The solar system part 2

0:00- [Instructor] You probably know our solar system has the sun at the center and the eight planets going around it. But that's not the whole story because it's also filled with comets, asteroids, meteors, dwarf planets, and even vast regions of icy debris far beyond the planets.

0:19So let's explore what these objects are, where they come from, and how they all move through our solar system. Let's start with the comets. A comet is essentially an icy body made of frozen gases, rock and dust. When a comet moves closer to the sun, the sun heats it up, right?

0:42And so the frozen gases now begin to vaporize and stream away, forming a glowing tail. And that's why the tail of a comet always points away from the sun, no matter which direction the comet is moving. Now, some comets follow regular paths around the sun, much like the planets.

1:06These are called the periodic comets. The most famous one is the Halley's Comet, which appears in our sky roughly every 76 years. So its next visit will be in 2061. So mark your calendars, but of course not all comets are so predictable. Some burn up completely as they come close to the sun while others swing past the sun once, then escape the solar system forever.

1:30We call them non-periodic comets. All right, now let's look at asteroids. If comets are icy, asteroids are rocky. They're basically space rocks, a leftover building block from the early solar system. And as you can see, they come in all shapes and sizes. In fact, many look like lumpy potatoes rather than smooth spheres.

1:56And some are just a few meters wide, while others, like say Vesta, are hundreds of kilometers across. And most asteroids are found in this region called the asteroid belt, located between Mars and Jupiter. And there are millions of asteroids there. But despite what we see in this image, they are not packed closely together.

2:24They're actually very far apart. Again, a reminder of how this diagram is not to scale at all. But where did they come from? Well, scientists once believed that this belt might be remains of a destroyed planet. But now we believe Jupiter's strong gravity actually prevented these objects from ever coming together to form a planet in the first place.

2:51But guess what, asteroids aren't the only space rocks that orbit the sun. Our solar system is also full of smaller objects called meteoroids. Think of them as small pieces of rock or metal moving through space. And they can be as small as a speck of dust or, you know, as large as a small asteroid.

3:15Okay, but where do these meteoroids come from? Well, they often form when asteroids collide with each other or when comets break apart or, you know, they can just be left over from the formation of the solar system itself. And sometimes these meteoroids can get trapped in a planet's gravity and fall down towards the surface of the planet.

3:37And so if a meteorite enters the Earth's atmosphere, it'll burn up and it can produce a bright streak in the sky, which we now call shooting stars or falling stars. But, of course, they're not stars, they're just meteorites that are burning up in our atmosphere.

3:53And now this is technically called a meteor. And sometimes Earth passes through streams of debris left behind by comets. When that happens, we see many meteors at once, a meteor shower. And if parts of it survives the journey and reaches the ground, then it's called a meteorite.

4:15Most meteorites are metallic, and they're some of humans' first sources of iron. Every day about 50 tons of space dust and rock enter Earth's atmosphere. Now, most of it burn up completely, but sometimes large pieces survive and create impact craters, like the famous meteor crater in Arizona.

4:35Anyways, before we move on, just to make sure we're not confused with the naming system, because I used to always get confused over here, whenever a meteorite enters our atmosphere and starts burning up and starts giving these beautiful streaks in the sky, we call it a meteor.

4:50And if parts of it survives and reaches the ground, and that part is what we call meteorite. Okay, now let's move farther out. Beyond Neptune lies a vast region called the Kuiper Belt. Yes, it has a U in it, but still we usually pronounce it Kuiper. And this Kuiper Belt is a huge ring of icy objects orbiting the sun.

5:19And it not only contains rocky material, but also frozen substances like methane and ammonia. And we believe many comets actually come from here. If one of these icy bodies gets nudged out of its orbit, it can head towards the inner solar system and become the comets we see in the sky.

5:40And again, even though this image is not to scale, you can still easily see that the Kuiper Belt is much larger than the asteroid belt, and it extends way beyond the orbit of Pluto. Speaking of Pluto, this now brings us to dwarf planets. For a long time, Pluto was considered the ninth planet, but in 2006, astronomers created a much stricter definition for what counts as a planet.

6:09So according to that definition, to be a planet, the object must be round, it needs to orbit the sun, and it should clear the neighborhood around its orbit. Now, Pluto meets the first two conditions, but not the third. So it was reclassified as a dwarf planet.

6:28So what are dwarf planets? Well, these are round, they orbit the sun, but they share their orbital space with other objects. Now, Pluto is a good example of this because Pluto shares its orbital space with a lot of objects in the Kuiper Belt. And guess what, Pluto is actually smaller than Earth's moon and its orbit around the sun is quite elongated, and it takes about 248 years to go around the sun.

6:58And Pluto has five moons with Charon being the largest. In fact, Charon is about half the size of Pluto. Because it's so big, some scientists like to call this a double planet system. Anyways, we have also identified other dwarf planets. For example, Ceres is a dwarf planet that lies in the asteroid belt, and we think it contains significant amount of water.

7:20And the dwarf planet ERis was discovered in 2005. It's slightly smaller than Pluto, but it's more massive than Pluto, making it the most massive dwarf planet discovered so far. It also has its own little cute moon, and it was Eris that helped trigger the whole redefinition of the planets, and Eris orbits beyond Pluto.

7:43It takes about 557 years to go around the sun. And of course, scientists believe there may be hundreds or thousands of dwarf planets in our solar system. Anyways, if you thought that the Kuiper belt was the outermost edge of the solar system, you're sadly mistaken because far beyond the Kuiper Belt is something called the Oort Cloud.

8:08Unlike the flat disk of the Kuiper Belt, the Oort Cloud is thought to be spherical shell surrounding the entire solar system, and it's incredibly far away. "How far?" you ask. Think of it this way, light takes about eight minutes to reach Earth from the sun. To reach Pluto, it takes about five hours.

8:29To reach the outer edge of the Kuiper Belt, roughly 10 hours. But to reach the outer edge of the Oort Cloud, well, it could take up to three years. That's how far it is. So our current best estimate is that the outer edge of the Oort Cloud is somewhere between 1.5 to 3 light-years.

8:50Now, remember, light-years is not a unit of time, it's a unit of distance. So the number says that it's so far that light could take somewhere between 1.5 to 3 years to reach the outer edge. And just for context, this is more than halfway to our neighboring star, besides the sun, Proxima Centauri.

9:11And here's a to scale picture from NASA. If this represents the outer edge of the Oort Cloud, then the Kuiper Belt would be just this much. You can clearly see how far away we think the Oort Cloud is, but what exactly is it made of? Well, we don't know exactly because we haven't seen it directly.

9:32I mean, we infer its existence based on the fact that we see a lot of long period comets coming from this region over here. And so we think it's probably got a bit of rocks and frozen ice, but its exact structure and its origin, well, those are still active areas of research even today.

9:53So let's put everything together. Our solar system is much more than the sun and eight planets. We have comets, which are icy bodies that grow glowing tails near the sun. We have asteroids, which are rocky remnants mostly found between Mars and Jupiter. We have meteoroids, which are smaller fragments that can become meteors or meteorites when they reach Earth.

10:17And beyond the planets, the Kuiper Belt and the distant Oort Cloud, they're filled with icy objects, some of which occasionally visit us as comets. And scattered among all this are dwarf planets, like Plut and Eris. Hopefully we can now appreciate how the solar system is much more than the sun and the eight planets.