Pluto Pluto has been designated a dwarf planet and the image here you're seeing here Pluto and its largest moon Charon to scale to the United States and as you can see Pluto and its largest moon fit within the United States so that gives you an idea of how small of an object the Pluto is we'll talk about the dwarf planet characteristics in the next tutorial but here we want to talk about what do we know about Pluto when Pluto was first discovered one of the things that we always do when we discover something is figure out its motion in its orbit and it was quickly discovered that Pluto's orbit is very elongated now this image is exaggerated for emphasis but what it shows here is that for part of the time it's actually closer to the Sun than Neptune and as you can see here on the dates the last time that was true was from 1979 to 1999 Pluto's orbit takes 240 years so 1979 plus 240 so the Year 2219 will be the next time that Pluto is closer than Neptune so odds are anybody listening to this will not be seeing that happen in their lifetime so you see this where it looks like you know the orbits cross and you think oh my god Pluto and Neptune are going to collide well they're not and the main reason they're not is because of the tilt of Pluto's orbit it does have a very very big tilt now this is showing it relative to earth here but Neptune's orbits about the same it's not tilted very much either so if Pluto and Neptune were in the same location as far as distance from the Sun and angle from the Sun they're still not going to collide because one's going to be above the other so it's either going to be Pluto over Neptune or Neptune over Pluto but they're not going to hit each other if they did end up in this configuration where they're relatively close to each other that will probably do some dramatic things to Pluto's orbit because of Neptune having so much more mass but they're not going to collide Pluto has five moons and these are all probably the result of a collision so when we talked about the formation of our own moon we found that the most plausible explanation is that our moon is the result of something colliding with earth when earth was still in the formation stages Pluto all five moons composition wise look like they were knocked off of Pluto the largest moon is Sharon and this was discovered by James Christie in 1979 and this is the discovery picture and it's hard to tell but what you're looking at here that's Pluto this little bump sticking off the side that and Charon so this was the discovery photograph and obviously 1979 imagery of Pluto not very good but that was the way it was discovered in mythology Pluto is the god of the underworld and to get to the underworld you have to cross the river Styx and Charon actually pronounced Charon in mythology was the boatman that would take you across the river Styx James Christie was married to Sharon and so he combined her name with the mythological boatman to the underworld to get the name of Charon for Pluto's moon it wasn't until 2005 that we started finding other moons and the first two were discovered in 2005 Nix and Hydra and here we see imagery looks a lot better than 1979 so here we can clearly see Pluto and Charon and here we see these two little dots three days later you can see Sharon has moved in its orbit and these two guys I've also moved in their orbit from where they were before so that was the discovery of these two and continuing in the underworld theme the names Nix and Hydra come from that same mythology one thing to notice things are orbiting Pluto in a vertical plane Pluto system is like Uranus in that it is tilted about 90 degrees so we see everything in the Pluto system I'm on its side orbiting vertically around Pluto and Pluto rotates on its axis in that same orientation and then that vertical system orbits around the Sun the last two to be discovered also with Hubble imagery were Tara burrows and sticks again mythological names Kerberos was p4 Styx was p5 so the order they were discovered you can see Nixon Hydra and Cher on here so at this point as of summer 2014 Pluto has five moons and a year a spacecraft is heading to Pluto called New Horizons and that will reach Pluto in the summer of 2015 and so it's going to do a flyby it's not going to go into orbit but this will give us our first actual up-close pictures of Pluto everything we've got is earth-based and the best we've got now is Hubble but that's just outside of Earth's atmosphere in Earth orbit so who knows what we're going to find come summer 2015 what we do know because Pluto has a moon that means we know the mass of Pluto and by imaging it we know its size and if we combine those two we get the density and if we know the density then we can figure out the composition so based on that density we think Pluto is a mixture of rock and ice which sounds very familiar we saw that as the composition of comets plus a lot of moons have the same composition especially the larger moons of the jovian planets so pluto has similarities to comments and remember Pluto is located in the Kuiper belt which is our source for short-period comets Pluto sort of has an atmosphere at least part of the time when Pluto is farthest from the Sun temperatures at Pluto are negative 370 degrees Fahrenheit very very cold at that temperature Pluto does not have an atmosphere it is frozen solid the picture here is Hubble imagery of Pluto we can certainly see that there are features on Pluto that have different colors we don't know what those are so again we're waiting on New Horizons to give us some clue about what's going on at Pluto when Pluto is closer to the Sun because its orbit is elongated its distance changes enough that that affects the temperature it warms up to negative 350 degrees Fahrenheit so balmy balmy negative 350 degrees Fahrenheit but that is enough to vaporize some of the ices and that's what this picture is showing is this idea of the ice is vaporizing and kind of spewing out the gases so that develops a very tenuous atmosphere again very much like a comment when comets get closer to the Sun the sun's heat vaporizes the ice and it develops a coma comments we call it a coma here we're calling it an atmosphere but not really different as far as what's happening now that I said the atmosphere was tenuous here's our atmospheric pressure one ten-thousandth of an atmosphere remember earth is one atmosphere and so here a ten thousandth of Earth's atmosphere that's less than the amount of atmosphere where the Space Shuttle orbits or the space station orbits so it's not much of an atmosphere in reality but there are gases there and that's about all we can say about Pluto's atmosphere