 Welcome to how to stream your webinar. In stereo multiple times over. Excellent. All right. I hope that that one again. For all of us panelists, we got to mute our extra. Looking good. Can those of you on YouTube hear us as well? I guess if we talked, we'd have something for them to hear. I think so, because I think the echo is my YouTube. I don't hear an echo. And I see that it is we are at the top of the hour. And so I, I think we're going to get started here. So let me move this around here a little bit and let me. Well, hello everyone and welcome to the June NASA night sky network member webinar. We're hosting tonight's webinar from the U.S. Naval Society of the Pacific in San Francisco, California with Dave in way up in upper New York and Vivian and east of Francisco Bay and Carl. I do believe that you are in somewhere in Maryland and Carolyn. I suspect that you are also in Maryland. So we're all over the place today. So we're very excited to bring this webinar with our guest speaker, Dr. Carl Adams from the U.S. Naval Research Laboratory. So welcome to everyone joining us on the YouTube live stream. We're very happy to have you with us. These webinars are monthly events for members of the NASA night sky network. And we're having a great time live streaming these as well for more information about the NASA night sky network and the astronomical site of the Pacific. At some point, there will be some links in the chat so you can find out more about us before we introduce Carl. Here's Dave prosper with just a couple of announcements. And hi, everyone. And I just got a couple of quick items here. First, NASA has a new exoplanet citizen science project out called exoplanet watch. And it's like brand new. It asks amateur astronomers to contribute their own exoplanet observation data either from their own telescopes or from robotic observatories. And to NASA studies of worlds orbiting other stars. It's all transit based like a, you know, Kepler and tests. So while it's so new, you may have a, may not see it right off the front page on exoplanets.nasa.gov, right? But it is going to be there in a day or two. Or you can also click on the handy link I am putting in the chat right now and it will take you to this new project and it'll be in the newsletter in July with an article on the front page too. So we'll make sure you don't miss it too. So quicky, the IAU wants to know how the new ish satellite mega constellations have affected your views of the night sky. They're going to have a convention about a satcon to meeting about that next month. So I know a lot of folks have strong opinions about that. So put those in the survey link for the IAU folks. It's a voice your opinions about how this is affected your own enjoyment of the hobby. I will put it in the chat and you can also go to bit.ly slash sat survey two. That's a number two. And last but not least, and this is a very fun one, there are some new stamps from the US Postal Service that are highlighting the views of our sun as seen by NASA's SDO or Solar Dynamics Observatory. They look awesome and they have a, I even like that they have like a, these nice little scientific labels like a stamp signifying like what feature to look for, like Corona holes or solar flares and that kind of thing. It's pretty neat. So just look up the sun stamps at the post office, go in and grab them or link in the chat as well. And that's about it. And back to you. I know a couple of folks at the Naval Observatory. I'm not sure if you're familiar with the Naval Observatory, but I'm sure you're familiar with the Naval Observatory, or the US Navy Research Lab. So Carl, I'll probably ask you to say hi to those folks later on. Save that for later. Take care. All right. Thanks, Dave. So for those of you on zoom, you can find the chat window and a Q and a window in the menu at the bottom edge of the zoom window on your desktop. Please feel free to greet each other in the chat window, but I think one person is having some audio challenges. And so hopefully you're getting those sorted out. Also with the Q and a window, please put any questions that you have for our speaker in the Q and a window that really helps us to be able to keep track of them. And a lot of times we will merge similar questions into one. So that we can get to as many questions as we can. So please make sure that all the Q and a questions go into the Q and a window. That way it will really help. Also, if you're having some difficulties, you could always send us an email at night sky info at astro society.org. So again, I want to welcome everyone to the June webinar of the NASA Night Sky Network. This month we welcome Dr. Carl Adams to our webinar. Dr. Adams is an astrophysicist and computational scientist based in the solar and heliospheric physics branch at the U.S. Naval Research Laboratory. He's the principal investigator of the Lasco coronagraph telescopes on the ESA NASA SOHO satellite. And for over 17 years, he's been the principal investigator of the NASA Sun Grazer citizen science project, which some of you might have participated in and you'll find out some more about that later on. And that project has discovered more than 4,100 experiments in the solar and heliophysics field. He's also a member of the science team for several other active heliophysics missions. Carl's research interests span from studies of the solar atmosphere, the comets and asteroids, and more. He's presented numerous times in the subject of comets to audiences of all ages and backgrounds. And given countless online news, media, radio and television interviews, as Sun Grazer comets on Twitter, we will put that in the chat in just a moment. And so please welcome Dr. Carl Adams. Carl. Thank you very much. Good evening everybody. I will go ahead and steal the screen from you. Go. And are we good to go? We are good. All right. Fantastic. Okay. So I appreciate you inviting me to talk this evening. So yeah, as as Brian's intro said, I've been the PI of this project called Sun Grazer project about 17 years now. And it's a project that allows absolutely anyone in the world to discover comets. But not just any comets. We're not talking about ordinary comets. The comets we discover through the program are not just ordinary comets. And in this talk, I'm going to kind of present to you exactly why these these are such extreme and extraordinary comets. And why I refer to them in the in the presentation title as supersonic snowballs in hell. So before I get into those, I just want to take a moment. I think it was good to have like a big picture of comets in general. What are they? Why we study them? A lot of people, of course, may be familiar with this, but it's good just to run over it real quick. There's this popular model, I guess, of comets called the dirty snowball model that says that comets are really just a snowball in space with lots of rock and dirt attached to them. It's not really a great analogy for comets anymore. They're a bit more complex than that, but it's still good enough in this sense because comets are a mix of frozen water and gases that are kind of weakly bound together with dust and rocks. They're not structurally super strong. They're like asteroids that are really dense. So they're kind of weakly bound together. And people have heard them call them celestial dinosaur bones. Comets are the pristine remnants of the stuff that our solar system is made of. So when all of our planets and moons and all that was forming, chunks of stuff were left over and got kind of flung out into the cold recesses of the solar system, and those are the comets. They're kind of the key building blocks of our solar system. So like when the solar system is being formed, you kind of go from atoms to molecule to small dust to bigger clumps, and then these bigger clumps stick together, eventually you get to comets, comets and asteroids kind of stick together, you get planets. That's a very rough picture, but there's kind of this progression of things that have to be created for you to end up with a solar system. We need to understand fully how our solar system was formed. We need to understand how comets are formed, what their structure is like, how they came together, how they came to be. And of course, there's always the big question that people put out there, like, are comets the source of life itself? Did they deliver Earth? It's water. Did they bring the complex organics and amino acids to Earth that initiated life on our planet? We don't really have clear answers to these questions. Certainly, comets delivered some water to Earth. When Earth was very young, did they deliver all of it? Probably not. We don't know how much. And again, with the complex organics and amino acids, the jury is still out. But this is generally why we care about comets and why we study them. And again, this next slide, I think most people can be fairly familiar, but for the context of my talk, I'm going to go ahead and refresh in people's minds the basic features of a comet. I'm just going to go ahead and give my laser pointer right here. OK, I've got my laser pointer. So the classical image of a comet is this one you've got up here. You've got this long, this big, broad, fuzzy, dust tail. And that's literally, as the name implies, it's a tail that's made of dust and chunks of ice, maybe pebbles, rocks. And that has lifted away from the surface of the comet and is streaming behind it. Some comets, more active comets, particularly will sometimes have a second tail called this ion tail. It's an ionized gas that streams away from the comet, always kind of points directly away from the sun. And that's caused by the solar wind, the outflow from the sun, passing over the comet nucleus and an ionizing gas that then streams away from the comet nucleus. And then, of course, in the nucleus itself, every comet has a solid nucleus, a solid core. This image happens to come from the Issa Rosetta mission. It's kind of a funky shaped nucleus. It turns out that comet nuclei tend more often than not to be kind of weird shaped. That's still under investigation, why they tend to be a little bit weird, but certainly this one was no exception. But again, this is kind of the main body of the comet itself. This is that frozen solid lump of ice and gases and dust and rock. And then surrounding, immediately surrounding that nucleus, we have what we call the coma, which is gases and very fine dust. The image in the upper right is a massive coma that appeared around comet homes, which I think was 2007-ish. Maybe I'm remembering wrong, but it was around that ballpark. But the coma is, it's material that's kind of lifted away from the coma. And even in weekly active comets, ones that aren't very close to the sun, as I'll describe in a few minutes, they do tend to have this coma around them. So those are generally the features that you get in kind of your standard issue comet. But just to give folks an idea of what's going on on the surface a little bit, this is an image from the surface of a comet. This is a comet 67P again from the ESA Rosetta mission. And in some ways it's almost familiar like maybe a rough desert landscape or something, but this is the surface of the comet. This is that frozen icy, gassy thing. It kind of doesn't look like it, but it's certainly a landscape unlike anything that we have on Earth. And I'll just point out this one boulder that's down the bottom that's kind of roughly house size. It's like 20 meters or so, I think, in size. And I'll refer back to this kind of size later on in the talk. Now comets under ordinary circumstances. We're still talking about ordinary comets here. We're not getting into these funky sun grazers. Comets tend to follow a set of rules that they behave fairly well within these rules that we set for them. When a comet is very far from the sun like more than say six astronomical units, the astronomical unit is the distance between the sun and the Earth. And the comet is like more than six times away from the sun than the Earth is. It's very little solar radiation hitting the comet. And so the gases and the ices are frozen in that comet. They remain frozen and they're largely inert. Some comets will have a little bit of stuff that's kind of melting off of them, but very little is going on with a comet when they're out of these distances. But as they start to kind of come into the solar system, between like three and six astronomical units, they're getting exposed to a little bit more solar radiation like the sunlight is getting a little bit more intense. And it's enough to at least sublimate like the very most volatile gases like the carbon dioxide, carbon monoxide, like blocks of dry ice that are frozen carbon dioxide. Like that sort of thing will start to out gas at these distances from the sun. And as they do that, they will release little bits of dust and stuff that kind of stuck to the surface of the comet. But still the comet is mostly inactive, like water ice will remain frozen. So you might get a bit of a fuzzy coma around the comet, but there's generally not much of a tail at these distances. The fun stuff really starts to happen inside 3AU. When you get near to the sun, like 0.3 is Mercury's orbit. So you go from 0.3 to 3AU, stuff really starts getting a lot more intense. The solar radiation is very, very strong then on the comet surface. So not only are the volatile gases like CO2 really sublimate and kind of furiously lifting off large volumes of dust and stuff, but now also the frozen water and stuff is also starting to sublimate. And so you've got more and more material that's coming from the surface of the comet. It's releasing dust, pebbles, rocks, maybe some boulders. You get the tail behind the comet. You get the iron tail. What also happens with comets, and this is something I'm going to refer to later, is what's called a non-gravitational orbit effect. With all this stuff that's pouring off the surface of the comet, it acts kind of like a jet. And the momentum of all this dust and rock and stuff flying off the surface of the comet can actually nudge the comet very slightly in the opposite direction, such that it doesn't follow the orbit that it would have done without that activity. So ordinarily a comet follows just a standard gravitational orbit, like the sun's gravity dictates the path of the comet. But with this extreme outgassing, we get what we call non-gravitational forces that just nudge the comet a little bit. We have equations and things that account for these, and more or less we can still model this stuff in comets. It's not too complicated. Problem is when we get very near to the sun, once comets get inside Mercury's orbit, and particularly once they get to the sun grazing all the bits that I'll talk about, sometimes things really get kind of crazy. And that's really when we start talking about supersonic snowballs in hell. This background image right here is an image taken by the Japanese space agency, Hanoi Satellite, and that is a portion of the surface of the sun. And down here in the lower left, that little dot is a sun grazing comet called Comet Lovejoy that we saw in 2011. And this is really a remarkable image. It's like kind of David and Goliath kind of thing going on. You've got this tiny little comet that flew right by this huge sun. And this is the perfect example of one of these supersonic snowballs. So why do we call these comets sun grazers? It's literally because their orbits take them to the point that they are grazing the sun's atmosphere. Like they're not necessarily hitting the solar surface, that they are skimming really close to the solar surface. It's literally the most extreme environment in our solar system for sure. Because they're going so close to the sun and they're under that gravitational pull from the sun, sun grazers can reach velocities approaching 600 kilometers per second. That's 0.2% of the speed of light. So if you think back to a couple of slides ago, that boulder that I was showing you on the surface of that comet, that was like a house size boulder. That's kind of the size of the sun grazers that we see. They're very small comets. But still to me, the picture of like something house size going 0.2% the speed of light grazing the surface of the sun, it's just such a crazy, it's almost an inconceivable scene. It's such an extreme scene. Now, most sun grazers belong to a particular comet family. This Croix group, you're going to hear me mention this quite a few times. The Croix group is a family of comets that all relate to a single parent. So it's lots of little comets that are following the same path through space. The several or few thousand years ago were part of one single comet that went past the sun. It fell apart. It came back past the sun. Those pieces fell apart and it did this two or three times. And now we have this long kind of debris trail that stretches way, way out into space. And that's known as the Croix group. So they are all sun grazers. But not all sun grazers are Croix group comets. Many of the audience members may remember Comet Ison, which was all over the astronomical news in 2013. I'll be talking about Ison later in this talk. But Ison was a sun grazer, but it was not a Croix group comet. But the final point I want to make about these supersonic snowballs is unfortunately because of that extreme environment they're going through, and the overwhelming majority do not survive their passage past the sun. So it is kind of a fatal journey, but it's one in which we get to watch this pristine lump of the solar system and getting completely deconstructed and atomized as it goes by the sun. Real quick, this slide. We knew that sun grazers existed before the space age. And several ground-based observations of Croix sun grazers. So we knew that there were a few out there. But it was in 1979, so actually some colleagues of mine at Naval Research Lab, Neil Shealy, Russ Howard, Don Michaels, Marty Cooman, they had been analyzing some images from one of the very earliest chronograph telescopes on an instrument called Solwind on a US Air Force satellite. And they saw this bright streak in their images and their initial reaction was that something had gone wrong with the camera. They thought, oh, rats, that's the end of that. But no, it turned out that it was actually a sun grazing comet and they thought it was cool. But what a lot of people don't appreciate is that was actually kind of a milestone moment in modern space science because that was the very first time that any solar system body had been discovered from space. And we take it for granted now that asteroids get discovered by space telescopes and satellites find all these comets. This was the very first time any kind of solar system body had been discovered from space. So it was really sort of a watershed moment. They actually went on to, there's several of nine comets that got discovered by that satellite, that instrument, until 1995. And then there was another satellite that followed on and found another 10 comets between 87 and 89. So by 1990, there were more or less 30 cruise group comets on record. And I mean, at the time, people thought, wow, that's a big comet family to have 30 comets in there. Goodness, that's a really big, that's a really big comet family. No one imagined there were that many out there. And then along came Soho and that really changed everything. So the bulk of my talk is going to be referring to Soho. So real quick, it is the Solar and Heliospheric Observatory. It's a joint ESA NASA mission that launched in December of 1995. It has more than a dozen instruments designed to study the sun, its surface, magnetic fields, the space around the sun. It's sort of described as the Hubble telescope of solar physics for a long time. Soho is still operating today. It's in a limited mode. Most of the instruments have been turned off. Thankfully, the one that hasn't been turned off is the one that we discover all the comets in, which is the Lasco telescope or telescopes, I should say. Lasco is a coronagraph telescope. And a coronagraph is a special type of telescope that uses a solid disk to block out direct sunlight so that the camera isn't blinded by the sun and instead can see the faint corona that surrounds the sun. So it's literally just like a solar eclipse on Earth during totality when the sun's corona reveals itself. We just make those and put them in space so that we can look at this 24-7. So we have two cameras that we view with the C2 camera on the left here, C3 on the right. So C3 has a wider field of view. It has about a 30-degree field of view. C2 is, I think, it's like a 6-degree field of view. That white circle in both represents the size of the sun. And because of the nature of this telescope, because we are blocking out the blinding sunlight, it allows us to see essentially the night sky that surrounds the sun. So we can see all of the stars that are out there. We see all of the solar outflows of corona, corona mass ejections. We see planets that are going by the sun. And it turns out that we see a lot of comets. There are far more comets out there than anyone has. Any idea would be out there. And it's just a region of space that you cannot look at from Earth because when you look at the sun, all you see is blue sky and sun. Once you block the sun, then you get these beautiful night skies. And because of the nature of these telescopes, SOHO has discovered 4,182 previously unknown comets, which is way more than half of all known comets, just from this one satellite. And of course, I'm going to be showing you some pictures and some movies of some of the SOHO comets, but I just want to kind of ground everyone a little bit of reality first because you might be thinking, oh, great, like comets. This is what comets look like. So I'm expecting to see lots of beautiful images like this. Unfortunately, kind of a little bit of a reality check on this. You're going to be seeing comets are a little bit more like this. SOHO's comets are tiny. So I mentioned that they're typically maybe tens of meters in size. So just like that little boulder that was on the surface of 67P that I showed earlier, they're really not big comets at all. There's just an awful lot of them, but they do get very bright. Some of the slightly bigger ones can be very pretty. And I'll show you some examples of those right now, in fact. So on the left here, let me see if this movie wants to start. There we go. So if you follow my laser pointer, there's a bright sun-grazing comet going right in there. There's another pair of sun-grazing comets following in behind it. There's another bright sun-grazing comet just above the laser pointer there. They kind of go quick pretty fast. You see stars moving in the background. You see a planet moving in from the right there. I believe that's probably Mercury. This solid thing right here is just a structure inside the telescope that actually holds the disk in place. So these are examples of comets in the Lascaux C3 field of view. And then Lascaux C2, which has got one in this particular movie. This is a really nice bright sun-grazing comet that you see streaking right in towards the sun. It looks like it's on an impact trajectory with the sun. None of these actually hit the sun. This is kind of the effect of seeing a three-dimensional system just in two dimensions. So the comet isn't hitting the sun. It would have curved around in front of the sun, but it got vaporized before it even got that. The really cool thing, the thing that I think is one of the most amazing aspects of SOHO's 4,000 comet discoveries, is that nearly all of them have been discovered by citizen scientists. And that's through the Sun Grazer project that I have been fortunate to run for several years now. Sun Grazer, it's a citizen science project, enables anyone in the world to report and discover new comets. Essentially, it's a matter of the participants downloading images from SOHO's website, searching the images for little faint dots that are moving, and then they report them to the project website. And then it's my job to kind of look through the reports and confirm, deny, catalog the comets, and then make the scientific measurements of the comets. So it's pretty straightforward in principle, but it's actually a very time-consuming and sort of technically challenging in some ways to observe, to detect these comets. What I really love about this program, though in particular, is some of the stories that come out of it. So, Sebastian Honig, he was one of the earliest participants in the project. He was actually doing the project before I'd even, when I was in undergraduate in school. Around 99, 2000, he was also a student, I believe in Germany, and he was working with some other amateur astronomers, and they were looking through the SOHO data for these comets. He was one of the first people to do it. And that astronomy background stuck with him through his college education, through his PhD. And he's now a senior professor at the University of Southampton in England. And then kind of at the other end of the scale, the story from last year, which I think is awesome, is Rafael Beros. He's a Polish student. He's 12 years old, and last year became probably the youngest person ever to find a comet. His uncle introduced him to the Sun Graser program, and it took him about five months before he found his first comet. And he's found, I think, three comets now with the program. And I think it's just amazing that we have this program that's been running for so many years, and we've had many teenagers that have grown up and gone into space related careers. Even one of my collaborators on papers, a couple of my collaborators on papers, were teenagers on the project that are now PhD astronomers working in the field. So it's wonderful to me that the program can really inspire like that. I don't want to get too much into the statistics here, but we've found 4,182 comets as of May, so actually it's probably closer to 4,200 now. More than 100 individuals from all over the world have found these overwhelming amateur astronomers. Nearly all of our comets are Croix Group comets, these Sun Grasers, so about 86% of them. The rest fall into a few other families of comets. But what's really cool here is that three families of comets, the Maya Group, the Marsden Group, and the Croft Group, were completely unknown to astronomy until people started finding comets in the Soho images. So these comic families were discovered within the Soho data as well. So again, like the science return is really, really rich. And that's kind of what I want to talk about now is what kind of science we're getting out of these, because we've found 4,000 comets. We've seen a whole bunch of other comets. What can we learn from comets that are really close to the Sun? And there's a huge amount that we can learn, and hopefully I've got plenty of time to get through these. Before I get into these science nuggets, a lot of the best science that we have has been enabled by our extended heliophysics fleet. So we're not just talking about the Soho satellite anymore. In 2006, we launched the stereo satellite. So my group at NRL has an imaging suite, a bunch of telescopes on the stereo. So those are returning some amazing images of comets and the solar atmosphere. So there's a lot of science that have come from that NASA launch, the Solar Dynamics Observatory, SDO in 2010. SDO just looks at the solar atmosphere. It looks at the million degree solar atmosphere in extreme ultraviolet light. And no one, I certainly never imagined it would have anything to do with comets, because I really didn't see how a comet could possibly show up in the SDO data. And I was proved wonderfully wrong, as you'll see in a little bit. The new kid on the block is Parker Solar Probe, or PSP. Again, my group has a camera on PSP. It only launched a couple of years ago. The mission is still evolving. But we have seen several comets with the camera. What's really cool about PSP is it gets really insanely close to the sun. And it's actually the satellite is almost following a sun grazing orbit. Like it's not that far from being a sun grazer itself. It's just fortunately one that seems to be surviving the passage so far. But it's a really amazing mission that I encourage folks to check out what's going on with PSP. And then coming soon, we also we've got a camera on Solar Orbiter, ESA's mission that launched in 2020, but it's still kind of in the commissioning phase. We haven't really started mission ops with that yet. And then we've got a couple of chronographs that we'll be launching around 2024, 25 timeframe. But again, these should be observing comets like we should see sun grazers release. So even though these satellites are not at all designed for comet studies, we can still use them for comet studies. So let's talk a little bit about comet ison. I mentioned that one earlier before. This is a really great science story. As I've said, comets are active because of the sun, like they have their tails and their coma because of the sunlight, the solar radiation hitting them. And they become increasingly active the closer they get to the sun, as you would expect. But we can study their activity as they're approaching the sun, we can study their activity and study their brightness and just simply looking at the brightness of a comet. We can learn something about what it's doing. This plot here, I don't need to get too locked up in the details of it, but essentially the vertical scale is brightness. And the scale along the the X axis along the bottom is distance from the sun and then the dashed line is like actually at the sun and then to the right is further away from the sun. And this shows that the brightness of comet ison with some different filters on our camera as it was approaching the sun. And we saw that as it was getting closer to the sun, it got brighter and brighter, it got really super bright. A little ways before it reached its closest point to the sun, but then curiously it started fading before the closest point to the sun. And that kind of had a scratching our heads for a minute until you realize, oh, well, the reason it's doing that is probably because it's in the process of being destroyed already. If it was going to survive, then it should peak in brightness right around when it's near the sun and then fade gradually because it had already peaked before getting close to the sun. We kind of knew straight away, oh, this thing was not going to survive. This is a movie of comet ison in the last cameras. And you'll see, as it goes past the sun on its way out, it looks very different on the way out as when it came back in and already now up here it's just this faint fuzzy diffuse cloud. It's all kind of drawn, your attention is drawn to the chrono mass ejections that pop in off from the sun as well. It's a really beautiful image. None of those hit the comet, the comet did not set any of those off. But just take a look like right here that the morphology the shape of the comet before the sun and after the sun are very different. Again, paints a picture that tells us something. And basically we can do dust modeling and sort of model that the ages and the size of the pieces of dust that are coming from the comet. And that can kind of tell us that all paints a picture of how comet ison basically fell apart completely like a day or so before reaching the sun. And it just vaporizes it went past the sun. So all that was left afterwards was just a dust cloud with no actual nucleus in there. So another process that happens with sun grazers quite frequently again because of this ridiculously extreme environment they're going through is fragmentation, which frequently observe pairs of comets in the data. So you can see like these two little blobs there. They're two separate comets, but they're really close together. And what that means is they had to have been part of the same object fairly recently, at least within the past few years. And we see this a lot with Soho will see. Sometimes we'll see one comet that we know is going to come back five years later and when it does come back five years later. It's not one comet anymore now it's two comets. And so we see this ongoing process of fragmentation it's kind of like the evolution of the comets. We also see it in comets that weren't discovered like by Soho like comet 96 p mack holes that's a kind of a fairly famous ground based observable comet gets close to the sun every few years. We discovered in 2012 that there were two tiny little fragments ahead of 96 p mack holes. No one knew that it was doing that it doesn't surprise us because that's a particularly weird comet but no one knew it was doing that. But it turns out that this particular comet also appears to be the parent of a much larger extended population of near sun comets that include two comet families that Soho discovered so I mentioned earlier the Marsden that had been discovered in the Soho images they are children of 96 p. There's also two meteor showers that are related to 96 p there's at least one asteroid that seems to be related. So it's this big whole weird complicated family that all seems to kind of hinge on this one comet. These are the kind of stories that are coming out of things that we're learning just by observing the return or lack there of sometimes of individual comets we're really getting a picture of the evolution, sort of the end state really of large comets. This was another really cool story 322 p Soho this is a short period comet. Maybe it's a comet maybe it's an asteroid is an object that was discovered in the late 90s in Alaska we've seen it six times now. But it says little kind of dot inside of that yellow box, and it was always a puzzling one because when it got near to the sun, it got very bright. So it had to be a comet because that's what comets do, but it never had a coma around it and never had a tail. So maybe we thought well maybe then it's an asteroid. And as soon as it went far away from the sun, it got extremely faint extremely quickly, which means what only asteroids would do that if it was a comet it would stay bright for longer so it must be an asteroid. But if it was an asteroid, then to be as bright as it was near the sun, it would have to be a really big asteroid which means we'd see it far from Earth which means it can't have been an asteroid it must have been a comet. And there's this whole back and forth like what's going on with this thing. Thankfully we did get some sort of closure with this. My colleague Matthew Knight was able to eventually image it with a ground based telescope in 2015. When it was far from the sun, and he was able to confirm that there was no comet activity. It looks like a relatively small like 150 to 300 meter asteroid. And essentially what we think is happening with this, we still call it a comet but what we think is happening is it's just an asteroid that gets far too close to the sun and gets super hot. And I mean we're talking like more surface temperatures of 1000 degrees Kelvin. At that point it doesn't matter if you're an asteroid or a comet or whatever the heck you are, once your surface gets to 1000 degrees, you're going to be sublimating something. And that's why it brightens up near the sun. So we see like these really cool objects like this. And there's questions like this surround so many of our discoveries. And then other stuff we see with the comets is some amazing interactions between the solar wind and comets. This is Comet Mcnaught in 2006, which most people remember. This is an image from our stereo satellite shortly after we, right after we opened the doors on this camera right after launch. We've got this extraordinary sequence of images with the comet going fairly close to the spacecraft these amazing dust striations in the tail. Of course the comet was so bright it was saturating the camera as a couple of planets coming in there. We see these just absolutely incredible structures within the tail and when you analyze the data you see all sorts of weird interleaving striations. There's of course been some science that's come out of that and essentially we're seeing dust interacting with some magnetic fields far away from the sun. And then another one that was kind of cool. This is Comet 2p Enki and that one had its tail ripped off by a coronal mass ejection. So you see right about here comes the CME and boom it rips the tail right off of the comet, the tail grows right back. But this was one of the best images we've ever had of a comet interacting with the coronal mass ejection. And again that gave us some science and essentially what's going on is we're seeing how the solar wind is driving the tail dynamics in comets, the morphology of the tails. And that has applications for studying space weather, for studying the sun and heliophysics and how does the sun affect like the earth environment. Because you can essentially use these comets as near sun probes like they are, they're telling us kind of like a windsock on an airfield they're telling us something about the conditions in space very close to the sun. Now what we didn't ever anticipate and this was the one that really surprised me were comets in extreme ultraviolet light. The background image there is an image of the sun. It's an image of the sun's million degree atmosphere this is extreme ultraviolet light. And in 2011, my mind was blown when we actually detected a sun grazing comet that Lascaud had been watching. We actually saw it, excuse me, we actually saw it in the data getting completely vaporized as it flew into the solar atmosphere. We'd never seen anything like this before. It was an amazing observation. And there was a lot of science came out of it. The comet got to within about 60,000 miles of the solar surface that's really close to something that's really intense. So I'm impressed that it got that far. We estimated about 10,000 tons of mass loss. And that's kind of equivalent to like a 10 to 50 meter diameter nucleus which is more or less what we expect these comets to have. So to me, this was like, I thought, wow, this is like the pinnacle of comets going by the sun to actually see this thing in extreme ultraviolet light. I never imagined we'd see anything better than that. But lo and behold, later that year, if you follow just above my laser pointer there, you see that little dusty thing flying in. These are images again from the Solar Dynamics Observatory. And that is comet lovejoy flying behind the sun. And again, these are just simply unprecedented images in comet studies in solar physics to see this object that is basically getting what's happening here is the comet is getting vaporized. The dust that comprises the comet, all of the elements, the molecules that comprise the comet are getting atomized within seconds, maybe tens of seconds. They're getting literally stripped down to bare atoms. And then those atoms are sticking to magnetic fields that are coming out from the sun. So like all of these loops and stuff on the surface of the sign of magnetic loops. But there's also a whole lot more that you can't ordinarily see out there in space. But this comet went through and dumped a whole bunch of tracer particles all across these magnetic field lines and they glowed for a little bit. And so we were able to look at that. And you can use it to validate models of solar magnetic fields. Guys looked at the electron densities around the sun, temperatures around the sun like it was an amazing amount of science that we were able to get just from watching the sun grazer go plunging through the solar atmosphere. So sun grazers really are extraordinary comments that the extreme intensity of the environment that they go through, it really removes them from all ordinary considerations. So I mentioned at the beginning of the talk that we have these set of rules that we apply to comets that work generally well. We toss that rulebook right out the window when we talk about sun grazers. So in terms of chemistry, the chemistry that's going on is insane. I'm not going to get into the details of this, but basically, comets obviously are a mix of all sorts of different molecules and stuff. We just have no concept of how a complex cometary composition would react in those near sun conditions. Like the processes that are going on are so extreme, like we can't even begin to model it. And it's not even like with a regular comet when you're talking about the frozen gases like CO2, even water. When those are sublimating, okay fine, you can model that, you can deal with it. But for a sun grazer, the entire exposed surface of the comet is vaporizing. It doesn't matter what the comet is made of, it could be made of iron, it could be made of quartz, it could be made of pure diamond. When they're that close to the sun, the entire surface is sublimating. And that is such an extreme environment, like we don't even know how to begin to process that from a modeling standpoint. They have these explosive outbursts. Comets are known to have outbursts from time to time that let off puffs of dust and water and stuff. Sun grazers do this on such an extreme scale. Comet ISON was a great example. Even though ISON was really a very small comet, a few days before it reached the sun, it was releasing almost as much water per second as the giant comet hailbop that we saw in 1997, almost as much water as hailbop was releasing. ISON was releasing about 16,000 gallons per second of water for a time. And again, for a small comet body, that's just completely unsustainable. So that kind of led to the demise of that comet. But again, that's something that you really can only see in a sun grazing comet, something that gets so close to the sun. And then finally, like in terms of the orbital mechanics, I mentioned earlier, the non-gravitational forces, like the outgassing from a comet can nudge it off of its standard orbit. When it comes to sun grazers, that happens on a ridiculous scale, like the non-gravitational effects, the outgassing, it's literally a jet effect. I mean, the comets just completely disappear off of the planned trajectory, off of a gravitational trajectory when they get near the sun. It is such a crazy environment, such a crazy process that they go in through. So to wrap all this up, under ordinary circumstances, ordinary comets will react to sunlight in dramatic and sometimes slightly unpredictable, but largely predictable ways. Sun grazing comets are going through the most extreme environment in our solar system. They encounter truly extraordinary conditions and behave in frustratingly extraordinary ways. Extreme sublimation, outgassing, explosions, they're flying all over the place. They really not only test our limits, they break our limits of understanding, but they still yield a huge amount of science for both comets, comet studies, and solar physics. And since around 1999, near 2000, it's citizen scientists that have driven so much of our understanding of sun grazing comets by discovering more than 4,100 new comets. And that is via the Sun Grazer Project, which is open to anyone. I recommend folks read up on it first. It requires a lot of patience and a very good eye for comets, but it's certainly open for anyone. And a little tester here, if you can see the comet in the animation in the bottom left, then maybe the Sun Grazer Project might be the right thing for you. And I think that is it for now. I've definitely used my time up. I hope folks have enjoyed and I'm certainly ready to go ahead and answer any questions that people may have. Alright, thank you, Carl, very much. I can see the comet. Maybe I should do those. Oh, good, go for it. Hey, we've got a couple questions from back in the very earliest time and so regarding the ion tails and so one is what's the longest recorded ion tail and when and why did the dust tail and ion tail come off at different angles. Okay, good questions. It's hard to answer the one about the longest ion tail because they really technically they stretch to infinity like the solar wind, which is the outflow from the the sign outflow of sort of particles magnetic field from the Sun that carries these ionized gases out, and that really goes out to the very edge of our solar system so technically they are ion tails they don't really have a set length so it's, you can't really answer that question as such. So the one about the two different directions that I certainly can answer the the ion tail always points directly away from the sun no matter where the comet is going as it's going around the sun, but the dust tail. That contains particles of different sizes, the bigger chunks of dust like boulders pebbles big rocks, they will continue to follow the the arcing path whatever the path of the comet is, they will generally follow that path around the sun. The really faint dust the really small tiny fine dust kind of like what you find in a vacuum cleaner bag. Over time that actually gets pushed out of the orbit by what we call radiation pressure which is actually the pressure of sunlight hitting on those particles actually pushes them a little bit. So those tails tend to more closely resemble the the orbit of the comet, but with some deviation of the faintest stuff due to the sunlight is hitting. All right. So Rachel asked a question in an article and new scientist back in July of 2015 you discussed the implications of a massive comet crashing into the sun. The question is, how and whether such an event could affect sunspots and or sunspot activity. Yeah, so there was there's always been talk about what would happen if a comet hit the sun. We do actually have one Soho comment on record that we're pretty confident would have hit the solar surface if it had survived that long. We're pretty certain that the comet was completely vaporized before it hit the surface of the sun. And even if it did it was tiny like it wouldn't have made a difference. But the bigger question is, okay, what if something like hail bot comes along which is like 40 kilometer comet and goes plunging straight into the sun. A colleague of mine. Sadly, he passed away a few years ago, Professor John Brown from who's the astronomer Royal in Scotland. He modeled he did a lot of comet modeling. And he always felt that if something that big hit the sun. There's a lot of energy that's that's going in. And there would be a lot of energy released just from the kinetic energy of the thing going in. There will be a lot of energy released probably akin to that of a moderately powerful solar flare. So we would definitely see something like if something that big did hit the sun, we probably would see some sort of kind of flare like event. It certainly wouldn't do the sun any harm whatsoever, and it would not create anything that would be harmful to us on Earth. As well I can't foresee any way in which it would create anything that's any more troublesome than any other solar flare that we have on a somewhat regular basis come towards us. But it is a very interesting question. And I really kind of hope that one day a nice reasonable sized comet does actually go into the sun. I don't want a giant one going in there, but nice reasonable sized comet that we can study that would be really awesome to watch that. That would be a pretty spectacular. Danny asks, how can small comets have so much water? That is a good question. So comet ison, when I said it was a small comet, we think the nucleus was about 500 meters or so they're about in diameter. So as comets go that's pretty small. But if you do the math, like if you think of a sphere that's 500 meters in diameter, that's big. I mean, that is a really, really big object. And like the 16,000 gallons per second number that I quoted the ison was releasing 16,000 gallons is probably a fairly big swim. It's like an average, maybe a medium sized swimming pool. But there's a lot of swimming pools that would fit inside. But a 500 meter sphere. And a lot of that, a lot of that stuff is locked up inside the comet and you got to remember that with comet ison what we think happened wasn't just a crumbling it wasn't just a falling apart. It was very much of an explosive boom they're like this thing just kind of flew apart in a bunch of different directions. All of the water ice that was embedded within that sphere within a relatively short period within a few days was all released out into the solar system so it sounds like a lot. But, but once you kind of appreciate the scale of these things and the math definitely checks out on it. Okay, so I do note that we're right at the top of the hour. We'll try to get through just a few more questions if you're okay to go a little over time here. I am and if folks want to reach out to me on on Twitter as well I'll make sure that my my Twitter handle is on is on the chat like you can always shoot me messages on there too I'm happy to respond. Well let's see if we can get to a few more questions. So Robert says do the sun grazers grazers go through the corona. Yes, yes they do. So the, the solar corona, which is that the sun's atmosphere. It's a very broad term, and the sun's atmosphere technically extends way way way out beyond sort of the our chronograph field of view. When we talk about the corona we're not just talking about like the, the hot stuff that that we see like in the extreme ultraviolet images like let me go back to my thing. This is nice movie anyway. So technically this is the solar corona, but also all of this stuff out here is the solar corona, all of the, the little stream as the rays that we see coming out from the sun in the last go images. That's also the corona to so it's a, it's a very broad term that for the sun's atmosphere. And that's an atmosphere that more or less extends to infinity. I think with the sun grazers kind of the more pertinent point is they get to within one solar radius of the surface of the sun so they're really getting extremely close to the most intense part of the sun like the, the, the million solar corona, where there's a there's an awful lot of physics going on and a really intense radiation environment. So john asked, and this is a good question kind of sticking with this idea of vaporization is material is vaporized from the comet surface, where does it go. That's a good question so when comets are far from the sun, like your ordinary comets, a lot of that will get it gets picked up by the solar wind, I guess, essentially all of it gets picked up by the solar wind, and pulled away from the comet so that like the, the ion tail or the dust tail in regular comets, that is all of the material that's that's been either vaporized or released, and that's it streaming away from the comet with sun grazing comets. It can be a little bit different. So like this, this animation that I was showing here of comet lovejoy going by the sun. In this case what was happening is, even the dust and the rocks and the pebbles were getting within minutes or seconds we're getting literally stripped down to bear atoms. Atoms were for a time, heating up to chrono temperatures stick into chrono field lines, but eventually most of them would have been thrown back out into the solar system via the solar wind. All right, sticking with the idea of vaporization Eileen asked a really kind of an interesting question. It would seem that vaporization of comets by the sun is gradually reducing the risk of comets colliding with the earth. However, are there constantly new comets being formed, you know, other than just the fragmentation of existing comments. No, we don't think comets are being formed anymore that the formation of comets really happened way back when when everything in the solar system was formed so they were kind of the leftovers they were the bits of stuff that didn't become planets or moons or the sun. So no new ones are being created. And yes, technically every year that goes by, comets are losing a little bit more mass. Some of them are getting vaporized by the sun and I mean I guess, technically, then the number of comets in our solar system is gradually reducing but it's is a very small number I mean it's it's kind of like taking a teaspoon of water out of the ocean and saying there we go I've lowered the level of the water in the oceans now like it's the number of comets that are out there particularly in the cloud which is way way outside of our solar system. It's probably an insane number of comets that we couldn't even begin to estimate the numbers of them, but most of them won't ever come anywhere near Earth and generally speaking that the risk to earth from comets is is tiny like the chances of earth getting kicked by a comet are very very very small. It's certainly not something that I lose any sleep over at all. If we were to be unlucky I mean it would definitely be a cause for concern but it's really something that's that's not a huge chance of that happening at all. Okay. Another question about vaporization, Philip asks, does vaporization pressure cause explosions and have you observed any particular explosive events. So that's a good very good question. We don't fully know why some of the sun gray why the sun grazes appear to explode when they get close to the sun and we're literally talking like explosion and boom like they they completely fall apart. We don't we still don't understand the physics is going on there could be a number of possible reasons for them doing that. One possible theory is that the the outgassing from the comet causes it to start spinning and because there's no friction in space it just spins faster and faster and eventually it spins so fast that it just shatters itself. There's an idea that the gravity from the sun essentially creates like a tidal force and just rips the comet apart but vaporization pressure is another possibility there's a colleague of mine I was a co-author on a paper that theorized a process called sublimation pressure which basically said that the side of the comet that's facing the sun. There's so much sublimation that's occurring on that side of it that it's creating a pressure that essentially kind of like pancakes and just crushes the comet up. So we can't say definitively that we have seen like a vaporization pressure causing destruction, but we really don't know exactly what the mechanism is so it's it's certainly something that's that's plausible that it's a factor. Okay we're going to go one more question here and we've got a couple of people have asked about spectroscopy and whether or not with these because of the energy that's being given off by these commentary fragments whether or not you're able to do spectroscopy and also is there any of the data available. So, regrettably, not not really our solar telescopes. We have color filters on them like SOHO last oh we have some color filters on there, but they are very broadband filters for spectroscopy you really need extremely narrow wavelength bands to look in so that you can precisely look at the different spectroscopic components. We don't have any of that capability with our solar spacecraft. Mainly because they're not designed to do that like they're designed to study the sun they're not they're not there for us to study comets as much as I wish they were. That's kind of a side gig for the for the satellites. So we don't have that kind of capability and ground based telescopes that might have that kind of capability. There is no way those guys are going to point their telescope that close to the sun that's that's all kinds of bad news to do that. So in terms of spectroscopy we're kind of in a difficult spot because we would desperately love to get some really good spectroscopic observations of these things as they're falling apart. So as I mentioned the chemistry that's going on is absolutely insane. And you've got an object that's being stripped down literally to its bare components so to be able to look at the full spectrum of that would be absolute gold mine. But unfortunately that is not on the cards anytime soon. Well thank you very much I apologize to all the rest of the people that we weren't able to get to all of your questions. Lots of really great questions so thank you so much. So that's all for tonight thank you Carl for joining us this evening, and thank you everyone for tuning in.