Rubble Piles in the Sky: The Science, Exploration, and Danger of Near-Earth Asteroids

[Music] good evening everyone my name is Andrew frack Noi I'm the emeritus professor of astronomy here at Foothill College and is a great pleasure for me to welcome everyone here in the Smithwick auditorium and everyone watching at home on YouTube to this lecture in the 18th year of the Silicon Valley astronomy lecture series each month we or for six times a year we bring noted astronomers from around the country from around the state to talk to you about new developments in astronomy this outreach series is co-sponsored by four important organizations NASA's Ames Research Center one of the premier NASA centers in the country the Foothill College astronomy program offering both day and evening classes in astronomy the Astronomical Society of the Pacific which since 1889 has been presenting materials and information about astronomy to educators and the public and the city or the search for extraterrestrial intelligence Institute which has an ongoing program looking for life in all forms in the universe tonight's speaker is dr. Michael Bush who works at the SETI Institute dr. Bush is a planetary astronomer based at the SETI Institute as I said his research focuses on characterizing near-earth asteroids asteroids had come perhaps uncomfortably close to our planet and he characterizes their shapes the way they spin how they move using both radar and radio techniques dr. Bush obtained his PhD in planetary science at Caltech he worked as a postdoctoral fellow at the University of California in Los Angeles and at the National Radio Astronomy Observatory before starting as a research scientist at the SETI Institute in 2013 asteroids are his specialty and we wanted you to we wanted him to tell you all about the sigh the expiration and the danger that asteroids represent he calls his talk rubble piles in the sky ladies and gentlemen please welcome dr. Michael Bush all right thank you everyone for coming out tonight and thank you to everybody who's watching this on YouTube several months from now so again I'll be talking about near-earth objects and to consider Leaney Earth asteroids but I want to give a bit of context what they are where they are in the solar system so we're gonna start on a somewhat larger scale this is a plot of the solar system out to the orbit of Jupiter as of last week when I put these slides together you can get the most current version of this from the International Astronomical unions Minor Planet Center they make a new version every day so we are here on earth which is just off to the left of the Sun I realize people watching this online will not see the laser pointer so I'm going to try to describe what I'm pointing at we have the orbits of Mercury Venus Earth Mars we go out out here is Jupiter you put her itself is down the lower-left right now and then everything else is a different small body orbiting the Sun there's a lot of stuff out there we have the main asteroid belt between the orbits of Mars and Jupiter which is the green dots we have the Trojan asteroids that share Jupiter's orbit 60 degrees in front of the planet and 60 degrees behind and then we've got comets passing through but what I'm talking about tonight are all the red dots in the figure those are the near-earth asteroids now near Earth is only near on the scale of the solar system when we say near-earth we're talking about objects that are on orbits around the Sun that come within 50 million kilometers of the Earth's orbit about 30 million miles at some point in there that orbit of theirs around the Sun so that's a long distance by the standards of the size of the earth it's nearby on the scale of the solar system where it's a hundred and fifty million kilometers from the earth to the Sun 93 million miles give or take depending on the time of year and Jupiter's orbit is about 1 billion miles from one side to the other side so that's how much space we're dealing with here there's a million asteroids roughly in this figure many hundreds of thousands there's even more empty space they were playing these Star Wars music earlier the you before the talk this is not like Star Wars the esterase are know about piled on top of each other you don't have to dodge your spacecraft around them this makes sense intuitively you go out at night area with a dark sky you look up you see stars you don't see asteroids blocking your view every which way the asteroids are as thinly spread as a grain of dust on one side of the room from agree on dust on the other side of the room that's how much empty space we're talking about here now the new Earth objects that we currently have that are able to pass near the earth right now are not four and a half billion years old on those orbits those will return at stable over millions of years they can fly by the planets they can fall into the Sun which is kind of dramatic when it happens they can get thrown out of the solar system completely they can get broken apart by a couple of different ways these asteroids have all only been on their current orbits for perhaps a few million years they're constantly getting removed and replaced the near-earth population is coming from the main asteroid belt object in the main asteroid belt gets scattered inwards typically by gravitational interactions with Jupiter Mars may some extent Saturn and this constantly replaces near-earth asteroids as a destroyed so the near-earth objects that we're seeing are remnants of escapees from the asteroid belt the asteroid belt in turn represents remnants of planet formation the reason there is no large planet between the orbits of Mars and Jupiter is that Jupiter happened first and it became so massive so quickly that it started scattering the orbits of everything in the asteroid belt around collisions between the asteroids were very very fast they erode rather than cut accumulate into a single large object so the largest few asteroids Ceres Vesta others of that size hundreds of kilometers wide are four and a half billion years old age of the solar system everything else is remnants of asteroid asteroid collisions over the last four billion years so we call this the collisional cascade so we're trying to understand some sense the origin of the solar system history four billion years old but we have to account for this last four billion years worth of somewhat energetic history if we were to zoom in on all the dots we see that history and impact craters I'm a lot of larger objects so this is a collage of various asteroids that have been visited by spacecraft there's also some comets down here but I don't have time to talk about them tonight M le lac de Walla at the Planetary Society put this collage together she has written extensively about all the different planetary space missions so the asteroid the tshe here the single largest one on this picture is 132 km/h 80 miles wide it's probably four billion years old but you can see it's lost large sections of a two-volume to collisions things just a little bit smaller than the t-shirt got broken up completely and all the other asteroids that we see over here are really mutated debris from previous s troit asteroid collisions they're piles of rubble cancer will pilot tell you when the talk you'll also notice a wide range of colors here there is in fact an asteroid over here on the right it may seem almost invisible because it is incredibly dark-colored there's a large section of asteroids called C class objects carbonaceous objects that are very rich in carbon compounds black tarry gunk basically and four billion years ago and slow system form they never heated up very much so they never lost these carbon compounds which some larger objects did when gravitational heating is they calculated and radiates active isotopes eating them up they melted boiled off the carbon compounds in the water the C class objects didn't do that and so they preserve one this very dark color and to a fair amount of water so if some of these objects are a few percent water by mass and there's arguments actually as to exactly where the Earth's water came from a lot of it may have been boiled off when the earth formed and then delivered later by objects from the outer solar system where there are more of these carbonaceous ones getting thrown in and then hitting the earth alright so most of these objects are in the main asteroid belt spacecraft flying through the asteroid belt on their way to somewhere else you can arrange to fly by an asteroid if you want to you don't have to do that you actually have to deliberately steer yourself to pass nearby but we have also visited a few near-earth asteroids a spacecraft and those are the highlighted ones there now there's widely varying size here I mentioned leticia is 132 kilometers wide there's lots of evil asteroids that big no near-earth asteroid is that large eros which you see down here is the second-largest one and it's a bit over 30 kilometers from end to end the largest near-earth asteroid Ganymede is just a little bit bigger than that but we have this whole distribution of sizes and there are more small ones than large ones so I'm gonna zoom in now on that dot which is the near-earth asteroid yo Kawa because it's typical for a lot of the other objects that I'll be talking about it's only a few hundred meters across there's about a thousand year asteroids large the 1 kilometer wide and there's many more of these smaller things this is what a rubble pile looks like when you zoom way in on it as advertised it's a pile of rocks but it's a very interesting pile of rocks because of the environment moraine here so you know Kawa is 540 meters call it a third of a mile from one end to the other for a comparison the International Space Station is 100 meters wide so that's the scale we're talking about that's so small this thing is although it's still fairly big as compared to say the International Space Station it's just very small as compared to planets it's a hundred meters across that single largest block that we see on IDO cowell and then there's a whole distribution of particles down to very very fine grain dust this is what happens when you have repeated collisions you just fracture the entire body and that repeatedly break it apart and pieces re accumulate because the gravity on something 500 meters across is so low physics gets very weird you could not stand on yo couch if you were go to ito Paola any slight twitch of your muscles you would fling yourself in your spacesuit off the asteroid it out into space and you might not come back down again because that's how low the escape velocity is and it's like all the other asteroids I've shown you and all but a couple largest ones it's very obviously not around so we've got what look like roughly two of the soil pieces sitting on each other but they don't slump down even though they are unconsolidated gravel and other sizes of rubble because there is less pressure in the middle there than there is if you stick your hand and put it on the table underneath your hand that is how little pressure is on the inside of the these objects so it doesn't take much strength for them to hold themselves in quite right varied shapes against gravity and we also get other weird effects that we don't normally think about for geology stuff like electrostatic charge so Christine Hartzell at the University of Maryland many others have worked on this gravity here is so low you have solar wind coming in depositing protons electrons you can charge up actually fairly sizable little grains of material and levitate them and they might can migrate around the surface and resettle elsewhere we also particularly importantly for the near-earth objects have to worry about effects of radiation pressure so sunlight has like all light has energy and momentum it doesn't have any mass but as energy a momentum so if you shine some light on the surface there's a very weak pressure being exerted again not something we normally worry about for geology but when the gravity is tens of thousands of times less than we have on earth it become significant this has been studied by astronomers actually for quite a long while now about a century ago even Ostrava tchaikovsky first figured this out on a theoretical basis it wasn't observed actually happened for decades afterwards but it's called the Yarkovsky effect so you have an asteroid out in space we have the Sun it's spinning everything is spinning to some degree some asteroids been more than others you have the afternoon side of the asteroid that is the spot where it's the hottest so there's the most infrared light coming off the asteroid in that part on the night side over here it's relatively cold less infrared coming off the surface infrared is heat is also photons are also light they carry momentum it's not balanced so there's more pressure being exerted this way due to there being more photons going off in the opposite direction Newton's third law there's an equal and opposite reaction more photons go out the asteroid gets pushed the other way the key point about the air Kowski effect is that it depends on the direction the asteroid is spinning so we have the asteroid spinning if it's been in one way it gets pushed forward in its orbit and its orbit eventually expands if it's spinning the other way retrograde rotation it gets pushed backwards along its orbit and the orbit eventually shrinks so this is this complicated interaction between the asteroid size shape and density determine how much the air Koski acceleration is and the direction that it's spinning which determines the direction of that push this was first detected in terms of actual application early satellite work there was a project called echo they launched a large balloon that was aluminized on the outside and slated orbit and you could bounce radio signals off of feet balloon accessible ooh and kept moving in ways that they had not expected because radiation pressure was pushing it around and thus the air Kowski effect has been observed now the blue one has very light weight it's very thinly spread gas inside rubble pile asteroid density is typically at least out of water although somewhere just a little bit less because they're fairly ports very heavy and yet with very careful observations particularly the radar astronomy tree we can get we can measure even one kilometer wide asteroids getting pushed around a few kilometers over a decade or so of observations so we're seeing rubble piles besides of mountains getting shoved around just by sunlight shining on them in different ways so that was kind of impressive the last maybe 15 years we realized something else which had been suggested theoretically again long before and this is the Yarkovsky O'Keefe Reds of etske pedak effect we will call this Europe so if we have an asteroid if it's a perfect sphere then this is your cow skis model but asteroids aren't spheres you saw I just have a regular they can be even if some overall shape is spheroidal it's gonna have piles of blocks all over the surface probably so these regularities mean that the net effect of this extra heat coming off can be offset from the asteroid center of mass so it can get a torque so that only is it getting pushed it's getting spun up or spun down so how does this work this is a binary asteroid called 90 99 kW for I apologize for the telephone numbers with so many asteroids it would be a pain to think of hundreds of thousands of names but Steve Astro who is my thesis advisor at one of my thesis advisors at Caltech observed this system quite some time ago now and realized that kw4 has a couple of interesting properties one it has a satellite orbiting around it so if a large asteroid and we have a small asteroid around it and two it has this big bulge around the equator where did that come from well consider the your perfect we have a pile of rubble city in space we keep spinning it up and up and up and up eventually it's gonna bulge out around the equator the earth bulges out by about one part in 300 because the Earth's gravity is quite large and the earth isn't spinning that fast we take a very small asteroid we spin it every couple of hours it's going to bulge out quite dramatically around the middle now if it's a sphere roughly speaking to begin with it was a pure fluid it would act like the earth it would become an ellipsoid but these are piles of rubble the fact that they have compressive strength and internal friction starts to matter and you end up just bulging out material around the equator and getting an actual Ridge as opposed to a smooth lips oil shape you also can get various every hilarities kw4 is pretty much round around the middle but there are other asteroids where we see larger dents in those equatorial ridges it's not clear if those are impact craters or if it's just we spun up this asteroid and polished it out and the arrangement of blocks and the inside happened to give it that shape as it spins up and up and up and reconfigures itself we have another complication I talked about how Europe depends on the asteroid shape the shape has changed oops now all the earth torques are different and so this is complicated to the random process or asteroids spin up over hundreds tens of thousands or hundreds of thousands of years reconfigure themselves and then may either spin keep spinning up or spin down again if they keep spinning up eventually a material at the equator goes into orbit so the asteroid literally flies apart this was the original suggestion for York this is the conversational Burstein the idea was that asteroids would spin up so fast that they would actually explode that relied on the object having enough tensile strength that you could spin it up so quickly that when it broke the pieces were traveling so quickly that gravity couldn't hold them together if it's a rubble pile very loosely consolidated we couldn't sort of shed off material and form a moon and it will stay in orbit and maybe 15% or so of asteroids a few hundred meters wide the earth what object anyway have satellites like this so that's pretty cool I thought so this is all very interesting and unusual physics but what does this have to do with the earth this is what the danger part of the title comes in it may seem a little bit overblown but it could have been worse Louie and Walter Alvarez who used to be over at Berkeley many years ago had a book they entitled t-rex and the creature of doom you can find it copies around and they were referring to this so this is the Yucatan Peninsula in southern Mexico 65 66 million years ago an asteroid 5 to 10 kilometers wide hit the earth right there it made a very large hole that hole is now actually not that obvious on the surface it's covered up by the last several tens of millions of years of sediment but if you do very detailed geologic mapping it shows up there's lots of fractures in the limestone rock so if you are on the part that's currently on land you find a huge number of sinkholes in the rock tracing along the crater rim if you look at the bedrock underneath all the sediment you see this nice double ring pattern so this is a very large crater 66 million years old geologists back in the 1980s were even before that we're going around the world trying to understand a pattern you find rocks that are 66 million years old there are many different sorts of dinosaur bones in them but there's a very narrow layer and then above that there are very few dinosaur bones no dinosaurs other than birds and a lot of other species disappear too there was a mass extinction event what triggered this well that layer that I mentioned the KT boundary the Alvarez is so again over at Berkeley back in the 80s it's some very careful geochemistry and they realized is that layer globally is loaded with iridium iridium is interesting element if you take the mixture of stuff that we may planets out of you tend to get to metal nickel and iron mostly rocks liquid oxides and then water and carbon compounds the earth is relatively low on the water and carbon and very high on the silicate rocks and the metal the metal all sinks to the middle of the earth so there's a very large ball of nickel iron several thousand kilometers below our feet right now that ball is what happens to contain almost all the iridium in the earth it mixes in with the nickel and iron very well and doesn't mix in with Rockwell at all so all this iridium at defining in the KT boundary layer had to come from somewhere it probably didn't come from the core of the earth one place it can come from is an asteroid because you have a differentiated asteroid you break it apart you know you can have pieces that have significant quantity of iridium in them or you have a non differentiated asteroid and has a certain amount just to begin with so they predicted that there should be a large impact crater somewhere in the world that caused a mass extinction 66 million years ago here it is so this is the dinosaur killer now impacts like this happen on the earth very rarely perhaps once per hundred million years they don't necessarily cause a mass extinction there have been a half a dozen different mass extinction events in the last few hundred million years only the one 66 million years ago is convincingly linked to an asteroid impact and the geologists and paleontologists can discuss that with much more expertise than I can but large impact events like this do happen just very infrequently now there are more small asteroids and large ones smaller impacts happen more often how many people here in the audience have been to meteor crater in Arizona okay quite a few of you you all recognize this picture so meteor crater is several hundred meters wide and pretty deep this was made by an asteroid about 50 meters wide so much much much smaller it is quite well preserved because it landed in the middle of the desert in Arizona and this whole area around it is the ejecta blanket so this object came down pretty much straight and vertically it happens to have been made of nickel iron which a couple of percent of asteroids are busted up cores of larger objects from the main asteroid belt hits the ground and you can go around now at the metal detector if the owners of the site will let you do that and you can pick up bits of that beat here so so blame this happens on the earth every few thousand years this one is about 50,000 years old I forget the exact age but it's quite well preserved most of the time they happen in the ocean and then even if they actually reach the bottom of the water they get covered over by sediment fairly quickly there's a bunch of other impact events of craters the different sizes scattered around the earth many of you may have seen this still from a video from a video if not you can go onto YouTube those of you are already watching on YouTube or can look things up while you're watching me you will see all sorts of videos of the place called Chelyabinsk in Russia it's a city of a million people roughly just over five years ago this happened just around local sunrise so the asteroid in this case was about 15 to 20 meters across what smaller than the even the meteor crater in Arizona impactor this one came in at very shallow angle and so rather than actually coming to the ground intact it was stopped pretty high up in the sky now the asteroid has fallen through the Earth's gravitational field at this point so it's picked up quite a lot of velocity in addition to the many kilometers per second had already had relative to the Earth's orbit around the Sun all that kinetic energy has to go somewhere it gets converted in this case to heat and light and sound the fireball of Hariri flee out shown the Sun there were a couple of cases of meteor sunburn which is not UV burns it's just the sunlight that's only the meteor fireball light getting focused a little bit people were standing in awkward locations and actually get significant skin damage from that we're common problem what do you all do when you see a bright flash of light in the sky I'm hearing various responses here and people tell you those had many different reactions a lot of people ducked other people went to the window the shock wave travels at the speed of sound 30 seconds to a couple of minutes later depending on where in the town they were shock wave hits the window there were a lot of injuries from broken glass there also a lot of injuries afterwards people stepping on the broken glass about 30 million dollars u.s. in damage 1600 people were injured nobody died but it was a pretty near thing so bill I could tell you abyss compactor happens somewhere in the world about once every 30 years most of the time over the middle of the ocean less of a problem but we'd like to know about the next one that happens over a city before it happens so how do we deal with this there's a large number of survey programs that have been funded by particularly NASA for the last more than twenty years now and also Pacific funding for other countries you see here the three most prolific at the moment the Catalina Sky Survey in Arizona the pan-starrs project in Hawaii the wide-field Infrared space explorer was initially an astrophysics satellite it's been repurposed for its extended mission solely to find and track near-earth asteroids and characterize them the goal here is find every possible near-earth asteroid before it comes anywhere near the earth if we can there's also a project called Atlas which aims to find things most things like to tell you best impactor with a few days to a couple of weeks of notice they still have a blind spot because we can't really observe directly near the Sun there's a proposal out of the different cultural Laboratory in Pasadena led by Amy Mainzer that would called neo cam that would use technology derived from wise to look right near the Sun in the infrared from space which you can't do from the ground and that way you can find asteroids that are coming straight towards us from that direction but the general goal here is find as many raspberries as possible predict their orbits out as far as we can and currently we're discovering about 2,000 near-earth asteroids a year I say we I involved in these survey programs myself there are many dozens of people involved in all of them and I don't want to take credit for the work of other people I do mostly characterization of asteroids that have already been discovered so this project has gotten called Spaceguard after an old arthur c clarke novel but it has done its job initially the goal was to find all near-earth asteroids larger to the one kilometer in diameter because smell like that no matter where it hits in the world we're gonna have a very serious problem fortunately we are now tracking all of those objects we know that we found almost all of them because the radio which had discovered them went up very steeply in the 1990s as CCD cameras got better and telescope surveys started operations and it's now dropped waste deeply down almost to nothing so we were finding and tracking it almost everything it's more than one kilometer across in the near earth population above a few kilometers in diameter we're tracking everything because spacecraft that are orbiting the Sun can see large asteroids even on the direct opposite side of the Sun from the earth they can't see the sort of one kilometer sized ones there may be a couple that are just on the far side of the Sun most of the time we'll wait for them to move around but we can say there won't be any impact by anything bigger than one kilometer across on to the earth in the next few hundred years there is one object that had called 1950 da that has a slight chance of hitting the earth in the year 2880 I cannot yet rule it out it's been annoying me for the past ten years fortunately we've got plenty of time to figure that one out we are now extending the survey program down to find and track stuff down to everything down to about 140 meters maybe we can push it down to 100 meters there stuff like Chelyabinsk sighs you don't get decade's worth of advance notice you may get a few days or a week which is enough to tell everybody in the affective zone to stay away from the window when we find the asteroids we want to characterize them as best we can and track them as precisely as we can this is stuff that I am working on particularly with groups of people at Arecibo Observatory in Puerto Rico you see it in the upper right and then the Goldstone site in Southern California which is part of NASA's Deep Space Network and run by a group at JPL for the radar program in this case we send out a radar signal be coded in time so we can image the asteroid we're bouncing the radar beam off and this gives us pictures like you see here they're not as detailed as the spacecraft images we can study a lot more objects and you see here just a wide range of shapes some are lumpy spheroids they're not entirely round but you've got rocks scattered everywhere you've got things like you know kaua to pieces sitting on each other this one here 1994 so you see is kind of fun it may not be entirely obvious there's a bright dot there and there above and below the asteroid itself that's two small satellites this is a triple asteroid system it has two moons orbiting and not just one so we're doing cool science here a nation to making sure they aren't going to hit the earth we do tend to get a fair number of false alarms because initially we can't predict the asteroids orbit all that well we measure its position on the sky very measured how fast it's going there's inherent uncertainty in that measurement you run the orbit out in time the uncertainty region where the asteroid could be in the future keeps growing it may not necessarily grow linearly but generally speaking further in the future the harder is to predict where is going to be so in 2011 we had this particular case after a 2011 a g5 was discovered early in January of 2011 hence the telephone number initially our predictions of the orbit are pretty uncertain there's a long region where it could be we didn't know its orbital period perfectly effectively so it's good spreads out along a line that line happens to intersect where the earth will be in 2040 so the earth is there there's this long streak hundreds of thousands of kilometers long we say at this point though there's one chance in 500 and hitting the earth but this is just a way of quantifying our ignorance of where exactly it's going to be the first thing we want to do is go get more data and refine our knowledge where the object is so a year later 2012 got observed again we now know that in 2014 2011 85 will be over here the earth is here so it'll be a couple times further away than the moon is from Earth no risk to anyone and if we're still doing radar astronomy in 2040 we will plan some cool pictures okay what do we do if we find an impactor the really small ones much smaller than tell you been sick we go meteor hunting in this case we is Peter unis skins at the SETI Institute Peter is a professional at meteor hunter so he gets to go to the most unusual places in the world if he thinks he can find meteors there he found some stuff up in Sutter's Mill a few years ago you may have heard about that one it was some of the old gold rush areas that had meteors dropped off on them he also got to go to northern Sudan in 2008 asteroid 2008 tc3 was discovered 30 hours later it flashed in the sky above the Sahara Desert this caused a certain amount of anxiety for a little while because a bright flash an explosion in the sky above Sudan is a little bit anxiety provoking for many people but all it did was drop a bunch of meteorites across this section of the desert so peter unisons flew over to Khartoum Moishe dad is a professor at the University of Khartoum and many of his students organized and they impede hiked back and forth across the desert and picked up a bunch of meteorites so many of you ever visit the SETI Institute offices you can see pieces of this meteorite those are the very small objects some be like Chelyabinsk impactor maybe Peter would run towards the explosion because he likes to run towards me yours I make fun of him about this most people would want to stay a significant distance away larger impactors you talk about moving people out of a city if you have a few days to a few weeks of notice there is a group at FEMA Leviticus Lewis been working with actually integrating what happens if we have to evacuate a city due to impending asteroid impact into disaster planning hey it happened once think about this if we have something like the larger objects though a few hundred metres wide then we talk about asteroid deflection so again nothing one kilometer across or large will hit the earth the next few hundred years there is a possibility of something a few hundred meters wide we haven't ruled out all of those potential impacts yet we haven't found all the objects and the orbits are still uncertain for a large number of them so how do we move an asteroid if we have to there are several different ways people have talked about for doing this two of them have gotten the most attention these are kinetic impact deflection and gravity tractor deflection kinetic impact deflection is in concept fairly simple you shove the asteroid out of the way but how do you move out of a rubble pile the size of a small mountain you take a spacecraft that has to be fairly heavy and you run it into the asteroid as fast as you possibly can so if you have a spacecraft that is 100 million times less massive than the asteroid and you are traveling at ten kilometers per second you will shove the asteroid out of the way by a tenth of a millimeter per second that may not seem like much but if you add it up over tens of years decades out you can deflect an asteroid by thousands of kilometers especially if you can time it such that you do it before or say a closer the closer is flyby before it could hit the earth because then its orbit gets changed for dramatically this has however one disadvantage which is that it depends entirely on the target that you hit you don't know exactly how what rubble pile is going to react to getting hit with a hammer let alone a large impactor like this so there's an inherent uncertainty had a rubble pile asteroids react to getting hit by ten kilometers per second we have done impact your experiments before the Deep Impact spacecraft flew into a comet to study the mechanical properties of comets it didn't change the comet / perceptively but comets and asteroids are two different classes of objects so we're like a test of that potentially on an object that can't hit the earth move it onto an orbit where it also can't hit the earth - has some confidence that we could do this in real time if we had to there's a strict rule here we're not going to create an impact hazard when we are trying to address the impact hazard there's also the gravity tractor deflection approach which we'll talk about for a couple of minutes this one sounds more like something out of Star Trek but it does actually work in concept your talk about how the asteroid has very weak gravity it's very weak but it's there so if I have a spacecraft you see in the artist's depiction here on the right hand side next to asteroid there is a very weak gravitational pull from the asteroid on the spacecraft pointed downwards at the same time again Newton's third law you clone opposite reaction the asteroid is getting pulled towards the spacecraft again this is very very weak we don't normally think of it mountains getting pulled towards us just because we're standing next to them but if you're in freefall microgravity around the Sun this can accumulate with time if you can find some way of adding momentum to the system you can do this by taking your rocket exhaust at angling it so that it misses the asteroid now rocket exhaust is going that way and if you balance everything correctly the distance between the spacecraft and the asteroid remains constant but the Astrid is getting very slowly pulled in this direction this has a couple of advantages one is that it's very very well controlled you can apply the deflection gradually and you can see how much you've done you can apply more and more and more whereas with the kinetic impactor deflection you only get one impact per spacecraft because they're destroyed on impact the gravity hacker deflection also is independent of the internal structure of the asteroid you pull on the whole thing nearly uniformly very slowly pull it off course the downside is that's very slow so you might need 50 years to move an asteroid by ten thousand kilometers and change an earth impact to a non impacting one but in principle this can work you do however have a formation flying problem you have to very precisely control where your spacecraft is and you have to have rockets that can run continuously at a low level of thrust for a very long time there are rocket engines solar electric propulsion designs of various concepts they have run for several years at a time not for quite so long and not for deflecting asteroids around so there have been proposals by NASA and other space agencies to test both of these asteroid deflection techniques so far only the kinetic impactor deflection project has actually been approved the asteroid redirect mission was the NASA concept for gravity tractor deflection demonstration that was cancelled a bit over a year ago but the dart mission is going ahead NASA missions have a tendency to have contrived acronyms dart is double asteroid redirection test this in turn is part of the asteroid impact and deflection assessment or Aida those are the mission names but the concept here is that we'll take a spacecraft and run it into an asteroid and see what happens now the dart project which is being led by Terrell Reid over at the Applied Physics lab right now the goal is to run into the satellite of a binary asteroid because in this case we have a relatively small asteroid did a most beta official designation for the thing that's an orbit around a larger asteroid and if we hit the spacecraft into the asteroid it could destroy on impact and it shoves both the orbit of these two objects together around the Sun slightly more importantly it causes much larger change to the orbit of the moon around the main asteroid so we have redundancy in the design if we can't measure the deflection directly by a monitoring spacecraft or radar ranging we can observe just the light we call the light curve of the system time when that satellite passes through the asteroid Shadow at particular times very precisely and measure even a very small deflection independently of any instrumentation that might be flown along with the spacecraft so dart is going forward you can get information at the web address there and it is to do this deflection of asteroid innermost beta in 2022 if the mission goes ahead we'll see what happens I'm just gonna finish up by mentioning that there's a lot of other asteroid missions that have happened I've talked about some of them already but it'll is actually just how many there are until I put this slide together despite actually knowing about all the missions it just struck me as how many there are when I made the list so there have been three asteroid missions in the past two near-earth objects the first one was the near shoemaker spacecraft which landed on the asteroid eros after mapping the whole place back in the 1990s through to the very early 2000s 2005 the Hayabusa spacecraft got to the asteroid Itokawa this is the other side of Ito Kalwa from what I showed you before and then in 2012 the chunga two spacecraft flew by the asteroid Toutatis Chonga to is part of the chinese space agency is a lunar exploration program it was interesting orbiting the moon they played some fun orbital mechanics tricks to fly it out of Earth moon space and arranged it to pass very very close to the asteroid Toutatis less than one kilometer from the surface actually which is a little bit closer than they had intended so I'm glad the radar predictions that where the asteroid was and how it was arranged in space were correct if I was giving this talk a month from now I might be showing you pictures from Hayabusa 2 which is currently on a final approach to the asteroid ryugu it's closer to the asteroid than we are to the moon right now but coach Leo chicawa team is doing very good work there and I do have a lot of data soon but right now it's just a dot on the spacecraft's cameras the osiris-rex spacecraft is on the way that's we did ask which we have radar observations of so we can make a computer rendering of it but we don't have actual pictures yet those will come in August of this year Ben who has a series of potential Earth impacts between 2175 and about 2200 the impact probability you may see assessed as one in thirty seven hundred or so right now again that's just a way of quantifying our uncertainty and where the asteroid will be osiris-rex will provide extraordinarily accurate measurements of where Venu is in space and how fast it's moving better that we can get from the ground and it will do that for several years until it leaves the asteroid to come back to the earth a few years and that should help resolve the ambiguity and where Benny will be at the end of the twenty-one hundreds and ideally it'll rule out the impacts or it may rule out some of them and not all of them we'll see what happens I talked about Aida in dart that will actually visit another asteroid 2001 CB 21 it just happens to be able to fly by it on its way to ditto MOS and then there's another pride other projects any a scout is a small satellite project by julie castillo rogas down at JPL destiny is another small satellite project by Tomoko RA in Japan that's to go to the asteroid faith on faith on this kind of fun it gets very very very close to the Sun closer to the Sun than mercury so it actually heats up to the point that not only do we have your Akatsuki effect pushing it around the heat stress actually causes dust grains to crack and fly off the surface so it causes a meteor shower on earth every year no hazards to the earth anytime soon but it does create a nice light show and then there's a proposed Chinese asteroid mission that would go to a couple of other asteroids including an asteroid called Apophis Apophis keeps getting featured in discussions of the impact hazard because it very briefly was assessed as having a few percent chance of hitting the earth II in 2029 this was back in 2004 it very quickly became clear that it will not hit the earth in 2029 it will however come extraordinary close to the earth so anybody wants to travel to Brazil you can see it fly by with their naked eyes overhead in 2029 if you want to make travel plans alright so I have talked about a lot of stuff and I think I'll finish up here and I'll switch over to questions thank you again honey are your Yarkovsky effect if you had an asteroid that was uniform on you know a surface and reflection and you know perfectly spherical wouldn't the effect of light from the Sun would be to add energy to the asteroids orbit without necessarily giving it more spin so that it would actually get into an elliptical orbit over time so there's actually a couple of effective is direct radiation pressure from the Sun some like coming in that itself has momentum when there's the air Kowski effects of thermal radiation heat going back out oh and I actually meant to sound let's to say the asteroid wasn't spinning so if it was spherical and not spinning and uniform and it was completely magically completely still and not spinning then you just have solar radiation pressure and that does change the eccentricity of the orbit right those the are calcia acceleration but the main effect of your cough ski in the short term is to change the semi-major axis yeah I know even in an asteroid that's spinning some of the light is instantly reflected and you have to correct for both reflective sunlight and reradiating yeah okay every year we seem to go through a a cloud of meteorites why doesn't that just sucked into the gravity of the Sun why does this sit out there so if somebody's in orbit around the Sun absent some other force changing that or but it will stay in that on that orbit so if we have something like faith on which is occasionally spewing out dust particles that become meteors they stay on nearly the same orbit they tend to spread out a little bit because of things like radiation pressure and typically the first effect is to spread them out along the orbit so we get a long string of dust particles sharing the orbit of faith on or whichever other comet or asteroid and that forms a ring around the orbit and then the earth can run through that cloud it also spreads out around the orbit so that it may be hundreds of thousands millions of million million kilometers wide and the earth runs through that over the course of a day or of a day and we see those flashes for however many hours so it is in orbit yes and unless the centricity changes to the point that it falls into the Sun or gets too close that it vaporizes it stays in orbit yes so late last year there was this cigar shaped near-earth asteroid that got a lot of publicity through NASA etc on the news and I was just curious if you could comment on that if you knew what I was referring to and if anybody else knows more if anybody okay so mu Lua is not actually a near-earth asteroid it passed it near the earth but amumu is something far stranger it's an interstellar asteroid so this came into our solar system from the outside we haven't actually seen that happen before we've seen asteroids and comets get kicked out of our solar system the eccentricity he takes them out to the orbit of Jupiter they fly by Jupiter they can get just enough energy a flat of the solar system to keep on going like the Voyager spacecraft and New Horizons have done and they never come back we expected that should happen around other stars giant planets until the double star systems you can do this more efficiently maybe we had ever seen one before Oh Momoa was discovered actually after maybe his closest approach to the earth and was on his way back out but it became clear is traveling in very very very fast so fast that it could never have been gravitationally bound to the Sun in the first place so that was very new and exciting said he actually has a talk about that which is on the SETI YouTube channel several of the experts on discovery and dynamics of those objects talked about it so I was wondering if you can talk about the practicality of maybe using some of the effects you were talking about for either walking out or perhaps focusing sunlight to deflect potentially dangerous asteroids so people have taught the question is using your Kowski effect to move asteroids around yes this has been suggested but it's very very very slow so somebody worked out I think if you were to take a container of powdered aluminum which is very reflective and you were to coat one side of 1950 da asteroid I mentioned that has the potential impact in 800 years you could change the outcome of that impact not impact by 10000 kilometers over 800 years that's really slow and we prefer to do the deflection faster than that if we can so the gravity tractor deflection and the kinetic impactor deflection much more rapid earlier you mentioned what might happen to to a person on the surface of an asteroid I was wondering if you could expand on that and if there's a kind of relatable analogy or metaphor that that would capture that experience something along the lines of maybe loose no I'm not sure about this because again our normal physical intuitions tend to break down so nASA has discussed sending humans to near-earth asteroids or bringing pieces of asteroids in space to astronauts who are in space one of the uncertainties was what happens when you grab the surface I talked about you can have electrostatic charge buildup you might end up with some massive dust bunny like thing where the astronaut touches the surface and now their hands are coated in electrostatically stuck dust clumps and they can't move their gloves anymore that would be really uncomfortable for everyone but I don't know what a good analogy to that is maybe a dust bunny thinking come up with okay worried about this asteroid may hidden 800 years what's the exact date and particularly how big is that I'm sorry what is the exact date to that asteroid may hit in 800 years and how big is it I'm recalling that it's March 16th but I'd have to look it up how big is it it's about a bung it's a little over one kilometer across okay and that would do how much damage if you go online you can Google 19 1950 da tsunami you can see a series of simulations what happens if you drop it in the middle of the Atlantic I can't actually tell you where on earth it would land yeah because we can plot the this line where the asteroid can be we could plot that line onto the earth but I don't know how the Earth will be oriented in space at that point cuz the length of the day is uncertain and what's its chance it's about 1% in the current assessment when there's less than one we're not sure if it's somewhere of that order and maybe you want to find our ignorance here ideally we'll rule it out completely and it'll be a problem anymore but we need more data I'm hoping for tax day so even at these low densities can you not why would you not just land a rocket object we're robbing a rocket on it with a perhaps a diss sized contact plate if you will just push it it is a pile of rubble and you put a rocket engine and press it into the surface it's not clear how it reacts so I mentioned the asteroid redirect mission which was a NASA proposal the idea there was to pick up a block from the surface of a near-earth asteroid something but might fit on the probably fit on the stage and bring that back to earth one of the big engineering challenges there was how do you design a system to grab on to a large block that's several tens of tons and move it around space in a controlled way with a rocket moving around the entire rubble pile as opposed to a block that has a certain degree of cohesion that becomes much more difficult the gravity tractor has the advantage that it it just pulls everything uniformly was there a question here I was wondering if you have to destroy the satellite so how we have to this is for the kinetic impact reflection why it has to get destroyed on impact yeah so I talked about how we need as much momentum as possible momentum is the product of mass and velocity okay so if I want to move a asteroid that is 10 million 100 million times more massive than my spacecraft by certain amount I need my space we have to be traveling 10 million times 100 million times faster so I want to move the asteroid by a millimeter a second I need the space we have to hit the asteroid at 10 kilometers per second six miles per second it is very very hard to make a spacecraft that can survive or running into a mountain at ten kilometers per second people have talked about designs for impactors that actually survive the experience but it's a very hard problem this is maybe going a little afield as you are mapping all of the paths of these asteroids has anyone thought about using them as shielding for missions to manned missions to the outer solar system because if you could park your spacecraft in the shadow of one of these close approach asteroids for the portion of the mission when you're close to the Sun close you know we're close to Earth you could ride that shadow out to where you're shielding issues are less and you don't have to launch as much mass off earth so it uses a shield for the manned mission there is a whole separate talk about space resources and near-earth asteroids which I didn't have time for tonight okay there are several different companies and space agencies working on this and I talked about how asteroids contain lots of water and carbon compounds people talk about using those for life support and fuel but one of the other primary products is just pure mass you take all the rebel pilots you don't have any other use for you pilot into sandbags and you put that on the outside of your spacecraft for radiation shielding for humans and sensitive electronics so it's been talked about and there are companies working on it I just have time to talk about tonight what is the current estimate as to when it is thought that humans could go to Mars I am NOT that sort of engineer and I wanted him to predict what investments people will make in space in that particular set of space travel know what last two questions please what's the possibility of mining yeah now it's right so that's the space resources stuff that I talked about people talk sometimes about mining asteroids for platinum because I mentioned iridium which is a platinum group metal it mixes in with the iron and you have also platinum and palladium and so on that is actually not valuable enough to be worth money in space and bringing back to the ground instead the products are stuff to be used in space so you have pulled water out of asteroid material you can use that for fuel for life support for humans you could put carbon compounds out make plastic make composite material and potentially life support you can talk about using nickel iron asteroid material for making structural elements if you want to get really fancy you can was you can make solar cells out of the silicon but that's a separate talk all right Michael thanks for the talk and I'm glad you touched upon the space resources side so we didn't only explore the dark side if you will of any O's and yeah we should talk to Andy about organizing another talk on the other side of the coin the the space resources side but a question you know when we did the the FDL workshop and we talked about these mitigation strategies and we had the the gravity tug and the impact there was a third one which you didn't touch upon tonight and I wonder if that is now for some reason off the table or just didn't want to talk about it a too controversial but that's the nuclear nudge if you will can you comment on that the project here that bill was describing was the idea originally developed in 1990s that you would deflect an asteroid by setting off a nuclear bomb this is overkill for these smaller asteroids so you don't actually blow with the asteroid to pieces you don't want to do that because then you have a rubble pile bits going every which way instead you set off the nuclear device a few hundred meters above the surface and the flash of x-rays and gamma-rays vaporizes that whole side of the asteroid and that gives you a shove on the rest of the mass Megan Brooks I'll over at Livermore among many other people can tell you in detail how that would work for the smaller asteroids if we've got lots of warning time it's not necessary the kinetic impactor and the gravity tractor can do the job without the complexities of such explosives and also we're not gonna test that ever because there's international treaties that say we're not gonna put nuclear bombs in space I want to make one final comment if I may because I forgot to highlight it during my talk I want to emphasize just how international and collaborative all of this asteroid stuff is so you see here all the different space agencies that have been involved in asteroid missions we have NASA we have Jackson's Japanese Space Agency we've got the European Space Agency we have the Canadian Space Agency the Chinese Space Agency and that's not including the many other countries where people who contribute to asteroid survey and characterization are based Australia Chile do lots of stuff in the southern hemisphere South Africa and many other places because we want to cover as much of the sky as possible and find asteroids in all directions and that also keep tracking them no matter where they go on the sky so this is an international and global project by necessity alright thank you all again [Applause]

Channel: SVAstronomyLectures

Views: 11,053

Rating: 4.7142859 out of 5

Keywords: astronomy, science, astrophysics, science news, asteroids, cosmic impacts, near-Earth asteroids, NEO's, planetary science, space, solar system

Id: X3Uox3siAG8

Length: 62min 15sec (3735 seconds)

Published: Mon May 07 2018

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Near-Earth asteroids are a population of small bodies whose orbits around the Sun cross or come near our planet’s orbit. They turn out to be unusual physical environments: essentially rubble piles. They represent a natural hazard we ignore at our peril, because some of these bodies have the potential to impact Earth. Dr. Busch reviews the near-Earth population, programs to track and characterize near-Earth asteroids, and current efforts to address the danger of asteroid impacts.