the king has called for unity and has offered a message of thanks to the police and emergency services, for restoring peace to areas affected by violent disorder across the uk. more than 740 people have now been arrested. ethiopia's tamirat tola has secured gold in the men's marathon on the final weekend of the paris olympics. team usa face france in the blockbuster men's basketball final tonight. 39 gold medals are up for grabs on saturday. now on bbc news...the sky at night: will an asteroid destroy earth? right now in the solar system, there are around 1,500 asteroids that scientists have identified as a possible threat to earth. but it's thought there could be millions of asteroids out there that we haven't

even found yet. detecting potentially hazardous near—earth asteroids is now a priority for astronomers. and they're developing planetary defence systems that feel as if they've come straight from science fiction. we're investigating the latest research on the threat of an asteroid hitting earth. i'll find out why we didn't see it coming. we will be hit again. i'll learn about the recent planetary defence mission that deliberately smashed into an asteroid to knock it off course. there is the potential to use a nuclear stand—off weapon. exoplaneteer george dransfield discovers the role asteroids may have played in starting life on earth. are you telling me that life on earth is extraterrestrial in origin? so wrap up warm, get outside and look up. welcome to the sky at night.

asteroids have been hitting our earth for around four billion years. most famously, the chicxulub asteroid wiped out the dinosaurs and transformed life on this planet. 0n the 15th of february 2013, a 10,000—ton asteroid entered the atmosphere over the russian city of chelyabinsk. it exploded with 30 times the energy of an atomic bomb, injuring 1,600 people.

and we didn't see it coming. professor alan fitzsimmons is an expert in the observation and measurement of asteroids. he's one of the scientists trying to make sure we don't miss the next big impact. now, i want to start with some jargon busting, because there's a lot of stuff out there. there's asteroids, there's comets. can you take us through that? sure. asteroids, like good old bennu here, are objects, rocky objects that orbit the sun. we also have comets, of course. comets have a lot of ice in them. now, if that asteroid enters the earth's atmosphere, then we see it glowing as a meteor or shooting star. if they make it to the ground, that is called a meteorite. meteorite. and here's one here. they're always far more dense than i would anticipate. so, how are you monitoring the asteroids out there? this is one of the atlas telescopes. this one is in hawaii. it's designed to pick up small

asteroids that may be heading towards earth on an impact trajectory. and down below here, we can see some of the images it's taken in the past ten minutes. so this is the early—warning system — it flags up for sort of further investigation? they detect, in total, about eight new near—earth asteroids every 2a hours. it's amazing. so far, they have found over 31,000. of these near—earth asteroids, around 1,500 have been identified as potentially hazardous. so, what asteroid should we be worried about right now? well, there's a few up there, and one that's been on the risk page for almost 20 years has been the asteroid apophis. and you can see it here. 0h, right. in fact, in 2029, on friday the 13th of april... it would be friday 13th! it would be. it's going to make a very close approach. we're worried about it because we know it will miss us, then. it's going to miss us when it returns in 2035.

but it keeps coming back, and it's about 250 metres across, so that, if it hit, this would wipe out a small area of the earth. you know, something, the size of a county or even a small country would really feel those effects. wow. it's reassuring that alan is monitoring these potential threats so closely. but what i want to know is why some harmful asteroids still get missed. one of the most recent sort of devastating impacts was chelyabinsk. now, why didn't we detect that before it actually hit? well, there are reasons. first of all, chelyabinsk itself approached on its last trajectory from roughly the direction of the sun, where our ground—based optical telescopes can't look, of course. now, we could have tried to find it on a previous orbit, but chelyabinsk was really small. it was only 18 or 19 metres across. it was just too faint for us to see. objects the size of chelyabinsk and larger, there's probably about a million,

and we are still very inefficient at detecting near—earth asteroids in that range. so these small objects, although they don't wipe out whole species like happened with the dinosaurs... yes. ..they hit much more frequently. chelyabinsk — it injured 1,600 people. yes. and we really do want to be careful to try to catalogue as many of them as possible. thankfully, the tech is catching up. in 2025, the vera rubin 0bservatory will give us the widest—ever view of our skies. and in 2025, nasa will launch a new orbiting mission, the near—earth 0bject surveyor. we hope, within about a decade, to have swept up most of the potentially hazardous asteroids in our sights. so, we should be confident? i think we should be confident, but we shouldn't relax at all. we are still finding new near—earth objects every day, and we know at some point in the future, we will be hit again.

tracking these asteroids and understanding the risk they pose is hugely important. but the next step is knowing if we could actually stop one if it placed us in harm's way. and lift—off of the i falcon 9 and dart. nasa's double asteroid redirection test, or dart, was an experiment to see whether we could redirect an asteroid by intentionally smashing into it. 7,6... oh, wow. ..5, 4, 3, 2... it crashed into it at more than 13,000 miles per hour. and for the first time ever, we deliberately changed the orbit of a planetary object. i want to know whether the success of dart means that we'll be safe when an asteroid poses a real threat to life on earth.

professor simon green at the open university was involved in the preparation for this mission. so, simon, what was dart trying to do? well, dart was designed to deflect an asteroid by using what's called the kinetic impactor process. so it uses a spacecraft to hit the asteroid and change its velocity ever so slightly, so that it changes its orbit. the surface of an asteroid will look something like this. it's called regolith. it's a powdered material with larger pebbles in it. so we're hitting a rubble pile, not a solid object. yeah, yeah. and it will throw off particles that change the way in which the asteroid will respond to the impact. the composition of the asteroid determines how it will behave when the spacecraft hits it. simon tests this in his lab using different materials. this is a momentum stage, and it's essentially a bucket on springs, and it allows us to measure

the momentum transfer when a spacecraft, here it is, hits an asteroid. which in that case is made of wet sand. 0k. so let's see what happens, shall we? bull's—eye! and it just sat there. yes. because the wet sand absorbed the impact of the spacecraft. when the ball hits the target made of wet sand, it should stop dead. i'lljust give you the ball back first. so, here you go. next, simon tries a material that is much more like the composition of an asteroid like dimorphos. just make sure i get my aim right. whoa! we've got ejecta — stuff thrown up. you can see this is bouncing much more this time than it did with the sand. yeah. when the ball hits the gravel, ejecta is thrown away from the surface. physics says that the more ejecta there is, the more the target is pushed in the other direction. this is called momentum enhancement. that amount of momentum carried by the ejecta has to be balanced by extra momentum in the asteroid

moving in the other direction. so, it'sjust like how a rocket works. you throw stuff out one way and the rocket goes up. exactly. and that's called the momentum enhancement, this magic beta factor that everybody wants to know. right, and that's what we saw with dart? yes. when dart hit dimorphos, the energy from the impact led to a crater being formed, and material from the asteroid was blasted out into space. this caused momentum enhancement, also known as the beta factor, and helped to propel the target further. it's the reason that a light spacecraft, weighing only half a tonne, was able to change the orbit of dimorphos, thought to weigh around five million tonnes. simon's colleague, zoe emerland, uses a high—velocity impact gun to calculate the beta factor at higher speeds in the lab. zoe fires an impactor at a target at likm a second. so this is what we get from the gun.

yes. and you can see the ejecta. oh, wow. do we know how much of an extra kick the asteroid got from this momentum? we know that it gave a significant extra kick. dart mission was an incredible success because it did... its first objective was to demonstrate that you can target a spacecraft onto an asteroid, hit it in the place you intended to, and deflect the asteroid. the impact produced a change in the orbital period by 33 minutes. that's quite a lot. now, if there were no momentum enhancement, that would have given you a seven—minute change in the period. but though momentum enhancement is useful, accurately calculating it is hard, as you need to know the composition of the asteroid. it's good because any momentum enhancement you get means you get a bigger deflection for the size and speed of the spacecraft you hit. it's bad because you don't know how much it's going to be.

when we find an asteroid that's going to hit us, we have to send a reconnaissance mission to measure its properties, so we can then adjust those models to precisely that body. and then work it out, yeah? and then when we'll know exactly what spacecraft we need to hit it, how early we need to hit it, because we'll be able to make a much better guess at what the momentum enhancement will be. what is really, really important is that we find it early. if we get it late, we might end up in the scenario where we have to launch several dart—type missions and hit one after the other. right. but of course, that is even greater risk. if you look at movies and science fiction, people send bombs and all sorts of things. they do, they do. and i have to say that, if you don't get enough warning, the asteroid is too big, then there is the potential to use a nuclear stand—off weapon. nobody wants to do that, 0k... right. ..but if it means survival of a country from total destruction, then, you know, that has to be in our planning.

but it is an absolute last resort. so nonetheless, you sound quite cheerful about where we are with planetary defence. so what i'm hearing is it's going to be ourfault, us astronomers who look at the sky, not you planetary scientists, but if we don't find the things early enough, you can't help us. we have to find them early enough, yes. i find dart really inspiring. having realised there's a threat from asteroids, humanity has pulled together and gone a long way to solving it. it's an effort that's involved astronomers with telescopes finding the asteroids, lab work like we've seen today, complex and some excellent spacecraft engineering. together, it's a potentially world—saving and fabulous effort. but to really figure out the asteroids, we need to understand their origins, and — surprisingly — the role played by the largest planet in the solar system. i remember in 1994, looking atjupiter with my small back garden telescope and seeing giant bruises appear on the planet's surface.

it had been hit by shoemaker—levy 9, a comet that got too close to it and had broken up. and as each fragment of comet hit the atmosphere, it sent up plumes of material, thousands of kilometres high. it was a reminder of the dangers of living in our solar system. butjupiter also has a role to play in the major threat to us here on earth — asteroids. most of them live in the asteroid belt, a region between mars and jupiter. and while they stay there, they're no threat to us at all. why are they there? blame jupiter. when the planets were forming out of the disc of gas and dust that surrounded the young sun, the giant planet's gravity seems to have stirred up this region, so the asteroids couldn't coalesce into one large world. so instead of a new planet, we get an asteroid belt. science fiction makes asteroid belts seem like scary places, like your ship might be hit by a rock at any moment, but actually, there's plenty of space. the average distance between large

asteroids is perhaps a million kilometres. if asteroids stayed in the asteroid belt, there'd be no threat to us at all. and yet we see tens of thousands of near—earth objects, asteroids whose orbits cross our own and which might one day hit us. why are they there? blame jupiter again. its gravity is still stirring up the asteroid belt, and altering the orbit of these asteroids so that they travel into the inner solar system, where they might pose a threat. butjupiter does do one good thing for us. comets and other bodies coming in from the outer solar system are much more likely to encounterjupiter than anything else, and it almost always sends them shooting out of the solar system. jupiter today acts as a vacuum cleaner, keeping the solar system clean, even while it stirs up our neat and tidy asteroid belt. asteroids can pose a serious danger to life on earth, which is why they're monitored by scientists across the world.

but this work isn't only carried out by experts. there's also a network of amateur astronomers helping to track the meteors in our skies. one of these meteor trackers is mary mcintyre. i love doing the meteor science, because it's amazing to just be part of a community that arejust doing so much amazing work. it's helping with meteorite recovery. planetary defence as well. and these cameras are basically low—cost cctv cameras, but for space. mary is part of a global network of over 450 cameras. and it's something that you can set up in your own back garden. these cameras are so accessible now. the global meteor network system is using a raspberry pi computer, which is fairly inexpensive. and the software that does all of the science is free.

the best place to mount the cameras is somewhere very sturdy. so it could be the back of a house or a solid wall, or it could be a shed wall like ours. and then you kind of want the camera pointing up at about a 45 degree angle. you just never know when an interesting event is going to happen. so never, ever turn them off. the camera's observations of a meteor automatically collate with others, onto the global meteor network. these cameras capture a huge amount of data. it will tell you how fast it was going, the angle that it came in to earth's atmosphere at. it will tell you the orbit, so you know exactly where in the solar system or even extra—solar system that these events have actually originated. the majority of meteors that we observe are seen as streaks of light that burn up in the earth's atmosphere. but sometimes we see a fireball, a really bright meteor that survives the earth's atmosphere and can land here on earth as a meteorite.

i think it's just the most exciting news ever when we discover that a fireball that's been picked up on our cameras has resulted in a meteorite fall that has been recovered. amateur meteor—trackers like mary are playing a major role in the study of how asteroids may have helped to kick—start life on earth, rather than destroy it. 0n the 28th of february 2021, a bright fireball was spotted in the skies above the uk. and it's led to new ideas in understanding the early solar system. astrophysicist and exoplaneteer george dransfield is at royal holloway to find out more. this fireball was so significant because it was caught on uk fireball alliance cameras, and they were able to track its trajectory. they could see that it was headed towards gloucestershire, specifically in and around the town of winchcombe. and crucially, this meant that scientists

could get to the right place immediately, and gather up all the fragments. 600g of blackened debris was picked up from people's gardens and driveways and local fields. are you sure? yeah. it totally is, it totally is. that is very obvious. 0h! it was a truly historic moment, the first time in three decades that a meteorite has been observed hurtling across the uk, and then recovered ready for analysis by scientists around the world, including planetary scientist dr queenie chan. why is it important and significant when we find a meteorite? asteroid are the building blocks of planets. so we get to see how the planet was formed at the beginning of our solar system. 0k. so they have, like, a fossil record of, like, early solar system. and what is particularly special about the winchcombe meteorite? over here, i've got tiny pieces of the winchcombe meteorite. it's very exciting for us, because it's been recovered

really quickly after its fall. so we want a clean meteorite, not as contaminated by the earth's atmosphere, but also it's a kind of carbonaceous or carbon—rich chondritic type of meteorite, a rare type of meteorite that's been recovered on earth. carbonaceous chondrites are some of the earliest materials in the solar system — older than the earth. they could hold the answers to what molecules were present when life on earth began. queenie has another example of this rare type of meteorite to show me. so here i've got an example of that. and it's called the murchison meteorite. it's a famous meteorite that fell on earth in 1969. the meteorite here... that's a piece of space rock! yeah. so if you look closely, can you see the white specks? yeah. and they're quite rounded. so they are called...what we call the chondrules. so, chondrules are one of the first solids that's been formed at the birth of our solar system.

queenie has been analysing the winchcombe meteorite, looking for what molecules existed at the very beginnings of the solar system. her focus is on amino acids, the building blocks of life. so, you've been working away at this and scraping bits off, and studying the winchcombe meteorite. what have you found? we've found that there are a range of amino acid molecules in the winchcombe meteorite, and it's quite exciting. some of them are even protein—forming type of amino acids. so the fact that we have found amino acids in winchcombe is a big deal, because we need those molecules for life to occur. and the reason why it is so exciting is because there are two theories of where our molecules of amino acid were from. so it's either that it's been totally earth—based. so it was all created by reaction on the earth's surface, or it could be delivered by asteroid from outer space.

and we know that both are possible. as well as these building blocks for life, scientists have found evidence of water in samples of the winchcombe meteorite, with a chemical composition similar to that on earth. this adds weight to the theory that asteroids could have delivered the ingredients for life to our planet. and it means that these same ingredients could also have been delivered elsewhere in the universe. hang on a second. are you telling me that, potentially, life on earth is extraterrestrial in origin? well, it's quite an interesting topic because life on earth, i don't know whether they're extraterrestrial, but we definitely know that the ingredients that need to form life, or ingredients that life needs to exist, can become...coming from outer space. we do often think of asteroids

as a bit of a threat, perhaps because of the whole dinosaurs incident. but we are learning more and more about how asteroids might have also contributed to kick—starting life on earth. and what was mad cool about this incident in particular is the way citizen scientists helped track its trajectory, so that we could collect it and then do some in—depth science with it in our labs. hello thanks for joining

hello thanks forjoining me. we have a dose of mediterranean heat. healing is it going to ask it's going to be a brief heatwave. some fairly intense heat across southern england. weatherfronts fairly intense heat across southern england. weather fronts are trying to push in from the atlantic to bring in rain and fresher air. just for a time we will see hot air blowing out of spain through france and that hot—air will reach our share shores as well. but after that the weather front of the atlantic will wind and we will sing fresher air. we could see temperatures as high as 33 degrees on celsius which would make it the hottest day of the year so far. when i can get many opportunities to see temperatures this high. we are starting to go into a caller part of the summer

now, relatively speaking. he was the short forecast. sunday evening may start off cloudy... the humidity will be rising saturday will be cloudy in the south. particularly in western areas. the rain may come and go into the afternoon. sunny on the south coast of england, some decent sunshine. certainly the lake district, showers with a breeze across scotland. temperatures on saturday not particularly high. the humidity is starting to rise. 0n humidity is starting to rise. on sunday this big high is starting to dominate our weather but the weather fronts aren't too far away. ahead of this weather front we start developing that warm hot and southerly flow of air, and temperatures could already hit about

30 degrees celsius. notice the values here across scotland and northern ireland, nowhere there is hot. that weather front is just approaching ireland and will spread closer to the uk during the course of sunday night and into monday. during... there could be some storms, certainly no heatwave on offer here. this is where the highest temperatures will be on monday. a conservative estimate about 31 degrees of course we got that fresh air further north. 0n that fresh air further north. on tuesday we got a couple of weather front spread across the uk. 0nce tuesday we got a couple of weather front spread across the uk. once the weather front spread across from west to east... sunshine in between,

this is now fresher and like together. by tuesday central southern and western and southern parts will notice the difference. beyond the middle of the week look how much cooler it is, in the low 20s. how much cooler it is, in the low 205. i how much cooler it is, in the low 20s. i think we'll see a succession of weather fronts heading our way to bring an atlantic cloud and rain with some sunshine from time to time.

live from london. this is bbc news. israel strikes a school building sheltering displaced palestinians in gaza city, killing dozens. israel says the school contained a hamas command centre. the family of bebe king, the six—year—old girl killed in the southport attack, pay tribute to their daughter. they said her sister witnessed the attack and managed to escape.

russia is trying for a fifth day to repel a massive cross—border incursion by ukraine. tight security measures are now in force. and dozens of gold medals are up for grabs on the penultimate day of the paris 0lympics with team usa facing france in the blockbuster men's basketball final. hello, i'm azadeh moshiri. welcome to the programme. we start this hour with the latest on the israel—gaza war after dozens of palestinians were killed in an israeli air strike on a school housing displaced families in gaza city. the al—ahli baptist hospital says 70 bodies that it's received so far have been identified. the total number of those killed is expected to be higher. these are some of the latest images from the scene — many are simply too graphic for us to show you. the israeli military says around 20 hamas and islamichhad militants

were operating from the building.