Lesson Video: The Formation of the Solar System Science

In this video, we will learn how the solar system formed from a large cloud of gas and dust.

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Video Transcript

In this lesson, we will learn how the solar system formed from a large cloud of gas and dust.

When we say the solar system, we mean the system of all of the objects that are around the Sun, which includes the eight planets and their moons plus a whole load, more asteroids, comets, rocks, and chunks of ice floating around in the space near to the Sun. And of course, it also includes the Sun itself. The word “solar” actually means relating to the Sun. So when we say solar system, we really do mean the system of all the stuff relating to the Sun.

We can recall that the Sun is a star similar to all of the other stars we can see in the night sky but a lot closer, which is why it appears so big and bright to us and why it keeps us warm and lights the days. We can also recall the names of the planets in the solar system and the order that they are from the Sun. Starting from the closest planet to the Sun, they are Mercury, Venus, Earth, where we live, Mars, Jupiter, Saturn, Uranus, and Neptune. Note that we haven’t drawn the sizes and distances here to scale.

In reality, the Sun and the planets are very far away from each other. Also, the four outer planets Jupiter, Saturn, Uranus, and Neptune are much, much bigger than the four inner planets, with Jupiter being by far the biggest planet. Even though Jupiter is so large, the Sun is much, much bigger even than Jupiter. In fact, the Sun contains 99.8 percent of the entire mass of the solar system.

So we know what the solar system is and what it includes, in this lesson, we will go back in time and learn all about where and what the solar system came from and how it formed.

Approximately four and a half billion years ago, the solar system hadn’t formed yet, but the space where it is now wasn’t completely empty. In fact, there was a large cloud of dust, gas, ice, and rocks in the place where the solar system would form. The name we use to describe such a cloud of dust and gas in space is a nebula, the plural of which is nebulae. So we would say one nebula, two nebulae, three nebulae, and so on. While we often use the word “cloud” to describe a nebula because they are loose connections of floating particles, nebulae are very different from the clouds we see on Earth. Mostly because nebulae are incredibly large.

The word “nebula” can be used to describe any cloud of space debris, and many nebulae can still be seen using telescopes nowadays. For example, this is a photo of a nebula called the Carina Nebula, taken by the Hubble Space Telescope. In the center of the photo, we see the large cloud of gas and dust, which is the nebula itself and over the course of millions of years will likely go on to form many stars and planets. Not all nebulae will go on to form stars and planets, but many of them will. And some, such as the Carina Nebula here are so large that they can form many, many star systems.

So let’s return to thinking about the nebula that formed our solar system billions of years ago and see how this huge cloud of gas and dust became the solar system that we see today. Gravity is a force that pulls objects with mass together. Gravity holds the solar system together now, and it also helped the solar system begin to form billions of years ago. Over time, the force of gravity pulls the particles of dust and gas towards the center of the nebula. And it begins to contract or get smaller. Over the course of several million years, this causes the nebula to form a roughly spherical ball of gas and dust, which continues to get smaller over time.

As the nebula continues to contract due to gravity, it eventually becomes a thin disk. The contraction of the nebula also causes the thin disk to begin spinning and also to heat up. And as a result, it also starts to emit light. Over time, gravity continues to cause the disk to contract. And it continues to get denser and hotter, especially in the center of the disk. Eventually, once this center region of the disk gets hot enough, the Sun forms out of the material in the center of the disk. The mass of the material that forms the Sun is the majority of the mass of the disk. And even now, the Sun contains the majority of the mass in the solar system.

The Sun is mainly formed out of the element hydrogen, with about 75 percent of the mass being hydrogen. And almost all of the rest of its mass is the element helium, with a tiny amount of heavier elements in there as well. Now that the Sun has formed, it will continue to shine for billions of years until the present day and well beyond. However, not all of the mass in the disk went into forming the Sun. There is still mass in the outer regions of the disk. Over time, this mass starts to clump together and form spherical objects which are orbiting the Sun. Due to gravity, these spherical objects continue to grow as more and more particles in the disk are drawn towards them. Eventually, they form the planets in our solar system.

This outer region of the disk that forms the planets isn’t as hot or as dense as the center region of the disk, which helps us understand why the sun formed as a bright hot object and why the planets aren’t as hot and don’t emit light. The contraction of the outer regions takes millions of years to form the planets, even after it takes millions of years for the Sun to form in the center of the disk. The process of the nebula contracting and forming the solar system is a slow one. But we finally have the solar system as it appears nowadays.

The initial, roughly spherical nebula collapsed into a thin rotating disk, heating up as it contracted. As the contraction continued, the disk got smaller, denser, and hotter until the center of the disk was hot enough for the sun to form in the center, followed by the eight planets forming in the outer regions of the disk, leaving the solar system as we see it now. So now that we know how the solar system formed, let’s take a look at an example question about this topic.

The diagram shows how the first part of the solar system formed. A cloud of gas and dust in space. The cloud of gas and dust begins to contract due to gravity. As the cloud of dust and gas contracts, it blank and starts emitting light. Which words would replace the blanks? (A) Heats up, (B) cools down.

So in this question, we’re thinking about the formation of the solar system, which started out as a cloud of gas and dust in space. The word we use to describe this cloud is a nebula. Over time, this nebula begins to contract due to gravity. As the cloud contracts, the particles of gas and dust move faster and faster, and they collide more often with each other. These collisions cause the temperature and pressure of the cloud to increase. And at the same time, they generate heat and light.

The cloud becomes most dense and hot in its center or core, which is where the Sun will eventually form. We can say that the gravitational potential energy of the nebula gets converted into thermal energy and kinetic energy. And so we know that as the cloud contracts due to gravity, it’s going to heat up and start emitting light. So the answer to this question is (A), heats up. And the full final sentence in this question then reads, “As the cloud of gas and dust contracts, it heats up and starts emitting light.”

Let’s finish by summarizing the key points that we have learned in this lesson. Approximately four and a half billion years ago, the solar system began as a cloud of gas and dust called a nebula. Gravity caused the cloud to contract, forming a spinning disk shape. The Sun formed in the center of the disk, where it is hottest and densest. The eight planets of the solar system formed in the outer regions of the disk.

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