1. The Solar System
8th Grade Science

2. The Solar System Evolves
The solar system is the sun, the planets, and all the other objects that revolve around the sun.
The nebular theory states that our solar system began as a huge cloud of dust and gas, which later condensed to form the sun and its nine planets.

3. The Sun Forms First
About 5 billion years ago, a star exploded in a huge supernova.
The nebula that was home to the star begins to collapse and pull matter toward the center.
At the center, a protosun forms.

4. The Planets Form
Gases and other matter surrounding the newly formed sun continue to spin around it.
Gravity causes the matter to gather into small clumps, then into larger clumps called protoplanets.
As the newly formed planets began to cool, smaller clumps of matter formed around them. Giving the planets their moons.

5. Motions of the Planets
In the second century B.C. Ptolemy proposed a theory that the Earth was at the center of the universe; and that all objects moved in perfectly circular orbits.
Nicolaus Copernicus then proposed a theory that the Earth and the other planets actually revolved around the sun.

6. Motions of the Planets
However, like Ptolemy, Copernicus also believed that the planets orbited in perfect circles.
It was Johannes Kepler who realized after carefully studying the planets movements that the planets actually moved in oval orbits called ellipses.

7. Revolutions and Rotations
Kepler knew the planets orbited the sun, but how?
Isaac Newton realized that a planet’s motion around the sun is a result of: inertia and gravity.
Inertia cause the planets to move in a straight line and gravity pulls them toward the sun.

8. Revolutions and Rotations
Another way to say a planet orbits the sun is to say it revolves around the sun.
The time it takes a planet to make one revolution around the sun is called its period of revolution.
Aside from revolving around the sun, planets also spin or rotate on their axis.
The time it takes a planet to rotate on its axis is its period of rotation.

9. A Trip Through the Solar System
The planets of our solar system have a wide variety of surface and atmospheric features.
Each planet has its own story to tell.

10. Mercury
Mercury is the closest planet to the sun and is its own crater-covered world.
The craters on Mercury were created billions of years ago, but without weather, there has been no change.
Mercury is one of the hottest and one of the coldest planets in the solar system.
Mercury contains steep cliff and vast plains, most likely formed by volcanoes during the planet’s formation

11. Venus-The Greenhouse in the Sky
Venus has about the same diameter, mass, and density as Earth. For this reason it is called Earth’s twin.
Astronomers were unsure about the surface of Venus because of its thick cloud cover. The lower level yellow clouds on Venus are made of sulfuric acid and carbon dioxide.
The surface of Venus has an orange glow and is dotted with the remains of many volcanoes.

12. Venus-The Greenhouse in the Sky
The temperatures on Venus can climb to 480°C, which is hotter than the surface of Mercury.
The heat from the sun caused the water on Venus to evaporate into the atmosphere causing a tremendous greenhouse effect. This eventually caused the oceans to evaporate completely.
Venus also has a retrograde rotation, which means it rotates from east to west.

13. Mars-The Rusty Planet
As you approach Mars, the first thing you would notice is the reddish color. This is because Martian soil is covered in rust!
The surface of Mars is rocky and covered in craters.
Mars gives evidence to a very active past. It is also home to the largest know volcano in the solar system
Today there is no liquid water on Mars, but frozen water can be found on Mar’s polar ice caps.

14. The Asteroid Belt
On your way from Mars to Jupiter you will enter the asteroid belt.
The asteroid belt contains hundreds of thousands rocks and “flying mountains.”
Asteroids are made of rocks, metals, or a combination of the two.
Most asteroids are small and irregularly shaped.
The asteroid belt formed from pieces of matter that failed to join during the solar systems formation.
Scientists suspect that Jupiter’s gravitational pull kept the asteroids from coming together

15. Jupiter Jupiter is the largest planet in our solar system.
Jupiter is made of primarily hydrogen and helium gases.
Scientists believe that if Jupiter had grown larger during its formation, gravity might have caused nuclear fusion to occur and a star to form.
One of Jupiter’s most well know feature is the Great Red Spot, which is a huge hurricane type storm that is three times the size of Earth and has lasted for more than 100 years.
Due to the pressure near the center of the planet, the dense clouds become an ocean of liquid hydrogen.

16. Jupiter
This liquid metallic layer of Jupiter is the cause of its gigantic magnetic field called the magnetosphere.
Jupiter is also strange in the fact that it gives off more heat than it receives from the sun.
It also has a total of 16 moons that circle it, but there are 4 very large moons discovered by Galileo.
IO is the closest of Jupiter’s moons and is very young and active.
EUROPA is ice covered and extremely smooth due to its volcano that spews water and ammonia ice.
GANYMEDE is Jupiter’s largest moon and is the largest in the solar system. It is about 1/2 rock and 1/2 water and is the only other object in the solar system known to have earthquakes.
CALLISTO is the most heavily cratered object in the solar system and is a very quiet moon.

17. Saturn-A World of Many Rings
Saturn is surrounded by seven major rings made up of icy particles.
Saturn is made mainly of hydrogen and helium gases and spins very fast on its axis, which causes its poles to flatten.
Saturn, like Jupiter, also has violent storms.
Saturn’s clouds also form the colored bands we see.
Saturn also has a very small density and would actually float in water.
Saturn has 21 known moons with the largest being Titan.

18. Uranus-A Planet on Its Side
Uranus is the seventh planet in our solar system and is almost twice as far from the sun as Saturn.
Uranus is also a gas planet made of mostly hydrogen, helium, and methane.
Strong evidence was found that Uranus is covered by an ocean of superheated water than may have formed from melted comets.
The axis on which Uranus rotates is one the most unusual features. The axis is tilted at an angle of about 90°. This makes it look like it is tipped completely on its side.

19. Neptune
Upon examining the orbit of Uranus, astronomers noticed that there must be an object beyond Uranus.
Neptune is a giant bluish world.
Neptune is often called a twin to Uranus because they are about the same size, mass, and temperature.
Neptune’s surface is probably and ocean of water and liquid methane, covering a rocky core.
Data was also found to indicate that Neptune has five rings made of dust particles.
Neptune also has at least 8 moons the biggest and most well known being Triton.

20. Pluto-A Double Planet
Pluto is little more than a moon-sized object than may be an escaped moon of Neptune.
Pluto is made of icy gases such as methane.
Pluto is the only planet with an atmosphere on its sunny side and none on its dark side.
Pluto also has a moon that is so close in size that it may be double planet.

21. Planet X-The Tenth Planet?
After discovering Pluto, scientists realized that it was too small to be pulling on Uranus and Neptune.
This causes scientists to believe there is another planet as far as 80 billion kilometers from the sun pulling on the planets causing their strange orbits.
Other scientists feel that they are being pulled on by a Brown Dwarf or possibly a black hole.

22. Comets
Most comets come from the Oort cloud, which is a vast collection of ice, gas, and dust.
The pull of gravity from a local star pulls parts of this cloud out into space.
Comets are made up of this ice, gas, and dust, which form a cloud around the core as it heats up.

23. Meteoroids, Meteors, and Meteorites
Meteoroids are chunks of metal or stone that orbit the sun.
When the meteoroid enters the atmosphere, friction causes it to burn. The streak of light in the sky is called a meteor.
Most meteors burn up in the atmosphere, but a few strike the Earth’s surface and are called meteorites.

24. Exploring the Solar System
Rocketry
Rocketry is based on Newton’s third law of motion.
In a reaction engine, such as a rocket, the rearward blast of exploding gases causes the rocket to shoot forward.
However, rockets must be able to escape Earth’s gravitational pull.
Escape Velocity
In order for a rocket to escape Earth’s pull, the rocket must achieve the proper velocity.
The escape velocity of a planet is determined by the mass of the planet and the distance of the rocket from the planet’s center.
Rockets also need a fuel source that will continue to burn.

25. Live Long and Prosper!!!