Your science questions answered

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Speaker 5 This is the podcast of BBC Inside Science, first broadcast on the 29th of May 2025.

Speaker 5 Hello, fellow Philomaths. I'm Marnie Chesterton and that is my new word.
Means a lover of learning. Epistemophiles, there's another.

Speaker 5 There are millions of us out there and I know that partly because I've seen Radio 4's listening figures and what is Radio 4 but an audio temple to knowledge.

Speaker 5 I also know because lots of you have been getting in touch with inside science wanting answers to various aspects of how the world around us works.

Speaker 5 Today we've assembled a panel with decades of dedicated study between them and we'll be tackling a selection of your questions on everything from life on the moon to the death of plastic bags.

Speaker 5 Let's meet them.

Speaker 6 Hello, I'm Catherine Haymans. I'm a professor at the University of Edinburgh and I'm also the Astronomer Royal for Scotland.

Speaker 1 Hi, I'm Mark Mazzon and I'm a professor of Earth System Science at University College London, which people look at me and go, what does that mean?

Speaker 1 So I sum it up by saying I study climate change and environmental change in the past, the present and the future.

Speaker 7 And I'm Dr. Penny Sasha.
I'm Managing Editor at New Scientist and originally a biologist by training.

Speaker 5 And we kick off with an international listener from Oregon in the USA who heard an Inside Science episode from back in March where we were talking about the global mineral grab.

Speaker 5 And let's have a listen to her question.

Speaker 8 Your episode about critical minerals got me thinking about lithium batteries. Is it known what happens to these batteries once they're discarded, whether into tips or in vehicles and scrapyards?

Speaker 8 And do we know what adverse effects there are on the environment, such as soil, water, air, if lithium batteries start leaking?

Speaker 5 Mark, this is tangential to climate research, I feel. So any ideas?

Speaker 1 Oh, absolutely. So the really good news is that lithium-ion batteries are currently being recycled.

Speaker 1 And just to make sure that the listener is reassured, there is a former Tesla co-founder who produced a company called Redwood Materials that recycles 70% of all North Americans' lithium batteries at the moment.

Speaker 1 And that's really important because then you take all those goodies goodies and then you make them into components for new electric vehicles. But I have to actually warn listeners about the internet.

Speaker 1 Okay, I feel this is something important because if you go on there, there is a commonly quoted figure from 2019 that says only 5% of lithium batteries are recycled.

Speaker 1 Now, this is what I call a zombie statistic, which is it's wrong, it was wrong when it was published, but it just won't die.

Speaker 1 So if you really want to be reassured, there's a 2023 paper that says about 59 of batteries worldwide are recycled is that all or just lithium just lithium batteries okay now of course that's nowhere near the hundred percent that we need and that comes to the listener's other point is it bad when we throw them away oh yes so the first thing is that lithium batteries contain lots of heavy metals so cobalt, nickel, manganese and toxic electrolytes.

Speaker 1 And in landfill over time, these materials can leach into the soil and the groundwater and this causes contamination to the drinking water and the soil, producing health risks for humans.

Speaker 1 Also, batteries are highly flammable. This is why when you go on a plane, they say, please don't put them in the hold.

Speaker 1 So of course, when these batteries go into landfill, again, they can easily catch fire or explode.

Speaker 1 Now, the problem is that fires in landfills are really, really dangerous because it's not just that waste that actually produces pollution, but you're looking at hydrogen fluoride, which is incredibly toxic gas, being released.

Speaker 1 And the other thing is, which really breaks my heart, is in many parts of Africa and Asia, they basically burn batteries to extract the actual valuable metals out.

Speaker 1 Now, as you can imagine, this is produces not just hydrogen fluoride, which is incredibly corrosive gas, but dioxins as well, and of course, persistent organic pollutants.

Speaker 1 And these airborne toxins we know are affecting the people doing the burning, but also the local communities. So we're at 59% recycling, if that paper's correct, but we really need to be at 100%.

Speaker 5 Yeah, I mean, I read something about the disposable vapes and the number of those that are just going straight in the bin.

Speaker 1 Oh, absolutely.

Speaker 1 In this country, that's become a huge issue because, of course, you can't recycle them as easily because you've got all that non-recyclable plastic and you've got the lithium batteries inside.

Speaker 5 Thanks Mark and of course all the issues with lithium and other battery waste are because we're looking for ways to power our lives. Which brings us to another listener question.

Speaker 5 Free electricity anyone? Have a listen.

Speaker 9 Hi Insight Science. I'm hearing everywhere on social media about Nikola Tesla's free electricity.
Is there anything like free electricity?

Speaker 9 Is it a load of rubbish or did Nikola Tesla really discover how to get free electricity out of thin air? If it really is something, why are we still struggling with fossil fuels?

Speaker 9 Please, would you debunk that for me? Thank you.

Speaker 5 Penny, I'm clearly not on the right social media. I've never been told about free electricity.

Speaker 7 It had not crossed my filter bubble either. And so, I guess at this point, I'll echo Mark's warning about the internet

Speaker 7 that there are a lot of conspiracy theories on.

Speaker 1 Not everything is true on shock horror.

Speaker 5 But yes, but what's free electricity supposed to be?

Speaker 7 So, this is a conspiracy theory and the idea is that Nikola Tesla came up with a way to get energy out of thin air and that this was suppressed or destroyed by perhaps a government or the industry to prevent us all from having cheap, free, clean energy.

Speaker 7 Wouldn't it be lovely if we could have that? Categorically, no, that didn't happen. The idea where people seem to get a bit confused is Nikola Tesla obviously had loads of interesting ideas.

Speaker 7 A lot of them did regard electricity. But the one that often kind of gets misinterpreted here was he was very interested in whether we could distribute energy wirelessly through the air.
Tesla towers.

Speaker 7 Yes, exactly. And that's about moving electricity, not creating it.

Speaker 7 So that's kind of what's been co-opted there. In terms of whether free energy could exist, the fundamental thing about energy is you can't actually create it or destroy it.

Speaker 7 It only gets converted from one form to another. And how do you define free? There's so much energy streaming out of the sun hitting our planet every second.
That's pretty free.

Speaker 7 We just have to convert it with solar panels or all the various other things. So there is kind of readily available energy sources out there, but we're always going to have to convert them somehow.

Speaker 1 Oh, I agree, Penny. We've got hydro, we've got deep ground temperatures, solar and wind, all that are easily accessible.

Speaker 1 However, the biggest cost usually is the distribution of that energy because where you produce the energy and where you want to use it are two different places.

Speaker 1 and that actually is where you lose quite a lot of the energy on transmission lines and in cables also we're looking at the future because of course fusion will be coming online in the next 20 to 30 years and this is where catherine is going to sort of like help out because of the wonderful equation by einstein it means that if you destroy a very very very small amount of matter you get this colossal amount of energy so you just have to go oh let's destroy that lots of free energy but But of course, the actual physical costs of building this stuff and researching it, that's where the financial cost comes in.

Speaker 7 And to speak to your point about distribution, Tesla's idea that you could wirelessly transmit electricity is true.

Speaker 7 We have wireless phone charges now, but it's actually not as efficient as just putting it down a cable. And that's why we don't have that means, you know, instead of the national grid today.

Speaker 5 And Catherine, coming to you, can you fact-check Mark?

Speaker 6 Yeah, yeah. So E equals M C squared, that's the famous equation.
You need quite a a lot of mass to create the energy.

Speaker 6 So, a single fusion reaction in the sun that converts hydrogen into helium only releases as much energy as there is in one trillionth of a peanut.

Speaker 6 But there are lots and lots of these reactions occurring in the sun, and that's why the sun is so bright.

Speaker 6 So, I was interested, Mikely thought fusion was going to be in sort of the 20-30 year time scale. I really hope it is.

Speaker 6 I think if people invested in fusion, it is a very powerful way to create green, clean energy.

Speaker 1 Catherine, I'm sensing scepticism.

Speaker 5 It's one of those things that's always been 20 to 30 years ago. And last time I checked, it was like, oh, 50 years away.
And I was like, hang on, it's got further away since I last looked.

Speaker 6 It's very hard to do because you need to get to such high temperatures to overcome the electromagnetic repulsion so you can get the protons close enough together to fuse.

Speaker 6 People are getting really excited about mining on the moon because there should be lots of helium-3 there which comes out of the sun on a solar wind and helium-3 is probably the easiest way we can get energy out of fusion reactions here on earth but mining on the moon is is way more than 20-30 years away but with some serious investment that's a great way of producing energy as well.

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Speaker 5 Just a reminder, this is Inside Science.

Speaker 5 I'm Marnie Chesterton, and I'm joined by climate scientist Mark Maslin, Astronomer Royal for Scotland, Catherine Haymans, and Managing Editor for New Scientist, Dr. Penny Sachet.

Speaker 5 This excellent panel has been assembled because we're dedicating the entire show to answering listener questions.

Speaker 5 Well, Catherine, since you've mentioned the moon, can I move us on to a question from Peter Cornish, who asks, why is the moon sterile?

Speaker 5 And he says, My understanding of the origin of the moon is that there was a collision into the earth by somebody, and a large chunk was carved out of the earth and formed the moon, presumably with some material of the colliding body.

Speaker 5 My question is: if the moon is, at least in part, formed of the same material as Earth, then why is the moon so sterile when the Earth is so fertile?

Speaker 6 Yeah, that's a fantastic question from Peters. He's right that the Earth and the Moon formed after a cosmic collision in our solar system about 4.5 billion years ago.

Speaker 6 And we know that to be the case because the chemicals on the moon are very, very similar to the chemicals in the Earth's core.

Speaker 6 So, if they're made up of the same stuff, why haven't we seen life evolve on both? Well, for life, we need two things: water and an atmosphere. So let's start off with the atmosphere.

Speaker 6 The moon is just too small to have enough gravity to keep an atmosphere on it.

Speaker 6 So even if there was gas after this collision it would have flown off into the universe so that's why our moon doesn't have an atmosphere. And then what about water?

Speaker 6 Well interesting there is water on the moon so there's been lots of different moon landers recently looking at the chemical composition particularly at the poles and but it is very very dry There's hardly any water there.

Speaker 6 And this is what makes us believe that the oceans on our planet arrived at a later date after this collision, and that that water was transported to our planet from the outer reaches of our solar system by asteroids and comets.

Speaker 6 And that's why we have copious amounts of water here on planet Earth and not on the moon. And that combination of water and the atmosphere gives life an opportunity to evolve and thrive.

Speaker 5 Catherine, can I check, is the moon actually sterile or have we contaminated it over the past few decades with a bunch of missions?

Speaker 6 That's a really good question,

Speaker 6 particularly because we've got lots of companies sending these moon landers up there to do various things. One of them recently contained an art exhibit of a lot of balls.

Speaker 6 I forget the name of the artist.

Speaker 6 And one does worry when it's not national agencies sending things to the moon, that the care and attention that's paid by national space agencies to ensure that we don't contaminate other planets, there's always a concern when private companies start sending things into space that they don't take that same care.

Speaker 6 And as we look forward, NASA is planning to send humans back to the moon in the Artemis programme. They've got grand plans of mining on the moon.

Speaker 6 So I think even if it is still sterile now, in the long term, it won't be.

Speaker 7 Penny. There's sterile and then there's also fertile, which was part of the question.
And so that's talking about microbial growth.

Speaker 7 But there is interest in, well, could we actually plant things on the moon? Can we grow things in regolith or moon dust? And we have to remember: you know, first life on Earth was microbial.

Speaker 7 It didn't need soil that was filled with loads of decaying organic matter.

Speaker 7 But when we're actually talking about planting trees and plants and crops and things, that's really drawing on millions of years of humus, isn't it? All the decayed organic stuff.

Speaker 7 So if you want to grow stuff in the moon dust, we're going to have to sort of add all of the nutrients that are needed ourselves.

Speaker 5 What? The Apollo missions left 90 plus bags of human poo.

Speaker 7 Could come in handy on the moon.

Speaker 1 I didn't know that, because that's a cracking thing.

Speaker 5 I know. So every kilogram of poo you leave behind means that, you know, it's easier to take back off again.
So we've really made our mark.

Speaker 5 And when I was asking about bacteria, I was thinking, there's got to be some interesting stuff in there. Anyway, that's there to fertilise future plants, Mark.

Speaker 1 I was also going to say that, of course, we know that life evolved on Earth about four billion years ago. So half a billion years after the moon was separated from the Earth.

Speaker 1 And so that genesis, which is either in deep vents or in the shallow seas,

Speaker 1 occurred here. And so there's no way of then going, oh, how do we get it to the moon? Unless, of course, as you've said, astronauts basically take it up there from their gut biome.

Speaker 5 Oh, well, thank you, team. So there might be bacteria on the moon.
Maybe we brought them. But basically, the moon is too small to have its own atmosphere, and so it's quite harsh conditions up there.

Speaker 5 On to our next listener, who's asking about microbes closer to home and whether they can help us out with a mess we've got ourselves into.

Speaker 5 They write: Hello, are there any microbes that consume the waste plastic particles in the ocean? If not, would we expect some to evolve? And if so, on what sort of time scale? Who wants this?

Speaker 1 I'm happy to go for it. Go for it.
It's a very cool question. So I basically dug into this because I was fascinated by this.

Speaker 1 It turns out there are some marine bacteria that can break down low-density plastics. We've also found some bacteria and fungus on land that break down plastics, but very specific types of plastic.

Speaker 1 I love one publication I read: the bacteria were found outside a plastic recycling facility in Japan.

Speaker 7 Ah, perfect place to evolve, then.

Speaker 1 Exactly. We've also found caterpillars of the wax moth can eat common plastics because they've got an enzyme in their saliva that breaks it down.

Speaker 1 We also know that polystyrene can be eaten by mealworms, and there's also gut microbes that can munch plastic in beetle larvae. So there are small isolated cases.

Speaker 1 The problem is, and I'm sure that evolution will eventually work out how to deal with this substrate, but we don't have that sort of time.

Speaker 1 So if we look at the facts, 300 million tons of plastic are produced every single year. Okay, and this is ending up in our rivers and our oceans.
We're literally drowning in plastics.

Speaker 1 So for me, one of the things that we're starting to do is accelerate evolution. So we're developing genetically engineered microorganisms that can actually munch on plastics.

Speaker 1 We've also isolated those enzymes from the caterpillars to speed up the breakdown and allow us to recycle plastics more. But I'll come back to a simple fact, which is that's really cool.

Speaker 1 But guess what? Why don't we just use less plastic? Why don't we ban single-use plastic? And the last one is, if we have to use plastic, let's stop making it go into the environment.

Speaker 1 Let's make sure that our water companies actually capture it and don't just flush into the rivers and into the oceans.

Speaker 5 Thank you, Mark. Lots to think about there.
And moving on now to an absolutely brilliant question from 11-year-old Owen, who asks, when you pick flowers, when are they dead?

Speaker 5 Is it when you pick them or when they're all dried up, or somewhere in between? Thank you so much, Owen.

Speaker 5 Team, the dead aspect of flowers really splits whether you enjoy cut flowers in my family, some of whom think that giving someone flowers is like offering them the chance to watch something die in a pot.

Speaker 5 Catherine, where do you stand on flowers?

Speaker 6 I really hope they're not dead after you pick them because I do really enjoy looking at them. I've got a lovely bunch of daffodils on my table at the moment.

Speaker 5 Yes, so are they dead? Are they alive?

Speaker 5 This is kind of a version of a brilliant Infinite Monkey Cage episode where Brian Cox said it was the most profound question they'd ever been asked which is is a strawberry alive and genuinely it still keeps the philosophy message boards busy.

Speaker 5 Penny I'm turning to you because you've got a doctorate in plant genetics and development. Is picking a flower the equivalent of chopping off a hand and putting it in a pot?

Speaker 7 Yes it is a bit but I think the key thing here is you compare animals and plants. It's actually quite difficult to define death even in us, in animals.

Speaker 7 We tend to go on when the heart stops and can't be resuscitated. But there's nothing like that at all in a plant.
So, the answer is that it is somewhere in between.

Speaker 7 If you've cut a plant and you have it in a glass of water, it can continue to respire and do cellular processes for a little while.

Speaker 7 Part of that's because there's no blood pumping required for oxygen to get into a plant. That can happen by diffusion, so it carries on.

Speaker 7 And similarly, for a few days, it can continue sucking up all the water it needs from being in a vase.

Speaker 7 But gradually over time, all of those cells stop getting quite what they need and you do get this gradual decay. And so there's no kind of dividing line.

Speaker 7 However, it's not necessarily the be-all and end-all. If you cut off the flowering part of a plant, that's kind of programmed to flower and then do its job and that's kind of it.

Speaker 7 So there's a limit to what that can do. But with a lot of plants, if you cut off another bit, a leafy bit for example, and you stick that in a vase, you might think it's on its way to then die.

Speaker 7 But obviously, this is a really common way of taking cuttings and it can use that water and oxygen to grow an entirely new root system.

Speaker 7 So, that is one of the cool things about plants: there's much more sort of fluidity when it comes to is it alive, is it dead, and can you bring it back to life?

Speaker 5 Okay, thank you, Owen. Thank you, Penny.
So, conclusion: somewhere in between, yeah, like the rest of us,

Speaker 5 Catherine. That's comforting, I hope.

Speaker 5 Your daffodils

Speaker 5 aren't a hand in a jar.

Speaker 1 But you can extend the life. So, the really interesting thing is, how do we get all these wonderful cut flowers from around the world?

Speaker 1 Because what we've discovered is if you keep them at between one and three degrees, they can last for weeks before they start to decay. So it's interesting that sort of a normal flower lasts a season.

Speaker 1 But if you cut them, there are ways of actually extending their life, even though you have basically started the decay process or you accelerated it by cutting it.

Speaker 1 So one of the things you can do, and this is for listeners at home, which is if you have cut flowers, put them in water, make sure there's nutrients and there's sugar, and also keep them in the coolest part of the house because they will last a lot longer.

Speaker 5 Keep your flowers in the fridge.

Speaker 1 That's great.

Speaker 1 I have pictures of you opening it going, oh, look, beautiful arrangement of clothes. Where's the milk? Exactly.

Speaker 5 Yeah, get rid of the milk, and that's where the flowers go now.

Speaker 6 Yeah, chuck the daffodils into the milk.

Speaker 1 Exactly, perfect.

Speaker 5 I'm sure Gardener's Question Time will be in touch with us on that.

Speaker 5 We could talk about flowers being dead or alive for hours.

Speaker 5 And for further listening, I do recommend googling monkey cage and dead strawberry, but we must move on because we've had a question from Tricia. Let's listen.

Speaker 10 Why don't they build satellites with the capability of being ordered to come home again?

Speaker 10 They should be capable of returning and being remotely guided back to the sender in much the same way as a drone. Then they can recycle the elements, saving themselves money and resources.

Speaker 5 This one's for you, Catherine.

Speaker 6 So let's think about the company SpaceX, which is currently really leading the field and revolutionising space travel by recycling their rockets. And that's really reducing the costs.

Speaker 6 I don't know if everyone saw the fantastic chopstick maneuver from October last last year. If you haven't seen it, google it because it's absolutely awesome feat of technology and engineering.

Speaker 6 This new super heavy rocket that SpaceX are developing at the moment is the biggest, most powerful rocket they've ever built.

Speaker 6 They captured its main booster on its way back down using basically a giant pair of chopsticks and that's the majority of the costs.

Speaker 6 The Crew Dragon capsule that they use to send astronauts up to the International Space Station and bring it back down again.

Speaker 6 That again is also recycled and it has a really strong heat shield on it because when it comes back down through the atmosphere it's tumbling at such great speeds that it reaches sort of thousands of degrees in temperature and so it needs a really strong heat shield.

Speaker 6 Now Trisha was asking specifically about the satellites. Now these are much cheaper to build than the rockets that get them up there in the first place.
They're fairly lightweight.

Speaker 6 Each satellite in the SpaceX fleet is about half the weight of of a cow.

Speaker 6 So not super heavy, it's about the size of a small car and they have a lifetime of five years and it's much cheaper to let them burn up in the atmosphere on their way down than it would be to kit them out with a heat shield.

Speaker 6 So when they come down they could be recycled here on Earth. I'm not a fan of these satellites, I must say.

Speaker 6 They make it really hard for us astronomers to do our job of looking out into the universe because there are so many up there. They're also starting to become a bit of a problem here on the ground.

Speaker 5 In what way?

Speaker 6 Some of them don't completely burn up in the atmosphere as they're supposed to.

Speaker 6 So January this year a giant chunk of SpaceX satellite metal came down in Kenya, about the size of a big car came down in a field in Saskatchewan at the end of 2024.

Speaker 6 And it's not just SpaceX that are putting these satellites up there. There is a global race for worldwide satellite internet connectivity.

Speaker 6 And at the rate that satellites are being launched at the moment there are going to be a hundred thousand up there by 2030 with them coming down at a rate of about one per hour and people are starting to get really worried now about the vaporized metals in the atmosphere as they come down that they're burning up all of the the aluminium that they're mainly made up of where does that go it just stays in in our atmosphere it's it's just vaporized metals and that that's a problem for our ozone layer and from an astronomy perspective I'm genuinely concerned about our ability to conduct science because our low Earth orbit is being clogged up with all of these satellites and sort of from a human perspective we've got this this new source of pollution in our atmosphere that really hasn't been well thought through yet and there's no regulations on this at the moment because these space companies are moving much faster than international space law can keep up with particularly when the the CEO of the leading company has the ear of the President of the United States.

Speaker 6 So, to answer Tricia's question, we can't get them back home again because it's expensive for them not to burn up in the atmosphere.

Speaker 6 But the fact that they are burning up in the atmosphere is a problem, and the fact they exist in the first place is, for me, an even bigger problem.

Speaker 5 Thank you, Catherine. We've got time maybe for just one more penny.
Take a listen to this.

Speaker 6 My name's Ali Slade. I live in Sub-Norton in the southwest of the UK.

Speaker 6 And my question is: there's a distinctive smell when rain falls on dry tarmac. And I wondered what caused that smell.

Speaker 5 In a word, petrichor. Hey, there we go.

Speaker 7 I'm so glad because it's one of my favourite words. And this is the phenomenon of the smell of rain.
What's mostly been studied, I have to say, isn't tarmac, so man-made surfaces.

Speaker 7 Mostly, the research so far has looked at kind of dusty, sandy clay soils.

Speaker 7 And it's quite well established that, that especially if there hasn't been rain for a while when it does rain and it has to be the right amount of rain not too much not too little what you get is kind of an aerosolization of all kinds of smelly things that have built up in little air bubbles in the soil so that these tiny little pockets of smelly things get pushed up into the air when the rain falls and some of the things are lovely so if you've had a really dry period plants start secreting growth inhibitors so that they kind of don't overgrow at a really difficult time that's part of the smell there's also spores of certain types of bacteria.

Speaker 7 That's part of the smell. And it's really evocative.
It's lovely.

Speaker 5 Any particular sort of, do you want to give us sort of a wine note?

Speaker 1 Oh, yeah.

Speaker 7 I'm never very good at that kind of sort of slightly grassy, dusty, musty, but there's a freshness.

Speaker 1 Yeah, what will that do? I'll have a glass of that.

Speaker 7 What I don't know is if tarmac would be any different. Potentially, you might be smelling the petrichor from the soil because that can carry a bit of a distance.

Speaker 7 And there's some evidence that our noses are really sensitive to it because we really care about when it rains. So this is something that we can pick up on.

Speaker 7 Or maybe, you know, I'd hypothesise with other man-made road surface materials, you might get off-gassing of other substances, maybe the less lovely biological ones and maybe more chemical ones.

Speaker 7 So I think it's plausible that tarmac might have its own kind of petrichor, but I don't know.

Speaker 5 Thank you very much, Penny. And that's us really out of time, which is sad because we have plenty more questions up our sleeves.

Speaker 5 And I hope that the philomaths listening have learnt something new and that the panel's answers have left you satisfied often.

Speaker 5 Our answers lead to more questions and if they do then please do send them our way. The address is insidescience at bbc.co.uk and we do read every single one.
Dr.

Speaker 5 Penny Sarge, Professor Catherine Haymans, Professor Mark Maslin, thank you all very much.

Speaker 1 Bye!

Speaker 5 You've been listening to BBC Inside Science with me, Marnie Chesterton. The producers were Dan Welsh and Debbie Kilbride.
Technical production was by Sue Mayo.

Speaker 5 The show was made in Cardiff by BBC Wales and West.

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