightly clumped together
Some asteroids are larger than your school
Comets also orbit the sun but produce a coma (bright tail) of melting ice; tail burns on opposite side of sun
Comets are loosely clumps of ice and gas
See p. 787

19. Meteoroids
Small rocky object that moves through space; produces a streak of light in Earth’s atmosphere called meteor; once it collides with another object/planet it is a meteorite
Most are the size of a grain of sand
The collision of meteorites forms an impact crater-round depression formed on the planet
More than 170 impact craters on Earth (Wetumpka, AL)

20. TEST TIME Know vocab Study main ideas on p, 792
Complete review p
Read about the confusing topics in the textbook
Google confusing topics
Study highlighted bullets on Power Point