Thanks to LEGO – presenting LEGO City - for their support of PBS Digital Studios. Humanity’s future is glorious. As we master space travel, we’ll hop from one cold dead world to the next. Terraforming as we go. Life will blossom in our path and eventually the galaxy will shimmer with beautiful Earth-like orbs. I mean... maybe. Sounds a little science-fictiony. But it wouldn't sound so far fetched if we proved we could do it at least once. If we successfully terraformed Mars. We already have the technology to bring humans to Mars and to set up small settlements - or at least we could do within a generation. But those settlements will need to be cocooned - shielded against the deadly cold, the intense radiation and the fatal lack of atmospheric pressure. Surely if we want to thrive on Mars – to turn it into our second home – these settlers, or their descendants, will need to be able open the airlocks, shed their spacesuits, and step out onto a survivable surface. We’ll need to terraform Mars, as our first step to terraforming the galaxy. Terraforming Mars has long been a science fiction dream – from Kim Stanley Robinson’s Mars trilogy to Total Recall to the Red Faction game series to Elon Musk’s Twitter feed. But what would it really take? How science-fiction-y is the whole concept of terraforming? In the end it’s a question of atmosphere. Mars’ current atmospheric pressure is 0.6% that of Earth – and that means circulatory shutdown within a minute for an unprotected humans. But it also means almost no greenhouse effect. Light from the Sun, which is already fainter due to Mars’ distance – is radiated directly back out into space. On Earth that same light first bounces around in our thick atmosphere, heating it up. At an average of -60 Celsius, water freezes on Mars. But even if the planet were warmer, liquid water would still be impossible in that thin atmosphere – it sublimates directly from ice to gas. And of course Earth’s atmosphere protects us from harmful cosmic rays and the most dangerous ultraviolet radiation from the Sun. All of that bad stuff has a direct path to the Martian surface. So, the most important step in terraforming Mars is to give it an atmosphere – ideally as close to Earth’s as possible. In the imaginations of sci-fi writers all we need to do is unlock the planet’s latent potential. After all, Mars WAS once a warmer, watery planet with a much thicker atmosphere. I mean, that's conclusive – our rovers and orbiters have found incontrovertible evidence of an ancient watery surface. The hope then, is that this water and the atmosphere that once supported it is now all locked in the planet’s crust and ice caps. We just need to release it. Surely we can just nuke the poles, melt enough carbon dioxide and water vapor to kickstart a feedback cycle of greenhouse warming and that'll release more gases… and voila! Earth 2.0 OK, not so fast. There’s a real risk that Mars actually lost its atmosphere to space, rather than absorbed it into the surface. The issue is that the planet is relatively puny. At 11% the mass of Earth, it has a weaker gravitational field that grips less tightly to an atmosphere. And that small size means that the Martian core cooled down more quickly than Earth’s core, solidifying long ago and shutting down its global magnetic field. Earth’s magnetic field protects us from the solar wind, as we saw in a recent episode. The unprotected and loosely bound Martian atmosphere may have been slowly shaved away by that wind over billions of years. And in fact that is exactly what happened. The ablation of what is left of the Martian atmosphere has now been directly observed by NASA’s MAVEN spacecraft, as we’ve also discussed before. And the lack of atmospheric material in the crust has been confirmed pretty conclusively by observations of the Martian surface. In a nice Nature Astronomy article last year, planetary scientists Bruce Jakosky and Christopher Edwards calculate the plausibility of using the remaining surface carbon dioxide to replenish the Martian atmosphere, based on observations of NASA’s Mars Reconnaissance Orbiter and Mars Odyssey spacecraft. They focus on CO2 because it’s the only plausible greenhouse molecule in any significant abundance on Mars. They assess whether release of the accessible CO2 reserves could get Mars anywhere near Earth’s atmospheric pressure. And… unfortunately they conclude that no near-future technology could hope to to kickstart the recovery of any useful atmosphere. But, you know what? Let’s go ahead and run the numbers real quick, because maybe something is still possible. After all, these researchers only ruled out NEAR future technology. What about medium future? Far future? So there are 3 broad sources for CO2 on Mars. First there’s the south polar icecap – which consists of water ice several kilometers deep, interspersed with thick layers of CO2 ice – discovered by radar soundings with the Mars Reconnaissance Orbiter. If all the polar CO2 were released, it would maybe double the current amount of CO2 in the atmosphere – which is a factor of around 100 times too low to make a difference. And by the way, that CO2 couldn’t be released with nukes alone - it’s too deep. Sorry, Elon. The second accessible source is CO2 absorbed into the surface dust – the regolith - up to 100m deep. Unlike, for example, Earth’s permafrost, this stuff wouldn’t just melt under global warming. It would shift in its equilibrium over 10,000 years to release a small fraction of its CO2. At any rate, even if we managed to heat the entire regolith across the entire Martian surface we’d only get 4% of the Earth’s atmospheric pressure. The final source is carbonate minerals in the crust. These carbonates would need to be mined and processed by heating to around 300 Celsius. But complete strip-mining of even the largest carbonate surface deposits on Mars probably get you less carbon than melting the polar ice caps. So much for near-future accessible carbon. But those carbonate minerals probably exist in much larger quantities deep beneath the surface. And that’s really our only hope to find enough CO2 - or really any native Martian material - to replenish the atmosphere. Let’s do a quick calculation to see what it would take. First, let’s pretend there’s an accessible layer of limestone – calcium carbonate – across the entire surface of Mars. There isn’t, but hey, we’re dreamers. We need about 10,000 kg of material per square meter to duplicate Earth’s atmospheric pressure. Seriously, that’s how much atmosphere is above your head right now. No wonder it’s so hard getting out of bed in the morning. High density limestone is 2500 kg/m^3 and yields 44% of its mass in CO2 when heated or exposed to acid. So to get 10 tons of CO2 for every square meter on the surface of Mars you’d have to dig down over 10 meters – across the entire planet! That’s a few quadrillion tons of rock. I hope you have your diamond pickaxe ready. In reality of course we’d need to first locate and then dig down some kilometers before we could access most of the carbonates. Extracting such a quantity from depth is hard enough, but let’s think about processing it. We can either heat the carbonates to hundreds of degrees Celsius or use acid to dissolve out the CO2. We’d need to process around 20% of all Martian water via electrolysis to get that acid. The electrolysis path might be better because it would give us oxygen as a byproduct of making that acid. The energy cost in both cases is similar, though – several septillion joules. Several thousand times the total annual energy consumption of the entire Earth. That’s definitely sounding far-far future. But not quite impossible. Finally we actually have a picture of what terraforming Mars would actually look like. Let’s say we want to finish the work in a single generation. We’d need to cover much of the surface of Mars in solar cells made from abundant silicon in the crust, or build 10 or so million gigawatt fusion power plants. There’s really no other viable energy source. We’d need to channel this energy deep into the crust to power vast hoards of robotic miners-slash-processing plants, meanwhile pumping water from the icecaps across the entire globe. This could get us a carbon dioxide-oxygen atmosphere in a few decades, or in centuries … or millenia if you scale down the power supply to something less insane. Nonetheless, our descendants could see a Mars with sufficient air pressure and greenhouse effect to allow liquid water to persist on the surface. Now, Mars actually does have enough water for a few lakes and rivers. The ice cap water would cover the entire surface to about 30 meters – which is not enough to start a proper water cycle or have oceans, but there may be a lot more water deeper in the crust. We’d better hope so. Our brand new CO2-oxygen atmosphere is not exactly earth-like. In fact, it’s instantly and fatally toxic to humans and animals, and not so great for plant life. Certain algaes can survive in a pure CO2 atmosphere –which is handy, because blue-green algae – cyanobacteria - was responsible for first oxygenating Earth’s atmosphere. And we’ll need that photosynthesis because otherwise oxygen will be quickly leeched from the atmosphere as it oxidizes the surface. So, there’s our next snapshot of the far future of a terraformed Mars – brand new oceans green with photosynthesizing, probably genetically-engineered, slime. And perhaps eventually a breed of post-humans genetically or even cybernetically adapted to deal with a CO2 atmosphere. I just described the “easy” path to building an atmosphere on Mars. It may be the only way to do it only using Martian materials. Variations are possible - like introducing “super” greenhouse gases like CFCs. But that still doesn’t give us the needed atmospheric pressure. At any rate, to get a true Earth-like atmosphere we need a non-toxic filler molecule. CO2 sucks. Nitrogen is much better - it works great on Earth anyway, but Mars has very little of the stuff. To really build an Earth-like atmosphere we have to turn our eyes to the rest of the solar system. One popular idea is just to smack some comets into Mars. Comets contain tons of frozen volatiles – gas-forming molecules like CO2, H20 and the presence of molecular nitrogen in comets was only recently confirmed by the Rosetta mission. But how many comets do we need? Well, assuming comets contain an amount of nitrogen similar to the composition of the pre-solar nebula then can guess that around 5% of a comet’s mass is nitrogen. That gives the typical medium-to-large comet a hundred billion tons of the stuff. So, to build a quadrillion-ton nitrogen atmosphere that’s, like, 10,000 comets. O-kay, so we’re still in far-future la-la land. But it’s actually not significantly less crazy, or more crazy, than melting the Martian surface. What would THIS effort look like? Imagine this - a vast fleet of robotic spacecraft swarming the Kuiper belt, nudging its plentiful iceballs in just the right way to send them plowing towards Mars. Hopefully with exquisite aim, otherwise Earth is in for a pounding, also. It would presumably take centuries to put such a fleet in place, and more centuries to “de-orbit” those comets. Once Mars has been suitably bombarded there’s still a lot of work tweaking the new atmosphere. The good news is that those comets brought with them a LOT of water, so we have deep global oceans at this point. OK. Let’s fast-forward several centuries. Mars has an atmosphere – either released from deep in the crust or brought in from the far outer solar system. The last step is to protect the new atmosphere. We canNOT restart Mars’ magnetic field – to do that we’d have to re-melt the entire core. But we can try to build an external magnetic shield. The easiest would be to do that in space – an orbiting field generator placed between Mars and the Sun, like a giant space umbrella. The resources and energy needed to build this is insane – but hey, we just built an atmosphere, so why not? Honestly, all of this is pretty insane. And frankly, unlikely. Would we really muster the resources to terraform Mars if we can’t do the same to re-terraform Earth? But there is another option. Why build a sky if we can build a roof? Instead of terraforming – what if we paraterraform. Build what is known as a worldhouse. We could cover vast tracts of land with an airtight bubble. Or, more likely, many many connected bubbles. These would be tall enough to encapsulate entire cities, and importantly – plenty of Earth-like natural wilderness. Oh, and I’m still a proponent of centrifuge cities – mag-lev rotating habitats to simulate Earth gravity. Also shown rather beautifully in this more practical design by James Telfer. If we wanted to cover, say, 10% of the Martian surface with a 300 meter tall worldhouse, it'd require several orders of magnitude less material than building an entire atmosphere. So, say a handful of comets and/or the polar ice caps should be enough to fill our worldhouse with air and water. Now, without a real atmosphere, space radiation is gonna be a problem for our worldhouse, as is the constant bombardment of micro-meteors. People who live in glass houses shouldn’t throw stones, nor live under a stone-throwing universe. But perhaps there are advanced or just very, very thick materials that would serve. So there’s our final image of humanity’s future on Mars: thousands of city-sized bubbles spread across the still-barren landscape. And inside each bubble an oasis – a lush, snow-globe replica of old Earth. However we do it, Mars will surely be our first step, our proof of concept if we choose that destiny - if we choose to terraform space time. Thanks to LEGO – presenting LEGO City - for their support of PBS Digital Studios. Can you believe it’s been 50 years since we landed on the moon? It started out with one small step for man and now the journey to Mars is right around the corner! Featuring sets inspired by real aerospace technology, LEGO City Space aims to inspire future space explorers to imagine what role they can play to get us to the Red Planet. To discover more go to the link in the description. So we missed a couple of comment responses. Today I'm going to cover two episodes: The episode "What Happened Before the Big Bang", in which we look at eternal inflation. As well as the episode on the exciting possibility that the North and South magnetic poles may be about to flip. Wabi Sabi asks why the inflaton field is assumed to be a scalar field. Well, that's a great question - but I'm afraid the answer may not be satisfying. It's because a scalar field is all you need. This is the simplest type of quantum field, consisting of only a single scalar value at all points in space. Give such a field a constant energy density and you get exponential expansion. But more complex fields like vector fields and spinor fields can do the job too - and some inflationary models use them, resulting in more complex inflation scenarios. But many physicists argue that you shouldn't add unnecessary complexity, so a scalar field tends to be the default for inflaton. Joshua Kahky asks whether the Inflaton Field could also explain Dark Energy. Well, the answer is yes, possibly. Inflation supposedly happened because the inflaton field had a very high energy density, and it stopped when that energy dropped to a very low value. But that low value may not have been zero. If the inflaton field was left with a very tiny but positive energy density, then it's possible that it could now be powering the current accelerating expansion that we call dark energy. But for that to happen, the inflaton field would have had to have transitioned between two stable or semi-stable states that are a factor of 10^27 different in energy. Now, we can try to imagine a single field with that property, or we can imagine two separate fields - It's not clear which of those two imaginings is more of a stretch. There were a lot more great questions on eternal inflation, but I'll get to those when we do the eternal inflation challenge question answer episode. For now, let's move on to the possible flipping of Earth's North and South magnetic poles. EarthKnight points out that while Venus lacks an Earth-type intrinsic magnetic field, the solar wind striking its atmosphere creates an induced magnetic field that does protects the planet. That's a nice point, EarthKnight. It's a very cool effect. The solar wind partially ionizes Venus's upper atmosphere. Electrical currents are induced and these produce a magnetic field that pushes back against the Sun's magnetic field. Venus's magnetic force-shield isn't nearly as strong as Earth's, however, so our Venusian floating cloud cities had better still have very thick roofs. As many viewers noted, what we currently call the north magnetic pole is technically a south magnetic pole - as in, what we would call the south pole of a magnetic dipole or a bar magnet. You know how the magnetic north pole of a bar magnet is attracted to the south pole of a second bar magnet? Well, your compass's north pole is attracted to geographic north - which means geographic north must correspond to a magnetic south pole. Nolan Westrich, while laughing in Australian, notes that with the flipping of the magnetic poles it will be America's turn to be upside down. Well, given that the northern hemisphere is currently the magnetic south, I think that means that North America, Europe, and most of Asia have been at bottom of the world all this time without realizing it. So hold onto something and don't look at the sky - it's a long way down.
