 Greetings and welcome to the Introduction to Astronomy. In this lecture we are going to continue talking about the outer planets and specifically focus on their atmospheres, and of course the atmosphere is really what we see when we are looking at the giant planets. So let's go ahead and look at their general properties again, and they are made up primarily of hydrogen and helium, and that's really just like everything else in the universe. While we've concentrated on other materials, especially in the inner solar system, most things like the sun and the outer planets and most of the rest of the universe is also composed of hydrogen and helium. Also many of the hydrogen compounds note that each of these contains hydrogen, as well as other elements such as oxygen, carbon and nitrogen. And we had the Galileo spacecraft that visited Jupiter and set a probe into its atmosphere, which is the one chance that we have to actually learn something about the atmosphere. So for at least that position, that part of Jupiter's atmosphere, we have a pretty good idea of what things like the composition of the atmosphere is. Now so what do we see when we look at Jupiter? Let's go ahead and take a look here. And Jupiter, here's a nice image of Jupiter. We see it has a number of different belts and zones. So you will see different things labeled there, and the belts are the darker areas, and these zones are the lighter colored areas. Now when we look at Jupiter, we are really looking at clouds in the atmosphere. Above that there is hydrogen, but hydrogen is clear and invisible, just like our own atmosphere. So it is specific clouds that we are seeing, and the actual layers of hydrogen around it are completely invisible to us. We see, as I said, there's two parts. There's the zones, and we see, for example, labeled the equatorial zone here. And then we have the belts, which are dark colored, and you can see a number of belts here that are labeled in terms of the temperate belts and equatorial belts here and down below. So the zones are lighter colored and are rising convective currents. They are up higher in the atmosphere and often consist of ammonia clouds. The belts are dark colored, which is where the material is sinking down. They are lower in the atmosphere, and their composition is less well known. Now when we look at this, we look at Jupiter and we look like we're looking at a surface that everything there is at the same distance, but they're not. These zones are much higher up above, and the belts are further down below, so there are areas that are higher up and lower down, and we don't really get that kind of perspective when studying it here. We also do see the great red spot, which we will talk about later on. Well, let's take a look at Saturn, and what we see with Saturn is the similar type of structure. We see, but we see them less distinctly. You can see lighter and darker bands there, but because Saturn is further from the sun, temperatures are cooler, and the cloud layers are buried deeper in the atmosphere under more haze, and it makes it harder to see them. One thing we do see when looking at it in more detail, looking at the polar regions, is the polar hexagon. So we can see the polar hexagon here in this image, and the north or south pole would be at the center, and then the hexagon of materials swirling around it, which is a very interesting combination. Again, we don't normally get patterns like this. Things like squares are relatively rare in space. We tend to get everything tends to be circular or spherical, or squashed versions of those, things like ellipses and ellipsoids. So the fact that it forms here is something very interesting, and may have something to do with the fluid dynamics in the atmosphere near the pole. Now, the other planets, Uranus, is a very bland, very featureless atmosphere, and is a very stable atmosphere. If you recall when we talked about the interiors, this is one that has no interior heat source, so the clouds are essentially invisible to us. Neptune, on the other hand, has some more structure to it, so when we look at images of Neptune, has a little bit more structure. We can see some banding. We can see signs of storms and clouds that are present here in the atmosphere. If you note, there's also a difference in coloring that they appear blue, and that is Uranus and Neptune. Now, why do they appear blue? Well, it's a concentration of methane in the atmosphere. So the atmospheres are not made of methane, but have enough methane, and methane is very good at absorbing red and orange light, and not so good at absorbing blue light. So it's very good at absorbing those longer wavelengths of light, and that means what's left to be reflected back is blue. So it absorbs the red and orange lights coming from the sun, reflects back the blues and greens, and gives us this bluish-green color that we see for Uranus and Neptune, and it all has to do with the composition of their atmosphere, and especially the methane present. Now, we can also look at these in terms of a temperature profile, and this is where we can see the clouds on Jupiter. Note where the clouds on Jupiter are forming. Here's the altitude. Altitude of zero is what we see as the surface. So those three layers of clouds, which are ammonia, ammonium hydrosulfide, and water, are all within about a hundred kilometers of the surface. When we look at Saturn, we see that these are much further down, going to 200 or even close to 300 kilometers below the surface, and that means that they're much less visible when we look at them. Uranus and Neptune very similar, but remember that Uranus did not have the internal heat source, so maybe that's some reason that even though they have very similar compositions in their atmospheres, we're not able to see much structure in Uranus. It might also have to do with the fact of the way Uranus is heated because it is tilted on its side. Now, we mentioned one great storm, which was the Great Red Spot. Let's take a look at that in a little bit more detail. Here we see the Great Red Spot, which is a storm that is bigger than Earth. And interestingly enough, this is a high-pressure region, not a low-pressure region. When we talk about things like hurricanes and tropical storms on Earth, they are regions of low pressure. The Great Red Spot is instead a high-pressure region, which is what we generally associate with good, clear weather. Now, this has been present for a long time. And in fact, we have images of it going back to the later part of the 1600s. And we don't know for sure that it's always been there. It hasn't been observed continuously for the last 150 years or so, but we kind of suspect that it probably has been present for hundreds of years. However, we do know that it is shrinking. It is changing in size, especially over the last few decades. So as we look at it, and here we see some images taken from the Hubble Space Telescope from 1995 through 2014, and it's definitely has shrunk a bit. But even going back a little earlier, we can see that it has probably gone down almost by a factor of two in size. If this rate continues, it could disappear in just decades. So in a few decades, the storm could be gone. Now, of course, we don't know exactly what powers it, why it is. What is the energy source? So is it losing an energy source? Is it just dying out as storms do here on Earth? You know, after a month or two, a tropical depression that started off of Africa and came up through over the Atlantic Ocean will then eventually fizzle out and be gone and will dissipate. So is this just a much longer lasting storm? And we're just seeing the very end of it. Or will some kind of energy source recur? Will it either stabilize at a smaller size? Or will some energy source reappear and therefore it comes back and will start to grow again? These are all good questions. And I can't really tell you anything except that we've seen that it is slowly shrinking. And that's all we know for sure what might happen with it in the future. We are just going to have to watch and wait and see. Now, this is not the only giant storm in the solar system. We also have the Great Dark Spot, which was visible on Neptune. That was seen in 1989 when Voyager 2 visited the planet. Now, we didn't have the resolution to be able to see Neptune, so we couldn't study it again. But by the time in the mid 90s when Hubble was up and able to look at Neptune, it was gone. Again, we don't know how long these storms last. They could last hundreds or thousands of years and maybe we caught this one right at the end. Or they may only last a few years and it may vary from planet to planet. So we really don't have enough data yet to be able to say anything in detail about these storms. But they do occur on all of the planets. Saturn has had global storms as we see a great storm stretching across the planet here. And Uranus has a dark spot similar to Neptune. But again, remember, in order to see any structure on Uranus, we have to have a highly processed image. And here we're looking at this little section right here, which is then enhanced to see a very storm there. Again, is it something seasonal because of the tilt of Uranus? It has very extreme seasons. For several decades, one pole is pointed toward the sun. And then the equatorial regions will go through their turn and then the other pole will be pointed toward the sun. So it has very unusual seasons compared to any of the other planets. But we do see that these storms are present every place we look in the giant planets in the solar system. So let's go ahead and finish up with our summary. And what we've looked at this time is that the Jovian planets have complex atmospheres. The structures are determined by the temperatures and internal heat sources of the planets. And large storms have been seen on every single one of the Jovian planets, not just the Great Red Spot on Jupiter, but other planets as well. So that concludes this lecture on atmospheres of the giant planets. We'll be back again next time for another topic in astronomy. So until then, have a great day, everyone. And I will see you in class.