All language subtitles for The Truth About Meteors BBC Horizon 2013 720p HDTV MVG EN Sub_Subtitles01.ENG

For the residents of the Russian city of Chelyabinsk, the morning of

Friday February 15 began like any other. As they set off to work, in

what has become a craze in Russia, many recorded their journeys. But

these cameras, usually used for capturing traffic incidents were

about to record history. A fireball, brighter than the sun, appeared

from nowhere. Before exploding with A minute later, a shock wave blew

in the windows of 4,000 buildings. The broken glass accounting for

most of the 1,200 injured. The people of Chelyabinsk had just

experienced the most powerful meteor strike more than a

century. The meteor is a spectacular reminder of how exposed

our world is. Earth is this tiny planet and a it is reminder of the

impact these alien rocks can have on our planet and us. This isn't

the first time it has happened. Over the last few years, scientists

have examined many other impacts in the past. Using this knowledge, I

want to answer the key question that the Chelyabinsk meteor strike raises

Where did this alien rock come from?

When will the next one strike? And can we do anything to

A fortnight after the impact the meteor strike is still big news in

Russia. In Chelyabinsk there is a popular new winter past time.

Hunting for any fragments of the mere yacht iet that remain.

Scientists have also been out in force, particularly around the lake,

where there is evidence of an impact on the ice. So many

fragments have been found. They're trying to piece together what

happened. Because the fact is no one in the scientific world saw

this coming. I was shocked. I never thought I would see an event like

this over a major city during my lifetime. We couldn't predict this

was going to happen. The piece of rock that came was small, maybe

only a few metres across. And so we couldn't see this before it entered.

When something like this happens, there is no doubt, it is

frightening. But I have to admit, as a geologist, witnessing a once

in a lifetime event - it is thrilling. You only had to look at

social media to see that scientist around the world were getting

excited about this as the news broke. It was exciting for me as a

scientist, because you want to know what is it and what has landed? Is

it a bit of Mars or from an asteroid. I'm almost ashamed I had

such great excitement about this, because people have been injured.

Chelyabinsk was the biggest meteorite to strike the earth since

we had the means to measure it. Every moment was captured. One 069

best documented 16 seconds in skrien. Alan fits similar Mondays

has been examining the footage. This is amazing. What it shows is a

great record of the entry of the object into the earth's atmosphere.

So you see it right from the moment it really penetrated and there it

is. It is coming down at a fairly shallow angle. As we play the movie

on. What we see is bang - there first of all it has got brighter.

Something has happened to the object. It is starting to break

apart. As it does, it releases some of its energy. That is causing that

flare up. Is that because the atmosphere incidencer? Yes. It is

finding it harder. -- denser. We get this huge flare up where

suddenly the whole object is starting to fragment and break

apart. That is where the majority of the energy has been released. If

we look here... There is little bits. Yes, there is another flare

up and we can still see it is glowing, with some major fragment

still falling through the atmosphere. Under that trajectory

you will have showers of bits of asteroid falling down and then

finally 16 and a half seconds later and what we are left with is this

contour trail and the shock wave coming towards us. It is about a

minute later that it has reached the ground. This guy driving

doesn't know the shock wave is on his way. Yes, he is happily

listening to the radio on his drive to work. The explosion generated a

shock wave so massive it was detected over 15,000 kilometres

away. The waves were picked up by monitoring stations. This is a

listening network? Yes. Not set up for fireball or asteroid impact,

but to listen for nuclear explosions. What the stations

picked up was some of the largest waves ever record. Here they have

been modified to make them audible. It has been detected down in

Antarctica and we have records of it up there this Alaska. The

pressure wave from the entry of the object and the fragmentation was

seen around the world. From the data, it is Arley days, what is

your best guess as to the size of the rocky lump? From the infrasound,

we know the energy was 500,000 kilotons of energy. That is a huge

amount. Because we know it came in from the video footage at about

17.5 kilometres per second, we can combine to get a mass of the object

and from that we can get a size and it is probably about 15 metres

across. That is a lairty. We think -- rarity. We think they come in

about 1,500 years. It is a really rare event of course. Meteor

strikes as big as this may be rare, but scientists have a surprisingly

detailed knowledge of what meteors are and where they come from. Long

before the meteor reached Chelyabinsk, it would have had a

different existence and gone by a different name. Meteorites begin

life in deep space, as part of larger bodies called asteroids.

These can range in size from just a few metres to more than 900

kilometres. The left overs from the nebula that creating the solar

system. And millions of them circle the sun in a trail known as the

asteroid belt. Here collisions create smaller fragments and then

these fall to earth, they take on one of two forms. The smallest

pieces will burn up in the atmosphere to become meteors. What

we call shooting stars. Only the largest fragments that make it all

the way to the surface are called meteorites. A meetsior iet is a

piece of rock from space that falls through our atmosphere and hits the

ground to be recovered and technically scientists love their

words, it is not a meteorite before it's found and discovered.

collecting and comparing meteorites, scientists have been able to piece

together a picture of how they formed. These studies have revealed

that some of the most remarkable rocks in the solar system. Few

places have as many meteorites as the natural history museum. Ones

like this. It is a crack isn't it? The once here on display are a

fraction. Most of the collection is behind the scenes that. Is where

All these are meteorites? Professor Sir Russell is expert at decoding

the messages hidden within fragments of space rock. This looks

rocky. What about that? It is a humble rock. This is older than the

Earth, the order thing -- the oldest think you'll ever hold.

Ordered them for 0.6 billion years? Yes, 4.6 billion years, the age of

the solar system. We know that from meteorites and the age of

components within it. If you can see, it has these rounded objects

within it, which are up to one centimetre in size. They were free-

floating, before there were planets, free-floating in the solar system

around the young son. They slowly coalesced to make asteroids and

larger objects until eventually, planets were formed. These were the

building blocks of planets. Russian media right, any news on

what kind it is? Early reports are that it is an ordinary one, like

this one. This is really exciting for us as scientists, because we

want to know how the planets formed and what was around before the

planets, what the environment was like and have a material that made

up the plan its first came together. These are the best way of finding

that out. Is this the most common in the solar system? It is the most

common type to fall down to earth. There is almost certainly a bias,

the only material we get at this stuff that happens to cross the

Earth's's orbit. It has to be going in at what direction to cost the

earth anyway. There is some kind of selection bias. This is a really

special thing for you to have in your career? Yes, if only something

like this would happen in Britain! I don't think too many people

watching the programme will be saying, I wish it happened in the

UK. Obviously some were uninhabited. How much of this stuff comes to us

of the year? Huge amounts of the Earth is growing by at least 40,000

tonnes a year, so a huge amount of material is falling to earth but we

don't notice most of it because the majority comes in the form of dust.

Right. Although several thousand meteorites land on Earth every year,

most of those go and be noticed. They fall too far away from people.

Biffa meteorite falls than maybe 15 feet away from you, you probably

won't notice. It will make a third and that will be yet, unless it is

very large. This event is special because it was so large. There was

no way you could not notice this meteorite falling. It really wanted

to get noticed. It said, I am here. Those events, spectacular, they

give us scientists these important pieces of rock, from which we can

learn about the solar system. remarkable how we are able to build

up this picture of what is going on, millions of miles away in the solar

system. It is one of the joys of science, really, almost like

detective picking up on the tiny clues to tell the big story. So

that the big question, the one that really needs answering, is why do

some of these asteroids suddenly heads straight towards us? Over 95%

of asteroids are found in an orbit between Jupiter and Mars, in a belt.

There is almost 200 million it kilometres across and home to

millions of these orbiting rocks. These asteroids have been following

the same path for millions of years. So long as they remain here, they

pose no threat to others. But occasionally, one goes astray.

Collisions are one of the reasons why this might happen. But in the

last decade, we have learnt that just a few raised of light are

enough because one scientist has tracked the orbit of one of these

Steve Jones Lee, of Nasa's's Jet propulsion Lab in California, has

made a study of the 200 million tonne asteroid. This is a model of

it. It is about 500 metres across, the size of a football stadium. It

rotates in this direction. As you can see, it has a very angular

shape to it. He set out to investigate a 100 year-old theory

that said asteroids were powered by the sun itself. The theory is a

small acceleration in asteroids. If you take a model and see the sun is

hitting the asteroid, warming the surface, as the asteroid rotates

the hot surface radiates the heat out in a different direction into

space and caused an acceleration. It is a slight acceleration, from

the photons emitted. This acceleration, slight as the tears,

can have significant effect upon the orbit of the asteroid and of

the years. -- over the years. was an intriguing idea. What sent

asteroids out of there orbit and on a path towards the earth was photon

proportion. What was lacking was This telescope is over 300 metres

in diameter. It is one of the most powerful telescopes in the world.

It uses radar to map the precise position of objects in deep space.

It was this telescope that would allow Steve to detect any tiny

alterations in the orbit of asteroid. More than 15 million

kilometres out in space. We knew that it would be in one place, if

the effect was not acting on it, and it would be over here if it was

acting and our models were correct. When Steve and his team studied the

data, the results were unequivocal. We knew from the radar measurements

where it was within a few tens of metres and yet it was actually 12

or 15 kilometres away from where it was predicted to be without the

effect, so these precise radar observations allowed us to see the

12 kilometre displacement caused by the effect. So photons, those

elementary particles of light, really can create a tiny force.

force is about one Urdd -- one house on earth. The weight of shot

glass, that is the force on the asteroid, the size of a football

stadium. Even for me, it is very remarkable, dramatic, that a force

so slight can have such dramatic changes on an individual asteroid's

orbit over millions of years. effect is subtle. It takes many

millions of years to gently nudge an asteroid out of its regular

orbit. But once that orbit has been disturbed, the consequences can be

profound. Now, it can come increasingly under the influence of

the solar system's largest planet. Jupiter. Jupiter has amassed -- has

amassed 300 times bigger than the Earth's, so it has a huge

gravitational field. Often, that works to our benefit. Stray objects

can be swept up in Jupiter's gravity, drawing them into the

planet. We have actually observed to be to acting as a shield in this

way. -- Jupiter or acting as a shield in this way. This photograph

from the Hubble space telescope shows fragments of a comet torn

apart by Jupiter's gravity. As the pieces were drawn to the planet's

atmosphere, the impacts left last scars, some as big as the Earth. --

blast scars. There is a downside to Jupiter. It can also deflect

asteroids into orbits that crossed the Earth's papped. -- PAT. The

meteor appears to be one of these typical Earth crossing events. The

likelihood is it was thrown out of its regular orbit by either one of

a combination of unknown causes. Collision, the effect, Jupiter's

gravity. It continued its new orbit for hundreds, thousands, even

millions of years before meeting its fate for Lent. We can even

begin to trace the exact path the Chelyabinsk meteor to comet

collision course with Earth. Within 16 seconds of action are all the

clues we need. From just one vantage point, it is not clear

exactly how far up it is, how far away it is, but that is what we get

from looking at other vantage points. So here, again, at a

different angle, the object is coming in almost out of the sun

there and by combining this video clip with the other video clips,

what you can do is trigonometry. Basically, you can't figure out how

hyped up the object was and how far away it was. -- you can figure out.

If you catch it early enough, you know where it was in the atmosphere

the first time you saw it. triangulating to get a fixed

position and it changes over time, so you get the trajectory? That is

right. The first part of the trajectory, what you have got there

is a path that is relatively unaffected by the Earth's

atmosphere, so we can use that part of the video but -- the ditch to

track back and figure out where it came from in the solar system.

know where it is going to come, you see it hitting the edge of the

atmosphere. It is just... Come on, come on. There it is! It is about

90 kilometres up at that stage, travelling at 17.5 kilometres per

second. Using the different camera positions, scientists have

pinpointed the exact position at which the meteor entered the

atmosphere. And by checking the speed and angle of the shadows that

the meteor casts, they have calculated its velocity. Together,

this is enough to track back the asteroid's pass from deep space.

Although the asteroid and Earth orbits are of different durations

and at angles to one another, their clockwork regularity means they

were bound to collide. So this shows, speeded up obviously, the

3.5 hours, the last 3.5 hours of the life of this asteroid. It is

nice to see it from the asteroid's point of you. This asteroid has

been in its orbit, going around the sun roughly once every two years,

we believe. Minding its own business. Absolutely. Unfortunately,

of Deborah the 15th, it found a planet in the way. -- on February

15th. Sure enough, that 9:20am, the atmosphere -- it entered our

atmosphere above Siberia. On this path and at this time it was

Chelyabinsk that took the full impact. But could there have been

another scenario? The meteorite landed at a latitude of 55 degrees

north. Had it arrived just a few hours later, we would have been

directly in its flight path. So was this a near-miss for us? If the

asteroid had been in a different part of its orbit so it did not hit

this year, but it hit next year, it would have still hitters of Deborah

the 15th, but instead of coming in over Russia it would have come in

over the UK and Ireland and would have entered the have's atmosphere

and the North Atlantic Ocean -- February 15th. In order for the

meteorite strike anywhere near Britain our path through space

would have had to be fundamentally So we know where asteroids come

from and the forces that shape their date with destiny. But what

exactly happens next, the moment but a meteor strikes? And what

determines just how devastating that strike will be? When there

Chelyabinsk meteor reached our atmosphere it was travelling at

more than 65,000 kilometres an hour and measured more than 15 metres

across. Apart from some unconfirmed reports of craters at the bottom of

Lake Chebarkul, there are surprisingly few signs of an impact.

Little of the 7,000 tonnes of space rock that entered the atmosphere

have been recovered. Perhaps 300 And yet the effects were felt over

3,000 square kilometres. The question is, how can apparently so

little do so much harm? There is a clue from the last time I first

experienced a meteor strike on this On June 30th, 1908, a huge

explosion tore through the forest in Siberia. It was 20 years before

the Russians mounted an expedition to the site. What they found

16 million trees across the at dashed across an area the size of

London had been levelled. Scientists thought it had been

caused by a meteorite strike. But then why was there no sign of any

kind of impact crater? The answer is that the devastation had to be

caused by a meteor or tackle the very particular kind. -- meteor

attack. Physicist Mark has been fascinated by how so much

destruction could be called without any apparent direct contact.

explosion was caused by an asteroid that entered the atmosphere, got

close to the surface and exploded before it hit the ground. But

explosion created a blast wave with hurricane-force winds that knocked

trees over for thousands of square miles. Scientists call it an

airburst, a massive explosion in the atmosphere rather than on the

$:/STARTFEED. The air resistance decelerates the asteroid so fast it

breaks apart in a huge explosion. Most om damage from an explosion

like this is the blast wave. The very high winds. Mark created a

simulation to see what size an asteroid would need to be to

generate such power. This this simulation I include more of the

physics to be more realistic. The shock wave comes from the point

where the fireball descends to. By the time it gets to the ground it

is stronger than it would have been and there is more damage on the

ground, because the destructive power was carried down ward. Based

on his calculations, the devastation at Tunguska could have

been caused by an asteroid as small as 30 to 50 metres in diameter. And

this carries a worrying implication. Smaller asteroids are more

dangerous than we used to think. Because there are many smaller

asteroids than bigger ones, we need to take that risk more seriously

than we used to. The lesson of Tunguska helps explain why in

Chelyabinsk there is so much damage, but very little meteor to be

found.? If we see the object coming in, when it is in the high

atmosphere it suffers very little effect. Just here you get this huge

flare up. That is because the atmosphere has become so dense that

it is almost impossible for it to push through any more and basically

something's got to give and the asteroid gives and breaks apart in

a huge catastrophic fragmentation event. That is what creates a shock

wave which we hear as this sonic boom. It is a balance between the

size of the object and its speed into the atmosphere and the

altitude at which it explodes. Too high, if it is too small and

explodes too high, the shock wave has little effect on the ground. If

it is... Quite low in the atmosphere, a large object and that

shock wave is devastating. Seeing it in real life brings home to you

the energy that these things carry and even though it exploded tens of

kilometres up in the air, so quite a long way from the ground, the

force of the explosion, the shock waver, was able to damage buildings

over a huge area and injure people. That was quite a shocking thing to

see. The power of an air blast is immense. But in a way the people of

Chelyabinsk are lucky. Because if - - out there is a different asteroid

that poses a greater threat. I have seen the evidence of what one can

do, the damage that it leaves and wah you realise the is the earth's

own destructive forces, great quaebgs and volcano Catos --

volcanoes seem trivial in comparison. This is Barringer

creater in America. The 50,000 year old remnants of a massive meteorite

impact. This place gives you 5 sense of the destructive power of

incoming meteorites. This blast could have vap ourised a city the

size of London. But it measured less than 50 metres across. Down on

the ground the scale of the impact is even more breath-taking. The

cairt is more than a kilometre across -- crater is more than a

kilometre across and nearly 200 The forces here were enormous. The

impact turned this solid rock into this mush. It just burst out in

your hands. Look at that. They started out as the same kind of

rock. The meteor that struck here was about the same size as the one

that flattened tub -- Tunguska. But there is a difference. At Barringer

the meteor didn't explode in the atmosphere. It struck the ground.

This is a fragment of the true devastation unleashed here.

Fortunately, to understand why ground strikes are destrucktive we

don't have to wait for another Barringer to happen. Because today

we can simulate this kind of impact and that is thanks to to the

research of this man and one special piece of equipment. So

was built during the Apollo time, because I guess they thought there

would be several made. This is the first and the last one. It is the

only one like it in the world. is NASA's vertical gun range and

was built to see how impacts affected the moon. We are reset.

Today, he uses it to mod it will dynamics of an asteroid impact.

ne that asteroid impacts are bad. But you want to understand how bad.

Pete uses the gun to fire projectiles at high speed to

stimulate an asteroid hitting the earth. We are going to fire this

tiny quarter inch sphere at high speeds up around five kilometres a

second and we will see what type of crater it produces. The target it

made of sand. We use sand because it records the shock effects

clearly. Outside of the impact chamber are high speed cameras to

film at up to a million frames a second. Capturing every detail of

the impact and the aftermath. Lights out. Everything good? OK. We

We have high voltage and the paddle in, the warning light. And we are

Perfect. Perfect. Now we are seeing the fireball come in. It is

brighter than the Sunday and then it hits the surface. -- brighter

than the sun and then it hits the surface. This whole region would

have been incinerated by this plasma, this exploding vaipour. --

vapour. There would have been wind that could have picked up house and

spread them hundreds of kilometres away. This would have been

Armageddon. Experiments like this reveal several important things.

One is it is not just the impact, it is all that vapour that runs

down range. You can see where there was so much wind it kafbed out

pieces of landscape. - carved out pieces of landscape. So this allows

to witness the event and try to understand the processes that are

going on. It is complex. But we have to see it to understand it.

Asteroid impacts unleash a trail of destruction greater than suggested

by the footprint of the crater alone. Cam pairing the -- comparing

the effects it seems Chelyabinsk got away lightly. It is estimated

that the largest piece to hit the ground weighed 500 kilos. A

fraction of the original mass of 7,000 tonnes. If a piece of rock

that big had hit that area it would have produced a huge impablgts

crater. And that energy is delivered into the ground and we

see things like seismic shock and people would feel quaebgs. --

quakes. So still dra mountainic and causing injuries, but it could --

still dramatic but it could have been worse had it survived down to

Ground strikes are amongst the most destructive hazard we know of. When

viewed from space, earth's encounters with asteroids are

revealed. There is evidence from our planet's past of a devastating

meteorite strike that altered the course of life on earth. Today,

millions of years after the impact, the evidence for that crater is

This is a gate way to the unique cave system in Mexico. Wow! Look at

the size of this. This is magnificent. That is beautiful.

This cave maybe stunning, but it provides the evidence for one of

the greatest events in the earth's history and that water is so clear.

There is much more to this amazing cavern than first meets the eye. To

understand the scale of what happened here, you have to go

deeper still. Under water. I am not sure if I'm ready. I have the

equipment. But there is something about going down into the water

when your not sure what it is. But I trust Bernadette. I am as ready

Descending into the depths of the cenote is like entering a new world.

Fewer people have visited some of these caverns than the surface of

the moon. As diverers have explored further, they have found they are

part of a huge complex of tunnels and caves. In fact, when you look

from above you can see there are cenotes across hundreds of

kilometres. And when they're mapped, it becomes clear they follow a

circular course through the jungle. They mark out the rim of a giant

crater. Scientific instruments show the structure of the underlying

rock has been deformed. Revealing the boundaries of a colossal

It is amazing -- this amazing cavern is part of a bigger story, a

much bigger story. 65 million years ago, this was a site of one of the

most catastrophic impacts in of's history. What became known as the

meteorite landed here and that triggered the extinction of the

The meteorite was 15 kilometres across, enough to cause a to

devastation across the whole planet. It exploded with the force of 100

million million tonnes of TNT. The blast sent a giant plume of

vaporised rock out into space. A crater was punched 30 kilometres

into the earth's crust. It was above this rim of weakened rock

that cenotes formed, millions of years later. The blast would have

But it was what happened next that made the impact of global

catastrophe. The blast plume that shot into space felt -- fell back

to earth. Billions of Malton particles superheated the heir to

temperatures of hundreds of degrees. Fires swept the planet, choking the

atmosphere with salt and dust. The dinosaurs and most other creatures

were doomed. That discovery, back in the 1980s about what happened,

changed everything. Up until then they thought the earth had changed

only through grindingly slow processes. But now we knew that

there was also sudden, violent catastrophes that made the earth at

the way it was. Of course, what that meant was that something like

this could happen again. At any moment. Luckily, the very biggest

asteroids are few and far between. But there are still plenty of rocks

out there that represents a significant danger to us. So at the

summit of a -- an extinct Hawaii volcano, this professor and his

colleagues are searching the skies for killer asteroid. Each night,

using a revolutionary billion pixel sensor or, the team scans a vast

swathe of the sky. Follow me up to the next floor, you will see a

better view of the telescope itself. They are looking for any

unidentified objects that could be heading our way. By capturing

several images of the same patch of sky, separated by several minutes,

the team can see if anything has changed against the background of

scarp -- the background of stars. You can see there is a dark thing

and a white thing. What that means is in these two exposures there was

an asteroid which was here in the first exposure and there in the

second one. Here is another one in the same image. In fact, we will

detect hundreds of asteroids in a single exposure. Their observations

are collected at the nerve centre of asteroid detection. The Minor

Its director is Tim, and his job is to keep track of every asteroid in

Tim has developed and marketed visualised location and one that

MAP, the most important are the Near Earth asteroid, the ones

closest to the planet -- he has developed a map. On a screen as the

map of the solar system and I have got the sun in the centre and the

third planet out it would be that of the Earth. The red dots are near

Earth asteroids. The green ones other regular main belt asteroid.

There are even mind 1000 Near Earth asteroid. -- the row over 9,000.

There are -- there is one kind he is concerned to locate, those

asteroids butter over one kilometre in diameter. And has been packed

with one of these would spell disaster. -- an impact with one of

Tim's data reveals the run 900 asteroids bigger than a kilometre

or, who won here first orbits but he has some good news. Right now,

there is no information that any of those large objects will hit the

Earth in the next 100 years, so we are safe from impact from those

objects for at least 100 years. there are no catastrophic asteroid

impacts on the horizon. But there On 6th October 2008, asteroid

Hunter Richard saw something that would change the assessment of

threat presented by asteroid impact. When I was proceeding normally,

upon screen came another asteroid. As I continued to make observations

throughout the night it it appeared to be moving slightly faster. This

indicates the object is close to the first. As with any of the

asteroid, Richard reported what he had found to the Minor Planet

Centre. I got up in the morning about seven o'clock and I had a

message saying I could not computer nor bid for a particular object. I

grabbed the observations of the subject and I computed an orbit and

it was immediately apparent, right then, but that object was going to

hit the Earth. The sort of ominous fashion, it said it was in 19 hours.

Following a strict written protocol, Tim quickly reported the findings

to NASA's asteroid investigation team in California. We got a call

from Tim at the Minor Planet Centre saying we had an impact in less

than 24 hours. That woke me up. NASA's expert on asteroid orbits

raced to verify the data. The first thing I saw was a 100% probability

of impact in less than a day's time. I had never seen anything like this

out of assimilation, software testing. The asteroid strike would

create a huge explosion. NASA feared this might even be mistaken

for a nuclear bomb. We wanted people to know this was a natural

event by Mother Nature rather than some sort of man made event, like a

missile or something dreadful. Information passed rapidly up the

chain of command. NASA headquarters notified the White House that this

was coming. Everyone wanted to know where it would strike. NASA

predicted a remote area of the At 2:45am, NASA were proved right.

The explosion created a vast fire bowl, burning as hot as the sun. --

fireball. It was so big and so hot, this image was captured by a

weather satellite. And yet the object that caused it was only four

metres across, smaller than the asteroid that exploded over

Chelyabinsk. I definitely think the impact was a wake-up call. I have

to admit, I never thought I would see that in my career, where we

would discuss a -- discover something and it hit the Earth that

day. What was worrying about what impact was that the asteroid was

too small to detect until it was very close to the Earth and of

course it was not even spotted until it was already here. But we

are getting better at spotting smaller asteroids. On the same day

that it was hit, another asteroid that created the Barringer crater

came within 28,000 kilometres of the Earth. Approaching from beneath

the planet, 2012 DA14 passed inside the satellite before heading off to

the north. This asteroid had been successfully tracked for a year and

despite its proximity, scientists So we know we are safe for at least

100 years from most Near Earth asteroids of a kilometre in size

and we are getting better at detecting objects up to 50 metres

across, like 2012 DA14. But for asteroids more than that, like the

one that exploded over Chelyabinsk, we still have little or no warning.

There is still some we haven't found, so there is this unknown bit

of the equation, where we are still looking for some. We know they are

there but we don't know where they are. This is a threat, but

hopefully as technology moves on, we will always have a much better

idea whether one is going to pose a risk to the earth. We can see an

event tomorrow, we could see an event in 20 years' time that we had

not previously detective. -- detected. That is the risk we face.

Until we can catalogue and identified the hazardous object to

the solar system, then that risk will always remain. And there is

one other factor that can make it particularly hard to spot an

incoming object. It is the reason why no one saw the asteroid that

was hurtling towards Chelyabinsk. It came in in the daytime sky, out

of the sun. We have got telescoped looking out there for these objects,

but they only work at night. Radar does not help you either because to

really use radar to find these objects above the Earth's

atmosphere, you have to know where to look. If you do not know where

it is coming in, you do not know -- you do not know where to look. If

objects coming at that particular direction, they are going to take

us by surprise at the moment with our current surveys. But even if we

can spot an asteroid heading towards us and in good time to

prepare, what if anything can we do? There is different options for

deflecting asteroids and it is a bit side fight at the moment.

idea of shooting it out of the scare was a nuclear weapon would be

a dreadful idea. It would shower us with radioactive debris and it

would be doing more harm than good. What would be much better is to

push it common object of its course, so it was not going to collide.

do you gently nudge an asteroid? There is lots of techniques you can

use to push it. The One I Love is called a mass driver. A machine

sits on the asteroid and throws off rocks, so it is accelerating rocks

and makes the asteroid gradually move in the opposite direction. You

can paint one side of the asteroid right. That reflects the sun and

there is this weird effect that makes the asteroid gradually drift

across. We can launch a mission now, which essentially can impact an

asteroid and then deflected, a bit like a billiard shot, a snooker

shot. We hit the asteroid extremely fast that the spacecraft and that

small impact really is sufficient to just alter its course, so that

it misses the earth. When you consider birth's history stretching

over billions of years, it is clear that meteorite impacts, far from

being unexpected are just a normal part of the life cycle of our

The Chebarkul meteorite is a reminder of something we would

probably rather not think about too often. How was sudden, apparently

random event, could have But this time we have been lucky.

Although it was terrifying for those who witnessed it, this meteor

struck without causing any fatalities and close enough to be

captured on multiple cameras. So it has given us a huge amount of

information to help us prepare for the next one. I think perhaps the

real lasting legacy of the Russian meteor will be the effect it has

had on the popular consciousness and perhaps some politicians.

Scientists have been saying for decades now that these things do

happen from time to time, but they could be very dangerous if they

happened over a populated area, but now we have factual proof. We have

an event we can point two. We know it could have been worse than this.

If this leads to more vigilance and perhaps the detection of future

impacting events, that would be a good outcome. When a bit of an

asteroid comes through the atmosphere and lands as a meteorite

it reminds us that the solar system is a dynamic place. It is not

finished. It is still working. It is still evolving. It is still

changing. So next time you look up at the night sky, spare a thought

for those thousands of rocky lumps whizzing across our path. A few of

them have got our name on them, but by analysing in detail the data

from the meteor, it means that next time, and there will be a next time,

we will be much better prepared.