Could We Terraform Mars?


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 lifeless world to the next. Life will blossom in our path and the galaxy
with shimmer with beautiful Earth-like orbs. Hmmm… maybe. This won’t sound so far fetched if we prove
we can do it at least once. If we successfully terraform Mars. — We already have the technology to bring humans
safely to Mars and set up small settlements – or at least could do within a generation. But those settlements will need to be cocooned
– shielded against the deadly cold, intense radiation, and the fatal lack of atmospheric
pressure. Surely if we want to thrive on Mars – to
make 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 in 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 – that means circulatory shutdown within a minute for 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 into 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. This is conclusive – our rovers and orbiters
have found incontrovertible evidence of the 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 that
will 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 its 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 meant the Martian core
cooled more quickly than Earth’s, solidifying long ago and shutting down its global magnetic
field. Earth’s magnetic field protects us from
the solar wind, as we saw recently. The unprotected and loosely bound Martian
atmosphere may have been slowly shaved away by that wind over billions of years. And in fact that’s exactly what happened. The ablation of what is left of the Martian
atmosphere 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 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. What about medium future? The far future? So there are 3 broad sources for CO2 on Mars. First there’s the south pole 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 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 next most accessible source is CO2 absorbed
in 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 around
10,000 years to release a small fraction of its CO2. At any rate, even if we managed to heat the
regolith across the entire Martian surface we’d only get 4% of Earth’s atmospheric
pressure. The final source is carbonate in the crust. These carbonates would need to be mined and
processed by heating to around 300 Celsius. But complete strip-mining of the largest carbonate
surface deposits probably get you less carbon than melting the polar ice caps. Nonetheless, 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 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 you’d have to dig down over 10 cubic 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 Martian
water via electrolysis to get that acid. The latter might be better because it would
give us oxygen as a byproduct. The energy cost in both cases is similar – several
septillion joules. Several thousand times the total annual energy
consumption of the 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 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. But there may be a lot more water deeper in
the crust. We’d better hope so. Our CO2-oxygen atmosphere is not exactly earth
like. In fact it’s instantly and fatally toxic
to humans, and not great for most plant life. Certain algaes can survive in pure CO2 atmospheres
–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 quickly be leeched from the atmosphere as it oxidizes the surface. So there’s our next snapshot of Mars’
future – brand new oceans green with photosynthesizing 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 – 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. A popular idea is to just 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 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. 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 also 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
are 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 could 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 would require several orders of magnitude less material
– a handful of comets and/or the polar ice caps should be enough to fill them with air
and water. Without a real atmosphere, space radiation
is still a problem, as is the constant bombardment of micrometeors. 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 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 might
be about to flip. Wabi Sabi asks why the inflaton field is assumed
to be a scalar field. Great question – but I’m afraid the answer
is unsatisfying. It’s because a scalar field is all you need. This is the simplest type of 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 is the default for the inflaton. Joshua Kahky asks whether the Inflaton Field
could also explain Dark Energy. 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
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. 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. 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 lots 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 Venus lacks an
Earth-type intrinsic magnetic field, but the solar wind striking the atmosphere creates
an induced magnetic field that protects the planet. Nice point, EarthKnight. This is 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
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 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.

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