Charon, Pluto's Companion: What We Learned from New Horizons

good evening everyone my name is Andrew frack Noi I'm the emeritus chair of astronomy here at Foothill College and it's a real pleasure for me to welcome everyone here in the Smithwick theater and everyone listening to us or viewing us on the web to this lecture in the nineteenth annual Silicon Valley astronomy lecture series tonight's program will be about Pluto's mysterious moon Charon our speaker tonight is going to as part of the team that's been exploring the world of Pluto with the new Horizons spacecraft and I will introduce him more formally in a second but let me just say that the prod this series of programs is sponsored by four worthwhile organizations that will hope you'll get to know more about the Foothill College science math and engineering division the NASA Ames Research Center one of the premier NASA centers in the country the Astronomical Society of the Pacific a venerable organization in public outreach and the SETI the search for extraterrestrial intelligence Institute and were grateful to all of them for their sponsorship tonight's speaker is dr. Ross Speier a planetary scientist with the Carl Sagan Center at the SETI Institute and also at NASA's Ames Research Center his interests include the surface features the surface processes remote sensing and photography of the solid bodies in our solar system as he likes to say if you can stand on it he's interested in what it's like and how it got that way he was a participating scientists with the Lunar Reconnaissance Orbiter camera serves as a co-investigator with the highrise instrument on the Mars Reconnaissance Orbiter and has worked to help certify safe landing sites for Mars Landers and Rovers starting with the spirit and Rover's he's also a member of the new horizons science team that explored the Pluto system and is currently exploring the Kuiper belt of icy chunks beyond Neptune he is going to speak tonight on Sharon Pluto's companion what we're learning from New Horizons it's a privilege for me to introduce to you dr. Ross Baier thank you Andy thank you all right well thank you for coming out this evening in the rain is they previously talked about tonight I'm going to talk about a small icy world that orbits far from the Sun and in the summer of 2015 surprisingly almost four years ago now I can't believe that it's been that long we flew through the Pluto system with the New Horizons spacecraft the the diagram that you see up there in the right now a lot of times you'll see spacecraft shown this way as artist's conception as they fly through the solar system but I often like to think about spacecraft as they are when they're real on the ground and this is an example of the New Horizons spacecraft when it was at the Kennedy Space Center right before launch these engineers are prepping it for launch it's a power system is being connected and it's about ready to get put on the spacecraft right it's about the size of a grand piano and this is also an opportunity for me to tell you about how important people are to space exploration as the p.i of our of New Horizons Allen Stern often likes to say space exploration is a team sport and that is certainly true for New Horizons although I'm up here in the spotlight this evening talking to you about the science that we've done a whole team of scientists have worked with me to come to these conclusions and behind that team of scientists are the flight engineers and and the others that have navigated us from the earth to the Pluto system and beyond and behind them are engineers like this that helped launch the spacecraft that helped build the spacecraft and to help all along the way so what happened after the spacecraft left the earth well this is a brief map of where went and how far it went it launched in January 2006 it flew by Jupiter in 2007 computer system in 2015 in just this new years we flew by our first Kuiper belt object mu 69 now our passage through the Pluto system was fast we were on a rail riding that red line out of the solar system and so Pluto and Charon and all the moons of Pluto zipped by very quickly and we tried to take photographs and measurements as we sped through the system and of course Pluto was certainly the star of the New Horizons show and it did not disappoint not by any means in 2015 I had only been with the new horizons team for about six years and of course others had been working on new horizons before it even was New Horizons to get it made and built and been involved with New Horizons for decades and even they were overwhelmed with what we saw and what we learned but tonight I'm not going to talk so much about Pluto only the fact that it has this really interesting satellite called Charon that we're going to talk about tonight but before I can really get into Charon we kind of need to get some basis for how big Charon is what it's like so I present to you here a scale portrait of some objects you should be pretty familiar with you live on one of them the other one we see in the night sky very frequently the moon and all these are to scale right and so you can see Pluto and Charon over there in the bottom right and Pluto is much smaller even than our own moon all right to give you an idea of how big these worlds are still very interesting in their own right but an interesting thing about Pluto and Charon is the fact that they are a large kind of binary pair not unlike the earth in the moon but also different in many ways so to get an idea of how they really are related to one another I'm going to show you an image of these worlds scaled together so now I've made Pluto and the earth about the same size and you can see how big Charon is compared to Pluto and how big the moon is compared to the earth and you can tell that Charon is a lot bigger relative to Pluto than our moon is to the earth right in fact Pluto Sharon's radius is 51 percent of the size of Pluto right so it's big it's almost half as big as Pluto itself whereas our moon is only about a quarter it's 27% its radius as 27% the size of the earth the other thing about the two this is how far apart the moon orbits from the earth and how far apart Charon orbits from Pluto in the very bottom which you can probably just barely see on the left I have the earth and Pluto and all the way over on the right you can probably barely see it is the moon this is how far away the moon orbits from the earth in distance right so the Earth's radiuses are gonna be our measuring stick the moon orbits 60 Earth radii away from the earth it's really far right it took the Apollo astronauts three days to fly there whereas Charon is only about 16 and a half Pluto radii away from Pluto so it orbits much closer and it's much bigger and the interesting thing about all of these things we often think about objects orbiting other objects in the solar cell right the planets go around the Sun the moon goes around the earth but that's not really quite true it's a very polite white lie that's often told just to get you seated right what really happens is when two objects are going around each other they really orbit something called the common center of mass often astronomers will call it the berry center of a system and this is not terribly different from the way that you might have two ice skaters right so here's a an image right you have these two ice skaters and they're holding hands right and they're spinning around right and they're not really going one around the other because the ice skaters are the same size right they're both adults right and so they're really kind of going around or orbiting this central part maybe where their two hands meet in the middle but if they're not both adults with one of the ice skaters is an adult and the other one is a child right then the center of mass right the the place where they kind of go around is closer to the larger object right and in this case maybe inside that larger object right and you can see that if you go to the ice skating rink right little kids are whipping around and the adults is kind of in the middle or if you have two adults right there'll be coal orbiting and so this is true of course in our solar system in our Earth Moon system and in the Pluto Sharon system in fact this diagram is of course not a diagram of ice skaters this is actually a diagram of the earth in the moon because the common bury Center of the Earth Moon system is about 75% of the radius of the earth away from the center of the earth the earth actually does this wobble with the moon when the moon orbits every month you don't notice it because the earth has so much gravity it doesn't really we don't notice it you have to be able to do a lot of precise measurements to even detect that and so when we take this concept and we go out to Pluto since Charon is so much bigger it actually drags that barycenter out from outside the surface of Pluto and Pluto and Charon orbit kind of CO or 'but this spot in space this is a diagram made by one of my colleagues at the SETI Institute mark Showalter and it shows the other satellites of Pluto spinning around and the thing that you may notice is that mark has put little white dots on one side of each object so you can see kind of keep track of what's spinning where and as you know the moon when you look up in the night sky the moon always looks the same because the same face of the moon always faces the earth it's called being tidally locked right so everyone everywhere on the earth looks up and they always see the same side of the Moon right but if you were stand on the moon and look back in the earth of course the earth is spinning underneath the moon so you could see different parts of yours from the moon and that's why everybody around the earth knows that there's a moon because they can see it from no matter where they are yeah but if you were on Pluto and you looked up at Charon you would always see the same face of Charon okay great it's just like here on the earth but if you lived on Charon and you look down at Pluto you would always see the same face of Pluto and more importantly if you lived on Pluto at the white dot Charon would always be in the sky always it would wane and wax but it would always be in the same spot in the sky and if you happen to grow up and live on the other side of Pluto from the white dot and you grew up and you got a job and you moved around a white dot city suddenly you'd be like whoa there's a moon because you would never see a moon on the other side of Pluto you just wouldn't all right so that's an interesting entree into Pluto's dynamics but none of that actually matters to the geology which is what I'm really here to talk about but the other thing I need to divert into is about how pronouncing the name of this moon right I pronounce it char on and those of you with the classical education or those of you that are in fact Greek will roll your eyes and say oh that's not how you pronounce that because what you think of when you see this word is you think of this guy the boatman of the Dead in classical Greek mythology and so since you know that that word is associated with classical Greek mythology and you know that other words that we have in English that come from Greek like chaos start with a hard ch right chaos you would assume quite correctly quite correctly that this word also starts with a hard K and it would be pronounced Karen but that's only because you know perhaps part of the story the other part of the story comes from the fact that when we discover when human beings discover new objects in the solar system they have a wide latitude of how to name their new object now there are rules of course largely object more rules there are and one can say so when Sharon was discovered by this guy this is Jim Christie in 1978 and in 1978 astronomers looked at photographic plates because they didn't have computers so much this is Jim in 1978 and Jim was taking observations of Pluto from the Naval Observatory and of course Sharon on the right as we know it today on the left here is a picture of Pluto and Charon right right so astronomers of course they look at photo negatives they don't bother generally to develop the plates so stars are dark instead of bright but you can get over that what Jim noticed is that if Pluto was a planet of course which everyone knew by 1978 it should just be a bright dot in his telescope right but what Jim noticed is that there was a bump on Pluto and a lot of other people had seen this and they thought oh there's just something funny about the plate that night or something but Jim took a lot of observations and Jim noticed that the bump kind of moved around Pluto like a clock and what we know today is that Pluto system that we were just looking at right Pluto Pluto system is tilted relative to the plane of the solar and so when we look at Pluto we see the moons going around just like we saw in that that image that I showed you before and so what's happening is that bump is Charon going around Pluto and that's what Jim detected in his photographic plate right and so Jim found a new moon right it's a big deal big deal 1978 and so Jim had the ability it wasn't just Jim he also worked with the Jama named Robert Harrington who's also crow Terabithia with the discovery but Jim of course was married this is a dark picture sorry didn't work out so well it's an old photo so Jim of course was married his wife's name was Charlene but Charlene was too long no one called her Charlene everyone called her char right and Jim thought wow I'd really love to name this after my wife but Jim also left science right he was an astronomer he loved physics and he loved protons and electrons and he thought that words that ended with O and we're really good words right there were good science E words right and so Jaron thought so Jim thought I'd really like to call it char on after my wife and after science right and so you know Jim loved his wife Jim loved science but he didn't maybe know Greek mythology so well and so we can only imagine his delight when he learned that this word was a great word to use to name something that was orbiting something named Pluto right so that's why many astronomers and you heard Andy pronounce it this way to pronounce it char on because that's how Jim pronounced it because he named it after his wife and there they are today still alive still doing great in Flagstaff all right so a lot of times people ask me what I do for a living and I tell them that I'm a planetary scientist and that usually is not super helpful for people right I'm a scientist that doesn't really give them an idea of what I do so sometimes I tell them that I'm like a geologist for other planets and they're like okay that also necessarily doesn't help them because they maybe don't know what a geologist does they know it has something with rocks right and so on good days on my best days I'm like Ansel Adams in the solar system right my computer screens are full of beautiful photographs and data from planets in our solar system right on bad days my computer screens are full of spreadsheets and documents and reports just like anybody else's bad days but even planetary geologist and and geologist for other planets may not be super helpful to people and so really what I am is a crime scene investigator right I have photos and data and I have to find out what happened right just like a detective or a crime scene investor they show up and there are clues and they try and figure out what happened right and so before I can really bring you along on this journey of how we figured out what's going on on Charon I have to train you a little bit right so we're going to work through some planetary crime scene investigations just to kind of get you warmed up all right so here's our first crime scene it's the earth just be easy rights the earth we have here some trees in the foreground surrounded by I'll give it you a plain of basalt all right what happened here ah very good but when what came first the trees or the lava the trees very good so the sharp-eyed among you may notice the smoke plumes in the background or even some of the cherry red spots in the foreground although this isn't a great photograph and so this lava is fresh right so certainly the trees came first the lava came after but one might wonder you know lava versus trees lava is pretty much gonna win why do we still have trees in this spot and the answer to that question is because the trees are on a little hill and so the lava flowed around and left the trees and the lava is around them okay great good first start I'm liking it you're doing great let's try another one a little harder this is a photograph of Canyonlands National Park in Utah lovely place I highly recommend going there but what you'll see here is a sandstone area here see this very regular grid of cracks and joints as geologists like to say and you see these big lays between the sandstone is very straight very empty lays as if someone took a giant rock clipper and just shaved off a couple of rows and then left right why are they like this what happened here haha well no some of that some of that so let me tell you so what happened here is that the rocks that make up the sandstone that you can see the high stuff actually slid apart like they were on a conveyor belt and you'll say why how well he's the geologist certainly he must know well let me tell you so you need a little more information than this photograph can give you so what I'm gonna do is I'm going to tell you a short story about this area so once upon a time there was a big rocky basin here and there was a big sea that happened that occurred in the basin see dried out and left a salty layer a layer of salt right and then sand came in later blue blue in lithified and became sandstone so what you've got is you've got the basin of rock you've got a layer of salt and you've got a layer of sandstone now the interesting thing about salt as a geologic material as opposed to salt as a condiment is that salt is a geologic material is plastic it flows so if you push on it with the heavy weight it'll it'll kind of deform right but since it was in this bowl the heavy weight of the sandstone above it really didn't do anything it just stayed there until the Colorado River up here cut through the Basin and cut through the sandstone it cut through the Basin and it cut through the salt layer and when it did that the salt layer had somewhere to go and so the weight of the sandstone pushed the salt and basically the sandstone Road on top of the salt layer like a conveyor belt and opened up these lanes in the sandstone okay good hopefully you're getting an idea of where we're going let's try an extraterrestrial example not super extraterrestrial this is our moon okay on the left many craters on the right not so many craters what happened here well the answer here is that craters in the solar system as Kevin hand who is here last month talking to you said craters in the solar system are like footprints in the snow in places where you see a lot of footprints that snow is probably pretty old in places where you see fresh snow and not many footprints that's probably a pretty fresh you know deposit of snow and what happened here is exactly that this area on the left is older the area on the right is fresher because a lava flow on the moon a long time ago flowed out and covered the right hand side of this frame right and so in reality there are just as many craters on the left as there are on the right it's just that on the right they're covered up by a layer of lava all right let's go to no let's go to Mars don't worry I'm not gonna go through the whole solar system although I could but that'd be a different talk here's Mars this is a very close-up view of Mars and what you're seeing here these little black dots that you might be able to see our boulders right as big as a car as big as a house and they have these trails behind them what happened here well what happened here is that these are actually on a hill it's high at the top of this frame and low at the bottom of the frame and you know there could have been seismic activity from the Mars quake a nearby impact or even just where the rocks were they finally eroded and these big boulders fell and so these tracks are the tracks that the boulders left in the dust as the rocks rolled downhill and in fact this one on the right is like my favorite because it starts up here you probably can't see it very well there's a track and it's bouncing it's like a dotted line right that means that this rock as big as a car is moving so fast that it is literally bouncing off the ground and it bounces and it bounces and it bounces until it hits this crater and on the right-hand upper side of the crater it jumps the crater and lands on the other side right there's no try across the crater but there's a track on either side it bounces a few more times until it comes to rest down here right and so these are all examples of how looking at a photograph can give you an idea of what happened and help you solve the mystery of how it happened and what happened there in the past okay let's talk about sharing what happened here well if you read my papers or maybe even read the abstract you might know but let's pretend like you didn't and you can't really tell from just a single image right so let me walk you through the crime scene so to speak I'm going to show you the data and then I'm going to talk about the conclusions that we've drawn about Charon and why it's so interesting is a little moon so a lot of the data that we can take as we fly by allows us to get images from multiple perspectives and allow us to recreate the topography of places that we see and that's what this image is this is a where the bright white bright yellows are high standing topography and the the Blues are low standing topography and for those of you that can't see the legend the span of topography on Charon is 10 kilometers that's a lot for such a small object so there's a lot of ups and downs on Charon and you can see I hope that there's a lot of variation there's this kind of belt that runs across the middle of Charon there's my dot this belt that runs across the middle of Charon and north of there there are these big kind of chunks and canyons and south of there the geology is very different if we zoom in on an area they're north of the canyons and adjust our color scale a little bit to give you a better feel for what we're seeing you can see that the crust here right we're looking at a whole planet so we're looking at big chunks of the crust here there are blue lanes in between these big chunks of Sharon's crust now just like the example that I showed you in Canyonlands where things slide apart and leave a trench in between them we think that's what's happening here but this is happening at a much larger scale and more importantly if you know anything about earth tectonics right plate tectonics you know that in some places on the earth the plates are spreading apart right you were creating a new crust for example in the Atlantic Ocean but in places nearby us like around the Pacific the plates are coming together right and so if you have plates if you have plate tectonics on a spherical planet in some places the plates are coming apart and in other places they're coming together is just a conservation of area on a sphere but what we find on Charon is that everywhere these chunks are coming apart and that just right it doesn't make any sense from what I just told you right if it's plate tectonics they got to come together somewhere otherwise you're not something's funny and the thing that's funny is that plate tectonics are not happening on Charon instead what's happening is that Charon got bigger all right so what I want you to think about is bone up a balloon right blow up a balloon and then I want you to take maybe some house paint like some good latex paint and paint the outside of the balloon right let it dry maybe overnight and now I want you to blow into the balloon a little bit more and when you do that the balloon gets bigger and the paint is going to crack and these little plates of the paint are all gonna get separated from one another none of them are going to come together because the whole balloon is getting bigger and that is what we think happened on sharing but I'll get back to that and so since sharing got bigger you have all of these tectonic movements of the large chunks of its crust and it gave rise to these beautiful canyons that we see and also these scarps right there canyons and and cracks of all kind on the northern parts of Chanin really all over and so that's part of Sharon's story these big cracks in the north part of the planet but in the south part it's different there's still some small cracks but the character of the surface is very different I'm going to call them smooth Plains a lot because that's a geology term that I use of course if you look here like they're craters and they're all kinds of things that's not smooth for me it's smooth in comparison to the north and if we zoom in on parts of this smooth playing move planes of course they aren't completely smooth we see places where there are small cracks that are lined up next to one another but also there's just this general smoothness at the highest resolution that we can find on on Charon from our flyby and this is what that is there are places where as in the upper left the surface is smooth there are places in the photograph in the lower right where the surface is a little more pockmarked at a very small scale and so that's fascinating we the story that we come up with to explain the crime scene has to incorporate all of these elements right the other thing about these planes on Charon is that there are some mountains that just randomly stick up out of the smooth plains there are three big groupings that are labeled here and this is a good point for me to mention that there are some names on Charon that are now official IAU names there are some names that are still unofficial and you can play the home game to figure out which ones are and are if you like but so we've named these mountains after science fiction authors write and and artists so Kubrick Mons Clarke Monte's and and Butler Mons and Kubrick Mons is really our our poster child here's a better view of it the upper-left image shows you what it looks like from the spacecraft just without any alterations right what it looked like as we flew over it the bottom image is mat projected so you can see what it might look like if you were looking straight down on it and as I said we have topographic information across this part of Charon and so the two profiles to the right give you an idea of what it would look like in profile and as you can see it's kind of a sharp mountain you can see Peaks on it and it just kind of sits almost randomly in this smooth plane and the other thing that you might notice about this mountain that's different from other mountains you may know is that it seems to have a moat around it right it's like a mountain in a moat how did that happen well I'll tell you I think that what happened is that the material that formed the plane came around afterwards and surrounded the mountain the mountain was there before just like the trees in our earlier example the other mountain the biggest mountain is Butler and this is an example of some of the maddening parts of being a planetary scientist these are all of the photographs of Butler Mons that humanity has the white arrow points to the peak of Butler Mons in all cases and is an example of when we're farther away right to remember we're like an arrow shot through the bull's eye of the Pluto system and when we're farther away the images are fuzzier as we get closer right to the bottom of the sequence the images get crisper but the other thing that happens of course is that Charon rotates and so you can see that Butler Mons is in sunlight in image a and as Charon rotates it rotates into darkness and so at our best resolution we could have seen it the best the Sun has set on Butler Mons but it's pink there's one little white pixel that you can probably barely see from the audience but there is one bright spot where the Sun is still shining on the very tip-top peak of Butler Mons but it's lower flanks are in darkness all right so that's that's a pretty cool thing in other places on these smooth Plains are these features not the craters not the sharp little cracks but these other things that look like puckers in the surface now when I write science papers I can't use pucker it's not a good science word and so I have to say things like convex swells and depressions right but these are weird right I mean I'm the geologist and I just looked at planetary images and these are weird right these are hard to explain what kind of process would have left features that look like this so I have a guess we call it a hypothesis in science dresses it up a little bit what we think happened here much like I told you that I think the surface that flowed around those mountains it flowed around the mountains and that's what emplaced the smooth surface and here what we think these are is these are drains where the smooth surface kind of drained back into a vent that it might have come out of right so you can imagine maybe you're making like a yogurt or a chocolate right and if you poured it right into a into a crack you would see these kind of waves is the fluid the thick fluid like went down into the crack and if you flash froze it you might see something that looks like this or something completely different maybe happening here but that's our guest right so this next is an image is a movie of a flyby over the terrain of Charon to kind of give you one more view of the data here we are flying west over that big Canyon you see the smooth plains to the right and the more chunky blocky northern terrain on the left here as we come over the canyon we take a bit of a turn to the north and you can look back over the canyon we just flew over as we come up toward the North Pole we see this big crater Dorothy Gale Crater and the dark polar area and you can see as you look at the limb that there are these just these big chunks and big depressions of the crust as they were pulled apart and then of course filled in afterwards but it's very chunky right as these blocks were as we come across that boundary these southern plains have a very different morphological character they look very different so any story that we come up with as I said has to be able to account for all of these clues right so what kind of a story can we tell that is consistent with all of these data to do that we need to talk a little bit about how planets are formed ok so in the beginning no let me fast forward a bit once we get to a spot in solar system evolution where you're starting to form a planet right this is the sequence of kind of how it goes a rocky planet right so in the beginning you got some rocks and they start glomming together right they hit into each other they start to build a bigger pile of rocks eventually there's enough of the rocks together that they start to get hot and that's what the the red coloring in the center of the second image on the left is trying to tell you so the interesting thing about planets from a geologic perspective is that there are basically little heat engines interesting geology happens when planets get hot okay so what happens how do you get this rock to heat up right because I mean is just rock how does it get hot well first off when planets form and all those impacts come together there's some heat from those impacts right everything you need to do to go from a small rock to a planet is about impacts that's what gets all the mass in and those impacts are going to heat things up a little bit we call that heat of accretion but the other thing that happens is when you build a rocky planet you have a wide spectrum of elements that make up the rocks and some of those elements are of course radioactive elements and so not very many but if you get enough rock you're gonna have some radioactive elements and certainly early in the solar system those elements still have a lot of half-lives left and so they are going to decay and give off heat right and so that primarily is what gets the heat engine starting there are other kinds of chemical reactions that happen in the deep cores of planets that also perpetuate that but that's the basic story and eventually you get things hot enough where differentiation of a planet happens and what that means is basically you get hot enough so that the light stuff rises and the heavy stuff sinks right and that's what leads to planets like our own earth that have that molten iron core or a heavy iron core right in the lighter elements float to the top that's how planets form right okay so what happens when there's a lot of ice involved with your rock what happens then so this is what's gonna happen for share on right we have a ball of ice and rock that's gotten together how does that differentiation story play out when you've got a lot of ice well this is what happens right you start with a kind of even ball of rocky ice and because of that heating process that we talked about it gets warmer and what happens when you heat up rock and ice well the ice melts and the water floats and the rocks sink but of course the water floats it's going to encounter the harsh coldness of space and so it's going to crust over right and so this image in the middle shows you a denser core maybe an icy and rocky mixture above that and then this layer of water a global ocean around the object that's covered by an icy crust now over time a small planet like Charon is going to cool off right as it cools off that icy ocean or that watery layer that ocean layer is going to freeze solid and you're gonna get left with something that looks like on the right now these layers are not to scale and there are people that spend lots of time trying to figure out the deep nuances of this heat budget of how planets form but this is schematic right and you have just solid ice all the way down now this is slightly different from what we might expect around giant planets like Kevin Hann talked to you about last month he talked about ocean worlds like Europa and Enceladus and Titan and Triton and those worlds have the benefit of orbiting a giant planet and when they go around Jupiter they have tidal forces and the tidal forces between Jupiter and these small icy worlds around them flex the ice shell and that flexing produces heat and so the heat curve for those doesn't peak and then decrease it goes up and so you can imagine that instead of freezing if you go from the middle image here and heat it up some more you're gonna melt all of the ice down in the bottom and you're gonna have gonna end up with three layers but you're gonna keep that ocean layer because it's still hot and that ocean layer is going to have a roof of ice and a floor of rock and that's what we think is happening in Europa and other icy moons that orbit the giant planets and this is the interesting thing about Charon before we went by Pluto and Charon the only icy worlds that we had really good information about were these ones that orbited giant planets and we they had these oceans but we didn't know whether oceans were magical from being close to giant planets right that you needed a giant planet to flex you to get you warm enough to have an ocean or if it was possible to be through the normal evolution of an icy satellite away from a giant planet whether you could get an ocean and Charon we think is evidence that shows us that that's just a normal part if you're big enough you have enough heat you can melt that ice and you can get a global ocean now it won't stay because Sharon doesn't have anything keeping it warm it's gonna cool off and freeze right so this is actually the core of the story that's going to help us solve the mystery of the images of Charon that we looked at but to get there we need to talk about ice now you're very familiar with ice maybe not because you live in California but you've been to icy places you know about them you certainly have experience with ice in your drinks and the interesting thing about ice as a geological material not as a beverage but also as a beverage be quite honest is that when ice gets I shouldn't say ice I should stop saying ice and water because those things means very specific things to you I should say h2o when h2o is a liquid right the liquid molecules flow around each other right but when h2o freezes it gets bigger right it makes these crystal lattices right that give us snowflakes right and it gets bigger and when the lattice takes up more space that water becomes that h2o becomes less dense and that's why ice floats right this is not a surprise you all notice ice floats but this is different from other kinds of materials usually when you go from a liquid to a solid and you cool down you get more dense and you get colder and you sink right most things get more dense when they freeze not less dense but it turns out that that's actually a very useful property for ice and for our data because the other thing that happens besides just the floating which is of course delightful is that if you put water in a container and then is it if the container isn't very strong it's gonna break right this is what happens when you freeze water in a bottle and we think that this very same thing is what happened on Charon right it had this global ocean and it ran out of heat and it froze and when it froze that water got bigger and because of that it cracked the outer shell just like that balloon I was talking about earlier it got a little bigger and it cracked everything and that's what has driven apart the pieces of the crust that we can see on Sheridan all right so the answer is global oceans freeze and cause blocks to spread apart causes an expansion of the whole planet not a lot but just a little bit enough for us to see and certainly make beautiful canyons like this good mystery solved oh right right the plains in the south okay so let's talk about the southern plains so before I hinted it to you that a lot of the features that we see on these Plains look like volcanic features flows right and in fact other places in the solar system that we know are icy like Sharon also exhibit these features they look for all the world like volcanic flows but we know that they're made of ice right and so you might say okay great you're the geologist super right we know that on the earth when we have rocky volcanic stuff that we have tectonics we often have associated volcanism maybe we have the same thing in an icy situation you have frozen lava or cryovolcanism as we say in planetary sciences that's got to hang together right well there's a there's a bit of a problem you see ice as I talked about when it freezes it floats right remember I mentioned that and so if you had a crack in the crust that opened up and there was you know water or cryo magma maybe its crystallized a little bit thicker and it opened up right it's the what it's denser down there it's not gonna come up it's just gonna sit down there and freeze and so there's really no way to make these features that look like lava features this gives planetary scientists that study icy surfaces much xed oh wait I'll get it and trust me we know the difference between glaciers and lava flows they're different that's not what we're talking about these things have features that look for all the world like they were in placed in a manner similar to the way that lava is in placed so how do we solve this mystery right because if it's just ice then then ice isn't the answer right and and messes this up but the answer is other stuff so it's not pure ice right it's not like there's a filter up there that's making a pure crystalline perfect ice there's other stuff in the ice not a lot of other stuff but some other stuff and so there's a story about some interesting water ice chemistry that's going to help us close the books on this particular case right and the other stuff that I'm going to talk about is nh3 good old ammonia because the interesting thing about nh3 or ammonia is that when it's mixed with water it changes some of the chemical properties if you have enough nh3 in your water it changes that density relationship and allows the mixture to be less dense or close to the density of ice that's good right all right awesome how much ammonia do we need in our ocean to do that to change the density relationship right you need about thirty percent ammonia all right so that's a lot of ammonia it's like a lot right so we have estimates for how much ammonia and other elements are in the you know the solar nebula from where Pluto and Charon were born and the percentage of ammonia is about one percent relative to the amount of water so we need to go from from one percent to thirty to get even close to be able to being able to use that as an answer the other problem of course is that if you had that much ammonia in your water you wouldn't get the relationship that cracks the surface right because then the density is all backwards its regular again right you wouldn't get the cracking so the answer is in something called fractional crystallisation so those of you that don't know what fractional crystallisation is it's fine I really don't expect you to what happens when you have a mixture of ice and water of water excuse me and nh3 ammonia is that water freezes first this is very important so let's assume we have this mixture you can see the ice lattice at the bottom and you can see the ice lattice at the top and you have this fluid that has water molecules mostly water molecules and there's one nh3 atom for every 99 water molecules not very many but as the temperature goes down the water molecules are gonna form water ice crystals and float to the top right so it's just like as if you had a big bin of LEGO bricks some were red and some were blue right you had one blue brick for 99 red bricks and you went into your bin and you just started making stuff out of the red bricks at some point the ratio of the red bricks to the blue bricks is going to change if you're only making stuff out of the red bricks and that's what happens in fractional crystallisation those ice crystals the water molecules get together and they don't get together with the nh3 they float away and so what happens as you slowly cool this ocean is you're slowly enriching it right that the relative percentage of ammonia to water changes and at some point you get to a level up to that almost 30 percent where the density relationship changes and now the liquid is buoyant or very close to being buoyant and will allow you to rise up and perhaps erupt and that is what we think happened on Charon this is a schematic diagram by my friend James keen who's a co-author on a lot of the papers James is a big fan of whimsy and so the excuse me the Orca in the bottom right is a not to scale and B not really appropriate but I think there's mostly James's way of reminding me that this that part was is liquid and the upper parts are icy and so this is a cutaway of share and you can see the highly Tecton eyes right those blocky chunky parts to the left and the smooth Plains to the right and so what we think happened is Sharon cooled that ocean cooled it started expanding and it started cracking the crust right and that's what gives rise to a lot of these cracks that you're seeing from the side but in the final stages of that ocean getting the point where it almost freezes in the ocean that's leftover starts to get a lot of ammonia in it that allows that ammonia water mixture to rise up above the ice and spill out into this area over here and create these planes right the other great thing about ammonia water slurry right it's not going to be liquid it's probably going to be like a thick mush of crystals and fluid right just like a lava is is that in the very cold outer darkness of where Cher and Liz it's super cold and pure ice would freeze real fast but ammonia and water right just like any freeze allows that liquid allows that material to stay liquid longer and to create the landforms that look an awful lot like lava and that is what we think we see on Sharon this material rose up and it surrounded pre-existing mountains or high points that flooded in the low places and left us the signature that we see on Charon and that is the answer to why Charon is so different in these two different places these are the clues that allowed us to create the story that is consistent I I hope you believe the story I just told you that accounts we think for all the clues and arrives at a world that looks like this orbiting Pluto so far from the Sun thank you very much just curious why Charon and Pluto are always facing each other and why these other satellites why they're spinning and why none of them is facing the Pluto that's a great question let me bring that slide back up so that it can spin behind me so this is actually a consequence of planetary formation has to do with tides that act between the two objects right just like our Moon is locked it only faces the earth it has to do with the tidal bulges and and material on the two objects eventually all objects give it enough right like if you run the solar system like a clock all the way to the end of time everything would end up being locked together like Pluto and Charon are and this is a consequence of tidal evolution and so the moon is locked to the earth but the earth still has lots of other stuff happening and the liquid ocean on our surface that kind of allows it to keep moving around lots of other satellites in the outer solar system are also tidally locked too right they always face Jupiter or always face Saturn and that's what's what's happened here these little guys in the outer the outer ring aren't tidally locked yet but they're often in resonances they spin around an integer number of times as they go around thank you yes I was hoping to get a little clarification about how the pucker marks formed so I think at one point in your talk you said that the pucker marks form when something flows up and then it goes back into a hole right yeah so are those holes the still the areas where Sharan was being you know expanded apart and it just made a lot of little like pinprick holes or is it that's something else yeah so we think that the the cryo flows that spilled out over this area are a lot like lunar March that a lot of different kinds of volcanism right you may be thinking of the classic kind of volcano there's one volcano you have a big flood of lava we don't think that's what happened we think that in this area all across this the southern part of Charon the because I just I need a visual marker all across the southern smooth part of Charon the crust was broken up and and this cryo lava came up in all in lots of places just like the lunar Marya and kind of filled it over so there's not like one big volcano that we can find it's kind of everywhere and so those we think those pucker marks are places where there's maybe a bit of a bigger vent and so when lava on the earth in lava situations in silicate in basaltic lava lava comes up right and it spills out and sometimes at the waning stages the flood after you know the the majority of the the energy is spent on a volcano sometimes the remaining lava close to the vent will drain back in to the vent and so we think that is a good analogy for what these things might be thank you yes these geologic processes you were talking about with Sean are they unique to Charon or do you see the sim same kind of processes occurring on other icy moons such as those around Saturn and maybe even the Jovian moons it's a great question so certainly other icy worlds in the solar system have tectonic patterns this telltale sign of expansion moon Ariel there are big grooves on Ganymede there are lots of other places in the solar system where we see this example of expansion where everything got just a little bit bigger we also as I mentioned we see other places so the tectonic story is seen in other places but when objects are big two giant planets there's a lot of other stuff going on as well and so sometimes it's hard to extract the variables one of the nice things about Charon is it just kind of did its thing and wasn't impacted by a giant planet that it was going around and the the smooth surface as I said there are other places in the solar system where we see kind of smooth icing material in lows or in other places nowhere as big as much area is on sharing so this really helped us put that piece of the puzzle together for how these things are happening thank you hi you mentioned or implied that New Horizons had to go pretty fast to get all the way to the Pluto system and therefore zip by it pretty quickly and so you have a limited amount of data you've got some high res and you've got some low res pictures some of the geologic features ended up in the shadow yep so the question is how much more analysis can you get out of that data is if you you investigated 90 percent of it or 8 percent of it or there you go sure that's a that's a fine question so all of the data from our Pluto flyby is on the ground of course and so there's that's a hard question to ask a scientist it's like what's your favorite child so you know as a science optimist you can certainly say well there's always more that you can do with the day there are always new ways to analyze the data to think about the data to process the data but science often happens in there's kind of a large hump and then kind of a long tail I often think certainly for flyby missions where we get data and then it's it's done it's very different for orbital missions but for Pluto right there were some big things like oh here's this for the first time that's crazy let's try and figure out what happened and there's a there's a hump there's like the initial press releases where it's essentially wow that's crazy we here's our first guess is that why we think it's like that and then after some time the first like real science papers come out where we've done the analysis of the data and then there's a really long tail and that tail can be very long right I mean there's still people analyzing data and finding new science and Voyager data and in Galileo data and so you know these datasets are treasure troves that that can be used by by future scientists to learn new things that we haven't even thought to ask of them yeah yeah so this question is more sci-fi than anything is there a chance that Sharon would be colonized by any means in the future maybe maybe so Sharon is like really far away right so it's Pluto they're hard to get to and they're super cold so you need to have a good reason to go and stay there and I don't know what that might be it'd certainly be an awesome place to vacation be supercool to go to but whether it has you'd have to bring a lot with you right you wouldn't be able to live off the land maybe so much but I mean there is ice there and there's water so you'd be able to use that to create oxygen to breathe and water to drink and maybe rocket fuel to get you off so it's not terrible but it's a really long ways away right so we launched in 2006 we got to Pluto in 2015 and we were going so fast we couldn't stop so it's a long trip so in that case you could build a second spacecraft to go in Splore Sharon once more and get more information I love it yes absolutely that'd be great because certainly there are parts of Sharon that we haven't seen as I said the system is tilted toward the Sun so we really mostly just saw the northern hemisphere of Sharon the southern poles us both Charon and Pluto were in darkness during our flyby because they were facing away from the Sun thank you I would I would think that methane would show up frozen methane in your your slurry and just like that did you consider that yes so we see there's a lot of methane chemistry on Pluto right now certainly methane would be a constituent component of the ice right would be part of that other stuff that I talked about methane doesn't have a big bearing on the the chemistry and the rheology of the flow so I really didn't talk about it much today on Charon we don't see a lot of methane Charon is small enough that any methane on its surface would mostly kind of escape today but certainly there hadn't been some when it was formed I'm curious about the the difference in gravitational lock between earth and our moon versus Pluto and Charon in that their Pluto and Charon are locked with each other always facing the same way whereas with Earth it's merely one way is that a function of the difference in masses or of the distance or as Charon generated earlier than the Earth Moon and this is just a function of time all of the above the other thing is right so the earth in many ways in lots of ways is special right and the Earth's the fact that earth has oceans that are on the outside and that slosh around actually hope are one of the things that help keep us moving around but certainly the size of Pluto and Charon relative to one another cause that so initially we assume that they were spinning independently but ultimately over time those tidal forces slowed them down until they get locked to face one another right so initially the moon too spun but now it's tidally locked to the earth and it has to do with all of the things that you mentioned the relative sizes the closeness the age at which the system was born all of those things factor into how that spin down happens and they get locked up I was actually actually have two questions my first is what happened if Shawon got too big and popped like a balloon and do deshaun getting really big do you think that it ever squish Pluto damaged Pluto in any means okay so that's a good question so the expansion that we talked about we talked about I talked about it like a balloon but the amount that it got bigger wasn't very much there's only a kilometer or two but that's enough to cause this cracking so it's unlikely that it would have gotten big enough to explode you would need a lot of water to freeze although that would be super cool to see happen and it it's not gonna get like I said you need a lot of water so it's not gonna get big enough to get to put right still 16 Pluto radii away it'd have to be really big to affect Pluto in that way now we don't think that wouldn't have happened okay did I answer both of your questions yes okay awesome yes I have a comment and a kind of guy and you're incredible how you present that story thank you and when you talked about the evidence that you put together from a forensic perspective what would be the evidence that would say that it was not the story that you told but instead a different story for instance again uneducated eye looking at that picture maybe it's material on the top half of the southern hemisphere that got removed that may have been liquid which would have left a smooth surface because it looks like almost like you take the kind of the top chocolate shell off ice cream from the bottom section of it and then it kind of looks like that top section it's bigger so right what would the evidence be that would say that couldn't have happened sure so you're asking the wrong guy cuz I got a story that I really like but you would have to create a story that is consistent right so if you had right so you're talking about a shell that chipped away rights like how would you do that you have to come up with some mechanism to pop that shell out a lot water and ice or something else edges right Yeah right so here so you'd have to find some way to write to explain that to find some mechanisms that that do that maybe there's some other exotic chemistry that would that would do that maybe it was just formed that way to begin with and maybe you had cracking in the north and not in the south maybe what we're seeing in the south is an original smooth surface right but you'd have to make that consistent with with all the data and I don't know how to do that but I'm sure someone will and write a new paper about why Charon is like it is and that's and do you think that mass on the southern hemisphere is actually different and slightly smaller in diameter than that Northern Hemisphere yeah so the thing is is that there are a couple of things we're talking about this as the north and the south yeah look at it right but really remember the Sun this is weird the Sun is coming kind of from the North Pole so really the equator of Sharon is right here and this low spot is on the equator oh okay and the South Pole is down here around the curve of the planet in darkness and so you're right in that the average elevation of this area is less but not by very much by a kilometer or two right and so we think based on complete guesswork that perhaps it's not smooth all the way down to the South Pole but there's really more of a band across around the equator maybe that's smooth like this or maybe it's just on this side because we really can't see the backside very well and so that's we're getting more data would be great but we just don't have it those are all great questions there's no great ways to start a scientific investigation is to ask those kinds of questions yeah yeah thanks for all the information and all the great energy yeah I guess my question goes back to your talking about this cryovolcanism that happens with the water freezing and then the ammonia the content getting higher so that was in the past does the chemical composition of what we detected on Sharan also confirm this you know what's left over and how long ago did that happen oh that's a great question I see you're wearing a new horizon shirt yeah all right so you might think this will sink me so the problem you have raised a great question so you might assume based on what I said that those smooth planes should show an ammonia signature right if they're made of ammonia water lava it should be ammonia on the south and just water on the north right it's all water but I've got an answer for that and that is ammonia gets if it's on the surface of an icy body we think that when over time sunlight just the simple irate radiation from sunlight causes ammonia to pop off of a surface and leave the water and so when that so my my counter to that is that when the ammonia water flow flowed out it was certainly rich in ammonia but over time right and this is an old surface this happened early in the solar system over time that top layer has been all the ammonia has popped off and and escaped into space and so the top layer of this lava flow my prediction is that the top layer of this what lava flow is ice and that's what we see from the spectrometers if we ever went down there with an excavator you would dig through that crust and you would see a top layer of mostly water ice and down below you might see some that mixture of ammonia water but you need an excavator so hope you get the simple one very good yeah this dovetails a bit on a previous question I don't think you mentioned whether the Pluto Charon orbit has is nearly circular or has has or had a pronounced eccentricity if the latter could that be a possible source of energy to drive some of the geologic processes through tidal stresses sure so so early on certainly the the tidal motion even though it's a lot less between Pluto and Charon than it would be between a giant planet and an object like Europa some of that does pump tidal energy and early on but just as objects as a normal kind of evolution objects tightly lock and face each other their orbits often also tend to circular eyes right so it's possible that early in the system's history the orbits were much were more elliptical but now as we see them today they are very very nearly circular and so it's kind of a low energy orbital state yeah it's a two-part question which side of the picture right here is Pluto tiredly love like the north south right okay so let me let me ask so the the sub like the sub Pluto point like where you if you were standing and you were looking straight up where where would the bat point be right so that would be on Sharon's equator right about here all right so this is the sub Pluto hemisphere of Charon right the sub I have to do this right otherwise I'll get to the sub Charon spot on Pluto is on the on the back side of Pluto that we did not see as well okay yes yes I forgot to ask this question in the beginning and it's kind of related to the semi previous question that was asked her asked so what I wanted to know is that it does do Pluto and Charon have a elliptical orbit kind of like the Halley's Comet does and if you mean around each other around the Sun around the Sun okay and the second part is that if true then is there a chance that Pluto and Charon would would complete a rotation around the Sun or it would crash into another planet or or satellite belonging to that planet and when okay so of course in reality all orbits are ellipses it's just that some ellipses are more circular than others Pluto and Charon the Pluto system orbits the Sun in a reasonably elliptical orbit it's not as not as elliptical as a comet orbit it's still pretty circular but there are some places right so you may have heard this there are some places where the when Pluto and Charon are closer to the Sun than the distance of Neptune and sometimes they're farther away so it is a little more elliptical than other of the big planets in the solar system but not by a lot and it takes Pluto and Charon about 250 years to go all the way around the Sun so we haven't seen a complete rotation yet also where they are it's pretty empty there's not a lot of stuff out there so right now the likelihood of them running into something else is pretty low but clearly things have run into them you can see the craters on their surfaces yeah yeah thanks thanks for your time I was wondering since for some reason I was assuming whenever there is a chance for living on some planet we study that planet but you answer that's basically very cold and very far away so I really like to know what's next what's what's the future plans or discoveries for for what for NASA for Humanity for the for New Horizons yeah yes good because that's one I can probably answer so so after we flew by through the Pluto system we right we were like I said we're on this rail out of the solar system we adjusted our orbit our trajectory a little bit we had a little bit of fuel to kind of bend the orbit and so we flew by the kbo object mu 69 this Christmas this New Year's and and he said that Jeff Moore will talk about what we learned there so I'll keep you in suspense but now we're a past mu 69 it's far behind us now we continue to move super fast we hope in our wildest dreams so the way that NASA funds things is it funds it in chunks and what we're planning to do is to propose for another extended mission to try and use new horizons as a telescope to find other Kuiper belt objects that are in the area that we can kind of maybe get to because we're so far out now that even though the cameras on New Horizons were built as cameras to look at things that we were kind of close to there's still better telescopes than telescopes that are 33a you away on the earth so our plan is to try and use a new horizon as an observatory to find other Kuiper belt objects that are in our path that we may have enough fuel to nudge our trajectory a little bit and maybe we'll be able to fly by another one and if not will will become an observatory in the Kuiper belt looking at other Kuiper belt objects thank you yeah hi um you mentioned about the loss of ammonia from the surface dude you said evaporation or sublimation sublimation yeah I was just wondering him what's the intensity is sunlight like out there is that image there enhanced can you give some idea how bright it actually is out there so it's certainly very dim there was a campaign appellations public relations is probably not the right word an educational campaign around the time we flew by Pluto I forget what it's called now I'm gonna get lambasted for not knowing what it's called might have been called our Pluto I'm not sure but it it was in a campaign to kind of show you how bright it would be if you were on Pluto and it turns out it's a lot brighter than you kind of think so there's there's a time at dusk so this there's a website I sure wish I could remember it that could say you could say I live here and it would say okay you live here today at you know this time of night is the brightness it would be if you were standing on Pluto right so there's a time it at dusk where so it wasn't full darkness on the earth it was like a period at dusk where the light level would be about the same if you were on Pluto so it's a little brighter even than I thought it was so kind of almost dusk almost dark conditions if that helps any and this is this is certainly brightened it enhanced so you can see it better one more question you are the last question sir thank you for the presentation or was it really amazing so I have two questions one is given that Pluto was the primary mission for New Horizons why why was a choice made just to do a flyby and not really get into an orbit around it and given that Pluto is no a planet will there be like is there any justification for further missions to Pluto okay so those are great questions the answer to the first question about why we did an orbit Pluto the answer is a combination of money and physics so to get to Pluto in only nine years we had to be going fast way fast right so new horizons like I said it's the size of a grand piano it could easily fit on this stage and we put it on top of the biggest rocket NASA could buy an Atlas 5 right which is basically right rockets if you don't know Rockets have a small engine at the bottom but the big silo is full of gas it's a fuel tank right so that huge rocket got us going fast in the solar system to cross the solar system to Pluto in only nine years for us to go into orbit around Pluto we would have to bring a Rockets worth of fuel tanks to burn to slow down to get captured by Pluto gravitationally and we just couldn't afford to launch that much fuel with the spacecraft or we could have chosen to go slower right and not go as fast we wouldn't have to break as much but then all of the people that started the mission would be dead and they would not like that they really wanted to see Pluto before they died so it's a combination of those factors and you mentioned what the like the prospects are for doing more exploration of Pluto and whether you believe that Pluto is a planet or not certainly the IAU it's still a planet right a dwarf planet is still planet so we like to say but it kind of it doesn't really matter what we call it Pluto doesn't care what you call it scientists that study objects in the solar system we don't really care what you call it if we can as scientists make a good case for why it's important for the American people or scientists in other countries can make that case of why it's important to send another spacecraft to learn more about pluto and charon if we can make that case to the government in the american people then a new mission will get funded and so we think that the things that we have learned that the Pluto system are tantalizing there's right there's a whole half of the planet that we haven't seen and another half that was in complete darkness of course we kind of have to wait 125 years for the other side to get lit so it's kind of kind of a problem but the data for Pluto and Charon the Pluto system are as I said they're tantalizing and so trying to get another mission in the future I think has probably pretty good prospects I think we can make a good science case for trying to go again and trying to figure out how a might be able to go into orbit instead of just screaming bye thank you very much [Applause] thank you for ending our series this year in such a splendid way everyone please drive carefully and we'll see you in October

Channel: SVAstronomyLectures

Views: 44,058

Keywords: astronomy, science, astrophysics, science news, planetary science, Pluto, Charon, New Horizons, Ross Beyer, solar system, Kuiper Belt, planets, moons, space exploration, space probes, planetary probes, planetary missions

Id: mtGVgh6aA4Q

Length: 76min 52sec (4612 seconds)

Published: Tue May 21 2019