Outer Planets
The outer planets are all similar. They are all gas giants that are made primarily of hydrogen and helium. They also all have at least one ring and many, many moons. The first two can be seen from Earth without a telescope and have been known since earliest times. The third was discovered in 1781 and started a discovery frenzy. The last was discovered in the mid-1800s using math and was later confirmed with a telescope.
Jupiter
Jupiter is the king of the gods in Roman mythology. It's a very fitting name (and a lucky one) as Jupiter is the largest planet in the Solar System. This a lucky circumstance when you consider that it was named before anybody knew just how big it was. It was just a fairly bright object in the sky. But it works. Jupiter is so big, that if you put every object in the Solar System (except the Sun, of course) inside Jupiter, there would be room to spare. 1,000 Earths can fit inside. It's big. It also has a big storm. In the image above, you can see a red spot in the lower right hand corner. That's the storm that's called the...Great Red Spot (I know, brilliant naming). This storm has been as big as 3 Earths at times in its history. But it does seem to be getting smaller recently. Oh, and Jupiter has rings. Not many, but they are there. Jupiter has the most moons at 63 (that we know of). |
Saturn
The "Lord of the Rings" is not a book, but the second largest planet. Saturn has been known from the dawn of man as something that moves in the night sky. In the early 1600s, we noticed its most striking feature for the first time...the rings! It's hard to get past them, but when we do, we find that the planet itself is pretty spectacular, too. It's the least dense planet. If the Sun were a giant tub of water and all the planets tossed in like toys, only Saturn would bob at the top. It's less dense than water, but we don't know why. It also has a crazy storm at its north pole: a hexagon! The storm has 6 sides! Saturn almost matches Jupiter's moon total with 62 total (that we know of). Check out this site for a wonderful tour of Cassini's trips around Saturn! |
Uranus
Besides being the most unfortunately named object in space, Uranus is actually the first planet that was discovered. In 1781, Sir William Herschel (we'll hear more about him later) saw a moving object in his telescope that was past the orbit of Saturn. He realized it was a planet and decided to name it George after King George III (you know...that guy we fought against in the American Revolution). But it was decided to stick with the mythology system and the planet was named after Saturn's father, Uranus. A truly bizarre planet, Uranus is sideways. In the image above, you are looking straight at one of the poles while the rings are circling the equator. Its 29 moons (which are named after Shakespeare characters) orbit the equator as well. Someday, we may find out why it looks like this, but for now...we don't. |
Neptune
Neptune is the last official planet in the Solar System. It's also slightly familiar looking. It's blue, like Earth. Why? We don't know. Earth is blue because of liquid water. Does that mean Neptune (the god of the sea, I might add) also has liquid water? Perhaps, but more than likely it's deep beneath the gas clouds. Either way, it's really cold. We found it using math. We figured that something else was out there due to irregularities in the orbit of Uranus. Calculations were done (by hand!) and telescopes were told to look in a certain spot at at certain time and we'd find it. We did! Yay for math! We, unfortunately, don't know much about Neptune. We've never sent anything to orbit it. Voyager II flew by in 1989 and took practically the only pictures we have of it. After this year, we'll know more about Pluto than Neptune. Someday, we'll orbit it and learn all of its secrets. We do know that it has 13 moons. |
Marvelous Moons
Of Jupiter's 63 moons, 4 were discovered about 400 years ago. Through his telescope, Galileo saw 4 dots orbiting Jupiter. These became known as Ganymede, Callisto, Io, and Europa. Ganymede is the largest moon in the Solar System. It's bigger than Mercury, but it orbits Jupiter and not solely the Sun; so it's a moon. Callisto is slightly smaller than Mercury but has more craters than any other Solar System object. Io has more active volcanoes than anywhere else in the Solar System. Because it's so active, we don't know how old is. The surface is constantly being renewed. Europa has a thick layer of ice surrounding an ocean of liquid water (maybe). We won't know for sure until we go there and drill a hole. If there is liquid water and a heat source of some kind (interior of the planet for instance), then there may be life. It's an intriguing possibility.
Two of Saturn's 62 moons stand out from the rest. Titan is the biggest and 2nd biggest in the Solar System. What makes Titan so amazing is that it has a thick atmosphere of methane. It's a moon with an atmosphere! Also, it has methane rain and methane snow (liquid and solid). Combine that with the gaseous methane in the atmosphere and you have solid, liquid, and gas of a substance at the same time. Sound familiar? It should. We have that too. Except for us, it's water. Even more amazing, there are methane oceans with waves and solid land. If we want to find truly alien life, I think Titan is the best option. The other of Saturn's interesting moons is Enceladus. This moon regularly has volcanic eruptions of ice and water! It makes you wonder what's underneath that's causing the eruptions and where the water is coming from.
Neptune's largest moon Triton is odd because it is in a retrograde orbit. All 12 of Neptune's other moons go one way around the planet while Triton, alone, goes the other way. We think that it's a captured Kuiper Belt Object because of this. Oh, and we also think it, too, might have liquid water somewhere beneath it's surface.
Of Jupiter's 63 moons, 4 were discovered about 400 years ago. Through his telescope, Galileo saw 4 dots orbiting Jupiter. These became known as Ganymede, Callisto, Io, and Europa. Ganymede is the largest moon in the Solar System. It's bigger than Mercury, but it orbits Jupiter and not solely the Sun; so it's a moon. Callisto is slightly smaller than Mercury but has more craters than any other Solar System object. Io has more active volcanoes than anywhere else in the Solar System. Because it's so active, we don't know how old is. The surface is constantly being renewed. Europa has a thick layer of ice surrounding an ocean of liquid water (maybe). We won't know for sure until we go there and drill a hole. If there is liquid water and a heat source of some kind (interior of the planet for instance), then there may be life. It's an intriguing possibility.
Two of Saturn's 62 moons stand out from the rest. Titan is the biggest and 2nd biggest in the Solar System. What makes Titan so amazing is that it has a thick atmosphere of methane. It's a moon with an atmosphere! Also, it has methane rain and methane snow (liquid and solid). Combine that with the gaseous methane in the atmosphere and you have solid, liquid, and gas of a substance at the same time. Sound familiar? It should. We have that too. Except for us, it's water. Even more amazing, there are methane oceans with waves and solid land. If we want to find truly alien life, I think Titan is the best option. The other of Saturn's interesting moons is Enceladus. This moon regularly has volcanic eruptions of ice and water! It makes you wonder what's underneath that's causing the eruptions and where the water is coming from.
Neptune's largest moon Triton is odd because it is in a retrograde orbit. All 12 of Neptune's other moons go one way around the planet while Triton, alone, goes the other way. We think that it's a captured Kuiper Belt Object because of this. Oh, and we also think it, too, might have liquid water somewhere beneath it's surface.