 Greetings and welcome to the Introduction to Astronomy. In this lesson we are going to talk about the planet Venus. In many ways Venus is considered the twin planet of the Earth because they have a very similar size and mass. But in other ways we'll find that Venus is quite different. That is intensely hot and its atmosphere is much thicker than the Earth and contains very corrosive materials. So let's start off a little bit with our understanding of what we have explored on Venus so far. Venus has been one of the better explored planets in the solar system. Venus, like Mars, has had a number of spacecraft visited. And if we look at just a few here, in fact, Mariner 2 was the very first spacecraft to visit Mercury back in 1962. So only five years after the first satellites were launched into Earth orbit, less than five years we already had craft visiting the nearest planet to us, which would be Venus. And that was the first successful planetary encounter. In 1970, the Venera 7 craft was the first to send back information from the surface of Venus. It actually landed on the surface and was able to take images for a short time before it succumbed to the intense conditions on Venus. And another one to look at is the Magellan craft. From 1990 to 1994, and that craft took detailed radar maps of the surface and gave us our best understanding of the planet today. So while we cannot see through the atmosphere of Venus, it's constantly shrouded in thick clouds, we can use radar waves to be able to see. It's only a few of the Venera craft that were able to land to give us direct images of the surface, but we have been able to map the entire surface through radar methods. So let's take a look at what we've learned about that. And here is a radar map of the planet. So this shows some of the surface features. We have two different sections. We have lava plains, which would be similar to the ocean basins. Those would be seen here in the blue and green. We can see some of them around here and some over here. Those are the much lower lying basins. So they would be similar to our ocean basins, but no water. So there is no water there. They are not filled with water or anything, but they are the lower lying areas. We also note that there are no sign of plate tectonics on Venus. So it does not seem that Venus actually has any kind of plates. Now that's interesting. It's about the same size as the Earth, so we expect it would cool off to a similar amount and would still have some heat in the interior, but apparently something about Venus does not allow it to generate plate tectonics. Now the other type of terrain that we see is the mountainous terrain. And we see a couple different continents here. The continents in the lighter greens and yellows, there is Aphrodite, which is the equatorial region over here. Aphrodite Terra is about the size of Africa. So that's one of them there. And then we have the Ishtar Terra, which is far north, and that's way up here. And that is near closer to the polar region and includes the highest region on the planet. The Maxwell-Monts, which are right in the middle here, are the highest level region going up 11 kilometers or about 7 miles up above the surface of Venus. So that is much taller than mountains that we get here on the Earth. We also see, when we look in more detail at some of the surface features, this kind of shows it overall, and you can imagine that if you were somehow able to flood Venus with water that it would be these lower lying areas here and here and all around it that would flood with water. And Ishtar and Aphrodite and some of these other higher areas would be the continents, would be the areas that would actually be up above the water level. Now, let's look at these, some of the features in a little bit more detail. What kind of features do we see on Venus? And we see craters and volcanoes. So two primary features we see about a thousand craters on Venus. That's a lot more than we saw on Earth, Earth had less than 200. So that tells us that the surface of Venus is older than the Earth, but still relatively young because we see vastly more craters than that on say the moon or Mercury. So it is a relatively young surface, and we do see that the craters as shown in the image here are sharp and fresh looking. And that is because of the lack of erosion. So no very little wind, very little water erosion, no water erosion on Venus. We also see lots of volcanic features. In fact, Venus is dominated by volcanic features. So when we look at some of those here, we do see things like syph moms, which is similar to the Hawaiian volcanoes, which is a hotspot volcano. That means it is a weak spot in the crust, and the lava has been able to flow up through it continually. And we have some evidence that these volcanoes are, if not active today, still have been active in the very recent past. So unlike volcanoes on say Mars that have been extinct for billions of years, volcanoes on Venus have probably been active within the last few million years if not currently active today. And as I say, Venus is dominated by these volcanic features. So some of the other features that we see on Venus as well are also volcanic, and that would include things like the pancake domes. And we can see one of those here. Pancake domes are flows of very thick lava. So it's much thicker lava pushing up and filling out the region. They're still volcanic in nature, but it's a much thicker lava, very thick flowing that fills these regions. And they come up sort of as the domes and are known as pancake domes for their little round appearance, kind of the shape of a pancake. Now the other one that we see is the coroni, and we can see an image of those here. And those are more a bulge in the crust. So material pushes up and we can see some of the cracks that occur there. And even some of the pancake domes around it. But we get some of the cracks in the crust where the material has bulged up and lava did not make it to the surface. So it was not able to break through, but it was able to push the crust up over time and cause a bulge in the crust. So we looked a little bit about the surface features of Venus. How about its atmosphere? So let's look at the atmosphere of Venus here. And in the atmosphere of Venus, we can look first of all at its composition. And it is quite different than the Earth's. It is 96% carbon dioxide, 3.5% nitrogen. No things like oxygen at all in it. And it is very, very dense. It is a very high pressure, 90 times the Earth's atmospheric pressure. Which would be the equivalent here on Earth of the pressure a kilometer below the ocean surface. So if you were to go down a kilometer below the ocean surface, that's the pressure that you would feel standing on the surface of Venus. It also has very corrosive compounds including things like sulfuric acid, which is one of the reasons that Venus was never able to be landed on for a long period of time. We've explored the moon for a long time. We've had rovers on Mars for years. But Venus, we've only had craft land on it for a very short time because of the intense conditions. And sulfuric acid and the high temperatures and pressures will slowly eat away at the craft and destroy it. So the craft were not able to survive a long period of time. And speaking of the temperatures, the temperatures get to be over 700 kelvins. And that is just a tremendous temperature, hot enough to melt lead. So while it wouldn't necessarily melt any, just any metals, it's hot enough to melt lead. Meaning, again, damage will still cause damage to components that are not used to such high temperatures. Now when we look at the atmosphere of Venus, we can look a little bit about the cloud layers that we see here. And on the surface, down in its troposphere here, we see that the temperature rises very rapidly. This is the temperature in Celsius, so reaching up to 500 degrees Celsius near the surface. It then cools off as you go further up. So it's a much simpler atmosphere than the Earth's. We do get hazy and cloud layers of sulfuric acid. So when we see clouds, we think of clouds here on Earth as being water. We do not get that. We get the cloud layers, our sulfuric acid clouds. But when you get down low enough, down below about 30 kilometers, or about 20 miles, the troposphere is clear. So while you can't see up above the clouds, it's not like the surface is foggy. The surface is nice and clear because all those clouds are higher up in the atmosphere, many miles up. But they do prevent us from being able to see it. Now the temperatures that we see on Venus are essentially uniform. There is really, it doesn't matter where you are if you're in the equatorial regions or the polar regions. And it doesn't matter whether it's a day or night. Over time, the thick blanket of Venus's atmosphere has just smoothed out all the temperatures. So it really doesn't matter where you are. The temperature is going to be essentially the same. Again, whether you're at the pole, whether you're at the equator, whether it's a day or whether it's night, you get very little atmospheric changes, vast difference from what you get here on the Earth. So the last thing we want to look at for Venus is why is Venus so hot? Why does it have this very high temperature? And in fact, the temperature was measured in the 1950s as being 700 Kelvin or about 800 degrees Fahrenheit. And if you think about that and a high oven, you put a oven on it at 400 degrees is a pretty hot oven. This is twice that heat. So incredibly hot baking temperature. So again, it gives you the idea as to why the spacecraft could not survive. This is due to the greenhouse effect. Remember what the atmosphere of Venus is made up of. It is 96% carbon dioxide. So it has a very high concentration of carbon dioxide, which has caused a vast increase in the temperatures. This is what we know as the runaway greenhouse effect. Perhaps long ago, Venus was similar to the Earth, and it had a lower atmospheric pressure. This would have been very, very early in its history. However, what could happen that you increase the temperature a little bit, and that could happen with Venus being a little closer to the Sun, that puts more water and more carbon dioxide into the atmosphere, and the effect can become amplified, causing more and more heat to be retained by the atmosphere. So more and more infrared is trapped by the water vapor and the carbon dioxide, and that raises the heat, which vaporizes more of any oceans that may have existed in the ancient past of Venus, and puts more water vapor into the atmosphere. Higher volcanic activity would spew more carbon dioxide, and that again, there'd be no way to get rid of that as you can using water here on the Earth. So it becomes an amplified effect, and eventually it does reach an equilibrium, but at a very high temperature, at this case, 700 Kelvin or 800 degrees Fahrenheit. So it does reach a balance. It's not that Venus is still getting hotter and hotter today. It does reach a balance just at an extremely high temperature. So let's finish up with our summary. So what have we gone over here for Venus? First of all, Venus has been explored by a large number of spacecraft. We only looked at a couple, but there have been dozens of spacecraft that have visited Venus. The surface does have some similarities to the Earth, including a number of volcanic features. We saw impact craters on Venus more than on Earth, but less than on the Moon or on Mercury, and they are very fresh because there is a lack of erosion. The atmosphere is very stable down low, so we don't get things like wind, and we don't have any water to cause water erosion on Venus. And finally, the runaway greenhouse effect has heated Venus' surface to very high temperatures. Hot enough to melt lead and is one of the reasons we do not significantly explore the surface of Venus. So that concludes our discussion of the planet Venus, and 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.