Pluto's strange ice patterns explained by new theory

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, explaining mysterious patterns on Pluto.

Host: Nick Petrić Howe

And how a social construct has warped genetics research in Latin America. I’m Nick Petrić Howe.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

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Interviewer: Benjamin Thompson

Pluto, whilst no longer a planet, still holds a great deal of interest for astronomers.

Interviewee: Stephane Labrosse

First seen from the Earth, Pluto is just a very tiny dot. But it was approached by a mission in 2015 called New Horizons.

Interviewer: Benjamin Thompson

This is Stephane Labrosse from the University of Lyon in France. NASA’s New Horizons probe was the first spacecraft to explore Pluto up close and it sent back some intriguing images. And these were especially intriguing for someone like Stephane, who’s interested in what goes on under the surface of planets.

Interviewee: Stephane Labrosse

One of the things that the mission could see was some very intriguing polygonal patterns. And I was like, ‘Wow, that’s very neat. What could explain this pattern?’

Interviewer: Benjamin Thompson

The patterns could be can be seen across the smooth surface of a basin filled with nitrogen ice, known as Sputnik Planitia. Here, dark lines formed geometric shapes several tens of kilometres wide. So, what’s behind these mysterious shapes? Well, this week, Stephane and his team have a paper out in Nature with a new explanation for Pluto’s perplexing polygons. But there have been a few other theories prior to this work.

Interviewee: Stephane Labrosse

When it was first observed, the people that worked on the mission, they very rapidly thought about convection because thermal convection, in particular in convection in solids, is known to make this type of pattern.

Interviewer: Benjamin Thompson

So, even though Sputnik Planitia is made of solid ice, slow moving currents are still a viable explanation.

Interviewee: Stephane Labrosse

Solids, if you look at them on long timescales, behave like liquids. We can see that with glaciers in mountains. We know that glaciers flow down the mountain, so they are like rivers but very viscous rivers. So, the ice of Sputnik Planitia is also solid but it convects in million-year timescales typically.

Interviewer: Benjamin Thompson

The convection currents that make these kinds of patterns are usually driven by heating from below. In this case, it was assumed to be Pluto’s internal heat.

Interviewee: Stephane Labrosse

That’s what happens when you heat a pan. You can see patterns. You can see motion in the pan, and that’s caused by convection because the fluid that is below gets less dense because it gets warmer, and so because its below and less dense it wants to move up. On the other side, the food that is on top, it’s cooler so it’s more dense and wants to go down.

Interviewer: Benjamin Thompson

While this all makes good sense for your saucepan, there was something about the patterns on Pluto’s surface that didn’t quite fit with this idea.

Interviewee: Stephane Labrosse

Heating from below would lead to actually a reverse pattern compared to what we observe, that is flow going up on the polygons sides instead of going down as we observe.

Interviewer: Benjamin Thompson

The visible lines delineating Pluto’s polygons are troughs, showing that the convection currents must be rising up from the centre of each shape and sinking at the edges – the opposite to what you’d get if you were heating from underneath.

Interviewee: Stephane Labrosse

So, we still think that convection is at the origin of these polygons, but instead of heating from below, we think that it is better explained by cooling the top.

Interviewer: Benjamin Thompson

To explain this cooling from above, Stephane and his team turned to sublimation. This is the process, similar to evaporation, by which the nitrogen ice of Sputnik Planitia turns into nitrogen gas.

Interviewee: Stephane Labrosse

This cools down the surface in a very similar way to the situation we encounter in everyday life when we get out of water and we feel cold because water is evaporating, which requires latent heat to do so, and it cools down the skin. And so, we think that’s exactly what’s happening at the surface of Sputnik Planitia.

Interviewer: Benjamin Thompson

So, to test this new theory, Stephane and his team developed a computer simulation of the surface. They inputted the conditions they thought might be present on Pluto and let the simulation play out over long timescales and, sure enough, polygons began to form.

Interviewee: Stephane Labrosse

And we found that with reasonable parameters for Sputnik Planitia, we obtained the same types of patterns as what we observe.

Interviewer: Benjamin Thompson

Their model suggests for the first time that sublimation can drive planetary-scale patterns and may well be behind the unusual shapes seen billions of miles away on Pluto’s Sputnik Planitia. Marks seen on the surface of Pluto’s ice suggest that sublimation is occurring there, but there’s only one way to know for sure if this is the explanation for Pluto’s polygons.

Interviewee: Stephane Labrosse

Of course, it would be good to back there and test some of the ideas that we propose because of course once you have a theory, you can make some predictions and then these predictions can be tested. So, for example, we made predictions on the thickness of the Sputnik Planitia ice layer, and so that would be good to test this. But of course, this is very far away and it’s very difficult to send missions there, and so I’m not sure we will be able to get more results on that in the short term. But I’m confident, yes.

Interviewer: Benjamin Thompson

That was Stephane Labrosse from the University of Lyon in France. To find out more about Pluto’s polygonal patterns, make sure to check out the show notes, where you’ll find a link to Stephane’s paper.

Host: Nick Petrić Howe

Coming up, we’ll be hearing about how the term ‘mestizo’ has impacted genetics research in Latin America. Right now, though, it’s time for the Research Highlights with Dan Fox.

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Dan Fox

Traditional bull runs – where thrill-seeking participants try to outrun animals charging down a street – defy the dynamics that normally govern crowds. A group of researchers analysed the running of the bulls that takes place in Pamplona, Spain each year, by scanning through videos, digitally tagging each person and their motion. In most studies of pedestrian dynamics, people behave roughly like the particles in sand, and their speed decreases when the crowd become denser. But the bull run violates those rules. Instead, participants directly ahead of a bull tend to run faster and bunch up, which simultaneously increases both the density and the speed of some parts of the crowd. Where the crowd becomes too dense, people stumble and fall, at the risk of being trampled, and cause others to fall, too. The authors say the study of unusual crowd dynamics could help to prevent stampede-related injuries. Take that research by the horns and read it in full in Proceedings of the National Academy of Sciences of the United States of America.

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Dan Fox

‘Living’ bricks made with bacteria and fungi can heal themselves and send signals to each other while still providing a sturdy building material. Materials laced with living microorganisms hold promise for constructing large-scale structures that can detect changes in their surroundings. But few ‘biocomposite’ materials have been capable of this responsivity while also being able to be used in construction. To tackle this problem, a group of researchers produced a new material, using a fungus of the Ganoderma genus. Within weeks, the fungus grew into its food stuff, in this case hemp waste, binding it together inside a brick-shaped mould. This engineered living material can repair its own cracks and even fuse with adjacent blocks to form human-scale structures. The team also found that the bacterium Pantoea agglomerans can grow well within the fungal network. They engineered two strains of the bacterium: one that makes a signalling molecule and another that produces a fluorescent protein when exposed to the signal. Blocks laced with the responsive strain glow under a microscope when detecting a signal from an adjacent block carrying the other strain. The authors hope that similar techniques could see future living bricks given new functionalities, like the ability to sense and react to pollutants or produce protective molecules. Build on your understanding of that research by reading it in full in Nature Materials.

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Interviewer: Nick Petrić Howe

While science is considered by some to be somewhat outside of society, in reality they inevitably get intertwined and, this week in Nature, reporter Emiliano Rodríguez has written a feature article about one such clash in Latin America. Emiliano’s focus is on the concept of mestizo people – a societal construct which, whilst once a marker of national identities in Latin America, has since led to discrimination and is warping genetics research. For his feature, Emiliano has spoken to people, including researchers, across Latin America and I caught up with him to find out more. I started by asking him what ‘mestizo’ means.

Interviewee: Emiliano Rodríguez Mega

So, ‘mestizo’ basically means a mixture. So, I remember when I was growing up in Mexico City, at school they would never talk to us about races or they would never even talk to us about racism. The idea was that all Mexicans were sort of like a mixture of these three ancestral populations – the Indigenous populations that lived in Mexico, the European colonisers that had come to the region, and also, even though this wasn’t officially recognised until 2015, the African slaves that had been forced to come. So, after centuries of mixture, sort of like this fusion had been so intense that we had all become this homogenous group of people called mestizos. And this is the same for with national variations to what happened in many other countries across Latin America.

Interviewer: Nick Petrić Howe

Now, one might naively assume that this idea of mestizo is a positive one. Historically, it was used as a unifying vision of national identities across Latin America, and this also garnered some support from early genetics researchers. But now some researchers are pushing back against it. What have been the consequences of this idea?

Interviewee: Emiliano Rodríguez Mega

So, I think the consequences are many. Specifically, the feature has to do with how the category mestizo has been used in genetic and genomic studies throughout Latin America, right, for many decades, and it’s something that is still being used. And for me, the most problematic thing about that is that the mestizo is essentially a social construct. It is not genetically meaningful, like it doesn’t represent a group of people that share some genetic variations. And so, the fact that some researchers are still using it, for some people it’s problematic because it means that they are sort of like ignoring all this historical and political and social baggage that goes with the concept of mestizo and mestizaje, which means essentially the fusion.

Interviewer: Nick Petrić Howe

And so, can you give me some examples of when this term has been used in these kinds of studies and what that has meant for the people of the region?

Interviewee: Emiliano Rodríguez Mega

I can think of a specific example. For many decades, geneticists in Brazil have published a lot of research that has demonstrated that Brazilians have an incredible genetic diversity, and essentially that this mixture has been going on for so long that it’s no longer possible to sort of like separate people into different categories, so they all fall into this one category of mestizo. The issue with that is that when these results went out into the public, a lot of people, including politicians and lawyers and also scientists, they said, ‘Well, if Brazilians are as admixed as they say we are and if races do not exist on a genetic level, then it doesn’t make sense to have sort of like these social policies for people who have been historically marginalised.’ And so, they submitted a request to sort of like declare these policies as unconstitutional. The thing is, right, I mean, you can talk about race not being a valid concept biologically. However, in society we do tend to discriminate against people based on how they look, based on how we racialise them, based on how we put them into these categories, and so that was incredible problematic. In the end, the Supreme Court decided that genetics is irrelevant when it comes to these sort of like social policies. But it was a hurtful message for many people, particularly people who did not and who do not identify as mestizo. I had a source who is a member of the Brazilian Association of Black Researchers. For her, at least, what she told me was that racism, at its core, it’s not a genetic issue.

Interviewer: Nick Petrić Howe

And so that raises a good point, and I think we’d be remiss to not say it as well, that despite these categories having unclear definitions in genetic research, they do have real impacts on real people.

Interviewee: Emiliano Rodríguez Mega

Yeah, absolutely. So, we found some figures from the World Bank and other studies that really did show a correlation between identifying as either Indigenous or Afro-descendant and facing more inequalities. And some of these examples have to do with how these populations have less access to water and electricity and sewage, or they face more inequalities when it comes to healthcare and educational attainment compared to people who don’t identify as Indigenous or Afro-descendant.

Interviewer: Nick Petrić Howe

This is obviously a very nuanced issue. Words and concepts do often have different meanings and impacts in society versus in science, and so taking into account these varying perspectives does often pose a challenge to researchers in fields like genetics. In this case, the people you have spoken to are telling you that the concept of mestizo has suppressed the visibility and recognition of some communities that don’t fall into that category. And in genetics, the word doesn’t really have a biological meaning and yet it is still used. Did you get a sense from the people you spoke to about ways forward?

Interviewee: Emiliano Rodríguez Mega

I did, but, I mean, I would also like to stress that there’s no easy solution. Because, first of all, this is not really a conversation that’s so widespread among the scientific community. I think some of the people I talked to, they are definitely trying to do things differently. For example, some geneticists are refusing to use the term ‘mestizo’ in their studies and they have adopted other terms, such as ‘admixed populations’, ‘cosmopolitan populations’, ‘urban populations’, which, of course, they can still be problematic in certain ways. But this at least strips away the whole historical and social and political baggage that ‘mestizo’ has. So, that’s one of the things that people have been trying to do. I think the good thing about this and one of the things that I learned throughout my reporting was that there is, I wouldn’t say a majority, but I would say, a group of people in academia who are trying to make this problem visible and who are trying to have conversations around it and who are trying to put it in the table for others to take a look and see and reflect and to discuss what sort of, like, implications this has had in genetic research. And many of these people are people who do not identify as mestizo, right, and they are the ones who are leading the conversations.

Interviewer: Nick Petrić Howe

That was Emiliano Rodríguez. For more on this story, check out the feature in the show notes.

Host: Benjamin Thompson

Finally on the show, it’s time for the Briefing chat, where we discuss a couple of articles that have been highlighted in the Nature Briefing, and, Nick, what have you got for us this time round?

Host: Nick Petrić Howe

Well, Ben, I’ve been reading a story in New Scientist that’s all about sleep and creativity and how, actually, interrupting sleep may be able to help creativity.

Host: Benjamin Thompson

Well, Nick, I have a toddler at home who kind of doesn’t really like to sleep, so I guess I must be maybe the most creative person on Earth? Is that how it works?

Host: Nick Petrić Howe

That’s not quite how it works, I don’t think, Ben. This article in New Scientist concerned a new study that has been done, and this study was focusing on an early stage of sleep known as ‘N1’. And essentially, what they were doing was giving people a maths problem, then letting them go sleep for 20 minutes, and waking them up just as they entered this early stage of sleep to see if it bolstered their creativity when solving this maths problem.

Host: Benjamin Thompson

Right then, okay, so 20 minutes nap and then do the maths problem. What did this work find then? How did it help?

Host: Nick Petrić Howe

Well, they had 103 people in this study and first of all there were some people who solved this problem anyway, so they got rid of those people and then focused on the other people who were then put in this room to be allowed to sleep. Twenty-three people actually did fall asleep and then were woken up during this N1 stage. Some people actually slept for a bit longer and went into the next stage of sleep, and some people just didn’t fall asleep at all. And so they compared whether people found a hidden solution to this maths problem and, essentially, the people who were interrupted during this early N1 stage of sleep, 83% of them found this hidden shortcut. Now, this was compared to 31% of people who just stayed awake during that 20 minutes and 14% of people who went for a bit of a longer sleep and ended up in the next stage of sleep.

Host: Benjamin Thompson

So, looking at the problem then and then having a quick nap maybe has helped in some cases to find this other solution, right?

Host: Nick Petrić Howe

Yeah, it seems to have done for those people. However, there are a few caveats here. The authors themselves say in the paper that there is actually very little literature on this, especially empirical work on this. So, we don’t know a lot about how this works and also, they didn’t compare how many people found this hidden shortcut who had been interrupted compared to those who had slept for a full eight hours or something like that because there has been work in the past that showed that just sleeping a lot bolsters creativity. And of course, as well, we know that sleep is important for a whole bunch of processes, so you may not want to just be interrupting it to stimulate creativity. But this study at least seems to show that there’s something there.

Host: Benjamin Thompson

And, Nick, I have to ask the question: why are they thinking that there might be something to look at all? You said there’s not much research being done in this kind of area?

Host: Nick Petrić Howe

So, there’s a couple of reasons to decide to look into this. One is that the parts of the brain that are involved in creativity have been shown in the past to light up when people enter this early stage of sleep, so there’s maybe a link there. And also, there has been anecdotal evidence that this sort of interrupted of sleep has bolstered creativity in the past. Famously, Thomas Edison apparently used this. He held metal balls in his hands as he fell asleep and so they dropped to the floor, made a loud sound, woke him up, and he claimed that that bolstered his creativity, and allegedly Salvador Dali did a similar thing. But those are anecdotes, so this is some amount of empirical evidence, but the authors themselves say as well that more work needs to be done to understand this and, as I say, it would be good to compare to having a full night’s sleep.

Host: Benjamin Thompson

Oh, if only, Nick. What I wouldn’t give for a full night’s sleep. But anyway, let’s move on. And so, I’ve got a story this week that was a news feature reported in Nature, and I’m just going to give a flavour of it because it’s really comprehensive and definitely worth a read. But it’s about developing a vaccine for a viral disease. Now, it’s not COVID. Obviously, we’ve talked a lot about vaccines over the past 12 months. This is another disease called respiratory syncytial virus (RSV).

Host: Nick Petrić Howe

Right, okay, and obviously, as you said, vaccines are of interest to a lot of people at the moment, but I don’t know that much about this disease. Can you tell me a little bit about what it is and how it progresses?

Host: Benjamin Thompson

Well, absolutely, Nick, and what I’ll say is it affects a huge number of people – potentially like 64 million people a year get an infection – and it hospitalises more than 3 million children under 5 years old and hundreds of thousands of older people every year. And it can be incredibly severe and potentially deadly in newborns and in older people so for decades, researchers have really been trying to develop a vaccine against this disease.

Host: Nick Petrić Howe

Well, I mean, it sounds like something that it would be really useful to have a vaccine against, but you said there decades of research.

Host: Benjamin Thompson

Yeah, a long time coming, Nick, to get to this stage, and there have been some really quite devastating failures. Back in the 1960s, a RSV vaccine was tested that actually made disease worse in vaccinated children when they got infected, and it hospitalised many of them and actually two of them very tragically died. And of course, there’s been further attempts as time went on and those didn’t work either, either because the vaccine was targeting the wrong protein or the wrong form of a protein. But things changed about eight years ago when researchers worked out the structure of something called the F protein, and this is what the virus uses to fuse to human cells.

Host: Nick Petrić Howe

And how did the understanding of this protein change things?

Host: Benjamin Thompson

So, this protein then, the F protein, is what the virus uses to fuse with human cells, and what’s been really key to developing these new vaccines that are being tested was getting the structure of this protein before it fused with the cells, the pre-fused structure because once it does fuse, it changes shape, and that wasn’t useful for making vaccines, and this is what’s being used. So, four new vaccines are being tested, and what they essentially do is they present this pre-fused structure to the immune system.

Host: Nick Petrić Howe

Well, four vaccines being tested sounds promising. How close are these to being rolled out and being put into people’s arms?

Host: Benjamin Thompson

Well, four companies have global phase III trials underway, and they’re currently testing their vaccines older than 60, so one of the risk groups. But of course, we know that newborn babies are at risk as well, but their immune systems present a bit more of a sort of complicated challenge. They don’t necessarily respond robustly to many vaccines, which is why childhood vaccines are often given after two month of age, but of course you want to protect newborns. So, a couple of phase III trials are being run in pregnant people to see if protection can be passed on to their newborns. And currently there’s also an antibody therapy in phase III trials as well to protect newborns from the disease.

Host: Nick Petrić Howe

Well, do we know when we might hear some of the results from these trials?

Host: Benjamin Thompson

Well, from what I understand, we might hear some interim results next year from one of these bigger trials involving older adults. But fingers crossed for good news from all of these vaccines because any vaccine or treatment would drastically reduce hospital and intensive care admissions for the vulnerable groups who can be affected by this virus.

Host: Nick Petrić Howe

Well, fingers crossed indeed then. But thank you for bringing that to the Nature Briefing chat. And listeners, for more on those stories and for how to sign up to the Nature Briefing, where you can find even more articles like them, then make sure you check out the show notes.

Host: Benjamin Thompson

And that’s it for this week’s show. But before we go, just time to mention a new video we’ve made. This one is about stretchable electronic components – diodes in this case – that could open the door for skin-like, wearable gadgets. Head over to the show notes once again for a link on where to find it.

Host: Nick Petrić Howe

We’ll be back in a week with our traditional festive show, so look for that in your podcast feed. And as always, if you want to ask us anything, then you can send us an email – we’re podcast@nature.com. Or we’re on Twitter – @NaturePodcast. I’m Nick Petrić Howe.

Host: Benjamin Thompson

And I’m Benjamin Thompson. Thanks for listening.