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When you consider the hazards of spaceflight, it’s hard to get worked up about dust bunnies. And yet, atmospheric dust is going to be one of the biggest problems astronauts will face when they reach the surface of other worlds. Where does this dust come from, and what does it tell us about the history of other worlds, and what can we do to mitigate the health risks?
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This episode is sponsored by: Swinburne Astronomy Online, 8th Light, Cleancoders.com
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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest-running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser Cain: Astronomy Cast Episode 326: Atmosphere Dust. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos. We help you understand not only what we know but how we know what we know. My name is Fraser Cain; I’m the publisher of Universe Today and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and director of CosmoQuest. Hey, Pamela. How you doing?
Pamela Gay: I’m doing well. How are you doing today?
Fraser Cain: Good. Last week we were complaining about cold weather but now it’s been relatively balmy throughout the west coast.
Pamela Gay: I hate you with love.
Fraser Cain: It’s great. It’s great.
Pamela Gay: I totally hate you with love. Yeah, no. We have four or five – it’s going to be a white Christmas here unless something radical and unpredicted happens.
Fraser Cain: So we get a lot of questions from people about our questions show, which is what we used to do back in the day. We would do our regular episode and then we would do a question show and people wondered, “How come you don’t do the question show?” We do the question show every week live on Google+ so if you ever want to join us and ask your questions about space and astronomy, just watch us live on Google+. We start at 12:00 Pacific, 3:00 Eastern.
We take about half an hour to do the show, which we’re doing right now, but then we also take your questions about space and astronomy and handle them at the end. So people wondering about that, it still happens.
Pamela Gay: Now, it’s even more timely so no more waiting for us to air your question. Just be on air with us.
Fraser Cain: Just be on air with us and join us and see what we look like and ask your questions. So we still do that. The other question people have been asking is whatever happened to the Weekly Space Hangout audio feed? How come it’s not in with Astronomy Cast? We got a lot of complaints with people that it was polluting the feed; it was too much. I know a lot of people still really like it so it’s actually in the 365 Days of Astronomy feed and there’s lots of other good stuff in that feed, as well. So it’s a great reason to subscribe. You’ll get both the Weekly Space Hangout, plus all of the great episodes that normally go into the 365 so that’s where it is.
Pamela Gay: Cheap astro learning space. Oh, there’s so many good things. I’ve been doing science fiction stories. Going ahead and doing narration for that.
Fraser Cain: Yeah, so there’s ton of content in the 365 feed so if you’re wondering what happened to the Weekly Space Hangout, which is still happening every week, you can still get it from there. So much space content.
Female Speaker: This episode of Astronomy Cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information, visit them online at www.8thlight.com. Just remember that’s www.8thlight.com. Drop them a note. 8th Light. Software is their craft.
Fraser Cain: So when you consider the hazards of space flight, it’s hard to get worked up about dust bunnies, and yet, atmospheric dust is going to be one of the biggest problems astronauts will face when they reach the surface of other worlds. Where does this dust come from and why does it tell us about the history of other worlds and what can we do to mitigate the health risks? In my house we call them dust dragons. They’re substantial collections of dust and have achieved sentience and —
Pamela Gay: Wow.
Fraser Cain: – require a constant battle. Yeah, but so you put atmospheric dust on the list and I know it’s – I mean we deal with these dust storms here on Earth, which can clog the skies and are pretty fantastic but on other worlds they’re going to be big problems.
Pamela Gay: Well, and it’s a completely different kind of problem, depending on that the type of dust it is, what atmospheric height it’s at. There’s so many different things to consider and the reason I rolled out of bed this morning and was like, “Today we’re discussing atmospheric dust!” is because there’s actually this upcoming, dusty inundation for spacecraft, I guess. We have the LADEE mission that’s currently up and happily orbiting the moon. At least, if you feel like anthropomorphizing spacecraft, it’s happily orbiting the moon and it just got this great take on Chang’e, the Chinese rover that landed and probably put a bunch of dust up into the atmosphere.
Then we have the MAVEN mission on its way to Mars and it’s going to arrive shortly after the Martian atmosphere gets to deal with a comet racing past. All of these spacecraft are both getting to look at these zero point of what atmospheres normally look like and then getting to see what happens when they get polluted with all kinds of stuff.
Fraser Cain: Rosetta. Gonna be harpooning a comet next year – later this year. Well, 2014.
Pamela Gay: Yeah.
Fraser Cain: We’re almost there. This is crazy. Okay. Anyway, so right. They’re having to deal with this dust and I think it’s one of these hazards that most people don’t think about but the planners really have to consider it.
Pamela Gay: The other place that this atmosphere dust is really gonna nail us over time is so we have to plan missions around it; we have to worry about solar storms. We have to worry about measuring it but if you’ve ever gotten sand or dirt in your clothing, you know that sometimes it makes you contemplate getting naked in public because it’s really irritating. So as we’re planning to put people on the moon and on Mars, we need to figure out how to mitigate the effects of dust.
Fraser Cain: Okay, so let’s – here on Earth how do we experience this dust?
Pamela Gay: Here on Earth, dust comes in the, “Oh, wow. The nearby desert is attacking where I live due to high-speed winds.” So we’ve seen massive effects in Beijing where the not pollution – which is another form of dust – but where the nearby deserts have blown in. We’ve seen this in Tucson and Phoenix with massive dust storms rolling into the cities. So this is literally the case of wind sweeping up the dust and carrying it along as a wall that can clog your lungs, clog your machinery, get into your clothes, get into your cars and it’s a wreck.
The other way we experience here on Earth is volcanism. Several years ago there was the Islandic volcano, which shall not be pronounced and it threw dust, in this case pulverized pumice stone and silicon bits, kilometers up into the air’s atmosphere where there was potential danger to aircrafts that would get their windshields scratched to the point that they could no longer be seen through and all sorts of danger to the engines on these aircrafts, so, well, basically all air flight was shut down going into Europe for a while.
Fraser Cain: We had Mount St. Helens back in the 1980s and there was a layer of dust-like snow on everything. All the cars, all the trees, all the house. Yeah, and it —
Pamela Gay: Yeah, I was living as far south as Los Angeles basin and we experienced Mount St. Helens all the way down there, as well.
Fraser Cain: Yeah, so we got a sense of what this dust looks like. We’ve got these wind processes that whip it up into these clouds. If you’ve ever seen pictures of these approaching dust storms, they’re pretty terrifying. So then let’s look at a nearby location that doesn’t have wind but the moon is going to have dust, right?
Pamela Gay: Right. With the moon, it’s actually one of the most bizarre situations where the astronauts who were there are able to see atmospheric dust and we use the word “atmospheric” loosely here. We’re able to see dust out on the horizon and while they knew that during the process of landing they stirred up dust, this was still more than they expected and Earthbound observers have periodically been able to see transient phenomena that could only really be explained as either things that weren’t actually being observed or as dust suspended in the atmosphere.
With a lot of mathematical modeling, it’s been realized that high-energy photons coming from the sun – so X-rays, ultraviolet light – heating the dust on the moon actually has the energy necessary to strip electrons off of some of these molecules and, as you strip enough electrons off the molecules, you’re getting more and more and more positively charged dust until the dust actually starts repelling itself and these individual grains of dust are capable of suddenly floating up above the lunar surface. So you end up with an electrostatically suspended layer of dust above the moon.
Fraser Cain: Is this somewhat related to when we see these great, big volcanic explosions? These eruptions? They always have these lightning bolts going through them, right? Because of the dust just rubbing together sets a huge static electricity?
Pamela Gay: The physics behind these two things is completely different. In this case —
Fraser Cain: Oh, never mind, then.
Pamela Gay: Yeah. So with the dust on the moon, what we’re actually looking at in many ways is nature’s way of saying, “Hey, Einstein got it right,” because when you shine the correct color of light onto something, the electrons fly away. This is the photoelectric effect. So the photoelectric effect, writ large on the surface of the moon with sunlight being involved, will cause charged particles – in this case, dust grains – to get so charged that they repel themselves away from the surface. The electromagnetic effect, its force overcomes that of gravity.
Fraser Cain: Now this dust on the moon is bad news.
Pamela Gay: Yes.
Fraser Cain: I mean it is really trouble.
Pamela Gay: Well, it’s generally dust made of glass and one of the most traumatizing yet humorous posters I’ve ever seen at a science conference was being presented about experiments that are being done where they actually will go to slaughtering yards where pigs are being slaughtered and get the freshly removed skin from pigs and use artificial lunar dust.
So they look at the chemical composition of lunar dust and recreate it in the laboratory, take this dust with them to a slaughter yard, take the pig skin of the freshly dead pig and then, using carefully measured, precise pressure and pressure over time – so how long they exert the pressure – they will grind the dust into the pig’s skin with different fabrics to figure out which fabric causes the least abrasion to occur and try and understand what do we need to make that layer of fabric between the astronaut and his space suit made out of so that, well, those future astronauts get the least abrasion to their skin.
Fraser Cain: Yeah, if you read the reports that came back from Neil Armstrong and Buzz Aldrin and the other astronauts, this dust – as they carried it back into the spacecraft, it got everywhere. It was not this sort of nice, smooth sand that we’re so used to. As you said, it’s little pieces of glass that the bombarding of micrometeorites over the billions of years have just chewed up the landscape into this field of glassy dust. They were breathing it; it was getting in their lungs. This is going to be a big problem.
Pamela Gay: This stuff makes asbestos look friendly, at a certain layer, and you can’t just use filters to get rid of lunar dust because it’s so tiny, in some cases. When we’re looking at the dust on places like the moon and Mars, the dust doesn’t settle out of the atmosphere in as permanent a way as it does here on Earth. Here on Earth, you get atmosphere dust, whether it be from some volcano going off, whether it be from, well, weather stirring it up out of a desert.
Whatever the source, and we have to remember forest fires, their soot is a form of dust, pollution is a form of dust, all of these different forms of dust have the opportunity to eventually settle into water. Most of the surface of the Earth is made up of water and when the water and the dust mix, well the dust is removed. On the moon, it just moves around and the constant impact of micro meteors and larger meteors is generating new dust; same is true on Mars. So there’s nothing to get rid of the dust; it just gets blown around, settles back down. Gets blown around some more, gets settled back down. It’s a never-ending problem.
Fraser Cain: So let’s look at some other planets, then, like Mars for example. It’s classic for its dust storms. These global dust storms that can just encase the entire planet in this red mist.
Pamela Gay: In this case, the composition’s slightly different; you have more iron oxides, giving Mars its awesome red color. So this dust is dangerous in slightly different ways. What’s amazing is these giant dust storms that you see essentially enshrouding the entire world, we were extremely worried when we first started sending spacecraft with solar panels to Mars that this dust would have the effect of killing the rovers off rather quickly. As we learned with spirit and opportunity, well first of all, what the wind brings it also takes away.
While they did end up covered in dust, the wind would periodically clean them off nice and neat. The dust also isn’t as thick as we might have thought. It turns out that globally, that dust that gets chewed up into the atmosphere is only about three microns thick. So that’s three strands of hair, basically, thick if you take all the dust that gets put into the atmosphere and settle it all back out across the surface of the world.
Fraser Cain: It doesn’t require a lot of wind speed to get that dust moving. I mean I think when you see it in movies and television shows, it’s like a horrible windstorm with clogging dust and everyone’s in great danger but the reality is that you barely feel it. The visibility would be reduced but it would be perfectly safe, I think, to stand out in that windstorm – the dust storm – and go about your business, so it’s not as bad as I think we would expect.
Pamela Gay: With Mars, the gravity is significantly lower than it is here on Earth. That means that doesn’t take as much force to get the dust to overcome gravity, essentially. The other side of this is because of the Martian atmosphere is so much thinner than the atmosphere here on Earth, that dust stays in the atmosphere longer here on Earth. So you get these sudden dust storms blowing up and almost as quickly they settle back down. So that’s neat. Here, it can take a couple of years for dust from a volcano to settle out of the atmosphere.
Fraser Cain: I think it’s also important to note that the dust on Mars is not as dangerous as the stuff we’ve talked about on the moon because you’ve got this wind action that’s blowing this dust around and eroding it and smoothing it and you’re going to get dust everywhere but it’s not going to be this same, tiny pieces of glass getting into your lungs.
Pamela Gay: Yeah. It’s much more a thing about the wind version of rounded rocks on the beach. This constant interaction and, like I said, the composition’s just not the same. It’s not made out of broken up glasses. It’s made up of completely different sets of minerals.
Fraser Cain: Yeah. I think about the moon. Imagine a – someone took a big piece of volcanic glass. You know, this really nice, basalt glass and just smashed it up and then – just into a powder. Ugh, what a nightmare that would be. Okay, so then we’ve talked about Mars a bit and we’ve talked about Earth. Even asteroids, this might be an issue, right?
Pamela Gay: Yeah. With asteroids, it’s a different type of issue and we’re still trying to figure it out. In general, asteroids, they don’t have a whole lot of mass; that means they don’t have a whole lot of gravity. So when you shoot things at asteroids or when the universe shoots things at asteroids for us, you’d expect the impact to, for the most part, send things into a gravitationally escaping motion. Most of that dust isn’t going to settle straight back down to the asteroid itself but when we look at asteroids we see in higher numbers than were expected boulders and boulders, just like dust, you’d expect to have escape velocities after an impact.
What it appears is happening is over time the sunlight hitting an asteroid followed by that same asteroid going into shadow is heating and cooling and heating and cooling and heating and cooling over and over and over until the rock breaks. So you can end up with thermal conditions leading to things fragmenting, leading to dust being created. It’s a completely different process, so when we land on asteroids we’re not going to have the same dust issues that we have on the moon. They simply aren’t going to hold on to as much dust. We still are going to have dust that we have to worry about.
Fraser Cain: Hmm, and I know that a lot of comets are comprised of high amount of both rock and ice. You get those interactions with that heating and cooling that’s going on that’s going to be creating another particular set of dust.
Pamela Gay: You also end up with different chemical reactions occurring on the surface of the ices that can lead to larger and larger molecules being found. Essentially, the simple definition of dust is it’s a molecule of something that doesn’t melt when exposed to normal amounts of sunlight. So you have chemical reactions occurring that build these larger and larger molecules and this can occur with sunlight hitting the surface of the ice, creating organics through different chemical reactions.
Then, when the ice surrounding these different molecules gets sublimated, melts straight from solid to gas, the dust ends up getting shot away from the surface of the comet, creating tails that are made out of stuff as well as just Plain-Jane gases.
Fraser Cain: Then, of course as we have these meteor showers, this is us in many cases, getting hit by these microscopic pieces of dust that emanated from the comets and asteroids.
Pamela Gay: Exactly. Exactly.
Fraser Cain: Yeah, so then I guess as researchers are looking at the dust, as they’re trying to study it – I know that the curiosity rover’s designed to look out through the atmosphere of Mars – what kind of information are they trying to glean from the dust?
Pamela Gay: Well, at a certain level there’s the – well, dust, it changes the color of light hitting the surface of a world. Dust preferentially scatters light that is at shorter wavelengths, creating a reddening of the light that gets through. If we can get enough dust in the Earth’s atmosphere that will have the effect of cooling our world. We need a good, giant volcano to go off and spew dust into our atmosphere to help cool things down. There’s people who’ve tried to figure out can we artificially generate the dust that’s needed. We have to worry about the biological effects as human beings inadvertently end up breathing in lunar dust, Martian dust that gets through into future human settlements.
How bad of an effect is that going to have on our lungs? We’ve learned a lot from cigarettes; we’ve learned a lot from pollution. We’ve learned a lot even from people who are dealing with nanoparticles. Well, there is the potential for a lot of disease in the future so we have to figure that out. There’s so many different reasons to worry about dust; both the good effects of cooling off worlds and the bad effects of potentially killing humans. So we’re trying to learn all of that as we study the dust.
Fraser Cain: Yeah, but you brought up this concept of geoengineering; that we could release all this dust into the atmosphere and it could cool down the planet as a way to prevent global warming. It just sounds like a horrible idea with – you know? You get this situation where it might be the only idea that you’ve got left, apart from the world overheating, so —
Pamela Gay: In the grand scheme of things, ideas of launching a bazillion small satellites with reflectors, I’d rather have dust in our upper atmosphere. We’ve at least experienced that enough times over human history to understand how long it takes for volcanic dust and similar composition dust to settle back out of the atmosphere. It’s almost good to have reversible phenomena.
Fraser Cain: Right. Yeah. Now, I don’t want to put you on the spot. Is there dust on Venus?
Pamela Gay: There should be but I don’t know what frequency the sulfuric acid rainstorms occur at, so I’m not sure how – I’m not sure if the phase change frequency where you have dust that’s created through various effects becoming mud or clay or getting re-dissolved into the soils.
Fraser Cain: Yeah, and the atmosphere is —
Pamela Gay: Gross?
Fraser Cain: – 93 times more dense – like the surface pressure than Earth’s, so I wonder would things get more suspended? Would they be like a fluid? Like if you’re on the surface of Venus it’s like you’re a kilometer underneath the ocean.
Pamela Gay: Well, so there’s both massive winds and a much thicker atmosphere so that means that any dust that was able to survive the acidic nature of the atmosphere could be suspended for months and months and months at a time.
Fraser Cain: Another place that’s really fascinating is Titan. When you think about Titan has got about double the density of our atmosphere; double the surface pressure on the surface but it’s got this terrible cold and yet it rains hydrocarbons.
Pamela Gay: So here, there is the potential for all sorts of organic molecules to bind together to form dust and in this case, with the frequent rainstorms, you have to wonder how much of it’s going to be the equivalent of dust that gets trapped up in the Earth’s rainstorms. When it rains, you often get pollutants tied in with the rains as well or sandy dust tied in with the raindrops as well. So yes, there’s dust on Titan but you also have rainstorms. So again, you have to wonder is it nice, dry dust or nice, methane-wet dust, in this case.
Fraser Cain: What about Io? I mean it’s amazing how each of these worlds it just takes a different form. Think about Io with the volcanic plumes that fly up of the surface of the moon and rain back down.
Pamela Gay: So you’re, again, going to have the volcanic dust. In this case, also, just escaping away from Io, so you have that helping to add to the dusty rings that are around Jupiter and this is part of what you see with Enceladus orbiting Saturn where its ice geysers are helping to contribute to the rings of Saturn.
Fraser Cain: And on Europa.
Pamela Gay: And on Europa.
Fraser Cain: You hear that? Brand new research, right?
Pamela Gay: Yeah, I did. Yeah.
Fraser Cain: That they found ice geysers coming out of Europa.
Pamela Gay: I haven’t seen results on if those are contributing to Jupiter’s rings. I know Enceladus is.
Fraser Cain: Right. No, no. Absolutely. We don’t know if it’s actually welling up from below the surface like the actual ocean underneath Europa —
Pamela Gay: Right.
Fraser Cain: – or whether it’s closer to the surface and it’s just some kind of grinding effect but there is water ice emanating from Europa and going into the atmosphere. That is just like another reason to get to Europa and put spacecraft down. I cannot wait. So, cool. Okay, well thank you very much, Pamela.
Pamela Gay: It’s my pleasure.
Fraser Cain: Thanks for listening to Astronomy Cast, a nonprofit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com. Tweet us @AstronomyCast. Like us on Facebook or Circle us on Google+. We record our show live on Google+ every Monday at 12:00 P.M. Pacific, 3:00 P.M. Eastern or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at cosmoquest.org.
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Duration: 28 minutes
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