Our solar system is an exciting place. It is full of planets, moons, asteroids, comets, and many other exciting objects. The solar system was formed approximately 4.6 billion years ago. The formation was caused by the collapse of a giant molecular cloud. The mass at the centre collected to form the sun, and a flat disk of dust around it would eventually form the planets and other bodies. In this activity, you will learn all about our solar system!

Our solar system contains many different things: one star, eight planets, a dwarf planet, numerous moons, an asteroid belt, comets, and meteoroids. Even the eight planets are different. The four planets closest to the sun are known as terrestrial planets. This means they are Earth-like — they are smaller and rockier in composition than the outer planets. The terrestrial planets are Mercury, Venus, Earth, and Mars.

 

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The four outer planets are known as Jovian planets. A Jovian planet is a planet that is large and gaseous and is a great distance from the sun. The four Jovian planets are Jupiter, Saturn, Uranus, and Neptune. They are also known as the "gas giants," because they are made up mostly of gases, such as hydrogen, and small amounts of rocky material (mostly at their cores).

 

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As you can see, not all of the planets in our solar system are alike. Take a look at the image below to see the differences between the terrestrial and the Jovian planets.

But what about Pluto? Isn't Pluto also a planet? Pluto was considered a planet until 2006 when it was reclassified as a dwarf planet. An object is considered a dwarf planet when objects of similar size share its orbital space. There are over a dozen bodies the size of Pluto that have been discovered to exist a similar distance from the sun (about 5.9 billion kilometres from the sun). As well, to be considered a planet, it has to have a clear neighbourhood in its orbit around the sun. This means that the planet has to be the dominant gravitational body in its orbit around the sun. This is not the case with Pluto; therefore it is now considered a dwarf planet.

Comets have orbits different from the planets. Their orbits go well past Pluto. Comets are made up of ice and rock that are left over from the formation of the solar system. Because of their peculiar path, they grow "tails" as they approach the sun. As they heat up, gas and dust is expelled behind them. This is the "tail" that is sometimes visible in the sky.

So, how does Earth compare with the other planets? Why is Earth the only planet in our solar system that can sustain life as we know it?

Earth is considered to be in an area known as the “Goldilocks Zone” around our sun. It is just the right distance away from our sun to allow just the right amount of air, water, and heat to support life. Earth's distance from the sun ensures that it receives appropriate warmth and light, without being so close as to become uninhabitable. Sunlight is a necessary source of energy for all life on Earth. As well, Earth's rocky crust provides a stable surface for life, unlike gas giants, such as Jupiter or Saturn.

Just as important as Earth's rocky crust is its molten core. Earth's core provides a source of geothermal heat and energy as well as generating a magnetic field that protects Earth from solar storms. Earth also gains protection from its atmosphere, which keeps out excessive radiation. Finally, Earth has water. Besides being vital to life on Earth now, water is what allows initial life to develop.

Click on the Play button below to watch a video about why Earth is the only planet in our solar system that supports life.