Our Solar System

So eventually they make a small baby planet called a planetesimal. And if these planetesimals grow close to each other and combine, they can grow large enough to form a planet. In our solar system, the planets can be divided nicely into two categories. We're going to talk about the outer planets first because they formed first. So the outer planets include Jupiter, Saturn, Uranus, and Neptune. Pluto is actually a dwarf planet, and we'll talk about those after we talk about the 8 main planets. Jupiter was the first planet to start forming. And again, if a planet or a planetesimal gains mass, it also gains a greater gravitational force so it can pull more and more matter into it. So Jupiter started forming first, got a head start and therefore could pull lots of matter into it. Jupiter's name for the king of the gods because he is the largest planet. 

All of the outer planets had extra material left floating around the main planet. This extra material formed a disc around each planet and that disk combined together to make rings and moons. So all of the outer planets have rings and moons. We'll talk briefly about each of the outer planets and then you'll be completing a worksheet on blackboard about the planets will where you will read more in detail about each planet. Jupiter again is the largest planet, it is one one 800th as massive as the sun, which doesn't sound very big, but if you add up the mass of all the other planets and moons combined, it is two and a half times greater in mass than everything else in the solar system combined. Without counting the sun. Jupiter is also famous because it rotates the fastest. It spins so fast on its axis that the equator bulges and the poles become slightly flattened. The bands or stripes that you're seeing on Jupiter are wind systems. They create these light and dark bands. 

The winds are actually created by Jupiter's interior heat and convection currents. The spot you see here is known as the great red spot. It is a giant hurricane like storm that has been going on for hundreds of years. And if we could make it through to the core of Jupiter, we would find a solid rock and metal core about the size of the earth, but the rest of Jupiter is composed mostly of hydrogen and helium. There's a look at Jupiter's clouds. And Jupiter has a total of 63 moons, the one picture here is Io, which is volcanically active. Saturn is also a very large planet. All the outer planets are nicknamed gas giants. Saturn is famous for its rings, even though all the outer planets have rings, Saturn has the widest, most visible rings. So Galileo was the first to see these rings in 1610 because they are so visible. You don't have to have a strong telescope to be able to see them. Saturn is structured very much like Jupiter and is made of similar composition, lots of hydrogen and helium, and Saturn is the least dense of all the planets, so it actually has a density less than that of water. 

Saturn has 31 moons, its largest moon Titan is actually larger than the planet mercury. The next planet out is Uranus, Uranus and Neptune look very similar, they are often nicknamed the ice giants because they are very cold and made of lots of ice. Uranus is a sideways planet, astronomers think that Uranus made a collided with another object that turned Uranus on its side. So it orbits on its side. And it also has rings and a total of 25 moons. The last outer planet is Neptune. It is nicknamed the windy windy planet because it has the strongest sustained winds of any planet or any place in the solar system. It has a great dark spot, which is another large rotating storm. Neptune also has rings and a total of 13 moons. The inner planets are the four planets closest to the sun. They are made of solid materials like rock and metal, so they all resemble the earth, sometimes they are nicknamed the rockies or the terrestrials because they are made of earth like materials. So these planets formed closer to the sun, so the sun's gravity was able to pull in any extra debris floating around the planets. 

It pulled into the sun. So the inner planets didn't form rings or moons. The earth has a moon, but if you'll remember from our moon notes, earth got its moon as a result of the collision, which broke off parts of the earth to make the moon, and Mars has two moons, but we think they were later captured after the planet's formation. They were probably asteroids and asteroid belt before they were captured. And we'll talk about the ash rebuilt in just a second. Mercury is now the smallest planet since Pluto was named a dwarf planet. So mercury is not much larger than our moon, but it's surface resembles the moon because it's very cratered. And mercury is actually smaller than three other moons in the solar system. Mercury is known for having the greatest temperature ranges in the solar system and it revolves fastest around the sun. It was named after the messenger God, which would run messages to different towns very quickly. So mercury is fastest to travel around the sun. 

Here you can see the cratered surface of mercury again very much like the moon and mercury has a very thin atmosphere. So weathering doesn't clear away those craters. The next planet from the sun is Venus. It is named after the goddess of beauty because it is very bright in our night sky. So the only brighter thing in our night sky is the moon. So it looks very beautiful from the earth. Venus has also been nicknamed earth's earth's twin because they are very similar in size and in density. Venus was studied by a spacecraft known as Magellan, which actually took radar or sonar mapping techniques to figure out what the surface of Venus looks like. We've discovered that over 80% of Venus is covered in planes of volcanic flows. It has shield volcanos, similar to the Hawaiian volcanos on earth. Venus is famous because it has a very thick atmosphere, and most of that atmosphere 97% is carbon dioxide. And if you'll remember from meteorology, carbon dioxide is a greenhouse gas, it traps heat close to the surface. So this extreme greenhouse effect gives Venus the highest surface temperatures in the solar system reaching 475°C. 

So it's much too hot for life as we know it to exist. Venus axis is tilted a 177°. We think that Venus probably collided with something as well and it turned Venus upside down. So if you were standing on Venus, the sun would rise in the west and set in the east, the opposite as the other planets. Here is the picture of Venus as it crosses in front of the sun. The next planet out would be the earth, and we've been studying the earth already. So we will skip earth and move to Mars, which was named after the God of War because it's reddish in color, which reminded people of blood. Mars has a very thin atmosphere with a little bit of carbon dioxide. It can keep polar ice caps through the winter when winter temperatures get to negative 125°C. There are extensive dust storms on Mars and hurricane force winds that can reach 270 km/h. Mars surface is much like a desert. It's made of rock and sand, which are constantly the stand is constantly rearranged by the wind. And it's been studied by several spacecraft, Mars is famous for having the largest volcano in the solar system, which is named Olympus mons, Olympus mons at the base, is as large as the state of Ohio, but it is two and a half times higher than Mount Everest. 

Here is a picture of the Martian terrain. Taken by the rover opportunity. So now that we've talked about the planets, pause the video for a moment and try to fill in the part of your notes that compares the inner planets to the outer planets. Most information about the inner planets in outer planets can be categorized because the inner planets are very similar to each other and the outer planets are very similar to each other, but the two groups are very different. So let's review the information. The inner planets include mercury, Venus, earth and Mars. Outer planets are Jupiter Saturn, Uranus and Neptune. So their composition, interplanetary are made of rock and metal, which is why they've been nicknamed the terrestrials or the rockies. The outer planets have rock or metal cores, but they're mostly made of gas like hydrogen and helium. And frozen gases and liquids as ice. So the outer planets are nicknamed gas giants because they are mostly gas. Remember the inner planets are mostly small, the outer planets are very large. The density of the inner planets averages 5 times that of water. Whereas the average density of the outer planets is only 1.5 times that of water. So outer planets are much less dense than the inner planets. 

The atmospheres of the inner planets are thin and have small masses, whereas the outer planets are able, are larger and therefore able to hold on to even the light gases to make very thick atmospheres. The revolution in rotation of the inner and outer planets is also different the inner planets revolve around the sun very fast. Remember mercury is the fastest of all of them. Gravity has a greater effect on things that are closer to it. So since the inner planets are closer to the sun, the sun can pull them around the orbit faster. This gives the inner planets a shorter year and the outer planets are longer year. The rotation of the inner planets is slower so they have faster days. On the outer planets, they rotate fast so they have the longest days. And Pluto doesn't fit into either of these categories. It's outside the outer planets, but it doesn't fit with the outer planets because it is small, it is solid. And if you'll notice in this picture, it shows several orbits of the planet planets and planets orbit at very close to perfect circles, not quite perfect circles, but then once you get to Pluto, it doesn't have a very circular orbit at all. 

So that's one way that it doesn't fit. And again, it's not large, like the other planets, and it's made of solid material, not gases. So Pluto was placed in its own category and it's now called a dwarf planet. There are other dwarf planets. The first 5 to be named were Pluto, eris, which is a dwarf planet about the size of Pluto and notice again also doesn't have a circular orbit around the sun, has a very eccentric orbit. There is a there are some dwarf planets orbiting in the asteroid belt, which we'll talk about in just a second, series is one of those work planets. And the definition of a dwarf planet, it is more developed than an asteroid, which we'll talk about in just a second. But it's different than the known planets. So one of those ways we just mentioned is that it doesn't have a very circular orbit around the sun. It has a more eccentric orbit. 

So the definition of a dwarf planet is that it does orbit the sun. It has enough mass to assume a nearly round shape. So some smaller bodies called asteroids can have an oblong shape, but dwarf planets do have a round shape, and they have enough gravity so that they can clear the neighborhood around its orbit. In other words, Pluto has a moon that orbits around it, but it's not mixed in with other bodies. Its own size. And moons are not included in dwarf planets. If an object is orbiting around another object, it would be considered a moon and not a dwarf planet. So asteroids are miniature planets, they're leftover rocks that didn't get incorporated with the planet. They can range in size from the from a piece of sand to a thousand kilometers in diameter. But most have about a one kilometer diameter. Most asteroids are in a belt between Mars and Jupiter. And they orbit the sun anywhere from three to 6 years. And again, they are found between Mars and Jupiter and if you look at a map of the solar system, Mars is the last inner planet Jupiter is the first outer planet. So we think that these pieces of rock were just in that right spot where they were closer to Mars, so small Mars is trying to use its gravity to pull the rocks toward it, but Jupiter is so large, even though it's further away, its plain tug of war trying to pull the asteroids toward it. 

So these asteroids are in just the right spot. So where neither planets gravity can take over and incorporate them into a larger planet so they continue to orbit around the sun. Sometimes a piece of an asteroid will get close to earth. And if it falls into Earth's atmosphere, it is called a meteoroid. As it's falling through the atmosphere, it produces friction between the air particles in our atmosphere and this friction causes it to catch on fire and burn as it's falling to the ground. When it's burning, we call it a meteor and you see it as a streak of light through the sky, you may have called it a falling star or a shooting star, but it's really just a speck of dirt or rock that's burning as it falls through the atmosphere. And if the part of the asteroid reaches the earth and falls to the surface without burning up completely, it would then be called a meteorite. Sometimes meteorites are large enough to form impact craters. A comet is another object in our solar system. Comets are small bodies that are made from rock and metal, but are held together by frozen gases like carbon dioxide, water, and methane. 

Plummets have highly eccentric orbits around the sun, so they travel far out beyond the planets before they're pulled back in to their orbit. And some comets can take thousands of years to orbit around the sun just one time. When comets are very far from this done, they're just made of a solid core called a nucleus. The nucleus is the frozen part. When the comet starts to get closer to the sun, these frozen gases sublimate, the gases form a coma around the comet. And then the solar wind from the sun pushes those gases back behind the comet to make the comet's tail. So the tail of a comet always points away from the sun because it is the solar wind that's pushing the gases back behind the comet. The different pictures of comets. More than 3000 comets have been discovered, orbiting the sun, and some orbiting spacecrafts have actually reached the comets and the comets will eventually vaporize completely. 

Scientists estimate that there could be as many as 1 trillion comets held in the sun's gravity. Comets originate in one of two places. The Kuiper belt is a region outside Neptune's orbit. It's shaded in white in this picture and comets with orbital periods of 200 years or less orbit the sun beyond Neptune's orbit if something flies through space and bumps into one of these comets. It can be sent into the solar system where earth's gravity would take over and it would start or being the sun. The second place comets can originate is the oort cloud. This is a round shell around the solar system and comets with long orbital periods originate here. Notice in this picture, the tiny yellow dot represents our sun, the yellow or the red line represents Pluto's orbit, the Kuiper belt is the densely populated area in the oort cloud is a huge sphere around that. 

Again, when comments are in the Kuiper belt or the oort cloud, they're just frozen nuclei. Of the comet. And if they get bumped by something in space, they can be sent into our solar system and start orbiting the sun. And when they get close enough to the sun, they would begin sublimating. One example of a famous comet is Halley's Comet, which is one with a short year orbit, or short period orbit of about 76 years. It has a tail that's 1.6 million kilometers, and it was last seen in 1986. Meter showers are created if Earth's atmosphere passes through the remains of a comet. As the comet sublimates, it leaves behind little bits of dust and rock, so if these little particles fall into Earth's atmosphere, you can have lots of little particles catching on fire and producing streaks of light as they fall toward the earth. So if you see more than 60 meteor sightings per hour, it is called a meteor shower. And again, meter showers are usually caused by the earth passing through the remains of a comet.