1. Planet Types Terrestrial Planet Gas Planet Inner Four Planets
Closest to the Sun
Mercury, Venus, Earth, and Mars
Close to the size of Earth
Solid, Rocky Surfaces
Outer four Planets
Farthest from the Sun
Jupiter, Saturn, Uranus, Neptune
Larger
More Gaseous
Lack Solid Surfaces

2. How Do Scientists Know How Our Solar System Formed?
Earth Based Studies
Use of telescopes in all wavelengths of the electromagnetic spectrum.
Data From Probes
Scientists Examined
1). Why the planets are so different.
Especially Outer and Inner Planets
2). Asteroids, Meteorites, and Comets.

3. Formation of Our Solar System
Interstellar Clouds
Huge Clouds of Dust and Gas in Space
Made of Hydrogen and Helium
Form Stars and Planets
These Interstellar Clouds usually look dark because the dust blocks light.
Like Smog
Stars behind this cloud can’t shine through it.

4. Formation of our Solar System
Interstellar Cloud
But….Sometimes the light from stars within the cloud causes these interstellar clouds to glow.

5. Formation of our Solar System
Location
There are many interstellar clouds found within our Milky Way Galaxy.
We look for high amounts of gas and dust.
When enough gas and dust is present, scientist think these interstellar clouds will condense because of gravity.
Can form a star or planet

6. Formation of our Solar System
Collapsing Interstellar Cloud
Cloud begins collapsing slowly.
The smaller it gets the faster it begins to collapse and spin
This spinning motion with eventually form a rotating disk with a very dense center (core).

7. Formation of our Solar System
Scientist believe that one huge interstellar cloud called the solar nebula formed the Sun and all the planets.
The Sun formed first in the center of this cloud.
Fits with why our Sun is the brightest most dense thing in our solar system.
In the center of the cloud it was the hottest
On the edges of the cloud it was the coldest

8. Formation of our Solar System
So What?
This difference in temperature as the solar system cooled caused materials to condense and be located in very narrow regions of the solar system
This is why we see inner planets and outer planets have such different composition.

9. Development of Planets
Once these materials condense out they begin to collide and stick together.
Keep growing larger until they form planetesimals
Objects 100’s of km in diameter
To produce planets, planetesimals must collide and stick together

10. Development of Planets
Outer Planet Formation
1st planet of the gas to form was Jupiter
This is why Jupiter is the largest.
Had the most materials to build with
Then Saturn and the rest of the gas giants formed
Not as large because Jupiter hogged most of the materials; gas, dust, and ice to make itself.
Leftovers became Moons

11. Development of Planets
Inner Planet Formation
Inner planets were forming from the collision of planetesimals.
Made of very different things
Sun took all the gas and floating debris away from the inner planets.
Why they are rocky and dense
Why Moons are rare for inner planets.

12. Space Rocks 101 Asteroid Leftover pieces of Planetesimals
These were never planets
Asteroids can collide and break apart.

13. Space Rocks 101 Meteoroid Meteor
When an asteroid or any space material falls toward Earth and enters Earth’s atmosphere.
The streak of light produced when a meteoroid burns up in Earth’s atmosphere.

14. Space Rocks 101 Meteorite When a space object impacts Earth
Occurs when all of the meteoroid does not burn up in Earth’s atmosphere
Meteor Crater: Arizona
Gosses Bluff, Australia

15. Space Rocks 101
Comets
Small icy and rocky bodies with a highly eccentric orbit around the Sun.
When Earth is in the way of a comet’s orbit we see a meteor shower