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Everything in the universe was in that one 

super-heated and super dense speck. 

About 14 billion years that speck exploded 

and created all matter in the universe. That 

was the start of our universe.

The Big Bang is the theory about how the 

universe was created. It explains that the entire 

universe started as an extremely small and 

dense mass, then expanded into what we 

today know as the universe. 

The most popular theory of how our 

solar system was formed is called the 

nebular hypothesis. This theory states 

that our universe evolved from a giant 

cloud of dust and gas. Then that giant 

cloud of gases and dust began to 

collapse on itself and move in a giant 

circle. At the center of the circle a star 

(our sun) began to form. The star 

became larger and larger as it gathered 

more dust and gas. Then clumps of dust 

around the outside of the center began 

to form into planets, moons and  

asteroids. This was the foundation of 

our solar system. 

After the general shape of the universe was formed there were 

extremely powerful solar winds that began to blow. They blew excess 

gas and particles away from the planets which made them stop 

growing. 

This is why planets closer to the sun are smaller; because the solar 

winds were much stronger there and blew away the dust from the 

planets much more quickly. This made the interior planets stop growing 

much faster than the exterior ones. 

Another effect of the solar winds was that the inner planets are rocky 

while the outer planets are made up of a lot of gases. Because the solar 

winds weren't effecting the outer planets as quickly they had more time 

to collect gaseous materials. 

This theory of Planet formation is called Core Accretion. 

The Asteroid belt is a band of asteroids that 

lies between the orbits of Mars and Jupiter. It's 

made up of thousands of objects that are too 

small to be considered planets. Some are only 

the size of a speck of dust while others can be 

more than- 100 miles across. 

Astronomer theorize that the asteroid belt 

is either pieces of a planet that broke 

apart long ago or the pieces of a planet 

that never fully formed. 

As explained before the sun formed from the giant 

nebula of gas and dust from which the Universe was 

created. The giant cloud began to have a common 

center because of its own gravity. This is where the sun 

was formed about 5 billion years ago. The center of 

the cloud ha so much pressure and heat from the matter 

pressing into it and creating even more heat. When it 

reached a temperature of around one million degrees its 

core ignited and the Sun started to create its own 

energy through nuclear fusion. 

Our Sun is a quite common star in the universe. There 

are trillions of other stars just like it with their own 

solar systems. It is simply a middle sized yellow dwarf 

star with average heat and brightness. 

Mercury is made out of a large percentage of heavier 

elements, primarily iron. This is because of it's close 

proximity to the sun. During the formation of the 

planets,solar winds blew away much of the gaseous 

material leaving an extremely dense planet. Next to 

Earth, Mercury is the second most dense planet in our 

solar system. 

Mercury has no atmosphere, no moons, and very extreme 

temperatures. On the side facing the sun it can reach 

temperatures of 800 degrees Fahrenheit and on the side 

facing away from the sun it can be 300 degrees Fahrenheit. 

Like the other inner planets Venus was formed by the 

collection of gases and dust when the solar system was 

formed. Additionally, it is speculated that Venus experienced a 

very large collision at some point. This is theorized because 

Venus's orbit is opposed that of all the other planets. 

Venus is extremely similar to Earth in that it has essentially the 

same size, density, chemistry, and gravity. However, Venus is a 

very deadly world. It's atmosphere is made up of primarily Carbon 

Dioxide making it extremely toxic. Also, the temperatures there are 

very high; surfaces temperatures could cook a meal within minutes. 

Another attribute is the large number of volcanoes that are 

continually seeping lava onto the surface of the planet. Because of 

these things, no living thing would be able to survive on Venus even 

though it has a similar make up to Earth. 

The general formation of the earth followed the core 

accretion theory of how the planets were formed in that it 

was formed by the gathering of dust and gases and then the 

solar winds blew away the excess materials, however, more 

specific information about the formation of the earth is 

known...

Earth has a heated core and it's surface 

is made up primarily of water with land 

masses that we call continents. It has 

an extremely gentle atmosphere and is 

located at the perfect distance from the 

sun to have mild temperatures. All of 

these things make Earth the only 

known planet capable of supporting life. 

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