# Chapter 27: Planets of the solar system

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Chapter 27: Planets of the solar system

Section 27.1 – Formation of the Solar System
What exactly is a solar system anyway? Consists of the Sun, all the planets, and any other body that revolves around the Sun And what exactly is a planet? Any primary bodies that orbit the Sun (Earth, Venus, etc.) Where did it all come from?

Nebular Hypothesis 1976, French mathematician Pierre-Simon, marquis de Laplace came up with explanation for creation of the solar system Sun and other planets came together and condensed at the same time out of a rotating cloud of gas and dust

Solar Nebula Solar Nebula – the rotating cloud of gas and dust from which the sun and planets formed Also any nebula from which stars and planets (outside our solar system) may form 99% of the material in the Sun is matter that was originally in the solar nebula

Steps in the process 1.) Start with a solar nebula (rotating cloud of gas and dust) 2.) Contraction of gas and dust into rotating disk 3.) Cooling causing condensing into tiny (dust sized) solid particles 4.) Collisions between these form larger bodies 5.) The larger bodies accrete (or build up) to form planets

Let’s break it down into steps…
#1 Solar Nebula What “fuels” the nebula? Energy from collisions and pressure from gravity makes the center of the nebula HOT and DENSE 99% of all the material in the nebula is in the sun Think back to our solar nebula activity! Where is most of the material located?

Next Step… #2 The nebula flattens as it rotates and gets warmer near the center Starts to look like a disk Temperature begins to rise more at the center Think ice skater doing a spin!!

Third Step… #3 Things begin to form
Planetsimals begin to form within the swirling disk As they grow, gravitational pull increases and they continue to grow more Planetesimals - “mini planets” or small bodies from which a planet originated in the early stages at the beginning of the solar system)

Fourth Step… #4 Small planetesimals collide with larger ones and the planets begin to grow As the planetesimals get bigger, their gravity grows and they become protoplanets Protoplanets are planetesimals that have collided due to gravity to form larger bodies

Fifth Step… #5 The extra dust and gas is gradually removed from the solar nebula by the collisions The removal of the other material leaves mainly just planets around the sun and creates a new solar system

Creation of Planets KEY THOUGHT: THE FEATURES OF A NEWLY FORMED PLANET DEPEND ON THE DISTANCE BETWEEN THE PROTOPLANET AND THE DEVELOPING SUN IT ALL RELATES TO GRAVITY What has the most gravity in a solar system? THE SUN!

Inner vs. Outer Planets Inner protoplanets (which are?) contained lots of heavy elements Venus, Earth and Mercury contain lots of nickel and iron These elements stuck around because they couldn’t be blown away or evaporated by the Sun’s heat and wind

As the inner planets formed, dense material sank towards the middle of the planets and lighter material stayed on top, forming layers Inner planets have solid surfaces (like Earth) Inner planets are smaller, rockier, and denser than outer planets

Inner vs. Outer Planets Outer protoplanets (which are?) contained lighter elements Jupiter, Saturn, Uranus, and Neptune contain hydrogen, helium, and methane These planets are cold, have low densities, and are HUGE

More on outer planets Outer planets known as “Gas Giants” because:
Mostly made of gases and are low density Jupiter’s density is only 24% of Earth’s but Jupiter’s diameter is 11 times Earth’s Have liquid cores and gas outer layers

Pluto! Not considered an inner or outer planet
Characteristics of Pluto Very small (smaller than Earth’s Moon!) Very COLD – it’s an ice ball made of frozen rock and gas

More on Pluto Recently, scientists found many, many objects in the universe that are similar to Pluto beyond Neptune Because Pluto is more like these other common objects rather than other planets, it is no longer considered a PLANET.

Formation of Solid Earth
3 sources of energy contributed to the original HOT temperatures on Earth: Energy produced during collisions with other planetesimals Increased pressure on inner layers of Earth from weight of outer layers Radioactive materials were abundant in Earth during its formation

Early Solid Earth Differentiation – the process that occurred as Earth developed where denser molten materials sank to the center and less dense materials were forced to the outer layers

3 Layers of Earth Core – the center of Earth that is made of dense rocks Nickel and Iron most common Mantle – Earth’s thick middle layer Iron and Magnesium-rich rock Crust – Outermost layer of Earth Least dense material, including silica-rich rocks

Present Solid Earth As time went on, Earth’s surface cooled enough for solid rock to form While Earth already had distinct layers, the surface continued to change from: Heat inside the Earth Impacts and interactions with the forming atmosphere

Formation of Earth’s Atmosphere
Like the Earth’s interior, the atmosphere formed due to differentiation Hydrogen and helium (lightest gases) rose to surface of the Earth SO, the early atmosphere was mostly made of H and He

The Early Atmosphere Hydrogen and helium gas are so light, Earth’s gravity couldn’t hold them in for long The Sun’s heat heated them up and they blew away into space Also, Earth’s magnetosphere (protects our current atmosphere) was possibly not developed fully

OUTGASSING (no that’s not what you think it is)
The Earth’s surface continued to evolve with creation of volcanoes and other land forms Volcanoes released additional gases into atmosphere: Water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide, and ammonia What’s missing from this list?????

More on outgassing Gases released from volcanoes then interacted with sun light and heat Breakdown of ammonia and water vapor into OZONE (or three oxygen) Ozone is a shield against UV rays of the Sun

The PRESENT Atmosphere
Later, some plant life evolved that used carbon dioxide from the atmosphere to produce food (photosynthesis!) OXYGEN is the main product of photosynthesis About 2 billion years ago, the amount of oxygen in the atmosphere increased a lot Composition of “air” is now stable

Oceans – Where did they come from?
Possibly from space! Some icy bodies (ex. comets) collided with Earth and added water vapor to atmosphere As Earth cooled, water vapor condensed to liquid rain First ocean was probably FRESH water

Why are oceans salty? Although first oceans were likely fresh, as water flowed over land and rocks, it dissolved minerals and salts carried them to the oceans After the water cycle was in place, the concentration of salt in oceans increased

How did Oceans Affect Atmosphere?
Scientists believe the early atmosphere was changed as oceans began to dissolve carbon dioxide Current atmosphere likely has more carbon dioxide than original atmosphere Earth’s early climate likely cooler than today Does CO2 in the atmosphere affect climate today????

ASSIGNMENTS Outline Section 27.1 and Key Terms 27.1 Due: