Welcome to the Solar System

The center of our solar system is the sun. The word solar comes from "sol" which means sun.​ The sun is at the center of the solar system and makes up 99.8% of the mass of the universe.

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​Welcome to the Solar System

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Our sun is a yellow dwarf star. ​It's pretty small for a star but it gives off an immense amount of radiation. It is a huge ball of hydrogen and helium that's held together by it's own gravity. It is not solid or a liquid. It's considered plasma.

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​What is the sun?

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The sun is the only star in our solar system. The nearest star is 4.22 light years away​. It's called Proxima Centauri. This is an image the Hubble Space Telescope took of Proxima Centauri.

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​Are there any other stars in our solar system?

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Multiple Choice

How many stars are in our solar system?

• one

• two

• none

• millions

The solar system formed from a rotating disc of gas and dust. This gas and dust collected to form planets and their moons, asteroids, and comets​. These would collide to make bigger and bigger planets.

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​How did the solar system form?

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The solar system contains the inner rocky planets, asteroids in the asteroid belt, the gaseous outer planets, dwarf planets in the Kuiper Belt and comets in the Oort Cloud.​ The Oort Cloud is the end of our solar system.

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​Parts of the solar system.

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Multiple Choice

What is the end of the solar system?

• the sun

• the Kuiper Belt

• Earth

• the Oort Cloud

The rocky, or terrestrial, planets are smaller and have few to no moons. They are the first four planets orbiting the sun.​ Only Earth (1) and Mars (2) have moons orbiting them.

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​The inner, terrestrial planets

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Multiple Choice

True or false? All inner planets have moons.

• True

• False

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Multiple Select

Choose the inner planets.

• Mercury

• Venus

• Mars

• Jupiter

​The asteroid belt has over 100,000 asteroids found between Mars and Jupiter. There is one dwarf planet called Ceres, too. Asteroids are similar in composition to the inner, rocky planets

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​The asteroid belt

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​Ceres, the dwarf planet in the asteroid belt, is massive compared to asteroids. Ceres is spherical and asteroids aren't.

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​The asteroid belt

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Multiple Select

The asteroid belt is found between which two planets?

• Mars

• Jupiter

• Earth

• Saturn

Multiple Choice

True or false: Rocky planets and asteroids have a similar composition.

• True

• False

The outer planets are much larger than the inner planets. Jupiter and Saturn are gas giants. They have a similar composition to the sun. Uranus and Neptune are ice giants. ​They are composed of frozen ammonia, methane, and water.

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​The outer planets

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The outer planets have more moons, are more massive, and have thick denser atmospheres than the rocky, inner planets. All four outer planets have rings which are pieces of ice that range from 1 cm to 10 meters.

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​The outer planets

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Multiple Choice

True or false: : Only Jupiter has rings.

• True

• False

Multiple Choice

True or false: All outer planets have many moons.

• True

• False

Multiple Select

Choose the outer planets.

• Jupiter

• Saturn

• Uranus

• Neptune

Beyond the ice and gas giants is the Kuiper Belt.​ The Kuiper Belt contains asteroids and the dwarf planets: Pluto, Orcus, Haumea, Quaoar and Makemake.

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​The Kuiper Belt

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Multiple Select

Which would you find in the Kuiper Belt?

• planets

• dwarf planets

• asteroids

• moons

The Oort Cloud is out past the Kuiper Belt. It defines the boundary of our solar system. It contains comets. As a comet gets closer to the sun, it forms a tail of water and water vapor.​

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​The Oort Cloud

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Educator Guide: Comet on a Stick | NASA/JPL Edu

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