Meteor, Comet or Asteroid: What's the Difference?

14 February 2017
Presented by Chris Smith.

What's the difference between a meteorite, a comet and an asteroid? And we tell you how to find your own space rock here on Earth and track where it came from. Plus, news of quinoa as a possible solution to worldwide food shortages and we debate the role of vaping as an alternative to smoking...

In this episode

Smoking an e-cigarette

00:47 - Vaping: safer smoking, or a gateway to teen addiction?

Vaping seems to be safer than smoking, but is it causing more teenagers to take up the habit?

Vaping: safer smoking, or a gateway to teen addiction?
with Lion Shahab, University College London; Richard Miech, University of Michigan

The number of people using electronic or e-cigarettes has doubled in the last 5 years and now stands at about 15% of adults. Because e-cigarettes work by evaporating a nicotine-rich liquid to produce the vapour, rather than by burning tobacco, some people regard them as a much safer alternative to conventional smoking. But are they safer, and might the perception of safety encourage non-smokers to embrace the habit? This week two papers have been published examining these possibilities, one by Richard Miech from the University Michigan, and the other by Lion Shahab from University College London. Chris Smith spoke to Lion first...

Lion - In our study, we are interested to have a look at the relative risk of using e-cigarettes compared with standard conventional cigarettes. We looked at long term users of these products so these are people who have been using e-cigarettes for at least one and a half years and we compared their exposure to various cancer causing chemicals with people who smoke cigarettes. We also had another control groups which were people who were using nicotine replacement therapy for those who had stopped smoking. Nicotine replacement therapy are things such as patches and nicotine gum. Compared with cigarette smokers, those people who completely switched over the e-cigarettes dramatically reduced their exposure to these cancer causing chemicals to between 50 to 97 percent reduction of the levels of cigarette smokers, and the levels were very similar to people who use conventional forms of nicotine replacement therapy.

Chris - Therefore, on the basis of what you have seen from your study, what conclusion do you draw?

Lion - I think the main conclusion I draw from this study is that some of the literature out there on the risks and dangers of e-cigarettes probably overstates the harm that they can cause. Certainly, compared with the use of conventional cigarettes as those people who did switch over to using e-cigarettes dramatically reduced their exposure to cancer causing chemicals meaning that it’s likely that it reduces their risk of subsequent diseases, including cancer, greatly.

Chris - Well that sounds very encouraging but, on the other hand, Richard Miech, you’re coming at this from a different direction. What’s your perspective?

Richard - We looked at it slightly different research question. So, as you pointed out in the introduction, there’s a lot of debate right now about whether e-cigarettes and their use among teens is leading them to become smokers or whether, alternatively, kids are vaping instead of smoking. What we did is we interviewed a group of 17 year olds and then we followed them up a year later. So among kids who had never smoked at the baseline, those who were vaping as compared to those who weren’t vaping are about four times more likely to have smoked a cigarette in the following year. And among kids who had smoked in the past but weren't current smokers at the baseline, we’ve found that those who were vaping were also more likely to come back to smoking and there were about twice as likely to have smoked a cigarette in the past year.

Chris - I suppose you can’t really tell though whether those individuals who vaped and then smoked, or carried on vaping were just going to become smokers anyway?

Richard - We actually looked at that. We had a question at the baseline: how dangerous do you think smoking is? And we had a sizeable group who said that smoking was the most dangerous thing you could do. So we just looked at those kids who wouldn't seem to be likely to go onto smoking and, even among them, we found that those who vaped were more likely to smoke. We also found that among the kids who were vaping, those who thought that smoking cigarettes was highly dangerous at baseline were more likely to move away from that view. They’re more likely to reduce their perceived risk of smoking as they vaped.

Chris - What reasons did they give for taking up this habit in the first place?

Richard - The predominant reason for their vaping among those who vaped was they wanted to experiment to see what it was like and also that they liked the flavours. Because vaping comes in a wide variety of vapours, some which really appeal to teens like chocolate, or cherry, or bubblegum.

Chris - Lion, it seems that there’s a bit of tension here because, on the one hand, we have this tool that you're saying appears to really help on the basis of your data. On the other hand, we’ve got Richard here saying well actually, it’s pretty attractive to teens.

Lion - Well, yes. I have to say I’m not entirely convinced that it’s actually possible to prove a gateway hypothesis. We’ve looked at this in the UK, which has quite a relaxed attitude towards e-cigarettes, we have seen an increase in the use of e-cigarettes among youth as well. Although the use of e-cigarettes among non-smoking kids is very, very low indeed. And we can compare this with a country where e-cigarettes are not really widely available, such as New Zealand, and what you see when you compare the trajectory is that the decline is very comparable. So the proof is in the pudding, in a sense, that indeed, if there is a gateway effect from using e-cigarettes to using cigarettes, then you would expect, in the long term, that the decrease in cigarette consumption, in cigarette prevalence in youth should stop. But this is not the case, and neither is it the case in the US where I think the latest data shows that levels in cigarette consumption is the lowest since recording has started.

Chris - Richard…

Richard - Yes, that is true in fact that there’s a historical low in the level of cigarette smoking among teens in the US. There are studies, one that actually was the first to report this. But actually, that’s a long decline that started more than two decades ago and I’d like to point out that the decline started well before e-cigarettes even existed.

Chris - Do you think then, Richard, that these are an evil thing and we shouldn’t use them? On the basis of this, you’re only seeing a negative, it’s encouraging more people who have previously been extremely diligent and giving up, or not taking up smoking in the first place to embrace this habit?

Richard - My main message would be that many teenagers believe that vaping is completely innocuous and it has no negative consequences at all. But I think if word got out that kids who vape are significantly more likely to start smoking, I think many teens would think twice before vaping and, maybe stay clear of vaping devices.

Chris - Do you not think that’s a risk, Lion, that it’s not just kids, it could be some of the adults we are seeing who are not smokers but might be tempted to toy with the idea of vaping because it does taste nice perhaps, or it’s not regarded as so bad for you?

Lion - Yes, it is a theoretical risk but the data in the UK just do not bear this out. There’s no evidence that I can see currently that non-smokers are taking up vaping.

Chris - So in your view it’s a good thing, it’s going to help people to minimise the harms that cigarettes do?

Lion - Yeah. Just to reiterate, the vast majority of people who use e-cigarettes are either current smokers or ex smokers. And it is a sad truth that only 50 percent of smokers ever manage to stop smoking their lifetime which means that, in the UK for instance, still nearly 100,000 people die because of smoking and e-cigarettes are, potentially, a way of  helping some people who have failed to stop smoking with other conventional forms of support to stop smoking, and they appear to be significantly safer than continued smoking.

Chris - Richard, last word from you.

Richard - Yeah, I’ll point out that among 13 and 15 year olds, vaping is more than twice as prevalent than cigarette smoking. Amongst teens, vaping has really taken off to the extent that it is a bridge to smoking; I think that’s a message that teens need to hear.

08:19 - Could quinoa solve worldwide food shortages?

Sequencing the genome of quinoa improves our understanding of why the plant is able to grow in such harsh conditions.

Could quinoa solve worldwide food shortages?
with Mark Tester, King Abdullah University of Science and Technology; Sandra Schmoeckel, King Abdullah University of Science and Technology

The Incas called it the 'Mother Grain', while middle class residents of Cambridge and probably Camden call it lunch. But for many the quinoa plant - or Chenopodium Quinoa to give it its proper name - which can tolerate extremes of salt, and drought, and temperature and yet still produce nutritious seeds could be a future lifeline. Now scientists have decoded its genome to reveal where this extraordinary crop came from and how it can handle such harsh conditions. The ultimate goal is going to be to breed these traits into other quinoa strains and even completely different crop plants in order to combat concerns for future food security. Georgia Mills spoke to Mark Tester who led the work at the King Abdullah University of Science and Technology in Saudi Arabia...

Mark - About a third of the world’s food is produced under irrigation and a large fraction of the water sources that are being used for the irrigation are being depleted. We’re mining a lot of the world’s water and as the water is depleted so the quality of the water degrades, and it gets saltier. So we’re actually facing a very big challenge in global agriculture because a lot of the systems that are producing food at very high amounts at the moment are not sustainable. We need to be able to increase the salinity tolerance of crops in those systems.

Georgia - The amount of water is going down and, I suppose, at the same time the number of people and mouths to feed is on the up?

Mark - Yes. There’s an increase in demand for global food production. The UN Food Agriculture Organisation predicts that we will need at least 50 percent more food by 2050. And yet, one of the major systems of producing food at the moment is threatened with decreasing production, not increasing production.

Georgia - So quinoa, as a salt tolerant plant, suddenly looks quite important. Using several cutting edge sequencing technologies, Mark and the term worked out the most complete genome of the plant yet. But so what?

Mark - When you’ve got the genome sequence you can do a lot of things. You can have fun, and do things like understand some of the evolutionary processes that have led to the genomes being the way they are. But on a more applied level, once you have the genome then you can then start to look at differences in the genome between different individuals within the species. What we find often is that if you look at a large enough number of individuals and then you characterise those individuals: look at their salinity tolerance, the way they grow, the way they produce their flowers and so on. All the traits which are important to lead to a crop that we can harvest. And you can quantify each of those aspects of the plant and then look at all of their genomes and then what you can do is associate bits of the genome with particular traits and, with that, you can start to discover genes very, very rapidly. That’s what Sandra and the team did with the saponins.

Georgia - Saponins are a thorn in the side of quinoa growers. The plant creates these bitter compounds to protect itself, but it means that to wash away this bitter taste we need to use a lot of water which drives up the price. But now, knowing the genome the team have linked the production of these saponins to a specific gene which could make breeding sweet, cheap quinoa much, much easier. As post-doc researcher Sandra Schmoeckel explained…

Sandra - Saponins are only really harmful in the seeds or around the seeds. So you need to plant a plant, wait for it to grow and produce seeds and then you look at the seeds. So when you do your natural breeding and you’re looking for the sweetness now we have a marker. We know which gene is making it sweet so we can look at a plant and when it’s very little, tiny we can take a little piece of the leaf and look for it’s sweetness. That’s the major advantage of having the genome and knowing what genes are contributing to sweetness because we can look at them a lot earlier than conventional breeding.

12:53 - Mythconception: chocolate is a health food

Chocolate contains antioxidants but can we really call it a health food?

Mythconception: chocolate is a health food

With Valentine’s day arriving, you might have bought your beloved a box of chocs. But you might want to wait until you hear what Kat Arney’s been finding out about a common chocolate-based mythconception.

Kat - Love is in the air - or, at least, the sickly manufactured version of love that passes for Valentine’s day merchandising. And one of the traditional gifts that people buy to show their undying affection is chocolate. After all, everyone knows that dark chocolate is meant to be good for you - so it’s practically a health food, right? Wrong.

First let’s take a look at where the idea that chocolate is healthy came from. The key thing is the main ingredient that gives chocolate its name and taste: cocoa beans, or cacao. These are harvested from plants and then fermented, dried, roasted, crushed, ground and pounded to produce rich-tasting cocoa powder and silky-smooth cocoa butter. Like the produce of most plants, cocoa beans contain chemicals called antioxidants, specifically molecules known as flavonols, or polyphenols. There’s a lot of interest in flavonols for bringing all kinds of purported health benefits, from boosting brainpower and lowering blood pressure to helping cut heart disease or even reducing cancer risk. So it makes sense that if chocolate is made from cocoa beans, and cocoa beans contain flavonols that are really good for you, then chocolate must contain loads of flavonols, and must therefore also be really good for you!

Alas, it’s not quite that simple. The manufacturing process from bean to bar is not kind to these chemicals. All that fermenting and roasting helps to destroy them, and sometimes cocoa is also treated to make it more alkaline - a process known as Dutching - which gives it a milder taste but can also destroy more of the flavonols. Adding extra ingredients, such as emulsifiers, milk and sugar can also mop up flavonols along the way.

Another thing that makes chocolate something to be enjoyed in moderation as a treat rather than a health food is the other stuff that’s in it. Flavonols are very bitter, and are pretty unpalatable unless served with a side-order of fat and sugar. As a result, there’s more than 550 calories in a hundred grams of chocolate, and that includes the really posh dark stuff. Eating too much of anything will make you put on weight - which can increase the risk of heart disease and other illnesses - and packing in a lot of high-fat and high-sugar chocolate is likely to have more of a negative impact on your health than any positive benefits from the tiny amounts of polyphenols.

All is not lost, if you still want to believe that chocolate can be good for you. Currently there’s a trial underway in the US testing whether capsules of flavonols purified from cocoa have an impact on cardiovascular health. Unfortunately they don’t taste like chocolate at all, don’t come wrapped in a shiny box, and are way less romantic. And, just to be a total killjoy, fruit, vegetables and beans are much better sources of polyphenols and other antioxidants than chocolate. Of course, there’s nothing wrong with a chocolaty gift if that’s what the lady loves, but let’s stop kidding ourselves that it’s a health food. And if you really want to give the one you love a health boost this Valentine’s day, maybe a box of fruit and veg might be a better bet than a box of chocs. Although I can’t take any responsibility for any hearts broken over a bag of broccoli.

Timothy O'Leary in a sushi bar

16:35 - Neuronal sushi belt

Do the neurons in our bodies really behave like a sushi conveyor belt?

Neuronal sushi belt
with Dr. Timothy O’Leary, University of Cambridge

The nerves or neurones that send messages from one end of the body to the other have fascinated anatomists for over a century. An outstanding question is how do these cells, which can be metres in length, keep all of the remote parts of the cell supplied with energy and raw materials, which are normally made in just one central region of the cell. One popular idea is that neurones contain the microscopic equivalent of a conveyor belt system which transports materials to where they need to go inside the cell. But, by building a mathematical model of how this happens, Chris Smith met one scientist who has found that anyone waiting for their dinner to be delivered by a system like this would end up very hungry indeed, so something else must be going on…

Timothy - I'm Dr Timothy O'Leary, based at the University of Cambridge, and I'm a lecturer in information engineering and neuroscience. Today we're in a sushi restaurant in Cambridge and it's one of those sushi restaurants that has a snazzy belt mechanism, that allows all of the dishes to be delivered to the customers as they sit around the sushi belt. 

Chris - What has this got to do with cell biology?

Timothy - The cells I’m interested in are neurons, and neurons are the cells that essentially make your brain work. A typical person has around 86 billion neurons and one neuron can, potentially, connect thousands of other neurons and it’s this connectivity that give your brain it’s power.

So, how do neurons connect to each other? Well, in order to reach out and connect to their neighbours they have these long, thin, branch like processes called dendrites. So if we looked at a neuron under a microscope, it would look like a tree, a very bushy tree with lots of branches and some of them very long. If we were to zoom into this neuron and look inside one of the branches, we’d see there are lots of things moving up and down the branch. And this is because neurons are composed of lots of proteins and small components that all need to be manufactured and moved around inside the cell.

So sometimes material needs to be made in one part of the cell and then shuttled along to another part of the cell. And the analogy that we use is the sushi belt because there really is something inside the cell that moves this cargo along in a similar fashion to a sushi-belt.

Chris - Effectively you can imagine the analogy is the nucleus is the recipe book with the chef standing there cooking stuff, putting it on the plates that then go on the sushi-belt, and they’re carted round the cell and the customers (the parts of the cell that need them) are going to be lifting dishes off the sushi-belt at various points and using them.

Timothy - That’s just the picture that we have, yes.

Chris - What’s wrong with it?

Timothy - Life isn’t really like that. At the molecular level the movements of these particles are stochastic, that means that there’s a chance element in it. To explain what that would mean in the sushi restaurant analogy, let's imagine that we’re waiting for a tuna roll and it’s a few feet away, but then randomly the belt changes direction and starts moving the other way. That would be very frustrating. But what would be even more frustrating is if the person next to us, who doesn’t even want the tuna roll, just took the tuna roll, sat it on their table for a while and then maybe decided to put it back on the belt. Those are the kinds of things that can occur at the molecular level by chance and it’s for this reason that we can expect long delays sometimes in this transport mechanism within a neuron.

Chris - Can cells tolerate not getting it’s tuna roll for ages or, actually, are you saying that this is such a significant constraint there must be something else going on because cells would not be able to put up with that?

Timothy - That was actually the motivation for this study. What we did was we took experimental data where scientists had measured the movements of these microscopic particles. Then we simply took the measurements and we did the math and we figured out how long it would take, on average, a collection of particles to move across a typical sized neuron and the number turned out to be disappointingly large. It can take many hours or days to distribute cargo throughout a typical neuron. And this came as a surprise because many of us thought that cargo could be distributed on the order of minutes or hours at the very worst.

Chris - Is is not that the cell does something else, which could be it says well I’ll tolerate some constraints of the sushi belt but, at the same time, I’ll also have my own local solution? So I’ll make some stuff myself locally so I’m not held up, so if it’s not available on the sushi belt right now, I’ll make my own?

Timothy - That’s absolutely true and, in fact, in recent years it’s been observed that neurons do have the capacity to make things that they need locally. However, the ingredients for the things that they make locally, and the machinery for making them, still need to be delivered to those sites and our claim is that that may take a lot longer is currently thought.

Chris - I suppose what you have done is to highlight some of these inconsistencies but you’ve also now generated with this model a bunch of testable hypotheses?

Timothy - That’s absolutely true. So it’s now becoming possible to peer inside a living neuron and watch these components moving around. And the kinds of experiments people can do now can start to address some of the predictions of the model. We might find that actually neurons are far cleverer than we think and they’re able to distribute components far more efficiently than our calculations suggest and that’s why our model made the minimal possible set of assumptions. Now, if further observations contradict those predictions, then we know that there are actually parts missing to our understanding of this molecular sushi belt.

22:28 - Using cochlear implants to cure deafness

What's it like to be able to hear again with a 'bionic ear'?

Using cochlear implants to cure deafness
with Bob Carlyon, MRC Cognition and Brain Sciences Unit, Cambridge; Matt Davis, MRC Cognition and Brain Sciences Unit, Cambridge; Mel Jewett, National Cochlear Implant Users Association

Hearing and understanding speech is something many of us take for granted, but hearing loss is something that affects huge numbers of people. It’s estimated 1 in 6 people in the UK have some form of hearing loss or deafness. And one cause is damage to the inner ear or cochlea where sound waves are converted into nerve impulses that the brain can then understand. For some people a device called a cochlear implant - or as the Australian inventors dubbed it “bionic ear” - can be used to do the same job, but wearers often initially struggle to understand speech. Scientists have been looking into why, and they’ve come up with some strategies to help, as Tom O’Hanlon has been hearing, first from Bob Carlyon at the MRC Cognition and Brain Sciences Unit in Cambridge.

Bob - It looks a bit like a hearing aid in the sense that you have a thing behind your ear which has got a microphone in it. This microphone sends the sounds to a little processor worn behind the ear which breaks sounds down into the individual frequency bands, and it then transmits that information across the skin using a little radio frequency transmitter to a receiver stimulator underneath the skin. That then sends that pattern of electrical stimulation to an array of electrodes inserted inside the inner ear and those electrodes stimulate the auditory nerve directly, bypassing the damaged receptor cells which has caused the patient to become deaf in the first place.

Tom - When I’m speaking now, my voice is actually composed of many tiny vibrations happening at different rates or frequencies. You can seamlessly decode these with the helpful duo of the inner ear and the brain. So what’s it like when suddenly an implant does the job of the inner ear? Mel Jewett, ambassador for the National Cochlear Implant Users Association, is one of half a million people worldwide to have this implant and she took me through her experience…

Mel - When I try and describe what it’s like to hear with a cochlear implant, one way that makes sense to me is that natural hearing that we have is like an acoustic guitar, but hearing with an implant is like an electric guitar. It does take a lot of getting use to but, over time, it does become natural. My dad’s voice now sounds like how I remember my dad’s voice. My mum’s like my mums.

Tom - So while we have the luxury of an acoustic guitar world, rich in sound and meaning, for cochlear implant users there’s a tricky transition - an electric guitar world in which speech is much harder to understand. To get an idea of what this might be like, have a listen to this…

Could you make sense of that. I certainly struggled.

Matt - The speech is hard to understand, but if you give people hints and clues about what they’re hearing it starts to sound a lot clearer.

Tom - This is Matt Davies, also at the Cognition and Brain Sciences Unit. His research looks at how our brains understand challenging speech…

Matt - So, if I tell you that the sentence was the man read the newspaper at lunchtime and then play it again…

Tom - I got most of that actually that time.

Matt - It sounds strikingly clearer! This is an illustration of something that’s long been known about speech perception and perception in general. When you’re perceiving something, you’re not only processing the external sensory signals so the sounds in this case. You’re also using your knowledge, your prior knowledge of the world and of the messages and information that you’re expecting to change the way in which you perceive something. So that’s a very striking effect here, when you know what's being said, the speech sounds a lot clearer.

Tom - Do we know what’s going on in people’s brains when they’re unpicking this challenging speech?

Matt - That’s something that we’ve been studying a lot in the last year or to. We’ve been using two different forms of brain imaging to look inside the brain and see what activity is going on when someone listens to degraded speech, just like the ones that I’ve played to you. The theory that we’ve been developing that explains our observations is based on an idea called “predictive coding.” You’ve probably encountered “predictive texting” on your mobile phone now, in crude kind of way, that’s a model for what the brain is doing. So the brain is continuously trying the sensory signals that it’s receiving and, when it process sounds, it’s doing so in a way that’s guided and informed by the predictions that it had. When you know what’s about to be said you have very accurate predictions, and that’s what makes perceiving the degraded speech sounds easier is that your predictions become more accurate; they’re closer to the sounds that you’re hearing.

Tom - Matt and colleagues saw a reduction in brain activity when people in the study knew what they should be hearing compared to hearing degraded speech without subtitles. The same kind of brain response was seen with longer term learning and adapting…

Matt - What we found is really, really very interesting. It shows that once again, the brain predicting the sounds that it’s going to hear that seems to be involved in that tuning in process. So, people who start off an experiment finding degraded speech very difficult to understand, with minutes or hours of training get better and better at understanding that speech, and part of what’s making it better is that they’ve improved their predictions for what that degraded speech will sound like. And that’s a very useful thing to learn because it allows you not only to understand a particular sentence but also to understand other sentences and other speech sounds that you might never have heard in that degraded form. I think it’s very similar to what’s going on for someone with a cochlear implant.

Tom - So by listening to degraded or challenging speech with subtitles, you then get better at understanding degraded speech more generally?

Matt - That’s absolutely right. I was reminded of this when I watched the American TV series “The Wire.” The characters all have a very strong Baltimore accent which I found, initially, very hard to understand. Switching on the subtitles helped me understand what the characters were saying, but it also helped my tune into that unfamiliar accent. So by the time I’d watched two or three programmes actually I could do much better without the subtitles on. Having that extra support that you get from subtitles doesn’t just help you in immediate understanding, it also helps with learning.

Tom - Matt hopes that using these techniques may help implant users adapt to their new hearing more quickly.

Matt - What our research suggests is that during that period of adjusting and adapting it will be helpful for those listeners to watch the TV with the subtitles on. To listen to talking books whilst reading the text of the book. That that extra support doesn’t only help them in their immediate understanding but will also help them to tune in, to adjust to the sensations of sound that they receive through their implant..

29:50 - Our very own meteorite...

Naked Scientist Connie Orbach won a meteorite and Graihagh Jackson made it her mission to find out more...

Our very own meteorite...

One of our producers, Connie Orbach, won a meteorite last year from the Science and Technology Facilities Council - the STFC - they're the main funders of space science and astronomy research in the UK. This meteorite took some time to arrive and we were all very excited when it did turn up to unwrap it. And we discovered that it was picked up in the 1500's in South America so Graihagh Jackson made it her mission to find out as much about it as she could, starting with a chat with the new owner...

Connie - I'm not going to lie, I've never wanted a meteorite before, but now I have one I'm incredibly happy.

Graihagh - And it's come on quite a journey to get here because we have been waiting in the office for weeks in anticipation of this meteorite.

Connie - I think I'd say over two months - it's been a long time! So I won it; it was an incentive to fill in a feedback form. And so they said it would take a while because they said "we have to order it". And I said "where from, do you order it from space?" How do you order a meteorite in this day and age? But no, I think they just ordered it from the meteorite store which, apparently, exists somewhere. I'm holding it now and it's...

Graihagh - About an inch long, isn't it?

Connie - Yeah, yeah, about an inch long, half an inch wide and kind of bumpy. It's black but with a silver tinge to it when you look at it in the light. And the thing that really strikes you when you get this it it's really, really heavy.

Graihagh - Yes, I'm still shocked. I mean, even though we were pretending to open it I'm still shocked. I thought it was packaging that made it how heavy that is. I think that's maybe a kilo, maybe?

Connie - You think? It's definitely at least a bag of sugar so that's how I'd do my measurements, so it's at least half a kilo. And it feels like a visual illusion every time you're holding it, I think, because it just doesn't match up but my brain thinks something is wrong! And the other thing it came with is a lovely little sign telling me a bit about it.

Graihagh - Dare you pronounce what it says?

Connie - So obviously, I'm fluent in Spanish - Campo del Cielo.

Graihagh - Very good.

Connie - From Gran Chaco - oh this is tricky - Gran Chaco Gualamba, Argentina. Found - and so this is how I know they didn't order it from space - found in 1576. It's really old! I mean it's space rock so it's really old, but it's really old to this world too which I thought was quite amazing. And then it's kind of got what it's made of and the main thing is iron and that's why it's so heavy. 

Graihagh - Do you know anything more about it? I mean I'm thinking, meteor, meteorite, comet. I'm not entirely sure I know where these things overlap.

Connie - I have no idea.

Graihagh - Given we've all been so excited, none of us have looked anything more into it.

Connie - No, not at all. I was just excited I was getting a meteorite but, actually, probably not sure what that is!  I just know it's space rock of some sort.

Graihagh - So I'm going to make it my mission to find out as much as I can about this rock.

Connie - And if you can get some form of certificate, I'll be particularly happy.

Graihagh - So a certificate, and as much as there is to know about this lump of space rock as possible. 

33:04 - What is a meteorite?

What's the difference between a meteorite, an asteroid and a comet?

What is a meteorite?
with Dr Carolin Crawford, University of Cambridge

What's the difference between a meteor, meteorite and meteoroid but also a comet and an asteroid? Graihagh Jackson wanted to get to the bottom of which space rock was which, so spoke to meteorite enthusiast Carolin Crawford, from Cambridge University's Institute of Astronomy.

Carolin - Yes, it is complicated and astronomers do love our terminology. So, you've got lots of lumps of rock; the debris that you said floating around in the solar system. Now if it is made of ice - like a frozen iceberg 5-10 kilometres across or smaller, we tend to call it a comet even though it might have bits of dirt and dust within it. So comets are the icy bodies. Asteroids are the rocky debris. And we won't talk about things called Centaurs which are half ice half rock. They're out beyond Neptune - we won't worry about them so much. But, basically you've got your asteroids which are rocky and you've got your comets which are icy. Now a meteoroid is like a tiny asteroid. You're talking about a few microns across to a few metres across in size. So it's just debris, like the asteroids, left over or fragments from a collisions or protoplanets, that's been hanging around for billions of years in the solar system and floating around between the planets, around the Sun following their own orbits.
Now as soon as that meteoroid starts to enter Earth's atmosphere it becomes a meteor. That's what you know as your shooting star and that's when you see it burning up in the atmosphere. It sort of excites the air molecules and you get this trail of ionised particles which shine, and you also get the lump of rock, even if it's tiny, it will still give of an amazing amount of light because it's travelling quite fast. Most of them disintegrate in the atmosphere completely but, if they survive to hit the surface of the Earth, then they become a meteorite. So that's the distinction: Meteoroid when it's in space, meteor when it's in air, and meteorite when it's sitting on the ground. You get three basic types: The most common ones are the ones that are rocky. Then you get the iron ones, so that's iron and nickel alloy. And then you get stoney iron which are the mix of the two.
This is an example of a stoney one that is very nice because you see it's got a mottled appearance.

Graihagh - Dare I say, a bit like sometimes when I'm walking down the street and you see all the little bits of rock within, what's it called - pebbledash is what I'm thinking of but in a miniature polished form. Is that a terrible thing to say?

Carolin - No. You're getting the idea across beautifully there. It is just speckled and you've got these almost like spherical - we call them inclusions - little bubbles of dust and carbon materials that's held within the silicate base.

Carolin - Did you bring this meteorite?

Graihagh - I did.

Caroline - OK let's have a look - see which one you got.

Graihagh - How much do you know about meteorites?

Carolin - I'd say it's a nickel/iron one.

Graihagh - Gosh - that's impressive! I was going to bring out the label because I couldn't even remember what it...

Carolin - Sikhote Alin?

Graihagh - No.

Carolin - So it's not Sikhote Alin. It's not Campo del Cielo because it's metal rather than...

Graihagh - Oh - controversial!

Carolin - Oh it is! It's Campo de Cielo.

Graihagh - I'm going to ask you how much you can tell me about this because this is Connie's meteorite that she won and, other than giving it a quick look up on the internet, we know nothing.

Carolin - This is one of the more common falls.

Graihagh - Ah, OK.

Carolin - You've got two very famous falls - you've got the Campo del Cielo. And this is part of the Sikhote Alin fall.  I mean I like this one - you can see how it's just sort of melted as it's fallen through the air. It's all kind of deformed and ruffled up - I like it particularly.

Graihagh - It reminds me of... do you remember The Futurists (the painters) - The Futurists. You know how they had these very choppy, jagged types of paintings - that's what it reminds me of.

Carolin - Or it just looks like a parrot!  It is deformed. I mean you look at that and you see a mangled bit of metal and you think gosh, that metals gone through a lot to get to be that shape. So this fell in the Sikhote Alin mountains in 1947.

Carolin - They come from a number of different places, but you're quite right, they're lumps of space rock or, if you like, space metal that are floating around there orbiting round the Sun. Now some of them, especially those rocky/stoney ones, are left over from the original solar system formation. They are bits that just didn't get incorporated into being planets. Or they could be fragments of asteroids. You know, you can imagine protoplanets in the early solar system, asteroids now colliding and shattering fragments off. And then you have some that are really exciting and they're where a meteorite has impacted another planetary body. So it's something like the Moon or Mars or say Vesta, the largest asteroid in the asteroid belt. And when the meteorite impacts that body, it send ejector out but because things like Moon, Mars, Vesta don't have so much gravity, not all of it falls back down to the planet. It then goes out into space and starts orbiting the Sun and, maybe millions of years later, it happens to fall on Earth. So some of these meteorites are bits of Mars, they're bits of the Moon, or bits of Vesta.

Graihagh - Oh, are you about to show me a rock from Mars?

Carolin - No, this one's a bit of Vesta.

Graihagh - Wow!

Carolin - Which is surprisingly common. If you look at Vesta, this is the object that's about 500 kilometers across in the asteroid belt, it looks a bit more more like a punctured football. It's got a huge sort of gouge out of the southern pole and that's where we think it underwent a huge collision sometime ago in its past. So there are lots of fragments of Vesta around and this is one here.

Graihagh - How do you know that?

Carolin - You know because of the mineral makeup. I was telling you you've got all these different origins for different kinds of meteorites and, looking at the chemical composition of these rocks, you can tell a lot about whether they're pristine parts of the solar nebula or they've come from bodies that have undergone what we call geological differentiation. So you've started to have that geological processing, the separation out of the metals and the sort of silicate crust.
So, when you hold something like your Campo del Cielo that's completely metal, that would have come from the inside of one of these differentiated bodies. So like a small asteroid that was forming or a protoplanet that was forming before it got smashed so you've got a bit of the core part of the asteroid there. A lot of these stony meteorites are much more of the pristine debris left over from the early solar system.

Graihagh - So why is it them that we're interested in things like 67P, and we've sent out Roseta and we've seen Philae land on the comet? Why though if all this stuff is falling down on Earth all of the time?

Carolin - there's a lot of science you can only do when you're in contact with the astronomical body, like the comet Nucleus, and that was what was important about the Philae lander. And, of course, you've got to remember that comets are mostly ice, not just water ice, but also methane ice, and ammonia, carbon monoxide, carbon dioxide. If you want t understand the icy part of the comet, you've basically got to go out there.

Graihagh - Is it quite rare for this sort of stuff to fall to Earth or is it quite common?

Carolin - You have stuff coming into the atmosphere the whole time. You've got millions of meteors happening daily, it's just that most of them are tiny. A shooting star you can get from a thing about the size of grain of sand. Most disintegrate in the atmosphere but, even so, you get a lot that land on the Earth or, in fact, fall into the ocean probably at a rate of about 15 billion kilogrammes per year. There's a huge amount of stuff that is just continually piling onto the Earth

You don't look like you believe me.

Graihagh - Well, I was really pleased that we'd won there so now you're telling me (I say we), Connie has won this and it's not even that rare.

Carolin - They are rare. I mean it sounds like a lot but, in terms of volume and mass of the Earth, it's miniscule. Also, what you've got there is one of the metal ones - they're the rarer ones.

Graihagh - The reason why I ask if it's rare, and I'm glad you say it's rare, I've got this meteorite for the weekend now. If I was to go away and sell it, what sort of price does this thing fetch?

Carolin - For the size you've got there I would guess about £60 or something.

Graihagh - Oh, that's pretty reasonable!

Carolin - I think it's pretty reasonable. Well it also depends on which fall the meteorite comes from, so you can get very particular falls where there are fewer pieces found, or it’s particularly famous fall or something about it. For example people are very interested in the recent fall in Russia – if you want a bit of that meteorite you will get a higher cost per gram for the meteorite than you would from things that are a dime a dozen like cico tallin or im afraid your Campo del Cielo.

Graihagh - So why is it them that we're interested in things like 67P, and we've sent out Roseta and we've seen Philae land on the comet? Why though if all this stuff is falling down on Earth all of the time?

Carolin - there's a lot of science you can only do when you're in contact with the astronomical body, like the comet Nucleus, and that was what was important about the Philae lander. And, of course, you've got to remember that comets are mostly ice, not just water ice, but also methane ice, and ammonia, carbon monoxide, carbon dioxide. If you want t understand the icy part of the comet, you've basically got to go out there.

43:10 - Rosetta-Philae: sniffing out comets

What have we found out so far from the Rosetta-Philae mission? And what does a comet smell like?

Rosetta-Philae: sniffing out comets
with Matt Taylor, European Space Agency

In November 2014 the Rosetta mission was hoping to explore what comets are made of when its Philae-lander touched down on the surface of comet 67P. And Graihagh Jackson actually got to find out what that comet smells like...

Matt - My name's Matt Taylor. I work for the European Space Agency on the Rosetta mission that's gone to a comet. Was that OK?

Graihagh - That's wonderful. Tell me about the Rosetta mission, what did it set out to do?

Matt - Rosetta is a mission to a comet. It set out in 2004, took ten years to get to its target comet and why do we go to comets? We go to comets because we consider them to be representative of the building blocks of the solar system. So, by studying a comet, you get an idea of what the conditions were, what the material that went into building the solar system. In fact, there's material that we found from the comet by Rosetta that actually predates the Sun. So it's really the primordial soup, the ingredients for that soup, and we get a picture of it by looking at this comet.

We sent the spacecraft up in 2004, it chased down the comet over ten years. In 2014, we turned the spacecraft back on because we'd had the time period where we were in hibernation, we caught the comet, we landed on the comet with Philae and, for the last two years, we've been orbiting the comet and measuring - looking at it's surface structure and how it evolves in time because a comet is really interesting in that when it goes past the Sun it becomes very active. There's a lot of ice inside it that throws of tons of gas and that peaks when you get near the Sun, and then starts to drop off and move away from the Sun.

With Rosetta we've sat next to it all this time observing how that stuff evolves, what the surface does, the surface changes. We think about a metre of the surface disappeared in the time that we've been with Rosetta.

Graihagh - A lot has been measured and quantified and sent back to earth before Rosetta was crash-landed into the surface of 67P... but for scientists like Matt Taylor...

Matt - It's actually the beginning. It's when, although we have been doing science already, it's when you have only time to do science. And that's when we'll be doing the big leaps and bounds and the breakthroughs with Rosetta when we have all that time to do the science, and there's decades of work to do on this data.

Graihagh - I've heard something rather intriguing in that you've done something here where I can sniff the comet 67P?

Matt - Yes. There is a number of, how can I put it, aromatic compounds on the comet that we thought would be really nice to engage people with by saying, this is the stuff. You can visually see the tail and everything but you can't see the gas, but you can smell the gas. And we have a mass spectrometer on both Philae and also the orbiter Rosetta. The one on Rosetta has picked up some fantastic stuff; sulphite compounds, rotten eggs, ammonia, a stable so you can imagine what this comet smells like but we thought it would be best to provide a 'scratch and sniff' version for people to enjoy and there have been various reactions from 'it's not that bad' to the 'is it a perfume?' to a child was nearly vomiting on the monitor earlier on... so yes. It stinks basically!

Graihagh - Are you going to show me?

Matt - Yes...

Graihagh - I can smell something perfumed.

Matt - It's perfumy isn't it, yes? But, I mean, the thing is somebody's was saying it's got incense. This one's actually not as bad - maybe I'm used to it now! But, as I say, it's got hydrogen sulphide, ammonia, formaldehyde, methanol. We've also detected on the comet things like hydrogen cyanide but then you wouldn't want to put that on there because you'd sniff almonds and then pass out and and probably die.

Graihagh - Lets give it another sniff...

Matt - Well somebody was saying incense as well.

Graihagh - It does smell a little bit like frankincense. What I'd imagine going into a meditation shop or something.

Matt - Some kind of hippie head shop, as they're known in the US. I still get mothballs so it still smells like 'a Nan' basically. The comet smells like 'a Nan' so I'll go generic.

Graihagh - So, other than getting a whiff of what 67P smells like, what would be the best outcome here? I mean surely we're not going to unpick the entire origins of our universe and solar system?

Matt - Well, with Rosetta we are starting to do that. Really what we've got from Rosetta by spending the two years there by landing with Philae. And adding all of this stuff together, we're just starting to scratch on the surface of the capability of the data from this mission to the extent that we think we have identified primordial building blocks in the comet that are, actually, probably, common with other comets, that we can say we think we know how comets were made now. And that's quite a big result and the implications there lay in with the general solar system evolution, so that's what we have to look forward to. I wouldn't say that we've solved verytihng, but we've done a good job and there's a lot still to do and I'm pretty excited by the science that's going to come out in the next couple of years with Rosetta.

 

48:15 - Finding a meteorite for yourself...

Top tips on how to get your very own space rock...

Finding a meteorite for yourself...
with Dr Carolin Crawford, University of Cambridge

Top tips from astronomer Carolin Crawford on how to find your own hunk of Chelyabinsk meteorite fragmentspace metal after Graihagh Jackson found a rather intriguing question about a meteor falling into someone's wheelbarrow...

Question - Hello there, I was wondering if it is possible to test rocks to see if they are from space? I ask because, and this is true! Whilst I was gardening today a rock fell into my wheel barrow.  It sounds crazy, but it did happen.  The object is black, looks like coal, and is very light, I suppose like pumice.  If It didn't fall from the sky, I would say it was a piece of normal earth rock, but as it came from above I'm very curious.

Carolin - What did they say in response?

Graihagh - The response was something along the lines of - I doubt it very much because they're normally very heavy and that sort of thing. But it just tickles me. I read it and it tickled me to no end that these things were falling, and in these people's wheelbarrows or, you know, the idea of it falling in someone's wheelbarrow.

Carolin - A couple of years ago there was a lovely story of a French family who, as in the way of the French having their holidays, vacated their house in Paris, went off for their summer holiday and when they came they thought that's strange, our roof is leaking and they sent someone up to fix the roof. And what they found was the hole in the roof was created by a little meteorite that had just punched a hole through the tile and got embedded in their insulation in the roof. So they had their own little meteorite that had hit their roof - I think that's quite cool!

Graihagh - Yes, really cool, really cool! I imagine lots of people have got lots of interesting stories about how they've come into... I mean I was really excited about ours but I suppose it's not the most exciting way to come across a meteorite?

Carolin - No.  The most exciting thing is when you actually the event. You see the fireball and a fireball is just when you've got a bigger lump of rock that, as it disintegrates, it produces a lot more light and often they would just break into lots of pieces and you'd just get a fantastic show as they fall to Earth.

Sometimes, if you're fortunate enough to see one of these, especially nowadays with security cameras and you get all these serendipitous sightings of the fireball, you can track it's orbit, you can track its path through the atmosphere, you can predict where it's going to land, and then people can go out and look for the bits of rock.

So, for example, this has been done in places like Canada where, across the country, people saw this fantastic fireball in the sky. And then, when it had landed, they tracked it down to where it had landed, they went out to look for it and, it being Canada, it's a land of lakes. All the lakes are frozen and you just looked at the lakes and there were just fragments of meteorites scattered all over the ice on these lakes. I mean that must be so exciting to see those.

Graihagh - I was going to ask, because you'd mentioned we're in the peak of this meteorite shower at the moment, is there any chance if I looked really, really hard that I might find one in the UK?

Carolin - I think it would be very, very long shot. No I don't think you've got much chance and you've got to remember that for this particular meteor shower Perseids the grains that are coming in they're tiny - they're not going to survive to Earth. You need a much more sizeable lump of rock to be able to get any fragments from it landing on Earth.

Rocks in the desert

51:04 - Tracking meteorites with Desert Fireball

Desert Fireball need your help to find meteorites and track their origins back to outer space.

Tracking meteorites with Desert Fireball
with Philip Bland, Curtin University

Finding meteorites - little balls of rock from outer space - is key to understanding what's beyond our beloved planet Pluto. Meteor strikes are relatively common - 2009 Leonid Meteorthey happen five to ten times a year - but the difficulty isn't necessarily in finding them here on Earth, it's actually trying to figure out where they came from, as Philip Bland from Curtin University has discovered. He set up Desert Fireball to tackle this problem and told Georgia Mills how it worked...

Philip - It's a project where we've put out lots of little kind of observatories across Australia and they look at the whole sky and image everything that comes through the atmosphere. What we do then is we're able to triangulate the orientation of anything coming through, track it back to where it comes from in the Solar System and forward, if it lands to where it lands. We get its orbit and we get a full position.

Georgia - And are you also trying to use the great power of the masses to help in this project?

Philip - Yes, we are. So, if you see a fireball, you can pull out your phone and hold it up to the sky, click to where it started, where it ended, the colour. You can log all of these stuff and then blip us that information and that also helps us triangulate it. If we get enough data and we can tell you your fireball came from out beyond Mars and hit the top of the atmosphere at 20 kilometres a second.

Georgia - I guess it's people's first instinct anyway when they see something incredible in the skies, "Get your phone out!"

Philip - Exactly. So, this actually gives you a scientific purpose to get your phone up.

Georgia - Anyone taking meteorite selfies?

Philip - Well, we've not actually had that yet.

Georgia - When you get this data from all your observatories and maybe from people as well, what do you do? How do you go and find the asteroid?

Philip - That's the hard part. So, we build this wind model and then you head out in the middle of nowhere with a team of 6, 7 people and you've just got to be very optimistic and perky for a week, and try and keep them going while you don't find it, until in the end hopefully, you do. And then you will have a bottle of wine or several.

Georgia - I believe you've got something you have found with you here.

Philip - This is a meteorite. This was the first one we found. This kind of proves that it works.

Georgia - It looks and feels a bit like a sort of shiny lump of coal. You mentioned that this little guy - does he have a name?

Philip - Yes, this Bunburra Rockhole. The meteorites normally get named for the nearest post office, needless to say, the nearest post office is I think about a thousand kilometres away from where this was found. So, it isn't really narrowing down. Then you get named for the nearest topographic feature. Now again, I'd encourage people to take a look at the Nullarbor. There's no topography. So, from that point of view as well, it's a complete disaster.

Georgia - You'll just end up naming them all desert.

Philip - Yeah. I mean, the nearest thing on the map with any name was 40 kilometres away which was like kind of a little sinkhole in the limestone, and that's the only thing with any name which is kind of bonkers.

Georgia - Once you have this rock and you've used your tracking to work out where it's come from, what do you do with it once you find it?

Philip - We'll look at the isotopic composition, the chemistry, we'll use microscopy, we'll do CT scans over the thing. So, there's a ton of analyses that we can do to kind of build up a picture of its whole history. So, the exciting thing about - I guess, there's a few things. So, we've got an orbit for this and the orbit was very, very weird. The orbit is actually almost the same as Earth's orbit. So pretty much, the whole orbit for this one is interior of the Earth's orbit. It doesn't go anywhere near the asteroid belt and that's bizarre. The composition of the thing is also really weird.

So, the best we can tell is that this might be, it's not like a dead ringer for the precursor material that went in to make the Earth. But this sort of rock is part of that story. So, we're trying to work out what the precursor was that got the Earth got built from. This helped us get a little bit closer to that. So, having the orbit and the rock, were really, really useful for that.

Georgia - What's the furthest you've ever got anything from?

Philip - The furthest thing, I've never held it in my hand, but it was material from the Stardust mission. So, I was looking enough to be part of the preliminary analysis team for the Stardust mission and the goal in that mission which was very successful was to bring back dust from comet Wild-2 and the spacecraft flew through the tail of the comet, got pretty close actually and got pretty battered, and then put that in a capsule, reentered the Earth's atmosphere and then a whole bunch of researchers from around the world kind of joined together to analyse it. It was fantastic. This was when I was back in the UK and I was waiting for my samples and I was expecting some very official NASA kind of delivery man, kind of Men in Black-type situation with the briefcase locked to his wrist. It came in a DHL padded envelope.

Georgia - No expense spared.

Philip - No! but still very, very cool to get samples of a comet and a student of mine, Penny Wozniakiewicz did an amazing job analysing that material and people at Natural History Museum as well, colleagues of mine did a wonderful job analysing it and being part of that whole process with other researchers, an incredible amount of information has come out. It's been a really successful mission.

Georgia - And this was out from as far as the Kuiper belt. Would any specimens from the Kuiper belt actually fall to Earth? Is that something you're looking for?

Philip - We go through streams of comet debris on a regular cycle which are meteor streams. Most of that stuff is dust which means that it'll almost all burn up in the atmosphere really high up. But some of it is chunkier and there's one stream in particular, the germinids, it's a comet that's been cooked up a lot by many close approaches to the sun. So, it's certainly not in as good shape as it was originally, but what that's done is the material is denser now and it looks like some of that should be able to make it to the Earth's surface.

So, my kind of holy grail if we're ever going to find anything would be that we'd see something come in, we'd put those images together, we'd calculate its orbit. It's orbit would match one of these germinid meteors and we work out it had landed, and we'd going to pick it up, and that would be absolutely incredible. It wouldn't be nearly as pristine as some of the others, but technically, that's possible.

Georgia - Best case scenario, what could you learn from a meteorite that have come all that way?

Philip - That's a really good question. Best case scenario, I got into planetary science and studied meteorites because as a geologist, it felt like a lot of the things in geology, we'd worked out pretty well. We know the kind of grand unifying theory for geology, plate tectonics and it's been kind of a case of putting the finishing touches to that really.

But in terms of what happened before planets got made, or how we made planets, or why the Earth has the composition that it does, we really have very little idea. So, if you ask someone, "How do you make terrestrial planets? How do you get a planet that's got a very nice mix of rock and ice and water, and organic material?" Well, no one knows. There's dozens of different options. I find that really, really exciting as kind of a young researcher so that's why I got into it.

So, in the best possible case, we'd work out why we have terrestrial planets in the inner Solar System, why that process of depleting the inner solar system in what we call volatile elements, why that happened, and that's a big part of the key to... if that's a normal part of planet formation, then it means that rocky planets are common in the universe and that would be quite exciting to know that.

56:01 - How did birds survive the dinosaur mass-extinction?

If an asteroid wiped out the dinosaurs, but birds are dinosaurs, what the heck is going on?

How did birds survive the dinosaur mass-extinction?

Tom O'Hanlon put Fay's question to David Norman from the University of Cambridge.

David - The overwhelming evidence suggests that there was a massive meteorite impacted at around about 66 million years ago. And the explosion created a huge set of environmental problems, in a sense: lots of water vapour, lots of chemicals introduced into the atmosphere, completely messing up our ecosystems. The equivalent, I suppose, in terms of modern theorising is the nuclear winter. It’s as though there was a nuclear holocaust, almost destroying life on earth, but not quite.

Tom - Given that we’re still around today, some things clearly made it through. So was there a pattern to who lived and who died?

David - Certainly on land, anything over a metre in body length probably went extinct. It maybe something to do with the biological nature of small organisms. Most of the big ones are, you could say, top of the food chain and, perhaps, more specialist and most susceptible to environmental disturbance. That’s certainly the pattern we see in ecology today. The things that have most chance to survive are the scavengers, the small fast reproducing sorts of organisms. And, in a way, the lizards, the snakes, the small crocodiles, small mammals that were our ancestors, and various other little organisms seem to have got through because they were the most resilient to environmental disturbance. The little, insulated, feathered bird-like dinosaurs also got through and, therefore the dinosaurs did survive the extinction, but they survived because they were small bird-like creatures rather than big scary dinosaurs.

Tom - I suppose we’re really grateful for today?

David - I guess so, yeah. Although some of us would actually quite like to see a dinosaur in the flesh at full size. The nearest we’ll ever get to it is something like an Emu, or an Ostrich, or a Rea. They’re feet, especially with something like a Rea have those three classic taloned toes which look very, very reptilian and wouldn’t be so ; different, except in scale, from something like the feet of a dinosaur like T. Rex.

Tom - There you go Fay. I hope that managed to meteor your expectations.

Next week we’ll be looking at David’s question.

David - If we put a mirror half a million light years away and reflected Earth, could we see what Earth looked like a million years ago.<

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