 with tails from the outer solar system. It's a very special astronomer whose cats have more Twitter followers than she does. Please join me in welcoming Dr. Cat Cobra. Today we're about my favorite part of the solar system. It's the Kuiper Belt. So let's talk and do a quick overview of what the Kuiper Belt is and a little bit about how we actually detect new Kuiper Belt objects and any other moving objects in the solar system. And then talking about how complete or spoiler alert incomplete our inventory of the outer solar system is and whether or not there might be some planets lurking out there for us to discover. And then I'm going to make some predictions about what the Kuiper Belt is. So our solar system has two so-called debris disks if we were talking in a more astrophysical context. The first is the asteroid belt, the inner solar system, which Andy Riffin is going to tell you a little bit more about asteroids. And then in the outer solar system we have the Kuiper Belt. So this is a top-down view of all of the known objects in the Kuiper Belt as in when I made this plot a couple months ago. So these are just the four giant planets, their circles showing where their orbits are. So us on our little planet Earth are here in the center, not really visible on this plot because the solar system is too big and we don't really matter to the outer solar system and I know. So we've got Jupiter, Saturn, Uranus, and the Neptune out here at 30 AU and all of these little dots are known Kuiper Belt objects in the solar system. Now that's the top-down view, we can take a side view of the same plot and see that these things are roughly in the same plane as the planets but they're a little bit puffed up much like the asteroid belt is. Some of they're on inclined orbit, some of them are quite a bit away from the plane of the planets. But this is our picture so far that we have observationally. But how did we actually build this picture up? These are objects that are very far away. How do we actually know they're out there? And we find new objects by taking images of the night sky and looking for things that move against the background of the stars. So the stars are really, really far away and they appear to be stationary from where we are but things that are closer to us in the solar system appear to move against that background both because they're orbiting the sun and because we are on the moving observing platform called the Earth that is also orbiting the sun. So when we take pictures in the night sky here are Jupiter and Saturn over the course of 11 months doing their dance across the sky and doing this so-called retrograde loop where they appear to turn around that was the first clue that we were looking at something besides things that were orbiting Earth. And then over here a bit harder to spot is this asteroid which I'd be able to see the pointer moving against the background stars. So that's how we find things. Now we have a fairly good inventory of the asteroids in the solar system and that's for a couple of reasons. This is a plot from 1800 to roughly today although it's a little bit out of date now of the number of asteroids we know of over time. Now this is a log plot on the y-axis which means that the bottom is one object the next big tick mark is 10 than 100,000 you can see we are up here well over into the several hundred thousand known asteroids in the solar system. And early on we had quite a few even up to about a thousand objects by a hundred years ago and that's because asteroids are fairly close to both the Earth and the Sun. So we are looking at these things in a reflected sunlight when we take pictures of them. So the closer you are to the source of that sunlight the brighter you are and the closer you are to the observer us on Earth and the brighter you are. So asteroids are quite a bit brighter than things that are much farther away. So we move pretty fast because they are both orbiting the Sun fairly quickly and because we see parallax motion from the Earth moving and things display more parallax when they are close to you. You can do the trick of putting your finger out of your eye and linking your eyes back and forth and you will see more motion close to your face than far away from your face. So this allows many asteroids to be discovered on photographic plates of the night sky where you are actually just exposing chemicals on a glass plate and then you are doing this awful thing putting them on a blank comparator that the idea of makes me really motion sick where you have one image on the left, one image on the right and you look through this hole and you blink back and forth between the images and spot the difference. That's how we discovered Pluto one of the relatively few outer solar system objects discovered on photographic plates this way. So this is January 23, 1930. Pluto is indicated by the arrow because otherwise you can never find it without staring for a very long time. And then a few days later on January 29 it has moved. So Pluto was really hard to find on these photographic plates but it's considered an extremely bright Kyberville object. That's super bright by outer solar system standards. So this is going to play into the story and in a couple sides compare how our inventory looks for the outer solar system compared to the inner solar system. So a more modern survey of course uses digital cameras to take images of the sky and then we use computers to do a comparison of those images and the computers view this for will spot the difference game for us and spot the moving objects and you can pick them out nicely here. So this is an object discovered in the outer solar system origin survey which is a project I'm a part of but I did not do any of the data processing. Other people did that and harder work. And this is one of these objects here. This is considered a bright object from our survey and yet to get this detection here each image, and this is three images linked sequentially we had to expose on a four meter telescope for two minutes open the shutter let the digital camera collect lights for two minutes and then over the span of about two hours which is these three images and then you can see this type of object. Now for comparison I chose this particular image because there is an interloper in one of the frames that the person who did a lot of this blinking Michelle Bannister calls the vermin of the dataset there is an asteroid sneaking its way into our type of belt survey. So I like this comparison because so this red arrow here is showing you how much a type of belt object moves over the course of two hours and this is the motion of an asteroid this streak is the asteroid moving over the two minute image exposure so it's moving a lot faster. Also it's bright enough that even though it's trailing across many pixels on the camera it still shows up. If you have a type of belt object something the same brightness as this type of object trailing like that it would just look like a background noise. So this just illustrates why it is a lot harder just intrinsically applying to these outer solar system objects in these surveys. And that's why when we do the side by side comparison of the number of discoveries we've had over time in the type of belt versus the asteroid belt. Here this is starting to get 1800 and I didn't plot this until 1930 when we finally had a Pluto but then there's this huge gap before the invention of the digital camera essentially and we finally started to pick up in the number of cumulative type of belt objects known. So we're sitting right now at about 2000 or so known type of belt objects which is roughly where we were in the asteroid belt about a hundred years ago. So type of belt science is 100 years behind asteroid belt science because these things are just so much more difficult to find we had to wait until we had digital cameras and computers to process those images. So let's talk about the completeness of our inventory of these calculations. So for the asteroids we have probably seen all of the 10 kilometer asteroids. That's pretty good and we've seen most of the 1 kilometer ones and this is because they're easier to spot because they're brighter and also because there's money because they're hazardous which you're going to talk about in the next talk. For comparison the smallest ever observed type of belt object is 30 kilometers across very roughly. 30 kilometers compared to where essentially complete in the asteroid population for 10 kilometer things. And the other reason we even have one down at 30 kilometers is because of the lovely New Horizons mission. To discover this 30 kilometer type of belt object required using the Hubble Space Telescope because it was too hard to image from the ground. But we needed somewhere to send that spacecraft after it flew by Pluto so we were able to get those resources. More typically the things we're seeing in the type of belt and discovering are 100 kilometers or so across and we're frequently finding new dwarf planets Pluto sized objects. So we're pretty incomplete in terms of our object inventory in the outer solar system. And in fact there's been much a press over the last couple years saying that maybe there's some really big things lurking out in the outer solar system. So if we look at all of the orbits these are just kind of kind of top down and a little bit side on we see that these really, really distant orbits aren't quite randomly oriented or so they appear. And there's been some hints that maybe that's due to another gravitational influence in the outer solar system. There's debates about this may or may not be a real clustering but it's really spurred this idea of what could be lurking out there and I've even kind of weighed in on that and said maybe there's a Mars mass that you can closer in again based on looking at the orbits of the neuron type of objects. And you know this is not impossible because really the only thing we can say with 100% certainty about the outer solar system is we're pretty sure there's no more gas giants to be found. And that's because we have surveyed the entire sky in the infrared gas giants as big as Jupiter and Saturn give off their own radiation and they would have been seen probably within 10,000 or so AU of the Sun depending on your models of the planets we're one AU from the Sun the Kyber Belt is a few hundred AU from the Sun at most. So good, we know there's no more most likely gas giants but that's about all we can say with certainty because if we kind of look at a map of the sky and we kind of estimate how well we surveyed different parts of the sky to different depths looking for these really faint objects and there's quite a few gaps so in this plot here yellow and orange are really deep surveys that look for really faint things blue and black are places we haven't really surveyed where we're all and this is just approximate but it shows you that there's quite a few gaps in our coverage. So even for these dwarf planet size or even maybe planet sized objects we can do discoveries. And the thing I'm really excited about with LSST is how much this is going to improve the sky coverage map and give us some really good answers about the outer solar system because very roughly and I did this with like a rinse of paint but I'm just slapping things on but this is exactly what the sky looks like when LSST is done the entire southern sky and a little bit of this north emphatic part is going to be essentially orange on this scale surveyed very well for faint moving objects and they expect 40,000 new Kyberville objects remember our current inventory sits at 2,000 so it's going to be an entirely new era for the Kyberville with a huge playground of new objects to look at and that's going to start in 2022 it's going to take many years because these things move very slowly against the background stars it takes a long time to figure out what kind of orbits they're on figure out what kind of objects they are so it's not like in 2023 we'll have those 40,000 new objects for you but several years into this process we'll have a much better picture so I'm really excited to see what we're going to find with LSST and it's going to completely revamp our idea of the outer solar system thank you I'd like a larger object so the question is if we find a larger object in the outer solar system what would be the theories for where it came from how it got out there and that is a really good question because the answer is we don't have great ideas not how stuff would get out there so one possibility is that we think our giant planets in the solar system might not be the only giant planet the solar system has ever had it's possible that we have another Uranus or Neptune mass planets in the giant planets we're forming because they keep form or behind them today they have to move to their current locations and some of the different ideas about how they moved there engulfs extra planets that we could have injected into the outer solar system although it's really difficult to get them on a stable orbit from the outer solar system similarly you could capture a free-floating planet but again it's really difficult there's a whole bunch of new problems to solve if we find a really big object out there to track the objects into the inner solar system yes that's a good question so the questions are we monitoring these objects and kind of tracking how they come into the inner solar system and the answer is they don't come into the inner solar system on time scales like human time scales but they do come into the inner solar system on a million year time scales longer so some of those comments that you heard about in the last talk they come into the Kuiper Belt but they come in from the Kuiper Belt and they spend about 10 million years kind of intermingling with the giant planets before they come into the inner solar system so it's a very slow process but we see these intermediate populations and that is another thing that LSSC will give us a much better picture of is this intermediate population that you call the cent powers that orbit between Jupiter and Neptune so all these small body populations are related to each other so looking at the details and more data will definitely help us to do that so are we going to see things much smaller than that 30 kilometer the smallest stadium we've seen the answer does probably no for things that are in the Kuiper Belt currently we'll get smaller can you guys know what the smallest I know in visual magnitude so but getting down to 30 kilometers is very difficult for this intermediate population between Jupiter and Neptune we can get down to sizes like that but we're probably still stuck with the 50 to 100 kilometers around those things how do I get here why is there such a well defined region of like no sky observations on that map of what we've seen good question here the question is why are there regions in this plot that are black where we have not seen objects advance advance the answer is it's the black dick plane so we are in the Milky Way galaxy and when we look out into the night sky if you've ever looked out and seen the Milky Way there's a brighter patch of sky that's there because of all of the stars and the reality they're seeing now because we have not in the past been able to look at the entire sky typically for surveying we picked the easier parts of sky to survey the black dick plane was a really tricky area of the sky to survey because there are so many background stars that it's really easy to lose these faint objects against the background stars so LST is going to survey including the black dick plane and it's a potential area where we might find some really bright objects but we've been avoiding that because of limited time there are pictures of that sky and obviously it doesn't exist it's just that when you're doing a targeted moving object survey you stick to the easier parts of the sky you can't move the whole sky anyway but again that'll change the LST good question okay I have one more thank you what about Pluto to be found so much sooner than other type of objects so the question is what allowed Pluto to be found so much sooner than other type of objects and the answer to that is I think persistence and also a false idea of what was out there so they were looking for Pluto because they thought they were seeing some anomalies in Neptune's orbit around the sun so Neptune itself is discovered because when we observed Uranus the planet just inside of Neptune its orbit was being perturbed by something we could tell that there was something out there gravitationally tugging at it and low at the hole they found Neptune and they thought they were seeing a similar anomaly in Neptune's orbit and thus launched this search for this really big planet and the Pluto just serendipitous and it happened to be in the heart of the sky they thought it was but it was all a mistake it was far too small to have affected Neptune's orbit but they were really convinced and it's just persistence because it was a really hard discovery to make using photographic plates alright I think that was all I was trying to say thank you everyone and our last speaker wants you to know that he's completed the Kessel Run in less than 9 parsecs please join me in welcoming Andy Griffkin