Meteorites, Satellites and Avoiding Asteroids

Where meteorites come from and how we can find them...
29 January 2006
Presented by Chris Smith, Phil Rosenberg



This week we look to the solar system as Ian Sanders discusses where meteorites come from and how we can find them, astronaut Dr Stan Love describes how to avoid Armageddon asteroids, Maggie Aderin talks about satellites that monitor wind speeds, Richard Preece recounts the sticky tale of the hitchhiking snails, and Derek and Dave make water fibre optics in Kitchen Science.

In this episode

The Think-jet Printer

Scientists invent a way to 'print' live brain cells - Reconstruction and replacement of defective body parts may have moved a step closer this week thanks to an invention from UK researchers at the University of London who have designed a printer that can spit out ultrafine droplets containing live brain cells. The device is based upon the workings of an ink-jet printer, but instead of forcing the cells through a tiny hole - which damages the cells and has frustrated previous attempts to produce a printer like this - the new device uses an electrified nozzle, charged up to 30 kiloVolts, to produce tiny blobs of fluid which measure just a few thousandths of a millimetre across and contain a small number of live cells. Writing in the Biotechnology Journal, inventors Suwan Jayasinghe, Amer Quereshi and Peter Eagles, have tested the device on mouse brain cells and human white blood cells, which seemed to tolerate the experience without harm. The new approach could usher in novel treatments whereby doctors can build replacement tissues cell by cell in three dimensions, although it's early days yet and the researchers still need to confirm that the cells suffer no long-term harm and can survive being printed into the specific shapes that biomedicine is likely to require.

Cracking The Surface of Mars

Phil Christienson of Arizona State University has designed a new spacecraft in the running to be launched to Mars to search for water ice concealed below the surface. Setting it apart from the other possible mission plans is its ingenious method for searching below Mars' surface for the ice deposits. If selected the spacecraft will launch a 100kg copper sphere to smash into the surface of Mars at 15,000 km/hr. This sphere with a diameter around 60 cm will form a crater 50 m across and approximately 25 m deep. While this is happening the spacecraft in orbit around the red planet will observe the crater being formed and the debris created to search for signs of water ice and will become the first spacecraft to examine below Mars' surface. This is a similar strategy used to examine the comet Tempel 1 in the successful Deep Impact mission last year. Finding the ice deposits already thought to exist on Mars will have huge implications for future exploration. The water now locked in ice could once have been liquid making Mars habitable millennia ago and if astronauts eventually visit Mars the ice can be used to synthesize rocket fuel for the journey home. If selected we can look forward to launch in 2011.

- Where Meteorites Come From

The Naked Scientists spoke to Dr Ian Sanders, Department of Geology, Trinity College Dublin

Where Meteorites Come From
with Dr Ian Sanders, Department of Geology, Trinity College Dublin

Chris - Tell us a bit about your field. What do you actually do?

Ian - I'm a geologist and we study rocks. Meteorites are rocks and that's one of the things we study.

Chris - So where do you go to find them, because I've heard that the South Pole is a really good place.

Ian - Yes, remarkably about half the meteorites in the world's collections are from Antarctica.

Chris - is it just because they're easy to see against the snow?

Ian - Yes, but the story's a little bit more subtle than that. They land on the ice but immediately get covered by more snow and disappear. The ice in Antarctica is about four kilometres thick, and it's creeping out under its own weight. Icebergs are breaking off around the edge of Antarctica, and many of the meteorites in them would just end up on the bottom of the sea. But there are one or two places where that ice rides against a buried mountain range under the ice. That forces the ice up and the wind blowing over the surface evaporates the ice. So deeply buried ice ends up coming back to the surface.

Chris - Bringing meteorites with it.

Ian - Yes exactly. And once they get to the surface, they're stuck and can't go anywhere. So they accumulate in these places where the ice is evaporating. It's possible to identify these places because they're blue, as viewed from space. We send people to these blue ice fields and they collect everything they see.

Chris - So even Maggie can help you here by spotting them from space! So you can use cameras mounted on satellites in space in order to spot a meteorite?

Ian - Well no, from space you spot the blue ice field and know where to go.

Chris - But what about spy cameras, because they can read the text on a newspaper.

Maggie - Well there's lots of hearsay and lots of science from the movies. It's trying to draw the line between what's reality and what isn't. What the military is capable of is very hard to define, but we can get to better than one metre resolution with standard space cameras these days, and we're working on improving that as well. So in the one metre square we can see from space, we wouldn't quite be able to resolve the print on a newspaper. But you'd be able to see building densities and things like that.

Chris - So how long have the meteorites that we find in Antarctica been in the ice?

Ian - That's a good question, and remarkably scientists have a handle on that. They think they go back tens or hundreds of thousand of years. Maybe even as much as a million years. The reason they know that is that while they're in space, they're picking up radioactivity from cosmic ray bombardment. The longer that they're sitting in space, the more these new atoms are made. It's possible to measure how much has accumulated in the material, and that tells how long it's been sitting on Earth.

Chris - Now in the context of the meteorite that Phil was talking about earlier that came from Mars and people thought that it might show signs of life, an obvious question to ask is how did something from the surface of Mars end up on the surface of Earth? Did something slam into Mars and release that piece of rock, which then ended up drifting around in space for a long time, and then we picked it up like a giant hoover?

Ian - That's pretty well it, yes. For along time it was a bit like the story that bumblebees can't fly. Scientists said it wouldn't be possible for an impact into the surface of Mars to launch a piece of Mars at more than Mars' escape velocity. But indeed, as you said, these meteorites that we think come from Mars were proven to come from Mars from this trapped gas which is identical to the gas that was measured on Mars in 1977 by the Viking lander. So we know it comes from Mars, and so Mars must have been hit by a big meteorite, which caused rocks to fly into orbit until they got picked up by Earth.

Chris - Ok, so we're happy that these things are landing on Earth, but what actually are they? Apart from stuff being ejected from planets, there's other debris out there too.

Ian - Yes, in fact only a very small fraction are thought to be from Mars. The great majority are almost certainly pieces from the asteroid belt, which lies a good bit beyond Mars but not as far as Jupiter. Astronomers have known for a long time that there are a huge number of small planet-like objects in orbit around the sun in that zone.

Chris - Is this kind of debris left over from when planets were forming in the early days?

Ian - Yes. At one time it was speculated that there was a planet out there that exploded into lots of bits. But the evidence we have now suggests a very different mechanism. The idea is that when the solar system first formed, there were no planets, but there was newly formed sun surrounded by a disk of dust and gas. Gravitational instabilities within that disk led to small planets forming that were just a few kilometres across, and then they grew gradually bigger like snowballs. Over a period of perhaps ten million years, these small bodies aggregated and aggregated and ended up as the planets as we know them.

Chris - So studying them does actually tell us quite a lot about how everything formed in the early days.

Ian - Absolutely. The asteroid belt is part of this early disk that never made it to make a big planet. So we're looking at things that formed in the first ten million years in the solar system's history.

Chris - Now you've bought some bits and pieces for us to look at, so Phil, why don't you talk us through it and we can ask Ian what they are.

Phil - Well there are some quite interesting samples here. We've got different types. One is quite dark and grainy; another is light and grainy and there's another that doesn't even look like rock at all. It looks like a sheet of polished aluminium or something like that.

Ian - It's steel, and it's not far off stainless steel.

Chris - So it actually arrived in the form of unrefined steel?

Ian - Yes.

Chris - So tell us about these samples. What actually are they and where did they come from?

Ian - I mentioned this disk of dust that was going round the early sun. Well the dark grainy sample is primitive material in which dust has aggregated but nothing much has happened to it since those first couple of million years.

Phil - So all these little bits of grain inside this rock are actually the original bits of grain and rock that formed the original meteorite?

Ian - Yes. It turns out that the story is never quite as simple as one might like it. Those little grains themselves have a history. A lot of things were going on in that first two million years. They're not the very first bits of dust, as they've actually been processed through heating and melting before they were made into that aggregate of grainy rock.

- Using Satellites To Monitor Weather

The Naked Scientists spoke to Dr Maggie Aderin, Science Innovation Ltd.

Using Satellites To Monitor Weather
with Dr Maggie Aderin, Science Innovation Ltd.

Chris - The moon is our biggest natural satellite, but you work on artificial satellites. What is involved in making a satellite and getting it up there?

Maggie - The main thing I notice is lots of paperwork, because one of the difficulties in launching things into space is that you want it to succeed. You can't just go out and tinker with it, or if you do, it costs an awful lot of money like with the Hubble Space Telescope. What you're trying to do is make something bound not to fail. To do this you build in lots of redundancy. Also, rather than going for cutting edge technology, you try and use existing technology that is well known and established. Usually a consortium of people will get together. For example, I'm working on a project now with people from the James Webb Space Telescope, which is organised by NASA but this is a sub-system that's put together by ESA, the European Space Agency. We're building a detection system. One of the exciting things about these projects is that they work on a global scale. There are scientists all over the world working on the James Webb Space Telescope. What we'll do is build an instrument and put it through very rigorous tests.

Chris - What's it going to detect?

Maggie - The one on the James Webb is looking for infra-red and is looking out into space. Another system I'm working on looks at Earth rather than space. This is designed to look at wind speeds through the atmosphere.

Chris - How on earth do you see the wind because it's invisible?

Maggie - That's one of the beauties of the system. It uses the Doppler effect. This is just like ambulances get louder as they are going past. What we're actually doing is shining a laser beam through the Earth's atmosphere and it works in a similar way to RADAR. It's called LIDAR, because it's like a light RADAR. We pulse a UV beam and it bounces of particles in the atmosphere. As it bounces off particles, the light scatters and we pick up the return beam. This return beam is fair fainter than the one we send out. By looking at the Doppler shift, you can see a change in the wavelength and work out how the particle is travelling in the Earth's atmosphere. By looking at the time of the return, you can see whether it's close to the Earth's surface or high up in the atmosphere. For instance, if people fly kites close to the ground, it will travel at one speed. If you lengthen the string and it goes higher, the wind speed changes quite rapidly. This gives us a 3-D view of winds through the atmosphere.

Chris - I was just going to say, does it look at just one altitude, but presumably not. You can look at a whole lot of different heights.

Maggie - That's it. Just like with RADAR, you can look at different signals coming from different points in time. This means that you can look right from the ground where you get a ground return, which is the strongest signal, and then look at particles throughout the atmosphere.

Chris - How is this actually useful though? Do we know if this translates into better weather forecasts for example?

Maggie - Yes. It does two things. It does local short-term weather forecasting and so hopefully we can send this information to Michael Fish to get a better weather forecast for the future. It's also looking at long-term climate prediction. For instance we talk about global warming, but there are many models associated with global warming. You need data in order to verify them. This mission is set up to give global coverage of wind speeds through the atmosphere, and thereby able to verify these climate change models. So it's short term and long term data that we're getting.

Chris - So you're designing this probe. It then goes aboard a satellite and gets carried into space. When it gets up there, how does it actually get powered? How do these things actually work?

Maggie - It depends on what sort of orbit you're going into. Once it gets there, it's deployed and is contacted by telemetry, which sends signals to the satellite. The signals ask the satellite to deploy its solar panels. You can get some satellites which are powered by nuclear energy, but the sort of satellite we're setting up is actually solar.

Chris - And they never end up in the dark? Do they always have a supply of sunlight, or do they have batteries to back them up?

Maggie - They generally have batteries to back them up, especially during the launch when there's a period before the solar panels are deployed. Depending on the sort of orbit you put it in, you can tilt your solar panels so they're always facing towards the sun.

- Avoiding Armageddon

The Naked Scientists spoke to Dr Stan Love, Johnson Space Centre, Houston, Texas

Avoiding Armageddon
with Dr Stan Love, Johnson Space Centre, Houston, Texas

Chris - Now you reckon you've come up with a way to solve the problem that may have wiped the dinosaurs out 65 million years ago. But what is it?

Stan - My co-author Ed Lu and I have come up with a way to make deflecting an asteroid that's coming at the Earth a lot easier than some of the schemes that have been proposed over the last few years.

Chris - What kind of schemes have been put forward? There are things like blowing it up, but that doesn't work too well does it?

Stan - Blowing them up has been proposed but it's hard to do. Asteroids are a lot tougher on impact than you might think. They're like big flying bags of rubble and bags of rubble do a great job of absorbing impact and explosion damage. It's hard to calculate exactly how much explosion energy you need to break up the asteroid, and if you got that calculation wrong, the rubble would break apart and come back together again under its own gravitational pull. It would then still be coming at us, which would be a problem.

Chris - So what's your solution?

Stan - Our solution is to use a spacecraft to gradually tug the asteroid out of the way. Ideas like this have been proposed before where you nuzzle up to the surface of the asteroid. It's got such weak surface gravity that it's hard to just plant a spacecraft on the surface the way we land on Mars or the moon. It's possible to nudge an asteroid out of the way like that. But once you've landed, you not only have to worry about attaching, but also that the asteroid is rotating. The thrust that you've gone to all the trouble to get out there and landed is now hosing around in circles like a lawn sprinkler. Our alternative is instead of touching the asteroid, you sidle up next to it and turn on a very low thrust engine that just manages to balance the weight of the space craft as it's being pulled along by the asteroid's gravity. You just hover there. As you hover for months or maybe a year, the very slight gravitational pull between the spacecraft and the asteroid will change the asteroid's orbit. If you then got there ahead of time, say twenty years in advance, the orbit will change enough to miss the Earth rather than hitting it.

Chris - Do we know of anything that's likely to actually be amenable to this kind of therapy? Are there things bound to Earth in your time frame for deploying this kind of measure?

Stan - Right now there's nothing that we know of that's going to hit us. But there is an asteroid that we're going to be paying attention to over the next couple of decades. It's going to come swinging by us in 2029 and if it passes at just the right distance from the Earth in that swing-by, it will get kinked onto a new orbit that will bring it back to hit us in maybe seven or eight more years. Now we don't know yet whether or not that's going to happen. The probability of it happening is very small, something like one in five or ten thousand, but we'll be keeping an eye on that asteroid. If it should turn out that it's heading on that collision course, then if we could get a spacecraft like the one we're describing called a 'gravitational tractor'. Once we get it out there, a tiny change in the asteroid's path before the approach will translate into a very big change in its orbit after that close approach. So you can multiply the effect of your deflection scheme by doing that.

Chris - Is technology up to doing that at the moment or is this just a speculative thing that could work if we have another set of technologies coming on line in the next couple of years?

Stan - Stuff of the kind we've been proposing hasn't been flown yet. The baseline gravitational tractor that we're talking about is a twenty tonne spacecraft, which is very big. It would be powered by a nuclear reactor, which has been done a few times but is not commonly done today. So these are not mature technologies, but NASA was proposing to put together just such a spacecraft to fly out to Jupiter and go into orbit successively around each of Jupiter's big moons. So the technology is not mature, but it's within reach.

Cepaea nemoralis: Grove Snail or Brown Lipped Snail. Dormant pair on a tree trunk in Gamlingay Wood, Cambridgeshire, England, illustrating the variation in colouration of banded morphisms.

- Hitch-hiking snails

The Naked Scientists spoke to Richard Preece, University of Cambridge

Hitch-hiking snails
with Richard Preece, University of Cambridge

Geneticist Richard Preece, from the University of Cambridge, explains to Chris Smith how he has discovered evidence that snails hitch-hiked aboard migrating birds to travel from Europe to remote islands in the South Atlantic...

Richard - We wanted to understand how the snails on the Tristan da Cuhna Islands got there. We had suspicions that they might be related to a species that occurs in Europe, but what we've shown here is that these suspicions are very well founded. They are indeed exactly the same genus as the European one.

Chris - So the outstanding question is how does a single snail get to the islands. It doesn't swim and it doesn't have wings.

Richard - The most plausible way of getting there is to hitch hike on a migratory bird, maybe a wader. Waders are often found as stray vagrants on mid-Atlantic islands, and that would seem to be most likely vector.

Chris - How big are these snails then?

Richard - The adult snails are 7 millimetres, or maybe a little bit more when adult. These snails presumably weren't transported necessarily as adults. They might well have been transported as eggs or as juveniles. One of the things about these particular group of snails is that they have a very sticky slime. It's very noticeable if you tap them that the slime is tenacious and will stick to your fingers very readily.

Chris - So do you think that on eof these young snail would potentially have stuck itself onto a bird somewhere in Europe and then made its way ultimately 9000 kilometres away to the Tristan da Cuhna Islands?

Richard - Well it may not have done this in one leap. We know that these snails are hermaphrodite, so you only need a single individual to found a colony. That's quite important. It's quite interesting that this genus of snail also occurs in North Atlantic Islands, particularly on Madeira and on the Azores.

Chris - So it might have been some stepping stone down there then.

Richard - It could have been a stepping stone there, yes.

Chris - Just to play devil's advocate for a minute, how do you know that this wasn't a boat?

Richard - We know that the Tristan da Cuhna Islands were only discovered in 1506, and there are eight species of this snail on the islands. It is unprecedented for eight species of snail to have arisen in the 500 years that has elapsed since the discovery of the island.

Chris - When would that put the time at which the snails first took up residence?

Richard - We haven't got an accurate molecular clock to be able to pinpoint that, but perhaps in the future we might be able to get a better handle on that.

Chris - And given that these snails have travelled so far, do this make them the world's longest hitch hikers?

Richard - Well I think for a snail I don't know of a better example. It was quite interesting that way back in 1921 there was an article in Nature reporting for the first time the occurrence of one of these snails on the top of the mountain on Madeira. The article was claiming that that was an example of transportation by birds to that remote mountain peak. What we've shown here is not just that they were able to get to Madeira, but that they were able to get a good deal further, across the equator and right down into the South Atlantic.

- What are grenades made from?

I was just wondering what grenades are made out of, and why does it take a while to go off after the pin is taken out?

What are grenades made from?

If you look at a hand grenade, it looks a bit like an egg. It's got a hard metal shell around the outside and it'' packed with high level explosives. At the top there's a trigger, and on the trigger is a really big spring. The spring pushes down on a hammer which pushes down inside the hand grenade. When you hold the handle closed and the pin is in it, it's compressed and can't go anywhere. As soon as you pull the pin out and let the handle up, it drives the hammer down inside the core of the hand grenade. In the bottom of the core is a detonator and it fires that off and lights a fuse. The fuse burns slowly for however long the grenade has been designed to burn for and that fuse detonates the main detonator and charge. This occurs a certain time later. The idea is that you know roughly how long it takes to go of, because when you lob it, it doesn't give the enemy an opportunity to pick it up and throw it back to you.

- Do asteroids have a maximum speed or do they keep accelerating?

Do asteroids have a maximum speed or do they keep accelerating?

Do asteroids have a maximum speed or do they keep accelerating?

Asteroids are tumbling in space and spinning around and an interesting thing is that they're all spinning rather slowly. That is consistent with them being loose piles of rubble. They're not solid objects. When meteorites come to Earth, they tend to travel pretty fast, around twenty kilometres per second, although the maximum is seventy. The net result of that is that they make this wonderful fireball effect. If a big one comes, the atmosphere doesn't slow it down, and that's when trouble happens. It will come all the way down to the surface and explode. On eof the nest studied meteor craters is in Arizona and it's just over a kilometre wide. The object there was about thirty metres wide. The estimate for the asteroid that wiped out the dinosaurs is ten kilometres.

- How dependent are we on satellites?

How dependent are we on satellites? If somebody put a computer bug in them, what would happen?

How dependent are we on satellites?

It could vary. Communication is big business in terms of satellites, so that could have a very large impact. I wouldn't be so upset about losing some of the television channels! In terms of other impacts, I think we could usually work around them. As a scientists I spend my life trying to figure out ways of working around problems so I don't think it would be the end of civilisation but I think money changers would be brought to its knees for a while, but we would definitely recover.

- What do orbiting satellites look like from the ground?

I look out of my window and see something that appears to be a satellite. It rises in the sky through the night. It appears to flash. Is ...

What do orbiting satellites look like from the ground?

It's more likely to be a planet. When planets travel through a large depth of atmosphere, they appear to twinkle. Sometimes they twinkle very bright colours. You will eventually lose sight of it as it's orbiting around the sun.

Why did we send dogs into space?

The reason why we send dogs into space is because they are so intelligent. You can train a dog to do all sorts of things, and so that's why we want a dog to go up there and give us feedback. They're very bright!


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