Join us as we try to finish the interrupted episode Coming Home from Mars!
Landing on the surface of Mars is very difficult. In fact, it’s probably the toughest planet to land on in the whole Solar System. Today we’ll talk about what it’s going to take to get to and return from Mars!
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Fraser Cain: Astronomy Cast Episode 430: Getting To and From Mars
Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where 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, the director of CosmoQuest.
Hey, Pamela. How are you doin’?
Dr. Pamela Gay: I’m doin’ well. How are you doin’, Fraser?
Fraser Cain: I am doing great. It’s wet here. I’m really looking forward to summer again.
Dr. Pamela Gay: Yeah.
Fraser Cain: But apart from that, things are going great.
Dr. Pamela Gay: It’s kind of wet and gross here as well but that’s kind of just the way things are.
Fraser Cain: And for those of you listening, it is, of course, the day after Thanksgiving. This is the day we’re recording it anyway. I have no idea.
Did you have a good Thanksgiving?
Dr. Pamela Gay: We are very focused on cleaning the house around here. So, being a Canadian and someone who knows far too much American history, Thanksgiving has become a day for cleaning.
Fraser Cain: Cleansgiving, yeah.
Alright, so we’re going to continue our Mars journey.
So landing on the surface of Mars is very difficult. In fact, it’s probably the toughest planet to land on in the whole Solar System. Today we’ll talk about what it’s going to take to get to and from the red planet.
Alright. So let’s set the stage here. We’ve talked a bit about what it’s going to take to live on Mars but the reality is, is that getting to and from Mars is borderline suicidal. Right? When you think about – I just did a video about this – that we’re at 53 percent success rate sending spacecraft to Mars. That’s it. That half of any – Half of the pathetic space – intelligent space metal – you send to Mars is going to die. And so far, it’s only been space metal but, you know –
Dr. Pamela Gay: Imagine the kind of memorials there’s going to be some day. There’s going to be the “Here’s the happy place where Opportunity came to rest”, “Here is the sandpit of death, where Spirit came to rest.”
Fraser Cain: Right, right.
Dr. Pamela Gay: And there’s all the varying forms of crumpled, destroyed, embedded in the soil and everything in between, scattered across the surface.
Fraser Cain: Yeah. We’ve got sort of the Schiaparelli II crater on the surface of Mars.
Dr. Pamela Gay: Yeah.
Fraser Cain: So, needless to say, landing on Mars is a very dangerous thing.
So, let’s kind of roll the tape backwards here. What does it take to get to Mars?
Dr. Pamela Gay: So, I’m just going to lay out as a ground rule, we acknowledge there are issues with radiation. We don’t know how to solve them.
Fraser Cain: Right.
Dr. Pamela Gay: We’re going to assume that someone wiser, or at least more imaginative than you and I, has solved this problem before we attempt to send humans to Mars.
Fraser Cain: Right. Say it’s very safe; it’s very safe in our imagination now.
Dr. Pamela Gay: So we’re going to ignore the radiation problem.
Fraser Cain: Yeah, yeah.
Dr. Pamela Gay: Okay.
So, ignoring the radiation problem that we don’t know how to solve, the first problem is you have to get out of the gravity well of the planet, Earth.
Fraser Cain: And it’s big.
Dr. Pamela Gay: It’s big.
Fraser Cain: Yep.
Dr. Pamela Gay: It’s – Yeah, you need more than 10 kilometers per second. And the reason I’m framing it that way is you can sort of imagine: You launch part of your spacecraft to low-Earth orbit; you launch more of your spacecraft to low-Earth orbit; you join the humans with the spacecraft in low-Earth orbit and then you escape low-Earth orbit.
Fraser Cain: 10 kilometers per second; that’s about 28,000 kilometers per hour, which requires a – really, a bomb that you sit on top of and it explodes a little more slowly than a bomb might normally. The point being, it’s a lot of energy to get to – to break free of the Earth’s gravity.
Dr. Pamela Gay: So, once you’re in low-Earth orbit, you need to get yourself going about 4.3 kilometers per second to get from low-Earth orbit, which is where the ISS is – where we currently are very skilled at putting human beings. So, add in a Delta-v, a change in velocity, of 4.3 kilometers per second and now you can be on your way to Mars via a Hohmann transfer orbit.
Fraser Cain: Right. So you’ve taken your low-Earth orbit; you’re going your 10 kilometers per second. You then fire your thrusters at an additional – What was it? 4.3?
Dr. Pamela Gay: It’s 4.3.
Fraser Cain: Right. So, now you’ve made a transfer orbit and now you do this great, long, slow adjustment. So you essentially are raising your orbit to the point that it eventually intersects the orbit of Mars.
Dr. Pamela Gay: So the whole idea is orbits are ellipses and a circle is a very special kind of ellipse that happens to be the same radius everywhere you look. Most of the time, an ellipse is closer to the main bodies of the sun on one side, further away on the other.
And in this particular scenario, what we’re looking at is: Earth is the closest point to the sun on this orbit; Mars is the furthest point from the sun on the orbit; and you time things just right so that, when you leave Earth and get all the way out to Mars’ orbit, Mars happens to be at just the right place in its orbit so that you intercept Mars.
Fraser Cain: Right.
Dr. Pamela Gay: If you screw up, there’s no planet there; mission’s kind of a dud.
Fraser Cain: Okay. And that’s not the hardest part. The hardest part is what you do when you get to Mars.
Dr. Pamela Gay: So, with a Hohmann transfer, there’s two different things that you have to do. First, you have to adjust your velocity to get away from the planet, Earth. So here, you’re accelerating things to put yourself out further from the sun in the Earth’s orbit when you get to the other side of the sun. Now, once you’re there, you have to match Mars’ orbit, so you need to adjust your velocity again. So this is the Mars transfer orbit and here, we’re looking at about 9 kilometers per second for getting yourself in orbit around Mars. Sorry – .9 kilometers per second.
And that’s not too bad in the grand scheme of things but now you’re just orbiting Mars. And orbiting Mars is all well and good but we have this deadly idea that we want to put humans on the surface of Mars. Now, putting them on the surface of, like, Phobos or Deimos – really good, really easy; you’re looking at way less than a kilometer per second Delta-v, nice friendly surface. You weigh, like, a few hundred sheets of paper. It’s all good.
Surface of Mars, we’re looking at probable death.
Fraser Cain: Right.
So you just mentioned, sort of, one way to go about it, right? Which is that you arrive at Mars on a trajectory that allows you to then fire your thrusters and end up in some kind of elliptical or, eventually, circular orbit going around Mars.
The other option is: Go for broke and just enter the atmosphere in one fell swoop and aerobrake and then – the rest.
Dr. Pamela Gay: That’s a way to do it.
Fraser Cain: Yeah. Well, that’s what the – That’s what Curiosity did, that’s what the Mars rovers did, was they just entered directly – you know, right along their Hohmann transfer. Their Hohmann transfer just intercepted Mars and they tried to – or they did successfully land –
I have a dog whining in the back.
Dr. Pamela Gay: We’re sorry, Chad. It sounds like a squeaky toy.
Fraser Cain: I’m going to eject the dog here. Give me one second.
Dr. Pamela Gay: Okay. This is the episode that has dog interruptions. And here’s where I sit and fill dead air yet again, hoping that Chad catches this to remove it because this is what I did.
Fraser Cain: A dog got left out of the pack.
Dr. Pamela Gay: Okay.
Fraser Cain: Alright. Alright, Chad.
Dr. Pamela Gay: We’re sorry.
Fraser Cain: Do you want to just pick up from where I said what I said? Do you want me to say it again?
Dr. Pamela Gay: Say it again.
Fraser Cain: Alright.
So you’ve got this situation where the – where you can just make your, you know – If your path just crosses Mars – Curiosity did this, the Spirit and Opportunity did this – they just make a direct transfer, aerobrake, and then all of the rest of the things that you have to do to then make it to the surface of Mars, which is very dangerous.
Dr. Pamela Gay: So, I have to admit, one of the reasons I’m a little bit reticent to consider that kind of a future is, think about what the Apollo astronauts did. Because they wanted to go home – and we’re starting from the premise of: They want to come home. It’s a good premise, I think.
The idea of leaving the bulk of your spacecraft on orbit – admittedly, this isn’t what Elon Musk is looking to do – but, as a nice, safe starting point, have the bulk of your spacecraft, with all of the assembly that you need so that you have a nice, happy return – leave that in orbit and then have a lander that goes down and has the ability to come back up, and – like the Apollo missions – dock, but let’s not leave someone on orbit this time – dock up and then return.
So this is where I’m thinking: Put something in orbit, then land, rather than the go-for-broke aerobraking straight to the surface.
Fraser Cain: If I understand correctly, though, the go-for-broke aerobraking is the plan for SpaceX; for the interplanetary transport system. They are gonna – You know, the shape of the spacecraft is going to act as a bit of an aerobrake as it’s coming in.
Dr. Pamela Gay: And this is where I have to admit that I’m a bit more cautious. I’m fully willing to embrace my NASA-trained, overly-cautious-about-lots-of-things kind of way of thinking. This show is not brought to you by NASA. I simply have lots of listening-to-safety things running through my head.
So, what Elon Musk is currently looking to do, is: You have your spaceship, you go to Mars; go to Mars, land on Mars – but first, retrorocket.
This is a lot like how they’re landing on barges; how they’re landing at Cape Canaveral. This is like the cool Jetson’s technology that I kind of thought would never happen and Elon Musk has made it happen. And the thought is that, while you need the big booster rocket to get off the surface of the Earth, Mars, with its lower gravity – you don’t need that booster rocket to get off the surface of Mars.
So, what Elon Musk is proposing/hoping to do: Go to Mars; use various chemical elements, hopefully fairly readily abundant on the surface; create fuel; use the fuel to then take off on that rocket that you have safely landed and not had any leg failures – it has always done “leg day” –?
Fraser Cain: Yeah.
Dr. Pamela Gay: And then make it all the way back to Earth.
Fraser Cain: Right. Now, the problem with the Martian atmosphere, of course, is that it is – it’s like it’s too thick that you can’t just do what they did with moon, where you bring in – You know, you get closer and closer to the surface and then you fire your retrorockets and now you’re going directly down and then you land gently on the surface of Mars. But it’s too thin, so you can’t do the aerobraking.
Like, on Earth, you just enter the Earth’s atmosphere –
Dr. Pamela Gay: Parachutes.
Fraser Cain: Open up your parachute and you can land nice and safely and gently.
So, they don’t have that on Mars at all. You’ve got to do this crazy combination. And up until this point with NASA, they used this collection of methods: They would aerobrake for a little bit with a heat shell; they would then fire a parachute that would bring it down from supersonic velocities; then they would fire a retro thruster. And in the case of Curiosity, they had the Sky Crane. In the case of the – of Spirit and Opportunity – they had that wonderful beach ball that –
Dr. Pamela Gay: I loved that bounce-ah, bounce-ah, bounce-ah –
Fraser Cain: Yeah, that bounced across the surface.
So – but the problem is, that really tops out at, like, what they’ve got with Curiosity. You can’t go much bigger with that methodology. And so, the SpaceX ways are just gonna bring that thing in screaming hot and then it’s gonna turn, face the ground with its thrusters and fire its powerful SuperDraco thrusters and try to land gently. Let’s hope it works. We’re going to find out in 2018, so we’ll know soon if this is going to work.
Dr. Pamela Gay: One of my big concerns about this – and, here, I have to fact-check the last episode. I goof sixes and nines – it’s a thing I do – and in our last episode, I said that it’s a six-month trip to Mars. No, no – nine-months trip to Mars.
Fraser Cain: Nine-month, yeah.
Dr. Pamela Gay: Optimistic flipping of digits.
So, it’s a nine-month trip to Mars. Then you have to hang out and wait for Earth and Mars to get themselves aligned correctly to do the same Hohmann transfer orbit back. You’re looking at a whole lot of time in whatever-sized vessel you take with you. And with Elon Musk’s plan, you’re kind of trapped in a tiny space.
Fraser Cain: He said it sounds like fun – and you’ll float around and you’ll watch movies and you’ll visit the restaurant and it should be a lot of fun.
Dr. Pamela Gay: Restaurant?
Fraser Cain: It’s gonna have a hundred people on board. It’s gonna be a hoot.
Alright, so we talked about the thing landing and we’ll – You know, we’re going to talk about the long-term survival in space and how we’re all going to get space madness but I just want talk a little bit more about the physics before we move on to – you know, us going cruisin’ in space.
Dr. Pamela Gay: You and I have been on cruises. This sounds like such a horrible idea to me.
Fraser Cain: It’s an adventure! It should be a lot of fun.
So – okay. So we’ve got this rocket sitting on the surface. You know, it’s landed safely; it’s gone through the most dangerous part of this whole mission. It’s landed safely on the surface of Mars. In the idea of NASA and SpaceX, it’s going to refuel based on local elements.
Dr. Pamela Gay: So we’re looking at a couple of different ways that you can do this. There’s lots of carbon dioxide, water – all of these normal, happy gasses that we have here on Earth – that, it turns out, you can make fuel out of.
So, one of the ideas is you can do a monopropellant in the form of hydrogen peroxide. This is actually something that was used in some of the earliest rockets. It’s not the best propulsion system but it totally works.
The other idea is a little bit more complex and this is, you can create methane on the surface through a variety of different chemical reactions. So, H2O – break it out into oxygen and molecular hydrogen. Breathe for a while – and this is what we’re doing on the International Space Station right now. So breathe for a while and then you end up, as a human being, creating CO2. You still have that 2H2O – you now have some more 2H2O – sorry, not H2O. You have 2H2 – you have molecular hydrogen. This chemical reaction will lead to water and methane. Methane is a fuel, again. So, as part of the normal respiration system, we can be taking that water, transferring it into the oxygen we need, respirating it into the CO2 that we then need to make methane.
On the ISS, they just eject the methane. This is part of creating a closed system, for the most part. It used to be we had to constantly take water to the ISS; now we just take them hydrogen periodically. So, we’re looking to create methane.
Fraser Cain: Yeah, and this is one of the advantages of the system that SpaceX has proposed – this idea of using methane as a fuel. It’s sort of like the – I remember watching the SpaceX presentation. It’s sort of like the perfect fuel for what you could create on the surface of Mars. It’s sort of – It’s possible to make from the local elements; it’s safer and easier to store than, for example, liquid hydrogen and liquid oxygen, which are traditional rocket-launch fuels here on Earth. It’s sort of like the perfect fuel to build and, in theory, it should be easy to make.
So, let’s say you’ve set up this rocket factory. It’s landed on the surface of Mars. It has – You know, it’s brought in the raw ingredients. It has filled its fuel tank with methane and somebody, who is one of these colonists on Mars, has decided, “You know what? I want to come home again, please.” What happens?
Dr. Pamela Gay: Well, you fuel your tank up and you hope that you landed level enough that taking off doesn’t cause bad things to happen.
Fraser Cain: Alright. Let’s assume that bad things didn’t happen. How much – Now, we talked about Earth – that you need about 10 kilometers per second of velocity to reach escape velocity. What is the escape velocity on Mars?
Dr. Pamela Gay: So, on Mars, you’re just looking at 5 kilometers per second and so, it’s less than half. So, if you wanted to go from surface of Earth straight-away – you’re launching the whole darn thing at once – you have an 11.2 kilometers per second. I recommended you, instead, go to low-Earth orbit but if you just want to say, “I’m done with this place. I’m blowin’ this joint” –
Fraser Cain: Yep.
Dr. Pamela Gay: It’s 11.2 kilometers per second. From Mars: 5 kilometers per second. Mars, you also don’t have the same issues with atmospheric drag that you have to overcome because the atmosphere is trying to slow you down while you’re trying to get out. All in all, getting off the surface of Mars, if you have the fuel and if everything goes right, should be way easier than getting off the surface of Earth. But it all depends on how they got there.
The way that Elon Musk is saying is: You go. You take your whole spaceship with you. You land. And then you take back off with your entire spaceship that you have now refueled with methane that you have created via various processes on the surface of Mars.
This is a nice closed-loop system, where it’s kind of all or nothing, which makes me nervous. If I were the one designing this – and I’m not Elon Musk; by so many factors, I am not Elon Musk – I personally am a fan of how they did it with Apollo, where you have your part that goes down and comes back up but it’s not your whole spacecraft.
But the problem with that is, if it’s not your whole spacecraft, where do you put all the fuel? So this is where you have to consider – do you take your fuel or do you make your fuel? If you make your fuel, you probably need to land the whole thing, in which case – just take off and go. Just take off and go – fewer things to go wrong.
If you’re sending your fuel ahead, put it in orbit and catch back up with it.
Fraser Cain: And you can kind of imagine – Now, what about, like, docking with Phobos? I mean, is it sort of on the same kind of incline plane? Does it make sense?
Dr. Pamela Gay: Well, so the docking with Phobos falls into the: Where is your fuel? So, if you were able to get water on Phobos, you could – through respiration and other processes – go through – and you need to get carbon from somewhere. You can go through and end up with methane on Phobos. So, it depends on: Where are you making your fuel?
If you took it with you – put it in orbit, rejoin it in orbit. If you made it on Phobos, rejoin it on Phobos. If you’re just going straight to the surface, go straight back to Earth.
Fraser Cain: And so, let’s imagine that return journey then. How long are you looking at on the way home from Mars?
Dr. Pamela Gay: So, just like it took you nine months to get there, it’s going to take you nine months to get back. So we’re looking at a fairly short round-trip journey but you do have to manage to keep yourself alive longer than, like, for instance, you can go without food.
Fraser Cain: Right. And that was a big part of The Martian movie was, you know – that when the Hermes came back around Earth, they had to pick up more food and supplies because they were going to be stuck on the spacecraft for another 18 months –
Dr. Pamela Gay: Nine months there –
Fraser Cain: Nine months out, nine months back. And that was a whole, you know, lot more freeze-dried food and they would die and starve if they didn’t have that.
Dr. Pamela Gay: Well – and the thing that they didn’t talk about in The Martian is, under your nice, normal Hohmann orbit, you have nine months to get there; three months there, while you wait for Mars and Earth to get lined back up again; then nine months home. Well, they somehow did: Straight there, fire their engines – it wasn’t the lowest energy possible orbit. And so they used a different energy that uses even more fuel than your standard 9-3-9 would end up taking.
Fraser Cain: Right, right.
And then, coming back – you know, you arrive back at Earth; you get to the atmosphere of Earth and you just do a direct entry back into the Earth atmosphere.
And this is the great part about the Earth’s atmosphere, is it’s thick and stops spacecraft nicely, especially, you know – glad you brought a parachute.
Dr. Pamela Gay: And so there, we’re easy. But the only problem is – so, if you’re on the surface of Mars, there’s a lot of potential biological hazards, where the question is: Do you actually want to let those people back onto the surface of Earth? Or are we worried about War of the Worlds kind of bacteria warfare, with whatever we brought home with us.
Fraser Cain: Yeah, I don’t know. I mean, I know that this is actually a concern that NASA has experienced in the past; that they’ve talked about. Like when they brought the astronauts back from the moon, they had a bit of a concern about whether they’re going to bring some kind of contamination. But to have this stuff have never interacted with Earth life – although Earth would be a pretty great place for some of this stuff to be –
Dr. Pamela Gay: Oh, yeah.
Fraser Cain: – compared to Mars, the surface of Mars – but, right. So let’s imagine we’ve got – You know, they’ve come back, they – perhaps they return to the Space Station and they decontaminate themselves or they land on Earth and they decontaminate.
So, that’s sort of the – You know, that’s the full journey: They fly off from Earth, they potentially go into orbit, they go to Mars, they land on the surface of Mars, they make some fuel, they return directly back to Earth. That is – That’s the first stage. That’s the kindergarten version of this.
But let’s imagine we’ve sort of pushed forward. We’re 20 years, 50 years, 100 years in the future. We’ve got a more-established infrastructure for getting to and from Mars. So, instead of me wagon-training it from, you know – my house to Vancouver and taking a sailboat and so on – I could just take an airplane, right?
What is the future infrastructure going to look like, to make that journey to and from Mars?
Dr. Pamela Gay: So here, my goal, my hope – I can’t really say a goal – my hope is that we’ll end up with a future where you essentially have spacecraft that are on this permanent orbit, where they’re just going past the Earth, grab things, drop things off – keep going. So, the spacecraft that are controlling our ability to get from Mars to Earth, from Earth to Mars, are just happily orbiting forever. They get docked with near Mars, they get docked with near Earth; an exchange takes place but no one ever really needs to stop.
It’s sort of like at Disneyland, where you have the rides that never actually come to a complete stop for people to get on and off but rather, you have the moving walkway.
Well, for us, the moving walkway will be some sort of a transfer orbit between Earth and that permanently orbiting spacecraft. And we can probably have a couple of them that end up on – miss the Earth sometimes, catch the Earth other times, in order to make up fuel economy – but maybe you don’t even have to do that if all you’re doing is paying the Delta-v’s to catch you back up to the other world.
Fraser Cain: And you can imagine, like, whether they use ion propulsion or some – or they’re going to use that methane – that, as the spacecraft launch off the surface of Mars, they return fuel to this facility and then it can act like a way station of fuel.
And then you can imagine this kind of far future, where this same concept is just spread across the entire solar system; where you’ve got these spacecraft making these regular transfer journeys. You know, there’s – It’s a pretty wonderful idea.
And so, you can imagine you fly off. If you want to go to Mars or you want to go to some other world, you just move from one transfer vehicle to a different one, depending on how much time you want to spend; how much expense you want to – you know, how much fuel you want to use.
Your dog is attempting to climb into your chair while you’re doing this – while you’re doing this recording.
Dr. Pamela Gay: He desperately wants my attention and he knows how to operate doors.
Fraser Cain: And he knows how to operate doors. Yeah, I can’t believe your dog has thumbs. Just hold this again for about another second –
Which was, we talked about this future infrastructure but what about future technologies? What about faster rockets? What about ion drives? EM drives, assuming they actually work?
Dr. Pamela Gay: So, ion drives are kind of sad because they accelerate you so very, very slowly. So, when you’re starting to want to go the super-huge distances with very lightweight things, very small things, then ion drives are useful. Or if you’re trying to do something very slowly and fuel economically, like we did with the Dawn spacecraft.
But for your average human being, which is – even for the small ones, pretty big – and all the stuff we need to stay alive: The water, the water recycling systems, the – everything. There, we’re going to need something other than ion drives. Currently, the best we’ve got is fuel sources: Hydrazine, methane – pick a fuel source. The mono ones like hydrazine, hydrogen peroxide are pretty good for situations like this.
But what’s cool is, this is actually one of those things where science fiction writers have done a lot to pioneer what are the cool ideas. Again, Kim Stanley Robinson – I’m just going to keep promoting his books. He looks towards a future where, essentially, the more rugged asteroids – those that don’t fall apart when you dig holes into them – have been mined out, spun up and put into a whole variety of orbits that allow you to, basically, go from asteroid to asteroid, switching between orbits to get from one side of the solar system to the other.
Fraser Cain: It will just be amazing when we’ve got that infrastructure. And I kind of even imagine, like, laser systems that could be delivering –
Dr. Pamela Gay: Solar sails.
Fraser Cain: – blasts to solar sails and things like that. So it’s –
Dr. Pamela Gay: Although they’re laser sails at that point. Again, this also comes up in a Kim Stanley Robinson book.
Fraser Cain: Right, right. But the point is, the more you get that stuff out into space, the more easily it becomes to move from place to place. If you read Seveneves, they’ve got an entire system that’s all, like – almost mechanical-based. Like, their methods of moving you from orbit to orbit and place to place is tethers and rotating energy transfer systems; that it’s not rockets, it’s just huge rotating scoops that pick you up at one orbit and release you at a different orbit. Because all that really matters is just your change in velocity and your change in your direction, so –
Dr. Pamela Gay: And you can get picked up, essentially, as you glide through the atmosphere. It’s rather glorious and terrifying all at the same time.
Fraser Cain: Yeah, yeah. It sounded like a pretty sketchy way to get up into orbit and yet, very inexpensive. So it was great.
Alright. Well, thanks Pamela. We’ll see you next week.
Dr. Pamela Gay: My pleasure.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit 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 firstname.lastname@example.org. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
We record the show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern or 2030 GMT. If you missed the live event, you can always catch up over at cosmoquest.org or our YouTube page. To subscribe to the show, point your podcatching software at astronomycast.com/podcast.xml, or subscribe directly from iTunes. Our music is provided by Travis Serl and the show was edited by Chad Weber.
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Duration: 31 minutes