0:00:06 > 0:00:11High above us, out in space, there are millions of very strange,
0:00:11 > 0:00:16but very special chunks of rock tumbling between the planets.
0:00:16 > 0:00:20Each one has a different story to tell.
0:00:20 > 0:00:26And those stories are important to understanding the story of the solar system.
0:00:27 > 0:00:30These are the asteroids...
0:00:30 > 0:00:33debris from an extraordinary event...
0:00:35 > 0:00:40..The birth of our solar system, 4.5 billion years ago.
0:00:40 > 0:00:43Asteroids ARE fossils of the early solar system.
0:00:43 > 0:00:48They were accumulated from some of the starting materials from which everything else was made.
0:00:48 > 0:00:54But asteroids continue to present a threat to the very future of our planet.
0:00:54 > 0:00:58If one of hits, every man woman and child on the planet could die.
0:00:58 > 0:01:02Yet asteroids are about far more than destruction.
0:01:02 > 0:01:05Around the world there are scientists working to uncover
0:01:05 > 0:01:11what these messengers from the solar system tell us about our place in the universe.
0:01:11 > 0:01:16They essentially created the solar system we live in and the planet that we live on.
0:01:18 > 0:01:22And what they're finding is that while asteroids may not be beautiful,
0:01:22 > 0:01:27they do hold a surprising power over life and death on our planet.
0:01:36 > 0:01:39Are we alone in the universe?
0:01:40 > 0:01:43Are there other unknown planets in the outer solar system?
0:01:44 > 0:01:48Are the laws of nature the same everywhere?
0:01:48 > 0:01:50Is the solar system stable?
0:01:53 > 0:02:00High up above the clouds, Professor Dave Jewitt dares to challenge forces of the unknown.
0:02:00 > 0:02:02I like mysteries.
0:02:02 > 0:02:05I like to think about the things that are really not understood.
0:02:05 > 0:02:10And if I can see some way to do something to address a problem,
0:02:10 > 0:02:15that other people haven't really followed through with, then that's what I wanna do.
0:02:19 > 0:02:24And right now, he's believes there is nothing more intriguing and mysterious
0:02:24 > 0:02:27than the tumbling rocks of the solar system.
0:02:29 > 0:02:32If somebody told me 30 years ago I'd be studying asteroids,
0:02:32 > 0:02:36I would've said, "Yeah, you're nuts. All the hot science is elsewhere."
0:02:36 > 0:02:43Why would I spend my time on an object that basically is not going to go anywhere in my lifetime?
0:02:43 > 0:02:46So, how wrong can you be?
0:02:50 > 0:02:53And Dave Jewitt is not alone.
0:02:53 > 0:02:59Oh, Gosh. I just love asteroids. I suppose it makes me geeky, right?
0:02:59 > 0:03:04I love the motion, I love the equations of motion. I love the way all that works.
0:03:08 > 0:03:10We've seen very few of them up close,
0:03:10 > 0:03:15but every time we see a new one, we learn something new, we find something we weren't expecting.
0:03:20 > 0:03:24Asteroids are the debris left over from the solar nebula.
0:03:24 > 0:03:30They contain the raw material that never quite made it to form a planet.
0:03:32 > 0:03:35In a way, asteroids are fossils of the early solar system.
0:03:35 > 0:03:38On the Earth, all the materials we see have been processed
0:03:38 > 0:03:41by being sucked into the mantle and blown out of volcanoes,
0:03:41 > 0:03:46and so there's no material on the Earth which remembers what it was like when the Earth still formed.
0:03:50 > 0:03:55Asteroids are time capsules that contain information
0:03:55 > 0:03:59about the earliest times in Solar System history,
0:03:59 > 0:04:02information that's been lost from the other planets,
0:04:02 > 0:04:04that's been lost from the Earth, lost from the Moon.
0:04:04 > 0:04:08Asteroids have been around, and they've seen it all.
0:04:12 > 0:04:18Asteroids offer tantalising clues into the earliest moments of our solar system.
0:04:18 > 0:04:22But, for these scientists, the problem is, how do you get at them?
0:04:24 > 0:04:30For the vast majority of asteroids, we have no information at all,
0:04:30 > 0:04:34except the existence of the object and a guess as to how big it is.
0:04:39 > 0:04:42This fuzzy image helps explain the problem.
0:04:42 > 0:04:48This is what an asteroid looks like through the most powerful optical telescope on earth.
0:04:50 > 0:04:54So how do you begin to study an object you can hardly see?
0:04:58 > 0:05:01Well, one way is to study these.
0:05:02 > 0:05:07Tiny fragments of asteroids that have fallen to earth and broken apart, called meteorites.
0:05:11 > 0:05:17This is it's the oldest thing you can hold in your hand, really a piece of history back to the time,
0:05:17 > 0:05:23even before the Earth was formed, way, way before we were ever formed.
0:05:26 > 0:05:33Almost everything we know about what asteroids are actually made of comes studying these kind of fragments.
0:05:33 > 0:05:40Each one has its own history of the solar system, they're like a puzzle that we're trying to understand.
0:05:40 > 0:05:44We think some asteroids are made of iron, or at least they were so large
0:05:44 > 0:05:47that, when they formed, they heated and melted.
0:05:47 > 0:05:50They could get all the iron to their core,
0:05:50 > 0:05:52just like the Earth has an iron core.
0:05:52 > 0:05:58And when we take a big iron meteor, like this, and slice it open,
0:05:58 > 0:06:06the quality of the metal is really quite amazing. It's a very pure metal,
0:06:06 > 0:06:13nickel iron, some of the oldest metal in the solar system, in fact. More than 4. 5 billion years old.
0:06:19 > 0:06:25So out there in space, there are gigantic boulders, ranging in size from 900 kilometres
0:06:25 > 0:06:31to just a few metres and made of primordial metal and dust.
0:06:31 > 0:06:37But the more scientists have examined the remains of asteroids, the stranger they get.
0:06:38 > 0:06:40It is probably a complete zoo.
0:06:40 > 0:06:45And we find the meteorites have a huge variety of types and compositions.
0:06:45 > 0:06:51And it's telling us that the asteroids must have a wide variety of compositions as well.
0:06:51 > 0:06:58There is one type in particular that has opened a door on the strange and unfamiliar world
0:06:58 > 0:07:02that asteroids inhabit out there in the coldness of space.
0:07:02 > 0:07:05We think that most asteroids are probably like this,
0:07:05 > 0:07:08very stony, like the kind of things we'd find on Earth.
0:07:08 > 0:07:14But they have a completely different chemistry than Earth rocks.
0:07:14 > 0:07:22They're put together like little bits of rocks all reheated, re-melted and glued together,
0:07:22 > 0:07:27And it tells us that the asteroid belt is a place with an incredible impact history,
0:07:27 > 0:07:31asteroids colliding into each other, breaking apart, reforming.
0:07:31 > 0:07:34And so when we see these meteorite samples,
0:07:34 > 0:07:38it's telling us about that amazing collision history in the asteroid belt.
0:07:41 > 0:07:48Over 90% of asteroids are found in an orbit between Jupiter and Mars, called the main belt.
0:07:48 > 0:07:54Almost 200 million kilometres across, it is home to millions of these orbiting rocks.
0:07:54 > 0:07:58But perhaps the most pressing question is whether any of them
0:07:58 > 0:08:01are on a collision course with planet Earth.
0:08:12 > 0:08:14Arizona's arid desert air
0:08:14 > 0:08:18makes it the perfect place for a very special kind of job.
0:08:23 > 0:08:27This is the where people come to hunt asteroids.
0:08:30 > 0:08:34I started out hunting asteroids about 12 years ago, as an amateur.
0:08:36 > 0:08:39I had read an article in a popular magazine,
0:08:39 > 0:08:44and that got me really interested in the field because not too many people were working there.
0:08:47 > 0:08:54It might not seem it, but Richard Kowalski is in the front line of defending planet Earth.
0:08:54 > 0:08:59Every night when I come up to the telescope, I do have it in the back of my head
0:08:59 > 0:09:03that every person on the planet does have a vested interest in what I'm doing.
0:09:03 > 0:09:10If one hits, there's the potential that every man, woman and child on the planet could die.
0:09:22 > 0:09:28Richard wants to discover any asteroids that could be on a collision course with Earth.
0:09:37 > 0:09:43This is our largest telescope it's a 60-inch or 1.5m F2.
0:09:43 > 0:09:48It's the telescope that we've been using for approximately five years now.
0:09:48 > 0:09:53We discover as many as 3,000 new asteroids every night.
0:10:00 > 0:10:01But what Richard fears
0:10:01 > 0:10:05is that one of them could create destruction like this, or worse.
0:10:05 > 0:10:09Baringer Crater is just a few hundred kilometres
0:10:09 > 0:10:11from Richard's telescope.
0:10:15 > 0:10:20It is 1 kilometre across and 200 metres deep.
0:10:20 > 0:10:27It was made when a 300,000-tonne asteroid smashed into Earth, 50,000 years ago.
0:10:27 > 0:10:32The Earth has been hit in the past and will be hit again in the future.
0:10:32 > 0:10:37What we'd like to do is to be able to discover these objects before they hit the Earth.
0:10:45 > 0:10:50So, one of the great challenges for scientists is to understand
0:10:50 > 0:10:55what would happen if an asteroid were to strike planet Earth...now.
0:11:04 > 0:11:08Pete Schultz wants to understand the unique nature of the explosion caused
0:11:08 > 0:11:12if an asteroid were to impact with the Earth's surface.
0:11:12 > 0:11:14It takes a truly odd piece of equipment.
0:11:20 > 0:11:21OK. We're getting close.
0:11:28 > 0:11:31This was serial number one, it was built during the Apollo time,
0:11:31 > 0:11:34I guess it's because they thought there would be several of them made
0:11:34 > 0:11:39but this is the first one and the last one and it's the only one like it in the world.
0:11:42 > 0:11:44This is NASA's vertical gun range.
0:11:44 > 0:11:47It was built to study how impacts affected the moon,
0:11:47 > 0:11:51as the astronauts prepared to make the first lunar landing.
0:11:51 > 0:11:55We are armed, gated and reset.
0:11:57 > 0:12:04Today, Professor Pete Schultz uses it to model precisely the dynamics of an asteroid impact.
0:12:04 > 0:12:07We know that these asteroid impacts are bad,
0:12:07 > 0:12:12but you want to understand really HOW bad.
0:12:14 > 0:12:18Schultz uses the NASA gun to fire projectiles at very high speed
0:12:18 > 0:12:22to simulate an asteroid hitting the Earth.
0:12:22 > 0:12:28So for this experiment, we are going to fire this tiny quarter-inch aluminium sphere at very high speeds,
0:12:28 > 0:12:33up around 5km per second, and we'll see what kind of crater it produces.
0:12:35 > 0:12:38The target it will hit is made of sand.
0:12:38 > 0:12:44So we use sand because it records the shock effects very clearly.
0:12:46 > 0:12:49Outside of the impact chamber are special, super hi-speed cameras
0:12:49 > 0:12:53that can film at up to 1 million frames per second,
0:12:53 > 0:12:59capturing every detail of the impact and the aftermath for analysis.
0:12:59 > 0:13:03OK, lights out. Everything good?
0:13:03 > 0:13:04OK, we're out of here.
0:13:11 > 0:13:16We have high voltage, warning lights.
0:13:17 > 0:13:19And...rolling.
0:13:29 > 0:13:34The ball travels 15 times faster than the speed of sound.
0:13:34 > 0:13:38And it incinerates, exactly like some asteroids would.
0:13:40 > 0:13:42Perfect. Perfect.
0:13:42 > 0:13:44Now we're seeing the fire ball come in,
0:13:44 > 0:13:49it's brighter than the sun and then, kapow, it hits the surface, geez.
0:13:49 > 0:13:54This whole region down range would have been incinerated.
0:13:54 > 0:14:02It would have been incinerated just by this plasma, this exploding vapour plume, engulfing everything.
0:14:02 > 0:14:06There would have been winds that would have been going so fast,
0:14:06 > 0:14:10it could pick up houses and spread them hundreds of kilometres away.
0:14:12 > 0:14:16This would have been armageddon.
0:14:21 > 0:14:25Experiments like this reveal several important things.
0:14:25 > 0:14:27One is that it's not just the impact,
0:14:27 > 0:14:30it's all that vapour that runs down range.
0:14:30 > 0:14:38In fact, you can see areas here where there was so much wind it actually carved out pieces of this landscape.
0:14:38 > 0:14:41So what these experiments help us do,
0:14:41 > 0:14:44they actually allow us to witness the event,
0:14:44 > 0:14:47see it in real time, and try to understand
0:14:47 > 0:14:50the processes that are going on.
0:14:50 > 0:14:52It's really complex
0:14:52 > 0:14:55but we have to see it to understand it.
0:14:57 > 0:15:01So asteroid impacts unleash a trail of destruction
0:15:01 > 0:15:06far greater than suggested simply by the footprint of the crater alone.
0:15:06 > 0:15:09It means they are far more complex, and dangerous,
0:15:09 > 0:15:11than many had previously thought.
0:15:20 > 0:15:21One of the enduring puzzles,
0:15:21 > 0:15:25ever since asteroids were first discovered 200 hundred years ago,
0:15:25 > 0:15:29is why they come anywhere close to the Earth in the first place.
0:15:35 > 0:15:37Most of the time, asteroids
0:15:37 > 0:15:40are in a stable orbit between Mars and Jupiter.
0:15:44 > 0:15:49But some go wandering, leaving their orbit to propel themselves
0:15:49 > 0:15:53through space, and coming under the influence of Jupiter's gravity...
0:15:53 > 0:15:58a force that accelerates them towards Earth.
0:15:58 > 0:16:00Scientists have been hunting for
0:16:00 > 0:16:03an explanation for this strange behaviour.
0:16:13 > 0:16:18Steve Chesley of NASA's Jet Propulsion Lab in California
0:16:18 > 0:16:23has made a study of a 200 billion tonne asteroid called Golevka.
0:16:23 > 0:16:27This is a model of Golevka, it's actually about
0:16:27 > 0:16:30500 metres across, say the size of a football stadium.
0:16:30 > 0:16:33Um, it rotates in this direction.
0:16:33 > 0:16:36As you can see, it has a very angular shape to it.
0:16:37 > 0:16:40He set out to investigate
0:16:40 > 0:16:43a 100-year-old theory that said asteroids were powered
0:16:43 > 0:16:48by the sun itself, what's called the Yarkovsky effect.
0:16:48 > 0:16:52The Yarkovsky effect is a very small acceleration of the asteroid,
0:16:52 > 0:16:54and what it is, is, if you take a model,
0:16:54 > 0:16:56you see the sun is hitting the asteroid,
0:16:56 > 0:16:59warming the surface. As the asteroid rotates,
0:16:59 > 0:17:01that hot surface radiates the heat out
0:17:01 > 0:17:03in a different direction into space
0:17:03 > 0:17:05and that causes an acceleration, very slight acceleration
0:17:05 > 0:17:09coming from the photons that are emitted from the asteroid.
0:17:09 > 0:17:11The idea is that this acceleration, slight as it is,
0:17:11 > 0:17:15can have significant effect upon orbit of the asteroid
0:17:15 > 0:17:16over millions of years.
0:17:19 > 0:17:20It was an intriguing idea.
0:17:21 > 0:17:24What sent asteroids out of their orbit
0:17:24 > 0:17:27and on a path towards Earth was photon propulsion.
0:17:27 > 0:17:30But what was lacking,
0:17:30 > 0:17:31was proof.
0:17:39 > 0:17:43The Arecibo telescope is over 300 metres in diameter.
0:17:43 > 0:17:47It's one of the most powerful telescopes in the world.
0:17:47 > 0:17:51And it uses radar to map the precise position of objects in deep space.
0:17:55 > 0:17:57It was this telescope that would allow Steve Chesley
0:17:57 > 0:18:00to detect any tiny alterations
0:18:00 > 0:18:02in the orbit of asteroid Golevka
0:18:02 > 0:18:05more than 15 million kilometres out in space.
0:18:08 > 0:18:10We knew that it would be in one place
0:18:10 > 0:18:13if the Yarkovsky effect wasn't acting on it,
0:18:13 > 0:18:16and would be over here if it was acting and our models were correct.
0:18:16 > 0:18:22When Steve and his team studied the data the results were unequivocal.
0:18:22 > 0:18:25We knew, from the radar measurements,
0:18:25 > 0:18:29where Golevka was within a few tens of metres
0:18:29 > 0:18:32and yet, it was actually 12 or 15 kilometres away
0:18:32 > 0:18:36from where it was predicted to be without the Yarkovsky effect.
0:18:36 > 0:18:39So these very precise radar observations, allowed us to see
0:18:39 > 0:18:43the twelve kilometre displacement caused by the Yarkovsky effect.
0:18:46 > 0:18:50So photons, those elementary, massless, particles of light,
0:18:50 > 0:18:52really can create a tiny force.
0:18:54 > 0:18:56The force is about
0:18:56 > 0:18:58one ounce on Earth - say the weight of a shot glass
0:18:58 > 0:19:00is - that's the force
0:19:00 > 0:19:05on this huge asteroid the size of a football stadium.
0:19:05 > 0:19:09Even for me, it's truly remarkable, it's dramatic, that a force
0:19:09 > 0:19:11so slight can have such dramatic changes
0:19:11 > 0:19:15on individual asteroids' orbits over millions of years.
0:19:18 > 0:19:20Steve Chesley's research
0:19:20 > 0:19:23means that, for as long as the sun is shining,
0:19:23 > 0:19:27there will be a force that could send one of those asteroids
0:19:27 > 0:19:29hurtling on a journey towards Earth.
0:19:33 > 0:19:36Needless to say, this isn't good news.
0:19:36 > 0:19:40But with a threat like this, what can you do?
0:19:46 > 0:19:49Well, for now, there's really only one thing you can do...
0:19:49 > 0:19:52and that's to keep an eye out for them.
0:20:07 > 0:20:11Watching for asteroids is what Richard Kowalski does,
0:20:11 > 0:20:15night after night, at his observatory in the Arizona desert.
0:20:15 > 0:20:18What you can see on this screen is we have divided
0:20:18 > 0:20:20the sky into thousands of areas,
0:20:20 > 0:20:25we then choose a number of these areas into a single block
0:20:25 > 0:20:28which will then tell the telescope
0:20:28 > 0:20:31to observe each individual area in succession.
0:20:31 > 0:20:33Once it's gotten to the last area,
0:20:33 > 0:20:38it then goes back to the first area and repeats the process.
0:20:48 > 0:20:50Over the course of an hour,
0:20:50 > 0:20:54the telescope repeatedly scans the same areas of the sky.
0:20:57 > 0:21:00While the stars appear stationary, the telescope can spot
0:21:00 > 0:21:03any other objects that change position...
0:21:03 > 0:21:05which could be asteroids.
0:21:08 > 0:21:11As you can see, on this screen is the sequence of four images
0:21:11 > 0:21:13that came from the telescope.
0:21:13 > 0:21:16These objects around the screen are not moving
0:21:16 > 0:21:18so we know that they are stars,
0:21:18 > 0:21:21but this object in the centre is moving and thus we know
0:21:21 > 0:21:23that is an asteroid.
0:21:25 > 0:21:28The importance of surveying for near Earth asteroids
0:21:28 > 0:21:32is asteroid impact on the Earth is truly the only natural disaster
0:21:32 > 0:21:35that we can actually predict before it happens.
0:21:39 > 0:21:42So whenever Richard finds an asteroid he thinks could be
0:21:42 > 0:21:46on a collision course with Earth, he immediately files a report.
0:21:49 > 0:21:51It goes to the central body whose job is to monitor
0:21:51 > 0:21:54possible asteroid impacts.
0:22:09 > 0:22:13Just outside Boston, is the home of the Minor Planet Centre.
0:22:15 > 0:22:17It's director is Tim Spahr
0:22:17 > 0:22:22and his job is to keep track of every asteroid in the solar system.
0:22:24 > 0:22:26This is the nerve centre
0:22:26 > 0:22:27of the entire asteroid field.
0:22:27 > 0:22:30If somebody discovers something, it has to come through here
0:22:30 > 0:22:33and our job is to then distribute that to the rest of the world.
0:22:34 > 0:22:37Asteroids' elusiveness is part of the thrill.
0:22:37 > 0:22:39In some cases,
0:22:39 > 0:22:41if you're studying an asteroid
0:22:41 > 0:22:44that's moving extremely fast, er, we ambush it.
0:22:44 > 0:22:46We go ahead of where we think it will be in and set the telescope up
0:22:46 > 0:22:50in that area and then hope that it comes through the field like that.
0:22:50 > 0:22:51So, you know, it's actually ambushing.
0:22:51 > 0:22:55And then when you get the asteroid, then you chase it down and follow it.
0:22:59 > 0:23:03Not surprisingly, keeping track of thousands of objects in the sky
0:23:03 > 0:23:07isn't something that you can do in your head.
0:23:07 > 0:23:10Thankfully, help is at hand.
0:23:10 > 0:23:13This is really the brains of the Minor Planet Centre right in here.
0:23:13 > 0:23:17This computer system has information about where asteroids are,
0:23:17 > 0:23:19where they will be in the future.
0:23:19 > 0:23:21All the observations all the software is in here.
0:23:21 > 0:23:25We definitely need it to be running all the time, we need it to be safe.
0:23:25 > 0:23:28We need everything working here.
0:23:28 > 0:23:30- <- Do you feel a sense of responsibility?
0:23:30 > 0:23:32I definitely feel a sense of responsibility
0:23:32 > 0:23:36for keeping a track of the asteroids. I feel like it's our duty,
0:23:36 > 0:23:40it's our task to do that and I do feel personally responsible for it.
0:23:44 > 0:23:46And the task facing Tim, is growing rapidly.
0:23:48 > 0:23:52In 1999, only 10,000 asteroids were known of.
0:23:52 > 0:23:55Since then, hundreds of thousands more,
0:23:55 > 0:23:58of all shapes and sizes, have been discovered.
0:23:58 > 0:24:03Tim has developed a map to visualise their location.
0:24:05 > 0:24:07And on that map, there's one class of asteroid
0:24:07 > 0:24:09he's concerned with above all -
0:24:09 > 0:24:13those near-Earth asteroids closest to our planet.
0:24:13 > 0:24:20On the screen here is a map of the solar system.
0:24:20 > 0:24:24The Sun in the centre, and the third planet up there would the Earth.
0:24:24 > 0:24:27The red dots in here are actually near-Earth asteroids,
0:24:27 > 0:24:31the green ones are the regular main belt asteroids.
0:24:32 > 0:24:36There are over 7,000 near-Earth asteroids,
0:24:36 > 0:24:40but there's one type they are particularly concerned to locate.
0:24:41 > 0:24:46Those asteroids that are over one kilometre in diameter.
0:24:47 > 0:24:49These are the monsters of the skies.
0:24:49 > 0:24:52An Earth impact with one of these
0:24:52 > 0:24:55would spell catastrophe for the planet.
0:24:55 > 0:25:00If a one-kilometre diameter asteroid were to hit, say, New York City,
0:25:00 > 0:25:06that would very likely affect people in you know, 100 miles away.
0:25:06 > 0:25:09It might kill people 100 miles away. So you're talking, really,
0:25:09 > 0:25:13a catastrophe, instantaneously, as soon as it hits.
0:25:13 > 0:25:15Tim's data reveals
0:25:15 > 0:25:20that there are 900 asteroids bigger than a kilometre
0:25:20 > 0:25:23in those dangerous near-Earth orbits.
0:25:25 > 0:25:27But the big question -
0:25:27 > 0:25:31are any of them on a collision course with Earth?
0:25:39 > 0:25:41Right now,
0:25:41 > 0:25:43there's no information that any of those large objects
0:25:43 > 0:25:46will hit the Earth in the next 100 years.
0:25:46 > 0:25:49So we're safe from impacts of those objects for at least 100 years.
0:25:49 > 0:25:52But there are still smaller asteroids
0:25:52 > 0:25:55than one kilometre that we have not yet discovered.
0:25:55 > 0:25:57So I can't say we're safe from them
0:25:57 > 0:25:59because we don't know where they are, just yet.
0:25:59 > 0:26:06So, for now, we are safe from a catastrophic asteroid impact.
0:26:08 > 0:26:12Even if the thousands of smaller asteroids might still pose a threat.
0:26:13 > 0:26:17However another group of scientists have a very different mystery
0:26:17 > 0:26:19about asteroids to investigate.
0:26:21 > 0:26:24One that may help solve one of the greatest quandaries
0:26:24 > 0:26:25about life on Earth.
0:26:35 > 0:26:36This is Maunu Kea
0:26:36 > 0:26:39in Hawaii. It is home
0:26:39 > 0:26:42to some of the most powerful telescopes in the world.
0:26:47 > 0:26:50For 30 years, Professor Dave Jewitt
0:26:50 > 0:26:53has used them to probe deep into the solar system.
0:26:55 > 0:26:58And once Dave interrogates deep space,
0:26:58 > 0:27:00it's rarely ever the same again.
0:27:03 > 0:27:04In 1992,
0:27:04 > 0:27:07I discovered the first objects found beyond Neptune
0:27:07 > 0:27:09since Pluto.
0:27:09 > 0:27:11The biggest discovery in the solar system
0:27:11 > 0:27:13since the discovery of the asteroids.
0:27:13 > 0:27:19It was a discovery that led to Pluto losing its status as a planet,
0:27:19 > 0:27:22something the world had taken for granted for over 60 years.
0:27:22 > 0:27:26It established Dave's reputation as a pioneering astronomer.
0:27:26 > 0:27:30It's important not to work on things that other people are working on.
0:27:30 > 0:27:34All you'll do is get the same result as everybody else. You won't make
0:27:34 > 0:27:37any discoveries, you'll just confirm what is already known.
0:27:40 > 0:27:43Dave's desire to journey where others fear to tread
0:27:43 > 0:27:46has led him to this.
0:27:48 > 0:27:54This bright dot with a long hazy tail is called Elst-Pizarro.
0:27:56 > 0:28:00It was found alongside all the other asteroids in the asteroid belt.
0:28:00 > 0:28:04The problem was, it just didn't look like an asteroid.
0:28:06 > 0:28:10So why did it seem so out of place?
0:28:10 > 0:28:13it didn't look like the other asteroids so it was a freak.
0:28:13 > 0:28:16And it got a lot of attention straightaway,
0:28:16 > 0:28:18because it was such a remarkable object.
0:28:18 > 0:28:21Nobody had seen anything like that before.
0:28:23 > 0:28:27What had got them excited was that to astronomers,
0:28:27 > 0:28:29asteroids normally look like this.
0:28:29 > 0:28:31Just a point of light.
0:28:31 > 0:28:35No dust cloud, and definitely no tail.
0:28:38 > 0:28:41For years Elst-Pizarro, with its orbit of an asteroid
0:28:41 > 0:28:46but strange fuzzy appearance, left scientists baffled.
0:28:46 > 0:28:50Until finally, someone suggested an explanation.
0:28:53 > 0:28:55Finally, a paper came out saying
0:28:55 > 0:28:59it must be due to the collision between two asteroids.
0:28:59 > 0:29:01So two asteroids slammed into each other
0:29:01 > 0:29:04with high speed, and shattered
0:29:04 > 0:29:06and produced a cloud of dust.
0:29:08 > 0:29:12So the strange tail was thought to be the debris from a collision
0:29:12 > 0:29:15between Elst-Pizarro and another asteroid.
0:29:16 > 0:29:18And, very quickly,
0:29:18 > 0:29:22most of the scientific world forgot about Elst-Pizarro.
0:29:23 > 0:29:24But Dave didn't.
0:29:27 > 0:29:33He had a hunch that there was more to this puzzling little light in the sky than at first appeared.
0:29:35 > 0:29:41A hunch that, if proved correct, might help solve one of the great mysteries of life here on Earth.
0:29:46 > 0:29:50Dave decided to investigate, and began looking for someone to work with.
0:29:50 > 0:29:53Somebody with a head for the challenge.
0:30:01 > 0:30:05When Dave suggested that I look at this object, I didn't actually know anything about it.
0:30:05 > 0:30:10Nothing had really been said about it in the last 6 years since it's been discovered,
0:30:10 > 0:30:14so I just decided, OK, it's just an interesting thing to take a look at.
0:30:17 > 0:30:22Dave and Henry knew that if Elst-Pizarro's fuzzy tail really had been caused by a collision
0:30:22 > 0:30:25the debris should have dispersed by now,
0:30:25 > 0:30:30and Elst-Pizarro should look like a normal asteroid again.
0:30:30 > 0:30:35But when they looked again, what they saw was that the tail was still there.
0:30:35 > 0:30:39It was strong evidence the collision theory was wrong.
0:30:42 > 0:30:45Collisions are very, very rare.
0:30:45 > 0:30:49Either Elst-Pizarro is the unluckiest asteroid in the solar system, that keeps getting whacked
0:30:49 > 0:30:52and producing dust in that way, which doesn't make any sense,
0:30:52 > 0:30:55or there's another mechanism for producing the dust.
0:30:56 > 0:31:00Elst-Pizarro's appearance remained an anomaly.
0:31:00 > 0:31:05Dave and Henry realised that if they were going to make any real sense of it
0:31:05 > 0:31:10they needed to find another example of an asteroid behaving in the same strange way.
0:31:10 > 0:31:15Dave and Henry's problem was that, in the 200 years since asteroids were discovered,
0:31:15 > 0:31:18Elst-Pizarro was the only one like it.
0:31:21 > 0:31:25Finding another one could be a complete wild goose chase.
0:31:29 > 0:31:36Using the giant telescopes on Mauna Kea, Dave and Henry began to hunt through the asteroid belt.
0:31:37 > 0:31:40For four years, they scanned the skies.
0:31:43 > 0:31:46They studied 300 more asteroids.
0:31:48 > 0:31:50All of them looked identical...
0:31:52 > 0:31:54..except for one.
0:31:58 > 0:32:02When we saw these images, I didn't know what to think actually.
0:32:02 > 0:32:05Maybe this is what we've been looking for all this time.
0:32:05 > 0:32:12But we were maybe just a bit nervous. You know, we may be on the... the cusp of something big.
0:32:14 > 0:32:17What they'd seen was an asteroid
0:32:17 > 0:32:20sporting a tiny, faint fan-shaped tail.
0:32:22 > 0:32:26Just like with Elst-Pizarro, they were convinced it was impossible
0:32:26 > 0:32:30this tail was created by a collision between asteroids.
0:32:30 > 0:32:34They had another explanation that to many seemed unthinkable.
0:32:36 > 0:32:37This is an image of a comet.
0:32:39 > 0:32:42They are objects that are thought to have been born
0:32:42 > 0:32:46in the freezing outer reaches of the solar system.
0:32:46 > 0:32:48They have long, elliptical orbits
0:32:48 > 0:32:51that bring them towards the sun and the Earth.
0:32:52 > 0:32:57And in comets the tail is a sign of something very special inside the centre.
0:32:59 > 0:33:00Ice.
0:33:04 > 0:33:09Their appearance is due to the vaporisation of the ice, that blows material off to make a tail.
0:33:09 > 0:33:13So they have this distinctive appearance, basically of having a long tail of dust.
0:33:16 > 0:33:19For 200 years the asteroid belt was thought to be
0:33:19 > 0:33:23an orbiting collection of dry lumps of rock and metal.
0:33:24 > 0:33:29Dave and Henry's new idea was that those asteroids they had observed
0:33:29 > 0:33:33might look fuzzy and have tails because they too actually had ice inside them.
0:33:35 > 0:33:39It was a radical suggestion, because scientists had always thought
0:33:39 > 0:33:43asteroid orbits were far too close to the sun for them to be icy.
0:33:46 > 0:33:48People were uncomfortable,
0:33:48 > 0:33:52because of this prevailing idea that the asteroids are rocky,
0:33:52 > 0:33:55and the comets are icy, and there should be nothing in-between.
0:33:58 > 0:34:02The reason why ice in the asteroids mattered so much
0:34:02 > 0:34:06is that it could help explain something that makes our planet unique in the solar system.
0:34:18 > 0:34:23Our beautiful blue planet is the only one to have an abundant supply of liquid water.
0:34:27 > 0:34:32Around 70% of the Earth's surface is covered by the oceans.
0:34:34 > 0:34:39But there has always been a mystery as to where all this water actually came from.
0:34:45 > 0:34:50For a decade, Dave Jewitt has been investigating this problem,
0:34:50 > 0:34:56because scientists have established that when Earth formed, over 4.5 billion years ago,
0:34:56 > 0:34:59it used to be a very different kind of place.
0:35:05 > 0:35:10The early Earth was really hot. It formed from hot material in orbit around the sun.
0:35:10 > 0:35:13So hot that we think the entire surface of the Earth
0:35:13 > 0:35:17was covered by liquid lava for the first 100 million years,
0:35:17 > 0:35:20a bit like the land that we see behind us.
0:35:20 > 0:35:23Dave believes the searing heat of molten rock
0:35:23 > 0:35:27would have had a profound effect on the Earth's early climate.
0:35:29 > 0:35:32Because it was so hot, we also think the early Earth was very dry.
0:35:32 > 0:35:35It's like putting something in the oven and baking it for too long.
0:35:35 > 0:35:39It comes out bone dry. We think the Earth was bone dry when it formed.
0:35:41 > 0:35:45That would means that the lush, wet climate that we enjoy today
0:35:45 > 0:35:49must be the result of some dramatic events long after the Earth was born.
0:35:51 > 0:35:55The Earth got its water some time after it had formed and cooled down,
0:35:55 > 0:36:01by being hit by objects that carried water from somewhere else in the solar system.
0:36:01 > 0:36:06If Dave and Henry were right, a constant stream of icy asteroids hitting the early Earth
0:36:06 > 0:36:10could have played a vital role in bringing our planet its water.
0:36:12 > 0:36:17But for all their observations, they hadn't actually seen ice on an asteroid.
0:36:17 > 0:36:22So the one problem with our observations is that they only told us what the object looked like
0:36:22 > 0:36:29and with that information we knew... we thought we could only explain it with the presence of ice
0:36:29 > 0:36:33but we couldn't actually prove that that was the case.
0:36:37 > 0:36:42The last piece of the jigsaw finally arrived early this year,
0:36:42 > 0:36:45with help from the mighty telescopes of Maunu Kea.
0:36:49 > 0:36:53Andy Rivkin makes the invisible visible,
0:36:53 > 0:36:57by using a NASA telescope to look at objects using infrared light.
0:36:57 > 0:37:00The infrared part of the spectrum is useful
0:37:00 > 0:37:04because it contains information about the composition of asteroids and other objects,
0:37:04 > 0:37:08and so by observing there you get a better handle on the composition
0:37:08 > 0:37:10than you would if you observed only in the visible.
0:37:12 > 0:37:17Andy studies the shape of the infrared spectrum reflected off the surface of asteroids,
0:37:17 > 0:37:23because tiny differences in the peaks and troughs can reveal what the surface is made of.
0:37:25 > 0:37:30Andy became interested in an asteroid called 24 Themis.
0:37:30 > 0:37:32The shape of its spectrum
0:37:32 > 0:37:36meant something very odd must be happening at its surface.
0:37:36 > 0:37:41We started by comparing it to other materials and objects that we thought might be similar.
0:37:41 > 0:37:45We tried comparing it to other asteroids, but it didn't look like any of the other asteroids.
0:37:45 > 0:37:50We tried comparing it to meteorites, and it didn't look like any other meteorites.
0:37:50 > 0:37:53So we knew we had to come up with some other explanation.
0:37:58 > 0:38:04Finally, in April this year, Andy and his team published their explanation
0:38:04 > 0:38:09as to why 24 Themis gives off such a strange kind of light.
0:38:09 > 0:38:14We found that water ice was actually the best choice, and that was really exciting, because
0:38:14 > 0:38:19it was the first time, certainly that we knew of, that anyone had found water ice out in the asteroid belt.
0:38:19 > 0:38:22Even though it had been suspected for some time
0:38:22 > 0:38:26that it could be out there, no-one had ever seen it.
0:38:32 > 0:38:36Andy had finally proved an asteroid really could be icy.
0:38:40 > 0:38:44It now seems certain the strange behaviour and tails
0:38:44 > 0:38:49seen by Dave and Henry on their asteroids was caused by ice too.
0:38:51 > 0:38:55DAVE: I think any time you make a discovery it's exciting.
0:38:55 > 0:38:58Any time you find a new thing, it's a big thrill.
0:38:58 > 0:39:00Definitely a big thrill, yeah.
0:39:00 > 0:39:02Cos it's hard.
0:39:04 > 0:39:07It means that asteroids could have played
0:39:07 > 0:39:12one of the most important roles in creating the Earth we see today.
0:39:15 > 0:39:19We know that asteroids did hit the Earth, for billions of years.
0:39:19 > 0:39:21The question is what the asteroids brought with them.
0:39:21 > 0:39:23We previously thought mostly rock and metal.
0:39:23 > 0:39:27Now we understand that the asteroids would also have brought
0:39:27 > 0:39:30a lot more water and ice than we'd previously suspected.
0:39:31 > 0:39:36These discoveries are starting to change our understanding of the solar system.
0:39:36 > 0:39:41Water and ice really are abundant in the asteroid belt.
0:39:42 > 0:39:45And that maybe water and ice
0:39:45 > 0:39:50is more abundant throughout the entire inner solar system.
0:39:50 > 0:39:55Finding the water in the asteroid belt is the key to starting to change
0:39:55 > 0:39:59our thinking about where Earth's water may have come from.
0:40:04 > 0:40:10Astronomers still don't know how much of Earth's water came from asteroids
0:40:10 > 0:40:13and how much from other sources of ice such as comets.
0:40:16 > 0:40:20Without that water, of course, life on Earth could not exist.
0:40:23 > 0:40:28Which provokes what is perhaps the most intriguing question of all.
0:40:28 > 0:40:32Did asteroids play a role in the creation of life?
0:40:46 > 0:40:49Not far from San Francisco, California,
0:40:49 > 0:40:53there are scientists pondering this very question.
0:40:53 > 0:40:59Scott Sandford wants to investigate whether the basic chemicals of life could have been formed in space,
0:40:59 > 0:41:01perhaps even on an asteroid.
0:41:02 > 0:41:06So he's created the conditions of deep space in a machine.
0:41:09 > 0:41:14This machine has been developed to allow us to simulate environmentsthat are out in space,
0:41:14 > 0:41:17either in the interstellar medium, events where stars form,
0:41:17 > 0:41:22or the environments, let's say, in the icy satellites of planets in the outer solar system.
0:41:22 > 0:41:29Environments that have low temperatures, no air, so vacuum, and high radiation fields.
0:41:32 > 0:41:36He wants to see if the complex carbon molecules that are essential to life
0:41:36 > 0:41:40could be created from the much simpler chemicals found in space.
0:41:43 > 0:41:50In this chamber is a sample probe covered in a tiny layer of water, methanol and pyrimidine
0:41:50 > 0:41:57that is frozen to just 20 degrees above absolute zero, and exposed to intense ultraviolet light.
0:41:57 > 0:42:03In this particular experiment we're looking at whether certain conditions will form one of the nucleobases,
0:42:03 > 0:42:06so one of the molecules that makes up our DNA.
0:42:08 > 0:42:13And from his analysis of samples from experiments like this,
0:42:13 > 0:42:16Scott has made a remarkable discovery.
0:42:17 > 0:42:20By processing ices of the type we see out in space, we can make
0:42:20 > 0:42:25some of the building blocks that we see in biology on the Earth today.
0:42:25 > 0:42:29We're making the building blocks of life, that's what we're finding.
0:42:31 > 0:42:35Just because you can create these building blocks of life in a lab,
0:42:35 > 0:42:38it doesn't mean it really happens on an asteroid.
0:42:39 > 0:42:46So Scott has carefully examined meteorite samples to see if they contain traces of these chemicals.
0:42:46 > 0:42:49In some classes of meteorites, which we think
0:42:49 > 0:42:53come from asteroids, we find a variety of organic compounds.
0:42:53 > 0:42:56And these include things that some people are familiar with,
0:42:56 > 0:42:59like amino acids, the building blocks of proteins in our bodies,
0:42:59 > 0:43:04but also materials like the nucleobases, the building blocks of DNA.
0:43:06 > 0:43:09So hidden within the rock could have been the materials
0:43:09 > 0:43:12that made possible the emergence of life on Earth.
0:43:15 > 0:43:21And that means that when asteroids struck Earth billions of years ago
0:43:21 > 0:43:23they could have completely transformed our planet.
0:43:26 > 0:43:30Asteroids could have played an important role in getting life started on Earth
0:43:30 > 0:43:35by delivering the raw starting materials that we need to get everything going to get life started.
0:43:38 > 0:43:43It seems the story of life on Earth is inextricably linked to the story...
0:43:43 > 0:43:44of asteroids.
0:44:01 > 0:44:08The possibility that asteroids hold the key to some of the deepest mysteries about our planet explains
0:44:08 > 0:44:14why scientists have always dreamt of reaching out into space and bringing back a pristine asteroid sample.
0:44:16 > 0:44:21And earlier this year, that wish may finally have come true.
0:44:31 > 0:44:36In June, one of the strangest space missions in history came to an end.
0:44:41 > 0:44:44It might look like a firework display, but this
0:44:44 > 0:44:48is actually a Japanese spacecraft re-entering the Earth's atmosphere.
0:44:54 > 0:45:01Seven years after it first left the Earth, the Hayabusa probe landed in the Australian desert.
0:45:03 > 0:45:08The scientific team were careful to handle the crashed probe with extreme caution.
0:45:11 > 0:45:15Because within this small container is what scientists hope will be the
0:45:15 > 0:45:20first ever asteroid sample collected directly from space.
0:45:20 > 0:45:26The sample consists a lot of little grains, and some of the grains are as small as ten microns,
0:45:26 > 0:45:32so ten millionths of a metre across, so this is a particle smaller than the width of a human hair.
0:45:32 > 0:45:36Even in a microscope it looks like a dot, OK, and so, um,
0:45:36 > 0:45:41the analyses of such small samples is obviously complicated.
0:45:41 > 0:45:45Obviously our hope is that some of that material really is from
0:45:45 > 0:45:49the asteroid, but at this point we don't know for sure one way or the other.
0:45:49 > 0:45:56It may be months or even years, before the team discovers what if anything these grains can reveal.
0:45:56 > 0:45:59While many scientists are excited about what
0:45:59 > 0:46:02asteroids might tell us about the beginnings of life on Earth,
0:46:02 > 0:46:09new research suggests that it is how asteroids might put an end to life that should really concern us.
0:46:18 > 0:46:20On the 6th of October 2008
0:46:20 > 0:46:24asteroid hunter Richard Kowalski saw something that would
0:46:24 > 0:46:27help change the assessment of the threat presented by asteroid impacts.
0:46:27 > 0:46:34The night was proceeding normally and up on the screen came another asteroid.
0:46:34 > 0:46:39As I continued to make observations throughout the night it appeared to be moving slightly faster.
0:46:39 > 0:46:43And this indicates that the object is close to the Earth.
0:46:43 > 0:46:50As with any other asteroid, Richard reported what he'd found to the Minor Planet Center.
0:46:53 > 0:46:56I got up in the morning, about 7 o'clock.
0:46:56 > 0:47:02I had a message from the computer saying, "could not compute an orbit for a particular object".
0:47:02 > 0:47:06I grabbed the observations of this object and I computed an orbit
0:47:06 > 0:47:12and it was immediately apparent, right then, that that object was going to hit the Earth.
0:47:12 > 0:47:17and sort of ominous fashion, it said it was in 19 hours.
0:47:19 > 0:47:23Following a strict written protocol, Tim quickly reported the findings
0:47:23 > 0:47:26to NASA's asteroid investigation team in California.
0:47:29 > 0:47:31We got a call from Tim Spahr
0:47:31 > 0:47:33at the Minor Planet Center saying we had an
0:47:33 > 0:47:36impacter coming in, in less than 24 hours.
0:47:36 > 0:47:37So that woke me up.
0:47:39 > 0:47:45NASA's expert on asteroid orbits, Steve Chesley, immediately started to verify the data.
0:47:45 > 0:47:48Steve The first thing I saw was a 1.000,
0:47:48 > 0:47:51100% probability of impact and erm, in less than a days' time.
0:47:51 > 0:47:55This I'd never seen, anything like this outside of simulations and software testing.
0:47:57 > 0:48:00An asteroid strike would create a huge explosion.
0:48:00 > 0:48:04NASA feared this might be mistaken for a nuclear bomb.
0:48:04 > 0:48:08We wanted folks to know that this was a natural event by mother nature
0:48:08 > 0:48:14rather than some sort of a man-made event like a missile or something dreadful.
0:48:14 > 0:48:17Information passed rapidly up the chain of command.
0:48:17 > 0:48:20So, NASA headquarters notified the Whitehouse
0:48:20 > 0:48:22that this was coming.
0:48:22 > 0:48:25Everyone wanted to know where it would strike
0:48:26 > 0:48:31NASA predicted a remote area of the Nubian desert.
0:48:39 > 0:48:46AT quarter to three in the morning, NASA were proved right.
0:48:46 > 0:48:50The explosion created a vast fireball burning as hot as the sun.
0:48:52 > 0:48:57It was so big and so hot, this image was captured by a weather satellite.
0:49:00 > 0:49:05As dawn broke, the smoke trail it left behind was still visible from the ground.
0:49:07 > 0:49:11I definitely think the impact was a wake-up call.
0:49:11 > 0:49:14I have to admit I never thought I'd see that in my career, where we would
0:49:14 > 0:49:17discover something that would hit the Earth later that day.
0:49:19 > 0:49:24What makes this impact so worrying is that this asteroid was too small
0:49:24 > 0:49:29for anyone to see until it was very, very close to the Earth
0:49:32 > 0:49:37For one scientist, it's was a salutary reminder that
0:49:37 > 0:49:40we cannot afford to ignore the threat posed by small asteroids.
0:49:42 > 0:49:46Physicist Mark Boslough uses one of the world's most powerful
0:49:46 > 0:49:53supercomputers to study the hazards facing our planet, from climate change to nuclear explosions.
0:49:53 > 0:50:00But for years, he's been fascinated by a strange event at the beginning of the last century,
0:50:00 > 0:50:04and what it might tell us about the threat of asteroid impacts.
0:50:07 > 0:50:11On June 30th 1908, without warning,
0:50:11 > 0:50:14a massive explosion wiped out
0:50:14 > 0:50:17over 1,500 square kilometres of Siberian forest.
0:50:17 > 0:50:23Millions of trees were destroyed.
0:50:23 > 0:50:27Scientists thought it had been caused by an asteroid strike.
0:50:29 > 0:50:34But then why was there no sign of any kind of impact crater?
0:50:35 > 0:50:42The answer is that the devastation had to be caused by an asteroid attack of a very particular kind.
0:50:44 > 0:50:48The explosion was caused by an asteroid that entered the atmosphere,
0:50:48 > 0:50:52got close to the surface and exploded before it hit the ground.
0:50:52 > 0:50:56That explosion created a blast wave with hurricane-force winds
0:50:56 > 0:51:00that knocked trees over for thousands of square miles.
0:51:04 > 0:51:11Scientists call it an air burst - a massive explosion in the atmosphere rather than on the ground.
0:51:14 > 0:51:18As it enters the atmosphere at speeds of up to 20 kilometres per second
0:51:18 > 0:51:20the air resistance decelerates the
0:51:20 > 0:51:25asteroid so fast it breaks apart in a huge explosion.
0:51:27 > 0:51:32And crucially, it is small asteroids that are most likely to explode in this way.
0:51:32 > 0:51:38Most of the damage from an explosion like this is actually the blast waves, it's the very high winds.
0:51:41 > 0:51:45Based on the physics of nuclear explosions,
0:51:45 > 0:51:49the original air burst model estimates the Tunguska explosion
0:51:49 > 0:51:54must have been 1,000 times bigger than the nuclear bombs at Hiroshima and Nagasaki.
0:51:56 > 0:51:59But crucially, the air burst model suggests the
0:51:59 > 0:52:03asteroid would have packed this huge destructive force
0:52:03 > 0:52:07even though it was as small as 100 metres in diameter.
0:52:07 > 0:52:11But Mark realised there was another problem.
0:52:11 > 0:52:18The model was ignoring a crucial difference between nuclear bomb air bursts, and asteroids.
0:52:19 > 0:52:25Asteroids are extremely heavy and move so fast that they carry huge momentum
0:52:27 > 0:52:33He created a new simulation to investigate the effect this would have on their destructive power.
0:52:34 > 0:52:40In this simulation I include more of the physics to be more realistic, you can see that the main shockwave
0:52:40 > 0:52:46doesn't come out of the point of the explosion, but it comes out from the point where the fireball descends to.
0:52:46 > 0:52:49so by the time the shockwave hit the ground it's much stronger
0:52:49 > 0:52:52than it would otherwise be so there is more damage on the ground,
0:52:52 > 0:52:55because the destructive power was carried downward.
0:52:58 > 0:53:04Based on Mark's new calculations, the devastation at Tunguska could have been caused
0:53:04 > 0:53:09by an asteroid only one third as large as previous estimates.
0:53:09 > 0:53:13Perhaps as small as 30-50 metres in diameter.
0:53:13 > 0:53:17And for him this carries a worrying implication.
0:53:20 > 0:53:24Smaller asteroids are more dangerous than we used to think and because there are so many
0:53:24 > 0:53:31more smaller asteroids than bigger asteroids we need to take that risk more seriously than we used to.
0:53:33 > 0:53:37Mark's work means scientists may have to redraw the asteroid threat map.
0:53:37 > 0:53:41If a Tunguska scale asteroid exploded over London or New York it
0:53:41 > 0:53:47would be very destructive, it would be as destructive as a nuclear bomb exploding over one of those cities.
0:53:49 > 0:53:55Scientists estimate that there could be over a million of these kinds of asteroids up in space.
0:53:55 > 0:54:00But nobody knows where they are, or where they are headed.
0:54:06 > 0:54:10A 2010 report by the American National Academies of Sciences,
0:54:10 > 0:54:13was so concerned about the potential threat
0:54:13 > 0:54:19to Earth from the smallest kind of asteroids, that it has called for a new survey to track them down.
0:54:22 > 0:54:26The problems is that even for dedicated asteroid hunters like
0:54:26 > 0:54:30Richard Kowalski, they are extremely hard to find.
0:54:30 > 0:54:36Many of them are as dark as a charcoal briquette and we see them by reflected sunlight.
0:54:36 > 0:54:42So you can imagine a 100-metre charcoal briquette out in space is going to be kind of hard to see.
0:54:46 > 0:54:50And that means that if an asteroid like this is heading for Earth,
0:54:50 > 0:54:55we might only see it when it is very close, with very little warning.
0:54:55 > 0:55:00There's a reasonable chance that you'll see it for the first time, on
0:55:00 > 0:55:05it's terminal trajectory, just days, or weeks, before the impact.
0:55:07 > 0:55:14If that were to happen, there is nothing that anyone could to stop it from hitting the Earth.
0:55:16 > 0:55:20For the public authorities, the only option, would be to try to get
0:55:20 > 0:55:24the thousands or even millions of people out of the impact zone.
0:55:28 > 0:55:31I think Katrina, Hurricane Katrina,
0:55:31 > 0:55:34really illustrated how hard it is to evacuate a large area.
0:55:36 > 0:55:40It's not set up that we have an asteroid evacuation plan
0:55:40 > 0:55:42in place right now.
0:55:44 > 0:55:50I know it's been discussed at the UN, but if we were to be
0:55:50 > 0:55:54issued 3 days' warning, I really don't know what would happen.
0:55:54 > 0:55:55And it wouldn't be very good.
0:55:55 > 0:55:58I'm sure we're not ready for that yet.
0:56:08 > 0:56:10However far away they may be,
0:56:10 > 0:56:12and however difficult to find,
0:56:12 > 0:56:15scientists now understand that Earth's past
0:56:15 > 0:56:20and its future cannot be separated from these tiny rocks of destiny.
0:56:20 > 0:56:26The quest to understand them will continue on Earth and from space.
0:56:31 > 0:56:36NASA currently has a spacecraft en route to visit two of the largest asteroids
0:56:36 > 0:56:37in the solar system.
0:56:37 > 0:56:41It will arrive in July 2011.
0:56:41 > 0:56:47And President Obama has challenged NASA to send astronauts to an asteroid by 2025.
0:56:47 > 0:56:50200 years after they were first discovered,
0:56:50 > 0:56:55solar system science has finally entered the age of the asteroids.
0:56:55 > 0:56:59The good, the bad and the ugly.
0:56:59 > 0:57:02Are asteroids bad, good or ugly?
0:57:02 > 0:57:05I'd say all of the above.
0:57:05 > 0:57:08I wouldn't say that asteroids are good or bad.
0:57:08 > 0:57:11They essentially created the solar system we live in
0:57:11 > 0:57:13and the planet that we live on.
0:57:13 > 0:57:18They've shaped the Earth in ways, it's safe to say, humans wouldn't be around
0:57:18 > 0:57:20but for the asteroid impact.
0:57:20 > 0:57:24I take asteroids like people - I take them as I find them
0:57:24 > 0:57:27and try to learn their individual foibles.
0:57:27 > 0:57:31I think ultimately asteroids will be our friends
0:57:31 > 0:57:36because they have the capability of giving us resources for use as we try to explore
0:57:36 > 0:57:38and extend our reach into space.
0:57:38 > 0:57:42Asteroids are certainly not ugly. Asteroids are beautiful.
0:57:42 > 0:57:48The ones that we don't understand, I think that makes them more beautiful.
0:57:48 > 0:57:51That's the beauty of science. That's why we keep doing it.
0:57:51 > 0:57:55It's to try to learn more things and when we get a curve ball thrown in,
0:57:55 > 0:57:59that's part of the process. That's the fun.
0:58:03 > 0:58:08I have an asteroid named after myself. It's (2956) Yeomans.
0:58:08 > 0:58:10That's quite a hoot.
0:58:12 > 0:58:16I do have an asteroid and this is it.
0:58:16 > 0:58:20(17857) Hsieh 1998KR1
0:58:24 > 0:58:31I have an asteroid. It's called (6434) Jewitt. It makes me feel like I'm part of the cosmos.
0:58:33 > 0:58:39I have an asteroid named after me. Pete Schulz. It looks like I've got a bullet with my name on it.
0:58:39 > 0:58:41HE LAUGHS
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