1. The Sun formed just like any other Star It followed the Stellar Nebula Model we studied earlier

2. Gravity began to pull material in a nebula together. More material gathered in the center than on the edges of the swirling nebula.

3. The nebula began to take on a disk shape with more material continuing to gather in the center.

4. Eventually there was enough material in the center to cause gravity to be strong enough to cause fusion in the center of the mass A Star was Born! (the sun!!)

5. The nebula HAD TO HAVE contained material from the supernova explosion of a Massive star because we have heavy elements on earth like gold and uranium (which can only be formed in a supernova explosion) Therefore the sun is a second generation star (meaning the material we are made of was a star in the past!)

6. Most material in the Solar Nebula gathered in the center BUT NOT ALL OF IT! Gravity pulled material together along the edges of the swirling disk. There was not enough material in these smaller clumps of matter to form a star, but there WAS enough to form planets!

The Inner Planets

1. The four inner planets are small and have rocky surfaces. They are called terrestrial planets because they are small and rocky "Earth Like" planets

2. They would have originally formed from hydrogen (the most abundant element in the universe and therefore the most abundant element in the Solar Nebula) along with the other elements that make up the planet.

3. The original Proto-planets would have been made mostly of hydrogen and helium gas like the giant outer planets.

4. There are three reasons they are not gas giants like the outer planets

    
• They are close to the sun and receive a tremendous amount of Solar Wind, which would collide with the light weight gasses and physically knock them out of the atmosphere.     
• The energy from the sun received by the inner planets is much more intense and would heat the surface much more. This intense heat would cause the light weight gasses to vibrate much more giving them a high level of motion and they would move into space.
• The mass of the inner planets is much less than the outer planets and therefore the gravity is weaker. So weak that the inner planets cannot hold onto the very low mass gasses of hydrogen and helium.

1. Earth's atmosphere reaches more than 100 Km above the surface made of 20% oxygen, 78% nitrogen and very small amount of carbon dioxide and other things.

2. 70% of the surface is covered by water No other planets have oceans like Earth’s

3. Earth has three main layers

a. Crust- outer rocky layer

b. Mantle- semi-molten layer

c. Core- liquid outer core and solid inner core made of nickel and iron

4. The processes on Earth are our model for studying other planets. If we see volcanoes on other planets, like Olympus Mons on Mars, we assume that it formed by similar processes as they form on Earth.

Mercury

1. Not much larger than Earth's Moon

2. Has no moons of its own

3. Interior made of dense nickel and iron

4. Mariner10, 1974 space craft studied ½ of Mercury and gave us all of the information we know about the planet

a. Covered by flat plains and MANY craters

b. Has VERY thin atmosphere made mainly of Sodium any atmosphere it did have was heated to the point that the molecules moved very fast and the weak gravity could not hold on to them.

c. The side facing the sun reaches 450 degrees C, the side facing away from the sun drops to -170 degrees C This gives Mercury the greatest temperature range in the Solar System.

d. Orbits the sun in 88 days but turns so slowly on its axis that it presents the same side to the sun for 175 days! This is why the sun side temperature gets so high.

1. Size and structure is VERY similar to Earth, often called "Earth's Twin"

2. The bright "star" seen at times in the west after sunset- called "the evening star" at other times seen in the east just before sunrise called "the morning star" still at other times it is too close to the sun and cannot be seen at all. All caused by its orbit period.

3. Revolves around the sun in 7.5 Earth months, takes 8 months to rotate on its axis! It rotates so slowly that a day on Venus is longer than a Venus year!

4. Venus rotates from West to East, opposite the direction of rotation of ALL of the other planets! This is called retrograde rotation. Some scientists think this is because it was hit by a HUGE comet or asteroid during formation that caused it to change the direction of rotation.

5. Venus' Atmosphere

a. Completely covered by thick clouds made mainly of carbon dioxide with some sulfur compounds

b. Pressure from the weight of the atmosphere is 90 times the pressure of Earth's atmosphere.

c. Venus gets more solar energy that earth. This energy heats up the surface. As the heat is radiated from the planet toward space it is absorbed by the carbon dioxide in the atmosphere and radiated back to the planet causing it to heat up even more! This is called the GREENHOUSE EFFECT.

6. Exploring Venus

a. 19 spacecraft have visited Venus, more than have visited any other planet.

b. Venera 7, 1970 A Russian spacecraft lasted 23 minutes took the first pictures from another planet.

c. Most of what we know about Venus came from the Magellan space craft, 1990. It was equipped with mapping RADAR which could "see" through the clouds using the radio spectrum

d. Venus has volcanoes with lava flows, huge mountain ranges, flat plains and strange dome formations not seen on any other planet.

1. About 1/2 the size of Earth

2. Called "the Red Planet" because it surface is covered with iron oxide- RUST! Proves that Mars once had free oxygen molecules in its atmosphere.

3. Has a very thin atmosphere of carbon dioxide, only 1% of the pressure of Earth's atmosphere.

4. 1877 Giovanni Schiaparelli thought he saw "Canals" on Mars In the 1890's Perciful Lowell convinced people that they carried water from the poles to cities near the equator! This started the idea of intelligent Martians living on Mars that is still present in science fiction today.

5. There are no canals on mars and no life that we recognize! There is water though frozen in the ice cap on the North Pole covered by a layer of frozen carbon dioxide in the Martian winter.

6. Seasons!

a. Since mars is tilted on its axis, it experiences seasons just like on earth. The temperatures are ALWAYS cold compared to earth standards though! During the summer it might get up to 35 degrees F at the equator!

b. As the seasons change tremendous wind storms arise, winds have been measured at 400mph! This creates HUGE dust storms

7. Exploring Mars

a. In the 1960's the US sent many spacecraft to orbit mars that took many pictures and showed Mars has evidence of running water at some time of the past. It is covered by many craters. It also has the largest volcano in the Solar System -Olympus Mons- which is about 3 times the size of Mt. Everest on Earth!!

b. Viking 1 and Viking 2 landed on the surface in 1976 the Vikings took pictures and analyzed soil samples, proving the surface was covered with rust.

c. July 4, 1997 the Mars Pathfinder project landed on the surface. Made of three parts the Orbiter- which relayed information back to Earth and took pictures from orbit, the Pathfinder which acted as a base station and the Sojouner which was a kind of RC car controlled by people on Earth and drove around the surface taking pictures.

d. Later in 1997 the Mars Global Surveyor reached orbit around Mars and is mapping the surface to understand the layout of the planet better and to look for possible future landing sites.

8. Moons of Mars

a. Phobos about 27 Km in diameter (about from MMS to Newark)

b. Deimos about 15 Km in diameter (about from MMS to Dover)