Answers to even more questions

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1:04The gravity of the high tide is giving the moon energy to enable it to spiral farther and farther away.

1:13Caroline Steel:Welcome to CrowdScience, the show that answers your science questions, like this one. And learn that the moon was slowly moving away from the Earth. And that made me wonder if the moon will ever escape from Earth's gravity. If you're a regular CrowdScience listener, that question might sound familiar. And here's another you might recognise. I think like every dog lover in the world, I wonder why my dog can't live as long as I do. I'm Caroline Steele, and on CrowdScience we find that answering one of your questions often sparks a whole avalanche of new ones. This week we're answering some of those bonus questions, questions that were inspired by episodes of CrowdScience.

1:52We're at about 25 metres now and already you can see the sunlight starting to diminish. It's this beautiful shade of blue.

1:59Caroline Steel:First, we're starting with a question inspired by an episode that took us into the deep sea. We were trying to answer listener Watum's question. My question to CrowdScience is how is fish able to survive at great depth at the sea level, the ocean bed? In the episode called How Do Fish Survive in the Deep Ocean, Peter Raskmuller at the Danish Natural History Museum told us about fish with a fascinating adaptation. One of the really, really cool ones is the deep-sea anglerfishes. They all have in common that the first fin ray in the dorsal fin has been modified into a fishing rod with a little lure, and in that lure there is light.

2:45Caroline Steel:The anglerfish lures its prey in with a light that dangles just in front of its mouth. As the unsuspecting prey swims closer, hoping for a tasty snack, it ends up becoming the snack instead. This clever trick captured the imagination of listener Ivor from Epsom in the UK. He emailed crowdscience at bbc.co.uk with the first follow-up question that we're tackling in this show. Fish that live on colourful coral reefs seem to have developed excellent colour vision, but the deep sea anglerfish has adapted over millions of years to living in inky darkness. Has this reduced the anglerfish's ability to see colours?

3:27Caroline Steel:So are anglerfish worse at seeing colour than the fish who swim around the colourful coral reefs in the shallows? I love that question. So on coral reefs, there's plentiful light available across a different range of spectral wavelengths of the light. So it's a very rich color environment. This is Lars Schmitz, professor of integrated sciences at Claremont McKenna University in the US. It's true that reef fish have probably very excellent color vision. We can tell this from looking at the different types of photoreceptors they have, specifically like the visual pigments that they possess in their retina.

4:03And so what we see there that reef fish tend to have about four different type of pigments in the cone photoreceptors. And that would suggest that they are actually really good at color vision.

4:15Caroline Steel:Okay, so coral reef dwelling fish do have really good color vision. What about anglerfish? I assume they don't because they live essentially in the darkness. Yeah, so when we look at the visual environment in the deep, it's a superstar contrast to the coral reef. Like deeper than a thousand meters in the ocean, you would have essentially no sunlight at all. So one would think, why would they have color vision? And there's one really interesting thing is there's lots of bioluminescence in the deep sea. So light signals generated by organisms. And so we do actually have color signals in the deep sea.

4:57And it wasn't until like about five years ago that we realized that, look, actually these deep sea fish, at least some of them, have different types of visual pigments. And it's not the cones. Surprisingly, it's in the raw photoreceptors that are normally used for dim light vision. And there seem to have been multiple events of duplications and modification of these visual pigments that we now think actually would allow them to have pretty good color vision in the deep sea. And I think that's actually super surprising because there's no sunlight down there. It all relies on that bioluminescence in the deep part of the ocean.

5:34Caroline Steel:I've got another question for Lars from our listener Ivor. When he was thinking about the colour vision of fish in the deep sea, he wondered if there was a comparison with vision in animals on land. Here's Ivor again. Many mammals seem to have poorer colour vision than humans do and are what we humans would call colour blind. So why have humans and some apes evolved better color vision than other types of mammals? So are there any sort of parallels between fish and mammals in terms of color vision? Another really fascinating question. And I think one connection we could draw is a little bit on the history of mammals, the evolutionary history.

6:16So when we think about the deep sea and think of that very light, limited environment, mammals went through a prolonged phase of nocturnal activity. So night active behavior was dominant for millions of years, probably starting in the Triassic and lasting until the dinosaurs went extinct. And so this prolonged activity at night really had fundamental changes to the visual system of mammals. mammals tend to have only two different types of options, which are the visual pigments that help to absorb the light signal. So mammals on large cannot distinguish as many hues as many other vertebrates like fish or birds can do.

7:00And what's interesting is that in primates, so us, we have regained a third visual pigment. So now we actually have pretty decent color vision. And the idea here is that for primates, this really had an advantage that we could detect ripe fruit or fresh leaves much better against the background than if we only had two visual pigments in our cone photoreceptors. And that could be a significant evolutionary advantage and promoted this re-evolution of a third pigment.

7:33Caroline Steel:So Ivor, I hope we've answered your questions. Mammals once had excellent colour vision, but during a very long nocturnal phase in our evolutionary past, much of that was lost. But we humans got it back, possibly because being able to spot ripe, colourful fruit gave us an advantage. And as for anglerfish, they can see colour too. Even though there's no sunlight in the deep sea, some creatures produce their own light, glowing to attract prey, find a mate or as camouflage. For anglerfish, being able to see that light is a vital survival skill. Now, we're going to carry on answering questions that you've been sending to crowdscience at bbc.co.uk in response to shows that you've already heard.

8:19Caroline Steel:And we're sticking with our eyes and colour. We made an episode called Do We All See the Same Colour? which you can find by searching for CrowdScience wherever you get your BBC podcasts. In that show, listener Gregory in Minneapolis in the United States wrote in with a story about a conversation he had with a friend. We were looking at the colour of the sky, which was a really beautiful, vibrant blue. And she asked me, is the blue that I'm seeing the same blue that you're seeing? I got in touch with Professor Jay Knights, an ophthalmologist at the University of Washington in the US, to find out if Gregory and his friend were onto something.

8:58It turns out there is an impact of the colours we see based on the colours of our eyes.

9:06Caroline Steel:And when listener Katerina heard the show, it was the nudge she needed to finally get in touch with us about a question that had been on her mind for years. Hi CrowdScience. My name is Katerina. I am 25. I'm from Portugal. And after listening to the episode that asked, do we all see the same colour? I felt like asking, why do my eyes change colour? So when it's sunny, my eyes are light olive green and when it's dark, they are completely brown. Sometimes they are even in an in-between state, so brown in the centre and gradually green towards the edges. This has happened to me since I was a kid.

9:45People say that I have chameleon eyes. Could you help me understand why this happens? Thank you.

9:51Caroline Steel:Well, Katerina, I've got some good news for you. I met up with eye specialist Professor Piero Heise from King's College London in the UK and I told him all about your chameleon eyes. So our listener Katerina thinks her eyes look bluer or greener in the sunlight and more brown when it's darker. Why do people have different colour eyes in the first place? Why don't we all just have brown looking eyes or blue looking eyes? So there is a whole spectrum of eye colours. There are people with very dark eyes because of the pigment melanin, which has a naturally dark brown. And at the other end of the spectrum, there are people with blue or green eyes, even though there's no green or blue pigment.

10:33Caroline Steel:Wait, so people with blue or green eyes don't have blue? They don't have any melanin, but there's no green or blue pigment in the eyes. OK, so can I just check I understand this right? People with brown eyes, like, for example, me, I have quite brown eyes. I have a lot of melanin. So basically my eyes are absorbing all the light apart from the dark brown. Yeah, which is getting reflected back. My eyes look brown. I don't think they really change colour. Maybe they look slightly different in different environments, but I've never noticed. People with blue eyes have less melanin or no melanin? Some people have no melanin at all.

11:10Caroline Steel:Okay. And what happens if you have blue eyes? Exactly the same effect as you see in the ocean in a sunny day. So as the rays of the sunshine go through the water, the red and the yellow and the other colors that we normally see in a rainbow in that spectrum, they get absorbed by the molecules. They have that wavelength that is easy for the water and other materials to absorb. And it's the blue and the green light that are harder to absorb. And they get scattered around and that scatter comes to our retinas and we perceive the water to be green or blue. Okay, so with Katerina's eyes, she's seeing them appear bluer in the light and browner in the dark.

11:50Caroline Steel:What's going on there? She might get a mix from the brown colour, from the presence of melanin in her iris. But at the same time, she will get that greenness effect from the scatter in her iris. And the blend of these two colours would give that olive eye colour that she thinks she has. Now, on a sunnier day, she gets a lot more green effect because the light scattering in her iris is more abundant. And that addition of greenness in her eyes would give her eyes a lighter, greener colour than she would get in a different hour of the day or in different illumination conditions. So is it the case that everyone's or most people's eyes change colour a bit, but the closer towards the middle of the spectrum, the more your eyes change colour?

12:35Yes, that should be the case. it's not visible in everybody because of the presence of melanin and melanin is a very intense highly concentrated pigment so people have dark eyes they would have very little variability but even people with brown eyes there are darker shades of brown or lighter shades of brown depending on the illumination conditions.

12:52Caroline Steel:I'm going to have a look at my eyes in the mirror next time I go outside see if they change color I think I'm towards the darker end of my eyes are just always going to look brown but I want chameleon eyes I'm jealous of Katerina. Katarina, your eyes appear to change colour because of a delicate balance between two processes In low light, the melanin in your eyes reflects brown light and makes them appear brown But in brighter light, another effect takes over the very same one that makes the ocean look blue and your eyes shift to an olivey green Now we're leaving colour behind and exploring space next

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14:35Caroline Steel:You're listening to CrowdScience from the BBC World Service. I'm Caroline Steele. In science, when you find the answer to one question, you often end up with even more questions. And that's exactly what happened to listener Rakesh in India when he listened to the CrowdScience episode called Will the Earth Ever Lose Its Moon? In that episode, we found a reassuring answer to that question. Eventually, it will maybe escape. But to be honest, we don't need to worry about that because this is going to happen billions of years in the future. And by that time, the sun would have reached the end stage of its lifetime, which means it will blow up, expand and probably reach the Earth and the moon and will just engulf us and will be vaporised.

15:21So losing the moon is something I categorise and the things that just we don't need to worry about.

15:27Caroline Steel:Thank you, Sarah Russell from the Natural History Museum in London in the UK for clearing that up. And note to self, don't lose sleep over losing the moon. It makes more sense to worry about the sun vaporising the Earth. But that idea of moons escaping their orbit sent listener Rakesh's thoughts spinning. And he emailed crowdscience at bbc.co.uk with this question. My name is Rakesh Vajja and I'm from Gangawati, a city in Karnataka, India. While listening to your recent episode about moons, a question occurred to me. Our moon is moving away from the Earth at the rate of approximately 4 centimetre per year.

16:04Is this phenomenon observed with the moons of other planets as well? For instance, Jupiter has 79 moons. Are they also drifting away from Jupiter? And if some of the Jupiter's moons are moving away, is there any possibility of them colliding with one another?

16:18Caroline Steel:So, could Jupiter's moons crash into each other? And are any of them also moving away from Jupiter, just as our moon is slowly getting further from Earth? Rakesh, I felt like I was doing my own space mission, trying to track down the right person to answer this one, but I think you're going to be pleased. We've got an expert from the European Space Agency, and she's involved in the JUICE mission. JUICE stands for the Jupiter Icy Moon Explorer. So my name is Ines Belgesem. I am a science operations scientist based at ISAC, So that's the European Space Agency Madrid location. The mission is investigating whether Jupiter's moons are able to support life.

16:59Caroline Steel:As well as water, Inez is looking for things like carbon and nitrogen. I'm trying to understand the evolution of those surfaces and what it tells us about habitability. Now, we keep discovering new moons orbiting Jupiter. So I began my chat with Inez by trying to pin down exactly how many of Jupiter's moons we're trying to keep track of. so as of the last count about 97 confirmed that's so many more than earth why does you have 97 times more moons than earth so an important caveat on that number of moons it's really just io europa ganymede and calisto what we call galleon moons those are the most massive and are accounting for 99.99 % of the entire moon system.

17:48And Jupiter is the most massive planet of our solar system. It has a huge gravity pool. And it kind of picks up moons on the way. That's where most of them come from.

18:00Caroline Steel:Okay. How small is the smallest moon? That's a hard question. I don't know the answer to that. Could I be a moon? Or am I too small? I think you're too small. But actually, I know that some are only a few kilometres wide, which is really small. And with there being 97 of them, will they crash into each other? Have they crashed into each other? Some of those smaller moons might be the result of collisions. So we have basically three big families of moons. I've already spoken about the Galilean moons. then we have inner moons within the rings so Jupiter has rings little known fact but Jupiter has rings and then we have captured asteroids moons that are kind of chaotic so they're further away from Jupiter they're all kinds of sizes mostly small and some of them are actually the result of collisions and the reason that is is because their orbits are very chaotic and so let's imagine you have all those moons going in the same direction, like on a motorway, you might have the odd moon coming on the other direction and that will make collisions a lot more likely.

19:13Generally, they're kind of grouped by direction, but there's a couple of examples of rogue moons going the other direction that might increase the chances of collision.

19:24Caroline Steel:If we're looking at which moons might crash, they sound like good candidates. Yeah, they're probably the first ones that will get hit. And I guess, can we sort of guarantee that given enough time, another collision will happen again? In the outer moons group? Yeah, for sure. Of course, when I say it will happen, I'm speaking over billions of years.

19:50Caroline Steel:So we've got another question. So our listener, Rakesh, wants to know whether any of Jupiter's moons are moving away from Jupiter. and that's because Earth's moon is moving away from Earth, is the same thing happening on Jupiter? The short answer is it's complicated because there are all those groups of moons. So Io, Europa and Ganymede are locked into what we call a Laplace resonance. What it means is that when Io does one orbit around Jupiter, Europa does two and Ganymede does four. In celestial mechanics, this is a very, very stable situation. Calistone now is outside of that resonance. Models show that in, say, one and a half billion years, short time for the solar system, a very long time for us, Calistone might move away from Jupiter to the point that it gets locked into the resonance itself.

20:47And then there's all those irregular moons that I keep talking about. Those are very, very chaotic. So they're moving in all kinds of directions.

20:57Caroline Steel:So some might be moving away, some might be moving towards. Indeed. But like I said, it's very, very small bodies. And the chances of them interacting with the inner system are very, very slim. So Rakesh, like on planet Earth, some of Jupiter's moons might be drifting away. But they aren't going to escape its orbit any time soon. And given enough time, some of those chaotic 97 moons will crash into each other. It's just a shame we don't live for billions of years to see it for ourselves. Now, it's time for our final follow-up question. If you've ever lost a pet, then the CrowdScience episode Why Can't My Dog Live As Long As Me might resonate with you.