all right good okay so now this next video will probably not be quite as long we're gonna talk about the first planet the planet closest to the Sun and that is mercury so let me bring up a picture of mercury real quick so here we go now these are not both pictures of mercury the one on the left is a picture of the moon and the one on the right is a picture of mercury and they are roughly the right size compared to each other and you can see here mercury is not that much bigger than the moon is it's it's actually the smallest planet and in fact if I had not had the text down here at the bottom you probably would have had a hard time telling me which one was mercury okay so mercury has a surface that looks a lot like the moon so what's the most prominent feature on the surface of mercury craters we said this a little bit further back in this mercury has the most craters at least the densest craters it's the most densely packed with craters of any planet in our solar system so number one the first number one feature on Mercury is craters now why does it have so many craters well again remember mercury is very small so it lost a lot of its heat so it never got a chance to do almost any volcanic activity there has been some evidence that there are some very small very old dead volcanoes in a few places but basically it's pretty volcano free so it never got a chance to erase craters so craters everywhere okay other than that like we just got done saying there's not gonna be mountain ranges here and if it never really got to form volcanoes it's not gonna have a lot of mountains so overall mercury very flat and so the land between the craters is just called flat land but it uses the the technical term for flat land so what we call the land between the craters is the inter crater plains so let me get that up here the inter crater plains and all that really means is Plains means flat land and enter a crater it means between the craters so what we call the flat land between the craters we call it the inner crater plains basically all it is but it's a very very very flat planet compared to earth okay now a much more interesting feature on Mercury is one that you probably cannot see very well remember this is a picture from your book so you can zoom in on this picture if you look in your book later it's figure it's in Chapter seven but you look for that but if you look really really really close there's a couple of little what looks like long wrinkly lines Criss crossing across this let me see if it's a little bit easier to see in the next picture so this is a close-up picture of of one of the craters and if you look real close let me see if I can point it out there's some wiggly lines coming across now some of these are from the crater but you can see here some of these wiggly lines are going across here and those wiggly lines can extend for miles and miles and miles and miles now don't worry if you can't actually see it you might have to just trust me on that but those long wiggly lines are called hills or ways right there they're hills long Wiggly hills and they're called scarps so let me write that up because that's probably a word you've not seen before so the long wrinkly Hills are called scarps and those formed in a different way than the hills do on earth because Hills form on earth from plate tectonics okay hills form on earth from plate tectonics but is there plate tectonics on Mercury we already said no right so how do these form well these must have formed really really really long ago very early on in the history of this planet and what we what we're pretty sure happened is remember compared to the other planets because mercury is very very small it cooled off much quicker does that make sense it cooled off much quicker and does anybody know what happens to the size of rocks as they cool let me put that up in the in the chat what happens to the size of rocks as they cool yes somebody said it they get smaller they get smaller so what we believe happened is that as mercury first started to solidify once its crust fully solidified because it was cooling down so quickly we believe the crust shrunk so can you figure out what the scarps are if the crust shrunk why are these long Wiggly hills all over that crust what about shrinking could make Wiggly hills I I think you guys might be overthinking a little bit let me let me let me give you a metaphor oh there there we go that it rock has a hard time compressing that's uh that's part of it think about a grape if you uh shrink a great what do you make what do you make from a shrunken grape like if you try that grape out a raisin and what do you got all over the surface of a raisin yeah yeah that's it a raisin is covered in wrinkles because the surface couldn't shrink uniformly so essentially the scarps on Mercury our raisin wrinkles from the shrinkage of the planet so let me uh I think I have a picture that shows that so if you look right here they're trying to show that as the planet shrunk its surface God all wrinkled up does that make sense all right okay now oh and by the way okay so scarps our raisin wrinkles so if I ask how did the scars form you can basically told me that the mercury shrunk like a grape shrinks when it forms a raisin and the scarps are just raisin wrinkles on the surface it's a little bit different than the somebody asked if the surface of mercury dried out there my metaphor is breaking down a little bit here the surface is shrinking just because rocks shrink when they get colder and they grow when they get hotter so it's not necessarily that the crust is drying out here although it is solidifying all right okay so here's the next question I have while we're talking about the inside of mercury let me show you some pictures that compare the different planets and if we look in here on all these pictures they've combined the two cores into one just so they can compress the picture here so on earth we've got both cores the mantle and the crust and what do you notice about the pattern on Venus compared to earth they're roughly the same whereas on Mars here again still roughly the same in terms of proportions crust mantle so eye crust mantle core same basic proportions but what do you notice about this cutout of mercury here mercury is one of those layers is much thinner than it is on the other planets which layer is which layers different here on Mercury yes yes somebody got it clearly Mercury's got a whole bunch of core not a lot of mantle so compared to the other terrestrial planets the iron content of Mercury is much higher and we're not yet fully sure why that is we just know that overall mercury has a very high density from all that iron and the prevailing idea the prevailing hypothesis although this hasn't it's not unanimous yet is remember all of the planets formed from large essentially the chunks of rock and metal slamming together and what we think happened to mercury was well just before it fully formed when it was it probably was actually a little bit bigger than it is now but it was hit by something at least half its size maybe even bigger and normally we think of these kinds of collisions causing very big craters on the surface but that kind of Packt probably completely destroyed mercury okay so we think that at some point mercury was completely torn apart by a collision and I see a question up there I'll come back to that in just a second and compared to the other planets does mercury have as much gravity no so what we think happened on Mercury is because the gravity is so low the lighter materials essentially flew away because of the impact of that collision and the heavier materials stayed behind and what's heavier the iron or the silicates yes a couple you guys are getting it it's the iron so the iron it was easier for the iron to stay behind and reform a new mercury and only a little bit of the silicon materials stayed behind to form the mercury we have today and like we said earlier the stretching of the of the planet from the Sun keeps a little bit of that core does tiny bit of that cord artificially still liquid but it's so deep down that it can't form things like volcanoes okay and somebody asked if being much more iron contributes to it being more easily stretched by the Sun and I'll just be honest I am Not sure on that so I won't be able to answer that particular question now somebody's asking how did scientists figure out that mercury was destroyed and reformed uh remember I said that that was the leading hypothesis we do not yet have proof that that happened but we do know that the planets did form from collisions so it makes sense that something like that could have happened and it makes that could be a way to explain why this is but again we don't know for sure if that happened although in computer models we can figure out if that was the scenario what would mercury have to have been like and what would it have to have been hit by to end up the way it is now and the all of that lines up with things that are at least plausible that they could happen so yeah I can't say for sure that that happened to mercury but that is the leading idea at this point okay right now here we go here we go so we're done with the inside of mercury there's not too much more to say about mercury um remember does mercury have an atmosphere we talked about this in class does it matter member if mercury has an atmosphere oh so while you guys are answering that about the atmosphere somebody did have another question about how do we know how big the core is if you remember in class we said that we can compare the density of the material on the surface of the planet to the overall density of the planet and the by comparing those two numbers because Mercury's average density is a lot higher than the surface we know that the stuff inside has to be much more iron rich than inside the other planets so it's basically by looking at average densities compared to surface densities and are we 100% exactly right about exactly where the core cuts off probably not but we're at least close looks like we might have another question coming in oh that was that was that over there okay now so some of you were mentioning that mercury does not have an atmosphere and that is basically correct there's I mean there's some wispy gas here and there but not enough to really be called an atmosphere and that's because mercury is it has such a low gravity it has a hard time holding gas down and it's so hot because it's close to the Sun that the gas that is there tries to move around so quickly that it's easy for it to fly away to space if you're not good at holding it down so too hot at the surface and not enough gravity so there's not an atmosphere now what kind of temperatures would you expect mercury to have yep hot and why is it so hot because it's close to the Sun the average daytime temperature of mercury is around 660 degrees Fahrenheit although some parts near the equator can get up to around 800 so mercury is very hot so are we ever gonna land anybody on mercury no we're never gonna learn land anybody on mercury because they would absolutely die they would burn to death so a lot of people say okay if if it's too hot on mercury how about I land on the on the nighttime side cuz what happens to the temperature at night it gets cold would you want to land on the nighttime side of mercury and why not I'm gonna say no you don't why not why don't you want to land on the nighttime side of mercury yes um you guys are getting this even though we think of mercury being a very hot planet the nighttime side gets down to negative 260 degrees on average negative of 260 degrees Fahrenheit on average so if you landed on the nighttime side of the planet what would happen yet freeze to death and then eventually your body would spin to the other side thaw out and then cook like eggs and then you're you're cooked eggs body would go back to the nighttime side and refreeze and then it would melt again on this side so does earth drop like 900 degrees like this every day do we drop 900 degrees at night no we don't so here's my final question about this why is it that mercury drops a greater temperature than any other planet at night it gets so hot during the day but it gets so cold at night why you yes somebody got it no atmosphere to hold heat so you probably have heard the greenhouse effect which we have on earth that helps our planet trap heat for the nighttime side also mercury rotates much more slowly than we do and so it has a longer time to cool off so basically the lack of an atmosphere makes it so that this planet drops more temperature at night than any other planet now here's my oops did something did something there we go here's my last thing I want to say about mercury do we expect to find water on the surface in mercury No why not what happens to water in those kind of temperatures it would freeze in the nighttime side but that ice would eventually come over to the daytime side and it evaporates right so it will evaporate and because the gravity is so low on Mercury it won't be able to hold on to that water vapor and so that water vapor will escape to space so any water that mercury may have had at any point would have only lasted a very short amount of time before it was lost to space but it turns out we did find some water on Mercury recently just in the last 10 years we found ice on Mercury where would we expect to find ice on Mercury where's the only place it could possibly be and here's something important it's not underground it's ice just sitting right there on the surface some of you've got so it can't be the night side because the night side will eventually come to the dayside and this ice if we find it now it must have been sitting there for billions of years so it's at the poles yes it's at the poles but the poles themselves are hot enough for you to diet from the heat at the poles so the poles in general are too hot for ice to form so where is it well remember what's the main surface feature covering the entire planet what's all over the surface of this planet craters yes umm you guys are getting it's craters there there there are scarps there but those aren't as prominent as the craters so there are craters at the poles okay and what essentially happens is imagine I'm mercury and the sunlight is coming in from over there you can actually can kind of see the sunlight coming in from over there imagine I had a crater on my head if I spun in place would this crater ever point towards the Sun with this crater ever point towards the Sun like the bottom of this crater no correct it would never took point towards the Sun and at the bottom of that crater never points toward the Sun then that means that the bottom of that crater is always in shadow and that means that bottoms of those craters will be cold enough for ice to form that said if we were to go visit mercury at those poles and knock down the edge of that crater when the sunlight came in it would immediately vaporize that ice so this is only a very small amount of ice and we're still studying it right now yeah any questions