Why is dust so annoying? But where does it come from, and what can it do? And is dust responsible for the creation of life? I discuss these questions and more in today’s Ask a Spaceman!

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Hosted by Paul M. Sutter.

 

EPISODE TRANSCRIPT (AUTO-GENERATED)

I owe an apology. A deep, sincere, heartfelt apology. So I'm going to start this episode by just getting it out of the way. Clearing the air. Not actually clearing the air, you'll see why in a second. But making amends. Not becoming friends, that's a bridge too far. But still, we can be chill. To all the dust grains in the universe. If you're listening, and I know you probably aren't because A, radio waves pass through you largely unimpeded, and B, you're just a small collection of molecules and likely not sentient, I have this to say. I'm sorry. There. I said it. I feel better, don't you? I've spent years complaining about dust. There's dust on my desk right now as I'm typing the notes for this episode. There's dust floating through the sunlight in the window, and while I'm not allergic to dust, it feels like I am. Dust is annoying. It's everywhere. It gets into stuff, and it makes almost everything worse. You can clean dust in your home, and in a few days, it's back. Industrial dust gets deep in your lungs, and it's linked to respiratory diseases and cancers, which kills millions every year.

A black lung from working in the mine shafts? No, I haven't experienced that personally, but it sounds terrible. And sometimes dust can explode depending on what it's made of. If it's suspended in the air and reaches a critical ignition temperature, it can just blow up. And dust bowl, dust bowl, we had a period of time where like half of our food shut down because of dust. And if you want to do astronomy, dust is nasty. It can coat your lenses, which scatters light, which is really bad considering the entire goal of a telescope is to collect light. and you can't just wipe it off because that will scratch the perfectly shaped and ground glass that you have for your telescope. Dust in the atmosphere scatters light, and you can't just wipe it off because that would get rid of the atmosphere, which, while great for astronomy, would be generally bad for life in general. Oh, you want to get off the Earth and explore the wonders of the solar system? Too bad, there's dust. Lunar dust has these sharp, jagged edges because it hasn't been worn down by billions of years of wind and water, so it's exceptionally sticky and abrasive.

Apollo astronauts reported it as one of the most persistent and annoying problems of the entire mission. It stuck to everything, suits, visors, equipment, got tracked inside the lander, and they can even smell it. They said it smelled like burnt gunpowder, interestingly enough. It scratched visor coatings. It degraded spacesuit joints. It clogged seals. After just a few moonwalks, the suits were barely usable. It's electrostatically charged by UV radiation and the solar wind, so it actually levitates off of the ground. It clings to everything. It doesn't just settle down. It floats away and clings to more stuff. It made it hard to do science because we'd want to get a sample and oh yeah, there's some dust in the sample container and so it interfered with all of our instrument readings. In fact, dealing with dust is one of the biggest challenges facing extended lunar excursions like the upcoming Artemis missions. And Mars? Mars is even worse. Mars, there the dust has the opposite problem with the moon.

The dust hasn't blown around, so it has all these jagged edges. Mars, it's been blowing around for billions of years, so it's super, super tiny. It's like talcum powder. It's almost perfectly smooth and round. And it's nearly microscopic, which means it gets inside everything. You think you've sealed your habitat or your container? Nope. The dust is just going to worm its way in and out. It's so light and so fine and so everywhere, because basically all of Mars is a desert, that sometimes windstorms can kick up dust and literally blow it around the entire planet. We've had the entire planet covered in massive dust storms visible from the Earth with just a backyard telescope. You can tell that there's something funny going on on Mars, and that something funny is a globe-spanning dust storm. In 2018, one of these global dust storms blocked so much sunlight that it killed the Opportunity rover. Because it relied on solar power and then there was just less solar power and its batteries drained too low and it couldn't regenerate.

And we lost it. It killed one of our robots, man. Oh, and that dust, if you happen to be on Mars, this dust that is getting into everything, that's blocking the sun, that's getting into your habitat and into the visor of your helmet, everything, it often carries perchlorates. which is potentially carcinogenic. So now you've got Martian dust cancer to worry about. So dust interferes with our normal life. It interferes with backyard astronomy. It interferes with space missions. And it interferes with any kind of astronomy or cosmology or astrophysics you want to do. Because it just gets in the way. It contaminates. It ruins. Dust messes with light in really, really complicated, not-so-simple ways, and it's everywhere. If you go out into some random patch of interstellar space, you're not going to have a lot of stuff around you that's interstellar space for you. And about what you will find, about 99% of that stuff will just be hydrogen and helium. The rest is generally categorized as dust.

microscopic clumps of heavier elements like carbon and oxygen and iron, stuff like that. And yes, all of those elements are made inside of stars. So whenever someone is waxing poetic about, oh, we're all made of stardust, you have permission for me to roll your eyes in a really exaggerated way because stardust is awful. The smallest grains are just a few molecules, only a nanometer a few across, while the largest, the true giants of the dusty cosmos, are a thousandth of a millimeter across. We're talking about really, really tiny objects here. And because of that size, and because of their complex nature, and because they're made of all sorts of random elements and all sorts of random arrangements, is that what these dust grains do to light? That is so dang annoying is that they don't just do one thing in one way all across time and space. Each dust grain is slightly unique. It has slightly different elements in slightly different combinations in slightly different arrangements. And sometimes there's a little bit of dust in a particular line of sight or around a particular thing we're observing.

And sometimes there's a lot. And what the grains are made of and how they're arranged affects what the dust grain does to the light. So if you imagine some light source, like from a distant star, and it passes through the interstellar medium. No, it's not going to encounter a lot of dust. But there's a lot of interstellar medium between us and a distant star. So overall, it does encounter enough dust to make things annoying. And what happens to that light? Depends on how much dust there is, how dense the dust is, what the dust is made of and what the wavelength of light is. So sometimes certain wavelengths of light just get scattered instead of continuing to go forward to the earth and to our telescopes where we can study it. It just goes off in some random direction. It just like the dust grain and it's a bit of light and then spits it out in some random direction. And that's not useful at all. Some wavelengths of light, depending on what the dust is made of and how much of it is, just get absorbed.

They were looking at, oh, we're trying to study the particular wavelength of light from some sort of molecular emission line from the region around a black hole. And it's all really interesting. Oh, but we can't because that light got absorbed by a dust cloud. It just got eaten up and spit out in a completely different wavelength that we don't have a telescope for or we're not looking at right now. So... too bad you don't get to see it and then sometimes that re-emission of light happens in our direction and so we think we're looking at one kind of light we're like oh wow look at this wavelength of light coming from this object isn't that weird oh it turns out that wavelength of light isn't coming from the object itself it's coming from the dust cloud which absorbs some other random wavelength of light that we were not paying attention to at this moment and instead spitting out at this wavelength that we are paying attention to. And so it makes it look like the source that we're the black hole, the neutron star, the star, the galaxy, whatever, the thing that we care about, which is definitely not dust.

The thing that we care about is emitting a certain kind of light when actually it's not. And then you think, okay, okay, okay, fine. There's dust in the universe. It does weird things to light. Okay, let's model it out. Let's just say, okay, let's look at dust in the laboratory. Let's see how it affects light. And then we know the mapping. We can, like, subtract the dust every time we make a measurement. Nope. Because one clump of dust might have one behavior, and another clump of dust will have another behavior. Looking at one kind of distant object might go through certain kinds and densities of dust clouds. While looking at a totally different object, we'll have totally different dust grains with totally different compositions at totally different densities. And it does a different thing to the light. So everywhere we look on the sky, every line of sight you can pick, and then every target from Proximus and Tauri to the cosmic microwave background and everything in between, you're going to encounter different kinds of dust.

And the different kinds of dust and different varieties and densities of dust will affect everything. light in different ways so you can't just make one blanket this is what dust does and subtract that out to get at what the source whatever you're looking at what that's actually doing you don't get to do that and like i said yeah there's not a lot of dust one percent of the interstellar medium which is basically nothing and one percent of basically nothing is even less than basically nothing by density dust is barely there but there's a lot of space in space which is why we call it space So by volume, there's tremendous amounts of dust. If we're looking at something a thousand light years away, that light has to travel through a thousand light years of dust and different kinds of dust and different kinds of densities along different lines of sight. A typical galaxy like the Milky Way contains roughly 100 million solar masses of dust. If you gathered up all the dust in the Milky Way in one spot, you could build 100 million suns, which wouldn't work very well as a sun, but that's a different story.

Oh! Oh, I didn't mention the ice mantles. Yes, ice mantles. Imagine a tiny microscopic dust grain. Thousandth of a millimeter across for a really big one. These dust grains act as tiny little cores. And they... Other elements that are not dust... glue onto the surfaces of the dust grains. And we call these ices. Anything that's really volatile, anything that can evaporate really easily the moment you even look at it, we call it an ice. So like water is an ice. Carbon dioxide is an ice. Methane is an ice. Ammonia is an ice. No, these are not chemistry labels. These are astronomy labels. We call Uranus and Neptune the ice giants because they're made of a lot of water and carbon dioxide and methane and ammonia. For example, these ices, these other molecules, water, carbon dioxide, they can glue on to the dust grain and they make what astronomers call a mantle. Just like the Earth has a core, a really, really dense core, and then a really, really thick mantle around it. These little dust grains act as a little core with little ice shells around them.

And those ice mantles or ice shells can absorb UV radiation from starlight, which out in the middle of nowhere is really, really weak, but it never shuts off. So over the course of a few million years, you start to absorb. You should have packed your SPF. I tried to warn you, okay? There's a lot of UV radiation out there. But that UV radiation provides the energy for really bizarre and complex chemistry. feel free to ask me about that. And I can do a whole separate episode on the chemistry of deep space. This is the kind of chemistry that you're not going to get in a terrestrial laboratory. This is the kind of chemistry you can only get when you combine extremely low temperatures, like nearly absolute zero, no pressure at all, and high energy radiation. So these UV rays strike the ice mantles and which are really good at absorbing UV radiation. They receive the energy and then they transform and they produce all sorts of weird organic compounds and molecules that then live on top of the ice mantle, like a dust crust, if you will.

So you get dust grains with ice mantles with weird molecules scattering on top, which makes everything even more complex. And it's not like this dust can just go away. If you get out your interstellar vacuum cleaner, and I'm thinking of that scene from Spaceballs here, and if you sucked up all the interstellar dust, imagine you just took a broom between here and the nearest stars and you got rid of all the dust. Well, just like in your house, there's more dust around the corner. Dust is made of stuff fused inside of heavy stars, and heavy stars are like always dying dust. Giant stars shedding their outer layers to become planetary nebula, supernova going off. All these stars are constantly ejecting and emitting new sources of dust that pollute the interstellar ways. Oh, and sometimes dust can just form on its own. Like you have a little few molecules over here and a few molecules over there. And yeah, space is big, but you give them enough time. Eventually they meet, they stick together and you get more dust.

And it just messes everything up. It means that no observation in astronomy is raw. Every single photon we receive from the depths, from the nearest star to the cosmic microwave background, has been filtered through who knows how much dust. In general, the dust dims. It makes things less bright than they genuinely are. In general, it makes things look redder. than they are. Preferentially blue light gets scattered off of dust better than red light, which is exactly what happens in our own atmosphere. But it's not because of dust in our atmosphere, it's because of the nitrogen molecules. Blue light gets scattered, red light goes through. And so when we're looking at something, it looks redder than it should because all the blue light has gone away. And it scatters light so it makes things look fuzzier than they should. It can be said that the history of astronomical discoveries is A, not realizing just how much dust was in the way of something, and then B, slowly figuring it out the hard way.

Where we thought we made an impressive discovery, we thought we had a solid measurement, oh, turns out there's dust. And then we need to account for all the dust. We need to figure out where the dust is, how much of it there is, and then we can work our way backwards to our real result. If you don't properly account for the dust, you're going to be wrong. This is one of the reasons, if not the reason, that measurements of stellar distances prior to 1930 or so were way off because we just assumed that space was clean and that the light we got from distant objects was pure and represented the light that it actually emitted. Turns out that the actual light from the objects was brighter and bluer than what we were seeing. And once we made those corrections, we were finally able to get accurate measurements. Pretty much every single debate and discussion in astronomy and cosmology somehow involves dust. See a faint red galaxy? Well, are you sure it's a faint red galaxy? Or is it a bright blue galaxy surrounded by dust? See a distant supernova? Well, are you sure you know how distant it is? Is it actually closer? But it looks further away because of the dust? I need to model the dust is the never-ending headache of every astronomer.

We do have a lot of strategies. We're not working in the blind here. We do have a lot of strategies for dealing with dust. We've known about it for over 100 years. We've known about its effects and what it can do. We have many strategies for navigating dust. One is to switch to other wavelengths of light that we know pass through dust, like radio waves don't really talk to dust. Infrared radiation doesn't really talk to dust. This is why we developed the James Webb Space Telescope. and made it an infrared telescope so we could look through the dust. Also, we can use the fact that dust does different things at different wavelengths. Sometimes it will absorb, sometimes it will just scatter, sometimes it will do something else at different wavelengths. We can use that fact if we're looking at a source and it's big enough and we can have different lines of sight to that same source and we look over here in this corner and then that corner and then that corner and then that corner. We look for the things that are different.

We can say, well, that's the dust. And then the stuff that's the same is coming from the source. Like if I look at one star, the star should be the same from edge to edge. If I look at the cosmic microwave background, this is exactly how we model out the dust in the cosmic microwave background. Because we know the properties of how it was emitted. We can derive that from theory. We know that the cosmic microwave background should look the same wavelength to wavelength to wavelength. because that's the process that made it. And then we can pick out all the bits that are different from wavelength to wavelength to wavelength. We say that's the dust and we throw it out. There's, trust me, there's a lot more work. There are thousands, tens of thousands of pages of astronomical literature on the subject of how to do this right. And make sure you're just not fooling yourself or throwing out good data and all that. And make sure you're still not contaminated. All of that. But it's a headache. It's a real, real headache that takes tens of thousands of literature and decades of work in serious study.

People have devoted their entire careers to dust. You know, now that I think about it, I don't think this apology is going so well. So maybe you can make it better by contributing to Patreon. That's patreon.com slash pmsutter. Where you... can show your appreciation and your apologetic stance towards dust and also contribute to the show, that's patreon.com slash p-m-s-u-t-t-e-r. But you know what? Now that I think about it, this dust that's so ever-present and annoying and pervasive and aggravating, it's got to be kind of powerful, right? You know, in a dusty sort of way. Not every substance gets to play a critical role in so much of observational astronomy. It's to the point where the entire scientific discipline could probably just be called dust mitigation strategies. I'm not saying that dust is a good thing, but at least it's playing on the galactic stage. We care more about dust than, I don't know, black holes when it comes to day-to-day astronomy. That's pretty impressive. And I'll be honest, dust...

causes more than migraines. It causes stars. I mean, it's true. Like, if you take a random gas cloud, in order to make a star out of it, you have to compress it. You have to shrink it. You have to make it smaller. But that process of compression increases the temperature of the gas cloud, and then a hot gas cloud isn't going to want to compress anymore. If you want to compress a gas cloud, you have to cool it off, and dust emits light really, really effectively because it has all sorts of nooks and crannies. so many different atoms and so many different configurations, they're really, really good at emitting their own light. They're really good at dumping heat out of a gas cloud, which allows it to shrink down further, which allows it to make stars. And hey, you know, every gas cloud that collapses to form a planetary system in a star, you know, comes with a bunch of molecules, but UV radiation can break apart molecules and But the dust can shield that with their ice mantles, with their ice shields.

They can absorb, they can take the hits from UV radiation and protecting molecular bonds. Without the dust, galaxies would be totally unrecognizable. And hey, dust makes even more basic molecules happen. The most common molecule is just H2. It's two hydrogen atoms bound together. H2 is absolutely critical. It's the building block of molecular clouds, hence the name. Those are the fundamental nurseries for stars. But H2 doesn't just form on its own in the middle of space. It prefers to form on the icy surfaces of dust grains. And speaking of those icy surfaces, or ice mantles if you prefer, which you should, the UV rays that do hit those surfaces energize and transform those molecules into longer, more complex chains like amino acids, sugars, nucleobase precursors. Oh, and without dust, planets couldn't form. If you have a solar nebula, just a cloud of gas and dust around a solar system, it's the dust grains that cling together first through static forces, and those are the first rung of the ladder to building centimeter-sized pebbles and onto protoplanets and planetesimals and then planets.

Without dust grains gluing together, you can't get the process of planetary formation going. And flows of dust carry complex molecules across the galaxy. These dust grains are born in dead stars. They get blown by interstellar winds. They combine in interesting ways in the depths of space with that exotic chemistry happening at low temperatures and low pressures. And then when the dust grains trigger star formation and then planetary formation, they ride along with everything. They're a part of the formation process. And they ride along with comets as they impact young planets and And all the while, those little microscopic chemistry labs are creating the building blocks of light. And it's the dust that ensures that all those building blocks end up in the right place at the right time. No, no, no, no, no, no. No, this can't be true. If dust didn't exist, then stars, planets, life wouldn't exist. We wouldn't be here if it weren't for dust. We owe our lives. To dust? I'm going to need a minute.

And probably a better apology. Look, most of the dust you encounter in your daily life is terrestrial, even biological, local. Bits of skin, bits of critters that eat bits of skin, and lots of other things that you don't really want to think about too much. Some of the dust in your room comes from across the globe. Some of it is ash from a distant volcano or sand from the Sahara. And some of it, just a tiny portion, comes from outer space. Every year, about 40,000 tons of extraterrestrial material rains on the Earth. Most of it is micrometeoroids. They're bits of dust, so small you couldn't even see it. It just drifts down, contributing to the global dust population. Find the nearest dusty bookshelf. Swipe your finger on it. Think of all the countless grains on your fingertip. Some of them. Just some of them. traveled here for thousands of light years. And some of them even predate the solar system itself. We've identified individual dust grains that are more than 7 billion years old, created in stellar systems that no longer exist.

So right there, right at your fingertips, is the stuff that makes you possible. And some of it is the oldest thing you could possibly hold in your hand. I'm sorry, Dust. I won't be mad at you anymore. Thanks to atscruffminds and David S. for the questions that led to today's episode. Thank you for all the questions. Keep sending them to askaspaceman at gmail.com or the website askaspaceman.com. Please keep the reviews coming on your favorite podcasting platform. It helps the show visibility. If you can, I would appreciate a contribution to Patreon. That's patreon.com slash pmsutter. I'd like to thank my top contributors this month. They are Justin G, Chris L, Alberto M, Duncan M, Corey D, Michael P, Nyla, Sam R, Joshua, Scott M, Rob H, Scott M, Lewis M, John W, Alexis, Gilbert M, Rob W, Jessica M, Jules R, Jim L, David S, Scott R, Heather, Mike S, Pete H, Steve S, Lisa R, Kevin B, Eileen G, Stephen W, Dev A, Michael J, Philip L, and Stephen B. It is everyone who contributes that makes this show possible, but the most important thing is your questions and your time.

I appreciate all of it, letting me share these wonderful stories about the universe, even if they involve dust, which now I begrudgingly accept. I'll see you next time for more Complete Knowledge of Time and Space.

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