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Titan – The Moon with Rivers of Methane · Talking Science

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  I want you to picture standing under a sky that
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  is the exact color of a manila folder like a
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  perfectly calm air but it's so incredibly thick
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  that if you strapped on a set of wings you could
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  you could literally flap your way up into the
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  sky using just your arm muscles right which is
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  just a wild visual and then underneath your feet
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  instead of dirt or sand there are these rounded
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  pebbles but you know they aren't made of rock
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  they're solid water ice frozen completely as
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  hard as stone in this deep, deep cold. Yeah.
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  And just off in the distance, you can see a river
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  flowing, but it's not water. It's actually liquid
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  methane. Exactly. I mean, it's the exact same
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  simple molecule that makes up the natural gas
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  we use to cook with here on Earth. But here it's
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  a freezing flowing liquid carving up the landscape.
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  So today we are taking you on a deep dive into
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  Titan. That's Saturn's largest moon. Our mission
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  today is to give you a comprehensive tour of
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  what is honestly the most. Genuinely Earth -like
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  place in the solar system, but built out of completely
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  alien chemicals. It really is. And we're going
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  to take this step by step. You don't need any
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  prior astronomy background for this deep dive.
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  Just, you know, your natural curiosity. Because
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  to understand how you could fly with just your
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  arms, we first have to look at Titan's basic
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  stats. Right. So let's talk scale. Titan is huge.
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  It's Saturn's largest moon, and it's actually
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  physically larger than the planet Mercury. Yeah,
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  larger in volume, though it's less massive overall.
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  Mercury is a dense ball of iron and rock, whereas
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  Titan is made of a lighter mix of water, ice,
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  and rocky material. And it orbits Saturn from
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  about 1 .2 million kilometers away. Which takes,
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  what, about 16 days to make one loop? Exactly,
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  16 days. And it is tidally locked. So that means
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  the exact same side always faces Saturn, just
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  like our moon always shows the same face to Earth.
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  And because it's so far out there, I mean, it's
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  nearly 10 times further from the sun than we
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  are. The surface temperature is a savage minus
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  180 degrees Celsius. Minus 180. That is a kind
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  of cold that completely redefines physics. At
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  that temperature, water acts almost identically
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  to silicate rock on Earth. It's brittle, it's
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  hard, and it's immovable. So when you look at
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  a water ice mountain on Titan. You have to think
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  of it exactly like a solid granite mountain here
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  on Earth. It's just bedrock. That's a great analogy.
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  And, you know, for centuries, Titan was basically
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  just a mystery. It was discovered way back in
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  1655 by Christian Huygens with a home -built
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  telescope. But for ages, it was just a faint
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  dot of light. Right up until the 1940s, right.
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  That's when scientists used spectroscopy on it.
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  For those listening, spectroscopy is a technique
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  that spreads light out into its component wavelengths,
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  and it reveals exactly which chemicals are present.
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  Yeah, and that data changed everything. It showed
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  Titan has an atmosphere. Specifically, they found
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  methane. And finding an atmosphere around a moon
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  was revolutionary. No other moon we knew of had
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  a real atmosphere. But the bulk of it is actually
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  nitrogen, right? Like overwhelmingly nitrogen.
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  Yeah, much like Earth's, which is about 78 %
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  nitrogen. But Titan's atmosphere is about 50
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  % denser than Earth's at sea level. Which brings
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  us back to that flying image from the intro.
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  You've got this super dense air combined with
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  surface gravity that's only one seventh of Earth's.
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  So human flight under just muscle power is genuinely
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  physically possible. You really could just take
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  a running start and take off. It's an aviator's
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  dream. Okay. But if the atmosphere is mostly
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  nitrogen and nitrogen is invisible, where does
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  that famous orange color come from? Like in photos,
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  Titan looks like an orange billiard ball. Ah,
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  that is the photochemical haze. See, the sunlight
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  added Saturn is weak, but the ultraviolet radiation
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  is still strong enough to bombard the upper atmosphere
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  and break apart those methane molecules high
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  in the sky. And when they break apart, they don't
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  just stay broken, right? The carbon and hydrogen
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  fragments recombine with the nitrogen. Exactly.
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  They form what we call tholins. And tholins are
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  basically these complex organic residues produced
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  when radiation acts on simple ices and gases.
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  So these tholins just build up in the stratosphere.
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  Yeah, they drift down like a very fine global
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  haze. Over millions of years, they settle all
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  over the surface. At the equator, they've actually
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  built up into these vast fields of dark dunes,
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  shaped by the wind into long parallel ridges.
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  But I want to push back on the word sand dunes
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  here, because when you say sand, I think of crushed
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  quartz, like on a beach. But this is completely
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  different. Oh, absolutely. It's not sand. It's
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  more like soot dunes, right? Or maybe mountains
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  of dark coffee grounds, which is wild because
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  that makes Titan this natural laboratory for
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  prebiotic chemistry. Prebiotic chemistry, meaning
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  all those carbon -based reactions that happened
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  on early Earth before biological life actually
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  emerged. Titan is full of it. Even if it's way
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  too cold for life to progress as far as it did
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  here, the ingredients are literally raining from
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  the sky. Which makes me wonder if methane is
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  constantly being destroyed up high to make this
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  soot. What's it doing down on the surface? Well,
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  down on the surface, it is driving a complete
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  hydrological cycle. And a hydrological cycle
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  is basically a weather system of evaporation,
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  condensation, and precipitation. But titans...
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  mirrors Earth's water cycle using liquid methane
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  and ethane. That is just so bizarre. So the weak
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  sunlight evaporates the surface methane, it forms
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  clouds, and then it falls as rain. Rains down,
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  feeds into rivers, and pools into these massive
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  lakes and seas at the poles. Though I should
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  mention rain is a really rare seasonal event
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  there. Right, because a Saturn year takes 29
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  Earth years. So one single season on Titan lasts
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  for about seven of our years. Yeah, so when it
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  rains, it's like a massive desert downpour, a
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  huge flash flood of methane. And we actually
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  saw the results of this thanks to the Cassini
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  mission. Its radar instrument could see right
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  through that orange haze. And what it mapped
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  out was incredible. The largest sea, Kraken Mare,
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  is roughly the size of the Caspian Sea here on
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  Earth. And it's over 100 meters deep in places.
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  The volume is staggering. Kraken Mare holds several
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  times more liquid than all of Earth's proven
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  oil and gas reserves combined. Yeah. And there
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  are others, too, like Ligia Mare and Punga Mare.
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  Wait, several times more than all our oil and
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  gas reserves? That sounds like a literal gas
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  station planet just floating in space. I know
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  it sounds like that, but we have to clarify.
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  We are talking about cold, liquid gas acting
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  as a solvent, not refined, combustible fuel.
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  Ah, right, because there's no free oxygen to
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  burn it anyway. Exactly. It's a completely alien
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  liquid that just... erodes the landscape the
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  way water does here. Okay, so we saw these lakes
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  from orbit, but to really understand the surface,
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  we had to drop a probe right through that haze,
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  right? We did. The Cassini mission, which was
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  this huge joint project between NASA, the European
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  Space Agency, and the Italian Space Agency, launched
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  in 1997. It finally arrived in 2004. And then
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  in January 2005, the Huygens probe detached.
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  It basically parachuted blind down into that
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  atmosphere for over two hours. Yep. First spacecraft
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  to ever land on an outer solar system world.
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  I just marvel at the sheer engineering audacity
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  of that. Jumping blind into an alien atmosphere
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  where you don't even know what the ground is
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  made of. It could have been liquid. It could
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  have been a mountain of soot. But on the way
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  down, the cameras actually photographed drainage
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  channels. They looked exactly like dried earth
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  riverbeds. And when it finally landed, it found
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  those rounded water ice pebbles we talked about
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  at the start. Yeah, the pebbles were key. They
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  were smoothed out by flowing liquid over a really
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  long time. Just imagine. looking at a smooth
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  river rock on earth and realizing that the exact
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  same physical process happened a billion kilometers
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  away. just with liquid methane wearing down solid
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  ice. It's beautiful. It really is. Now, Huygens
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  only survived a few hours before the brutal cold
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  killed its batteries, but it gave us our only
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  ground -level view. Cassini eventually was deliberately
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  crashed into Saturn in 2017, so it wouldn't contaminate
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  any moons. But before it died, Cassini's instruments
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  found something even stranger hiding beneath
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  that rock -hard ice crust, didn't it? It sure
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  did. They tracked variations in Titan's gravity
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  and observed something called libration. Libration.
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  Yeah, it's a small, periodic, flexing and rotational
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  wobbling of the icy shell. It happens as Saturn's
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  gravity tugs on the moon. Oh, I get it. It's
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  like spinning an egg on a table. If you spin
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  a hard -boiled egg, it spins perfectly smoothly.
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  But if you spin a raw egg, the liquid sloshing
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  around inside makes it wobble differently. That
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  is exactly it. Titan wobbles like a raw egg.
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  And this evidence strongly points to a global
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  liquid water ocean sandwiched between that outer
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  ice crust and a deeper rocky core. But how is
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  there liquid water if the surface is minus 180
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  degrees? Well, the water stays liquid because
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  it's mixed with ammonia, which acts as a powerful
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  natural antifreeze. And there's also tidal heating.
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  Tidal heating being the distal heat generated
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  by that constant gravitational kneading and stretching
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  from Saturn, right? Right. And finding this hidden
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  ocean puts Titan in the same category as Europa
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  and Enceladus. Which naturally leads to the idea
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  of volcanoes. Does that subsurface ocean ever
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  break through? It raises the possibility of cryovolcanism,
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  absolutely. Cryovolcanism is when volcanoes erupt
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  cold, icy materials like a slushy water -ammonia
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  mix instead of molten rock. And Cassini found
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  mountains that look like volcanoes, right? Like
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  Dumon. Dumons and Sotroptera, yeah. They look
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  a lot like volcanic dones and calderas. But I
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  need to be careful here. This is heavily debated.
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  It is an open question, not a confirmed fact.
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  It could just be unusual erosional features.
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  Okay, fair enough. But still, you've got an ocean
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  of liquid water below and this complex chemical
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  soup of organic molecules above. I have to ask
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  the ultimate question. Could anything live there?
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  That is the million -dollar question. If we look
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  at conventional habitability like what we look
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  for on Mars or Europa, we want liquid water as
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  the essential solvent for life. By that standard,
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  Titan's buried ocean is a huge prime target.
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  But what about the surface with all that methane?
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  The surface offers a much, much stranger hypothesis.
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  Highly speculative. Could life use liquid methane
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  as a solvent instead of water? How would that
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  even work? Because Earth cell membranes are made
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  of fats, right? Lipids. They just freeze solid
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  in minus 180 degree methane. Exactly. They would
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  shatter. Yeah. So chemists theorize something
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  called an exotism. An azotosome is a theoretical
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  cell membrane built from small, nitrogen -containing
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  molecules. And they think that would work. Well,
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  computer models suggest it could function stably
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  in liquid methane. unlike our fatty cell membranes.
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  But I cannot emphasize enough the need for scientific
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  caution here. This is entirely a theoretical
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  thought experiment. Yeah, I'm glad you brought
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  that up because I see these sensationalized headlines
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  all the time screaming, you know, life on Titan.
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  How do you feel when you see that media hype?
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  It's frustrating. We have zero evidence of these
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  membranes existing, zero biosignatures, no proof
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  they can even support a metabolism. We have to
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  separate an intriguing hypothesis from actual
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  responsible science. So the azishum is basically
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  just fun on a chalkboard for now, not actual
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  biology. Exactly. So if we can't definitively
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  answer the life question yet, how do we actually
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  find out what's happening in this chemical laboratory?
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  By going back. And this time, we're going to
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  fly. The next NASA mission is called Dragonfly,
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  launching later this decade and arriving about
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  six years later. And this isn't just a wheeled
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  rover. No, it is a rotorcraft, basically a car
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  -sized drone. And it explicitly takes advantage
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  of that thick atmosphere and low gravity we talked
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  about earlier. I love that. We couldn't fly a
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  heavy drone like this on Mars because the air
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  is just way too thin. But on Titan, the very
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  atmosphere that creates that thick, oaring haze
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  makes it an aviator's dream. It really does.
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  Dragonfly will hop from site to site, sampling
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  chemistry and geology all over the place. And
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  one key target is the Selk Impact Crater. Why
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  that crater specifically? Because an ancient
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  meteor impact there may have melted the subsurface
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  ice, mixing liquid water with those surface organics.
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  It's the perfect spot to study prebiotic chemistry.
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  So it's like a giant mixing bowl of water and
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  tholins. Exactly. The goal of Dragonfly is to
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  study the chemical steps that actually lead to
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  life, not necessarily to find life itself. Which
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  brings us full circle. Titan is just this bizarre
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  yet familiar world. You've got rain, rivers,
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  dunes, oceans. But water acts like rock and methane
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  acts like water. It really just shows us how
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  incredibly inventive planetary chemistry can
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  be with whatever materials it has on hand. It
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  totally does. And it leaves me with one final
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  thought I want to throw out to you listening.
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  If scientists are seriously theorizing about
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  life using liquid methane right here in our own
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  solar system, just imagine the billions of exoplanets
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  in the wider galaxy. Oh, absolutely. The possibilities
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  are endless. Right. What other bizarre, completely
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  unrecognizable liquid solvents might be carving
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  rivers on distant worlds right now, potentially
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  hosting chemistries we haven't even dreamed of
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  yet? It's just wild to think about. Thank you
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  so much for taking this deep dive with us. Thanks
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  for having me. Keep looking up.