The End of Life on Earth

foreign tonight we're going to be thinking about what happens when a massive bullied of Space Rock hurtles towards planet Earth this has happened at many epochs in and especially before human history for example there was an impact in 1908 this was when a 60 meter asteroid the size of about five London buses impacted in Siberia this is known as the tunguska event it was a Tuesday morning of the 30th of June 1908 when over Eastern Siberia there was a bright blue light nearly as bright as the sun that appeared in the sky there was an air burst and then a shock wave from as though a Stony meteorite had exploded the impact event within Earth's atmosphere was believed to be at an altitude of 5 to 10 kilometers when this reached the surface of the Earth seismic activity measured to be magnitude 5 on the Richter Scale was witnessed this was a big deal fortunately it was a very under populated area only three human deaths were reported but there was widespread damage all across the forest over 2 000 square kilometers of forest were completely flattened apart from a few stalks and strong tree trunks just to help you calibrate two thousand square kilometers is larger than London fortunately that particular 60 meter asteroid landed in the forest it did not land in a human populated area let's fast forward in time to last Saturday last Saturday an even larger asteroid flew past larger than the 60 meters of the tunguska event asteroid and that asteroid last Saturday came closer to Earth than the gap between the Moon and Earth captured in this iconic photograph known as earthrise by Bill Anders on board Apollo 8. the first crude mission to orbit the Moon this iconic picture was taken on Christmas Eve in 1968 and I want you to think about the gap between the moon which is unusually for us in the foreground and planet Earth this large asteroid that whizzed by planet Earth last Saturday nipped between that Gap so I want to show you that asteroid this evening we had a remarkable fly past but before we get into that let's just consider what is an asteroid an asteroid that the name asteroid comes from the Greek word meaning star-like but it's important to be clear it is not a star it is not in any shape or form a star it's not radiant it's a lump of Rock it doesn't give off light so it has loads of mass and it's a funny shape has its own little craters if it's been pitted by other meteoroids and any dust debris that it's encountered as it's been orbiting within the solar system this one here 951 gasparah was the first ever asteroid to be photographed it was photographed by the Galileo Mission um during in in the early 90s so the craters the little craters that we can see on this asteroid are a strong reminder that in space things hit other things and we can see that very clearly when we look closely at the Moon the Moon is littered with craters the moon has no atmosphere at all to protect its surface from the impact of craters and so we see very many of them when we observe them with a telescope for example so it's unsurprising if our nearest neighbor the moon gets so many impacts which are made manifest because there's no atmosphere to burn up the little examples that rock up sorry for that pun by the way um it should be no surprise that some do come close to Earth but when they get as close as half the gap between the Earth and the Moon it is perhaps time to sit up so I want to show you first of all what is the orbit of this thing that came so close last Saturday what is the orbit of the asteroid known as Neo that's near Earth object 2023 that's this year the Year of its discovery dz2 whereabouts does it belong in the family of orbits within the solar system we're very familiar with the aware the array of planets and little dwarf planet Pluto just appearing there on the right this is the solar system as we're familiar with it but as we'll see later this evening there's a lot more in the solar system in terms of numbers of bodies that are accounted for on this slide but the orbit of this particular um asteroid is shown here in white so the outermost orbit here is that of Jupiter the deeper orange orbit um closer in is that of Mars and the majority of asteroids in the solar system are in between Mars and Jupiter there's a big asteroid belt there as we'll see later but as you can see the white um path indicated here represents the orbit of the asteroid that we're talking about you can see it's quite an elliptical orbit but nonetheless the sun is at a focus of that ellipse so it's part of the solar system it's orbiting the Sun but its path can impinge on the orbital path of Earth it didn't last Saturday why do we know that it's Wednesday we're still here how close did we get is quite an important question to ask well it was this half lunar distance could it come closer in the future well yes it might it really could so the orbital period of this asteroid is three years 1098 days three Earth years so next time it comes round it's had a little nudge or a little knock on route sure it could hit no it could hit Earth or it could hit the moon or it could be completely knocked off course but why was it if it's got this periodic orbit of every three years every 1098 days orbiting on its elliptical path around the Sun why was it only recently discovered and when was it discovered it was discovered on the 27th of February this year why was it only discovered so recently well it's worth commenting at this point that the discovery of near-earth objects is hard it's hard because as I mentioned earlier we're talking about moving rocks we're not talking about radiant Stars so they're relatively faint these stars are often these asteroids sorry are often only visible for a few days or a week or two depending on where they are in their orbit if they are The Far Side of the Sun we're not going to see them because if they're The Far Side of the Sun with respect to Earth then they're a daytime object and you can't do Optical astronomy during the daytime it's strictly a nighttime activity if you are talking about an asteroid on an elliptical orbit then the the sinking the phasing of its elliptical orbit with Earth's fairly circular orbit is going to track with time and until you understand what the answer is you may not spot the pattern so it's definitely hard so detecting near-earth objects is not easy however a wonderful project called euroneer was specifically designed to find near-earth objects this is an international Consortium initiated by our video vadiveescu and miral beerland from from Romania this is the Discovery image of the asteroid that we're talking about it's that faint innocent looking blob in the very center of the image with the arrows pointing at it now let's just explain what these diagonal streaks are going across those are stars and normally of course stars with a well-tuned telescope stars appear as pinpoints and the telescope will track them through the night sky their movement of course caused by the Spin of the Earth but if you set your telescope to have non-sidereal tracking rates so it isn't following the stars but it's following whatever it is you're interested in then whatever it is you're interested in if you've got the tracking rates right will appear like a point source and everything moving through the sky at a different rate will just appear as a streak so that's what's happening here and here are all the people involved in making that Discovery some of the people here are software Engineers believe it was costing Boulder who made the actual Discovery but amateurs contributed to the determination of the orbit that confirmed it was heading our way using our inclusively here to mean the Earth and the moon so a lot of people are involved in making these necessarily multi-e-pock observations in order to determine is the orbit of this particular asteroid potentially a threat or are we completely safe when I heard that this asteroid was going past last Saturday I decided I should observe it and so I used some of my Global jet watch observatories the one that were facing the right way and the ones that didn't have cloud cover um and on Saturday that translated to South Africa and to India um this is a picture of the India Observatory and this is a picture of the South Africa Observatory so I use both of these telescopes simultaneously on Saturday uh late afternoon and Saturday evening UK time to see if I could observe this same asteroid from two different points on Earth I was in Oxford where it was bucketing it down with rain and operating those two observatories over the internet and when I said the observatories weren't covered in Cloud that was fairly true but not completely true this is a view through the finderscope of the South Africa telescope and this gives you a sense of the clouds that I was facing um on that evening while I was observing and it was a pretty similar story in India however there were gaps in the clouds and I have two hands and I was able to track those telescopes through these rapidly moving asteroid moves like the clappers with respect to the sky background and this is the so I'm tracking with respect to the Stars and that diagonal line there is the movement of the asteroid going through that particular Stellar field this movie is speeded up by a factor of 20. each exposure that I took was 20 seconds long but I'm showing these here as Stills for about one frame per second so that was India and this at the same time was South Africa so there was actually a gap in the clouds at both observatories at the same time plenty of occasions where one was cloudy and one was not um but anyway that was it oh those you see that little appearance of a few things there that's independent of the it'll come round about now there we go those are just cosmic rays so they too are falling out of the sky but not quite so much danger but there was a lecture about two years ago on those the title of which was fast and furious because they are but they don't have the same kind of mass that asteroids have so ultimately I was able to end up with these two simultaneous time lapses of the passage of the asteroid last Saturday these two are simultaneous observations and you may be thinking to yourself well Earth isn't that big and indeed in the previous lecture on Christopher Wren we learned about how The Parallax angles of stars won't change very very much if they if they're reasonably far away even if we sort of move the Earth from one side of its orbit around the Sun to the other well that's true but that's for stars which are much much further away than the moon or anything which is half the distance to the Moon so these Stellar Fields being different is another reminder of just how close this asteroid is that is imaged moving here so just a reminder about the Parallax Christopher Wren and Robin Robert Hook built the monument to function as a Zenith telescope he was Ren's design in order to measure the distances to Stars the experiment didn't work it was a very intelligent attempt but they didn't know of course a priori how distant the stars were that was the point of the experiment but the stars were so far away it was not possible to measure any Parallax angle for these particular Stars the the job the geometric basis for what they were trying to do was completely sound but um how what angle you measure as you measure from different locations with respect to your target depends on how distant they are away from you the asteroid that appeared on Saturday was so close that even from the relatively close locations of India and South Africa measured at the same time so you're not you're not moving which part of the Earth's orbit around the sun you're taking the observations from those were simultaneous observations and the separation of my India Observatory and my South Africa observatory in latitude is about 45 degrees and in longitude it's about 60 degrees so they're not even an Earth's diameter apart and yet this is how far apart those two Stellar fields actually were so I'm just zooming in here to how far apart they actually were so these grid lines are about one degree apart and so that's how far apart on the sky when viewed from over here in South Africa the asteroid appeared to be whereas over here in India the asteroid appeared to have a completely different background of stars and so it was fascinating to um to realize that this exact same body was so close that they had different backgrounds even from two parts of Earth the dance so far apart much bigger camera and I could have got them on the same detector but the the size of the detectors on these telescopes is about half a degree Square from top to bottom so I mentioned earlier that this particular asteroid Neo 2023 dz2 was larger than the asteroid that caused the devastation in that Siberian forest in 1908. but exactly how large is it I needed to look this up and so I dialed this into the internet and probably the most helpful answer came from the Metro I mean seriously it gave me a really useful calibration it said an asteroid about the size of the Big Ben clock tower the Elizabeth Tower and that's that's the kind of size that those of us who passed through London occasionally can relate to it's possibly a slight overestimate by the way it's probably a bit nearer 70 meters orbital today I think we're out by probably a factor of two or depends on how big you think a skyscraper is but typically they're taken to be at least 150 meters probably the most surreal answer that I came across on the internet was um in the uh Jerusalem Post astronomy is famous for using different units but using the tuna fish as a unit of length is a new one on me but it's 22 of them and I must admit I don't think I've ever seen 22 tuna fishes in the same place but there you go it's it's quite large way larger than this lecture theater um so had it have hit Earth it would have done a lot of damage so let's now think about that kind of damage what does happen when a large asteroid impacts on the Earth a whole series of really bad things happens first of all there's a blast wave a shock wave because the asteroid is typically traveling at really fast speeds the fast speed of that asteroid through the images I was just showing you was in excessive 10 degrees per hour that translates to something like I think it was 17 000 miles per hour in excess of that so really really fast way faster than the speed of sound so you get a shock wave and that's a large shock wave because you're dealing with a large massive body wishing through Earth's atmosphere and so you get frictional Heating and so the atmosphere gets super heated it gets heated very very rapidly and very very hot things will set fire to whatever's in the vicinity except ocean of course but but that's not a great outcome either we'll get to that the kinetic energy of the large asteroids so that's the energy that the asteroid has by virtue of its motion by virtue of its speed and its mass that gets converted into heat tremendous amounts of heat when the asteroid impacts on Earth if the asteroid first impacts on the ocean then that water will get instantaneously vaporized into steam which isn't good for living things either whenever the asteroid ultimately hits hard ground there will then be something of seismic activity any oceans any nearby anywhere nearby massive tsunami much much faster than the one that did all that damage nearly 20 years ago so there will be a tsunami for sure many tsunamis probably steroid penetrates Earth's crust then molten rock will spurt out at many kilometers per second so these are like intercontinental ballistic missiles directionless just heading out to cause havoc and when those spurts of molten rock or lava eventually return to Earth they'll ignite fires forest fires bushfires cities anything in their path will catch fire so it's not a great outcome it's been conjectured that a large asteroid is what killed off the dinosaurs it's very widely accepted that the dinosaurs which had been stomping all over planet Earth for a very very long time disappeared very very suddenly so I think it's widely accepted that there was an apocalyptic event which led to the end of the dinosaurs I don't think it's completely conclusively determined that it was necessarily an asteroid but a large asteroid fits many of the fats sinking into the north Mexico Coast so obviously that if it was a large asteroid that did indeed Wipe Out the dinosaurs we know that that was well before humankind existed and there have been another set of examples of large asteroids that have impacted directly onto Earth's crust so I thought I'd show you a few greatest hits so what do we have here this is the uh the meteor crater in Arizona known as the baringa crater after Daniel baringa this is over a kilometer in diameter modeling suggests that it was formed about 50 000 years ago by the impact of a meteorite that was 50 meters in diameter so that's slightly smaller than the tunguska event slightly smaller than the asteroid that did its fly past on Saturday it's been modeled that it was moving at a relatively leisurely 12 meters per second so that was thought to be a nickel iron meteorite just so happens in our home we have one of these it's a family heirloom we don't have dinosaurs as our ancestors by the way but this particular meteorite was discovered by my great grandfather-in-law in a little plot of land where he would grow crops for the family to live on in a little village in Warwickshire so it's it's about the size of my fist so it was probably a spectacular shooting star when it came through the Warwickshire Sky assuming it wasn't cloudy assuming it was nighttime because this is quite unusually large for a meteorite certainly to be found in such pristine condition there are some exciting examples of greatest hits in Africa this one is in the Kalahari Desert in Moroccan in the Northwest province of South Africa not too far from the border with Botswana uh this is it without water and this is it with water so it's quite useful when it does fill up with water it's thought that the asteroid or great big meteorite that gave rise to this was between 5 and 10 kilometers in diameter in itself this this crater is about 160 kilometers it's thought that this happened about 145 million years ago but happily it fills up with water these days um in May of 2006 a group of scientists drilling into the site announced the discovery of a 25 centimeter fragment of the original asteroid so several times larger than the one we have at home the size of my fist it was about 770 meters below the surface and there were other little fragments as well of the meteorite as it landed so it seems like a very clear Association crater's meteorites or asteroids depending on the size things hitting into other things in the solar system besides the moon which we've already talked about happen with other planets as well in the mid 90s Comics Shoemaker Levy number nine collided with Jupiter so this was discovered by Carolyn Shoemaker Eugene Shoemaker and David Levy was discovered in 1993 it went thwack into Jupiter into 1994. before it went headfirst into Jupiter this Comet had an orbital period of about 200 years it was determined by successive observations working out the trajectory of the Comet with respect to the rest of the solar system it actually broke apart during approach but it was caused a lot of excitement when it was discovered because it was the first comet discovered to be orbiting around a planet admittedly a very massive planet Jupiter rather than orbiting around the Sun so that was pretty exciting almost certainly Jupiter which is really very very massive relative to the other planets captured this Comet probably a few decades previously so this is an image from NASA and Esa from the Hubble Space Telescope showing the different fragments as they went into Jupiter here's some other Imaging from ESO loads of telescopes all over the world observed it break up and then go head first into Jupiter so it's not just planet Earth that gets hit by asteroids and comets and meteorites other planets will have them as well but clearly they have the potential to do a lot of damage here on Earth the vertiford crater is in the free state of South Africa the diameter of this one is 380 kilometers it's conjectured that the diameter the asteroid which gave rise to this was 25 kilometers so this is the largest verified impact structure on Earth the time of the impact was dated to be about two billion years ago and the speed of this large asteroid was has been modeled to be 25 000 meters per second we're talking about enormous Energies so how many asteroids are out there and what how much risk are we at here on planet Earth well the short answer to how many asteroids there are in the asteroid belt between Mars and Jupiter is many have we found them all no we have not opinions differ as to how many asteroids we haven't found because we haven't found them it's an unknown unknown but I have seen some remarkably precise percentages for something which isn't actually known but I'm not going to quote those to you because I don't know how real they are how many asteroids are out there how many do we know about well this graph here from NASA plots year of Discovery on the horizontal axis and the cumulative number that have been discovered on the vertical axis so blue is the all of the asteroids including the little ones um the the red ones are those that are that bigger than a kilometer so blue is less than a kilometer but all the all the detritus really so that's the most numerous number of asteroids um and then this orange color is those that are lighter than 140 meters so as we might expect there are numerous small asteroids and there are a few but not vanishingly few very large asteroids so there are many more little ones than there are big ones as we might expect and that's also represented here on this plot where it's a slightly busy plot but let me just explain it so on the top horizontal axis we've got the diameter in meters so one meter 10 meters 100 meters it's a logarithmic scale and if you make assumptions about the composition of the asteroids then that gives you a mapping to kilograms on the second top at the highest top horizontal axis bullied energy um kilotons TNT equivalent large amounts of energy basically is plotted on the on the bottom axis the closer you are to the right the more energy so unsurprisingly the big ones more energy when they go thwack and then this is the cumulative number impacting Earth per year so there are lots and lots of the little ones and they just manifest themselves as things we never see because they burn up in the upper atmosphere or pretty shooting stars which are very nice to see or occasionally ones like the ones the one that we have at home that landed in that Warwickshire vegetable patch but then you can see the probabilities here um the uh every every Century you'll you'll see one um that's 10 to the seven kilograms um in Mass this is an averaged type plot but it quantifies how rare the larger asteroids are thought to be but it's important to appreciate a they're not vanishingly rare and B we don't know everything that's out there anyway the asteroid that did the close fly past on Saturday was only discovered on the 27th of February about a month and two days so this shows you the inner part of the solar system again Sun and Earth and Mars and Jupiter and then the asteroid belt which is as I mentioned earlier in between Mars and Jupiter there are different types of asteroids that are represented here the so-called typical asteroids belong in the main belt but we also have the so-called armor asteroids which are the ones in this sort of white elliptical orbit here so larger than the orbits of the earth and potentially um Mars as well so are more asteroids don't cross the orbital path of Earth but they may cross the orbital path of Mars and indeed a new crater appeared on Mars on Christmas Eve of 2021 that was not there before it suddenly appeared and it was accompanied by a magnitude for Mars quake which is martian for earthquake so those are the Amor asteroids but the Apollo asteroids of which dz2 which I showed you earlier the one that did the fly past on Saturday is an example of the Apollo asteroids and the Apollo asteroids is the collective name given to a particular type of near-earth asteroid it's the sort where the orbital semi-major axis so the radius if it were a circular orbit but most of them are elliptical because they keep or occasionally from time to time knock into other things in the asteroid belt this parameter of the orbit is larger than the earth sun separation which is known as one astronomical unit but the perihelion distance which is the dis the closest approach between the asteroid and the sun Helios that periastron distance is less than the earth sun separation of one astronomical unit one a u so those are the asteroids we really want to watch because they might well cross Earth's orbit had the angle a dz2 being a little bit different from what it was it would have gone thwack onto Earth and we would have been having a different conversation potentially um today if we were still here to have had the conversation of course how many Apollo asteroids are there well seventeen thousand five hundred and forty are known so far 12 of these are identified as potentially hazardous asteroids potentially hazardous objects pho's in the jargon JPL has a register a threat register a risk register if you like of all these things and it makes for some quite interesting reading but I don't recommend it as bedtime reading so if you have interactions within the asteroid belt or from other asteroids further out the Trojans for example if there's an interaction with the gravity due to Jupiter their orbits will change they will move along a different path so we have to keep watching we have to keep Vigilant if we're to spot these massive bullies of Space Rock coming towards us so how do you identify an approaching asteroid well this can be answered as a number of levels but I just want to tell you um what happened when my friend and colleague the instrument scientist on the global jet watch Stephen Lee started observing um a dz2 from his garden in Australia it was about the only bit of Australia that didn't have clouds on Saturday as far as I can tell and I joined him over Zoom this was a few hours before it was dark in India and several hours before it was dark in South Africa I joined him over zoom and as we watched as we looked at these images coming in from his telescope on his computer the conversation went something like which one is the asteroid there seemed to be a lot of streaks in this image well of course we know and we soon clocked that it was this little one here what are these other long streaks that we're seeing well those are satellites moving on their orbits around Earth but reflecting just enough light that they appear as streaks because they're moving faster than the stars are moving um so they generally muddle up the picture slightly here it was pretty simple to discern discern what was going on after a moment's thought you had a lot more satellites you'd make it a lot more difficult I'm going to return to this point in a few moments but first I want to show you an image of Sir Francis Graham Smith he was the 13th astronomer Royal and he wrote in 1982 the following warning the cumulative effects of an ever increasing number of long-lived satellites represents a very serious Hazard to Optical observations that warning was written four decades ago when the number of satellites that were up was vastly smaller so what do we mean by a serious Hazard to Optical observations we probably mean that the images we take have streaks much like the last few that I showed you but but I put it to you it's going to get a whole lot worse than that and let me let me show you why I'm concerned about this so can we see what's out there can we see what's coming towards us can we see the threat so this shows you the plot with um the year on the horizontal axis and the cumulative number of satellites on the vertical axis this plot and all the data were gathered by my friend and colleague at Harvard Jonathan McDowell he has a great website planet 4589.org that you might like to look at back in 1982 when Francis Graham Smith issued that warning there were about 350 satellites that were orbiting around Earth now it's above um seven thousand so the numbers have increased considerably but they're going to get bigger just in at the end of January in this year getting on for 4 000 SpaceX starlink satellites and over 500 one web satellites have been launched so what difference does this make when you're taking an astronomical image this is a nice astronomical image it's one of from one of the commensal cameras from one of the global jet watch telescopes lots and lots of stars to give us onboard photometric data to go together with our spectroscopy data fantastic for science unless these guys rock up these are starlink satellites whooshing through our field and here's a zoom in close to the Target that we were observing at the time so Starlight streaks across astronomical images are increasingly a thing these on this table here this is listing the expected number of satellites in the next few years so the total number is going to increase by a couple of orders of magnitude it's going to make it very difficult to do Optical astronomy without light contamination streaking through the sky moving illuminated graffiti through the sky Jonathan has plotted the distribution the expected distribution of I think this is just the starlink satellites now I don't know if you can make out underneath these Blue Points the shape of the the land mass on planet Earth underneath if you can't maybe that's sort of the point there are going to be a lot of satellites up there now of course on this plot the size of the dots does not scale with the size of the satellite but they're moving they're going to be streaking through our images so if you think that that romanian-led team euroneer did really rather well spotting an asteroid just a month ago and warning everyone on Earth and then it was determined that no it's not going to hit Earth we're good if you think they did really rather well getting all that data in a month when it's winter in the Northern Hemisphere and there are loads of clouds you're right they did really well but once you start littering the sky with this moving graffiti is going to get a lot harder to make the necessary observations to find more asteroids specifically the ones that might pose a threat to Earth and we do live on a dangerous planet at the in my first lecture at the start of this year's series on Cosmic conclusions I spoke about the end of planetary atmospheres and I spoke then about how the tiniest concentration relatively tiny about 400 parts per million of heteronuclear molecules such as CO2 such as methane can seriously lead to a damaging positive feedback effect in our atmosphere when it's a concentration of of those heteronuclear molecules that is as Slender as the number of caffeine molecules in a mug of coffee and I discussed in that lecture the end of planetary atmospheres that that we are in danger we need to plan ahead and understand the threat and we do need to put our Collective Minds together internationally to overcome it we need to do the same thing if we're going to survive asteroids impacting on Earth how we as humans respond to the threats that do face us from outer space from our own poor stewardship of this planet will determine our survival or not on a slightly lighter note I really recommend the movie don't look up if you haven't seen it it's it's great entertainment it is political satire Meryl Streep is a an extreme right-wing U.S president Meryl Streep is wonderful of course but the mind boggles and these two are scientists who are trying to make the case to politicians who don't want to hear because they've just got their eye on the next election the imminent danger that was faced by a much more dangerous asteroid in that film than we faced with gz2 last weekend asteroid impact avoidance is a necessary industry and it is a serious industry if we can see through all the satellites and the clouds and find out Rocky asteroids which are heading our way we can do something about it and this was exemplified spectacularly last September I want to tell you now about the dart impact this was not a dart in the sense that they're played with here on Earth Dart here stands for double asteroid redirection test it was a proof of principal test to see if you throw something reasonably massive at an asteroid can you alter its orbit that was the test so think of this like Galactic snooker in snooker you fire the cue ball at something and if you're really skilled that something is one of the other balls and hopefully the right color goes in the right pockets and all that sort of thing it's a highly skilled Jet game involving conservation of linear momentum transfer of linear momentum from the cue ball to the other ball sometimes Spin and all that kind of good stuff so Galactic snooker is how we might be able to solve asteroids that are heading our way so on the 23rd of November 2021 a little satellite was launched and and this was this was a big experiment this was doing something that had never been done before can you throw so much momentum momentum at an asteroid that you can change its orbit impact took place on the 26th of September 2022. so the goal of the whole project was land on something that's either a minor planet or a moon depending what you want to call it in orbit around a little asteroid so the little minor planet or moon is called dimorphous and it's orbiting around an asteroid I'll show you a picture in a moment an asteroid called didymus so the goal is you land the spacecraft on it with sufficient force that you change the orbital Dynamics now the reason for choosing binary asteroid an asteroid and a little Moon little mini Planet kind of thingy which which actually is an eclipsing binary as observed from Earth is that when you've got eclipsing binaries you can readily measure the orbital parameters so you know if when you hit it you've made a difference or not so it's an excellent choice of Target the success Criterion was that there would be a change in the orbital period of dimorphous which was in excess of 73 seconds so the normal orbital period was a shade Under 12 hours and they wanted to see if they could make the orbital period shorter by about a minute so here's a schematic showing didymus the asteroid and then dimorphous the slightly less massive um little Moon type thing it's in orbit around didymus this is Dart the spacecraft and this is the paparazzi lysia Cube taking pictures and of course back on Earth there were lots of images being taken so this was operated by NASA and many other groups out of Johns Hopkins University um the actual orbital period by the way was 11 hours and 55 minutes prior to impact following impact that orbital period got shortened by 33 minutes over half an hour so the success Criterion was 73 seconds and they really overshot the success threshold they achieved over half an hour change in orbital period in something whose orbit was less than half an Earth Day so fantastic success the orbital parameters did change a little bit lots of good photography was obtained I really recommend you go to the dart website to look at some of the Fantastic footage as the dart spacecraft gets closer and closer and closer hold on to your chair while you watch it though this is one of the observations showing the trail of dust and debris post-impact so it's pretty clear that when you swack a spacecraft into an asteroid does quite a bit of damage as well it's not quite as bad as an asteroidating a planet but nonetheless you you do break up the surface a bit and that streak could be seen for quite a few days afterwards so if we can detect asteroids coming towards us the dark Mission has demonstrated the proof of principle that clever engineers and clever orbital dynamicists can work together and can knock it off course so that principle has been demonstrated I think the difficult thing is finding the threats as they come towards us so even though we have Grounds for Hope that we might be able to deflect an asteroid and you don't you don't need to destroy it to Smithereens you just need to knock it off course much as you would in a game of snooker but we still will need warning to plan exactly how to direct the spacecraft and with what momentum and what angle of attack we should give it Advance warning to face these threats is critical so not only do I think there are grounds for concern because of the satellites that are going to be rocking around up there in the coming years I think potentially if we don't hold lots of ideas in our heads at the same time and face a great many problems that are facing humankind altogether such as climate Heating we could risk solving one problem and leaving ourselves very vulnerable to the other problem what am I talking about here what am I getting at I'm getting at some of the proposed Solutions or a small subset of the proposed Solutions to have a catastrophic climate Heating I'm talking about a particular type of geoengineering where you um you modify the solar radiation by putting up lots and lots of aerosols lots and lots of particulates so the motivation for doing this is that you don't get as much solar radiation and solar energy landing on Earth and Earth's atmosphere and heating it up quite so much is that a good idea hmm here's the problem I mean umbrellas are great parasols are great shade is a really good thing but if you do it in an uncontrolled way with the entirety of Earth's atmosphere I think that's a real problem if you inject particles into the stratosphere those particles won't just absorb the solar radiation or some of it and hopefully reflect some of it back but they'll also be reflecting it and scattering it in all directions including back to Earth so that particular kind of geothermal proposed solution sorry geoengineering proposed solution is fraught with Danger we will no longer have blue skies if that happens we will have white Skies much like we get in the UK on cloudy days this is a really dangerous idea and it could go horribly wrong we will lose the ability to see deeply into space if you've ever tried observing when your neighbors have had a barbecue and the smoke in the air or there's there's lots of Cloudy particles or there's high cirrus you don't get to detect very faint objects and it's a disappointing um astronomical evening we need clear skies if we're going to be able to detect the threats that may face us on that cautionary note I will end this lecture but I would like to say keep looking up thank you [Applause] many many thanks we have time for probably two questions so I'll start one from one line this one is apart from the impact from an asteroid what is the danger from a nearby Supernova explosion or for example a gamma-ray burst pointed towards death thank you so if we had in our local neighborhood in the vicinity the kind of progenitor star that could undergo a supernova explosion then that would be pretty bad too however as I mentioned a couple of lectures ago I spoke about the end of massive stars there are no really massive stars sufficiently close to planet Earth that that's believed to be a real Danger we think um gamma-ray burst could be could be um again same sort of answer yes in principle yes in theory but we don't believe that in our context planet Earth in the solar system there's any progenitor of a gamma-ray burst that's quite close enough to be a danger so I wouldn't worry about those two too much um how big could an asteroid get and the impact which still allow us to survive in the earth to survive oh goodness um the answer to that would depend very much where um the asteroid lands if you go to a carefully if the impact of the asteroid were to be in a carefully chosen bit of the Pacific Ocean so nowhere near the Marshall Islands nowhere near Hawaii just a nice big deep bit I should have thought so any of the greatest hits that I showed earlier in my talk would result in tsunamis and that that would certainly cause significant loss of life on low-lying land but humankind I think would survive if you had one of those really big ones um to land on the UK for example it's conceivable you could wipe out an entire nation how big could it be it it certainly wouldn't need to be um I'm somewhat guessing here but I think I think if you were getting on for several tens of kilometers you would really want to be putting all your resources into deflecting that one rather than doing the calculation and wondering if you'd wipe everyone out I think those are really rare by the way so don't lose sleep do we have any questions in the room thank you as dz2 comes so close to the Earth is it likely to be affected by the gravitational field and could we track a new orbit thank you I think we'll certainly be tracking dz2 um because it's of such great interest to us I think it's unlikely that there would be a very dramatic um kick or swing from planet Earth because we're nowhere near as massive as Jupiter um for example having said that the um the trajectory so close to Earth was probably non-negligible but my guess would be without having done any calculations you probably wouldn't see that play out for a few orbits and indeed it might be completely um impossible to pick out if there are other deflections and direct hits with other things on its orbital path I think it's not likely that it will be too significant I'm afraid that's all the time we've got this evening Professor blundell's neck sector which will round off the series will be the end of the universe and that will take place on the 31st of May we hope you can all join us then thank you very much and thank you [Applause]

Channel: Gresham College

Views: 12,646

Keywords: Gresham, Gresham College, Education, Lecture, Public, London, Debate, Academia, Knowledge, astronomy, physics, science, Tunguska, meterorite, moon, Bill Anders, asteroid, 951 Gaspra, NASA, Global Jet Watch, Near Earth Objects, EURONEAR, ParaSOL, Stellar Parallax, Morokweng, Shoemaker-Levy 9, comet, Vredefort Crater, Mars, Lucinda Douglas-Menzies, Francis Graham-Smith, astrophysics, DART, Dimorphos, Didymos

Id: o39KtAA9flE

Length: 60min 11sec (3611 seconds)

Published: Wed Apr 12 2023