There's a Planet Where the Rain is Gasoline

[00:00:00]Picture yourself standing on a beach at dusk.

[00:00:03]There's a soft orange light in the sky and it's raining.

[00:00:06]Big, slow drops drifting down almost lazily, the way snow falls.

[00:00:11]They land on a wet black shore and gather into puddles that catch the light.

[00:00:15]Somewhere out in front of you, waves lap against the rocks.

[00:00:19]It looks like the most peaceful evening on Earth.

[00:00:22]It isn't on Earth and almost nothing here is what it looks like.

[00:00:26]That rain is fuel, not water.

[00:00:28]The same stuff we pipe into our homes and set on fire to cook dinner.

[00:00:32]The black beach isn't sand. The gentle waves aren't a sea of water.

[00:00:36]They're a sea of freezing liquid gas.

[00:00:39]And the rock your boots are standing on, that's water, frozen so hard and so cold that it behaves exactly like stone.

[00:00:48]If you took off your helmet to feel the rain on your face, you wouldn't drown, you'd freeze solid first in air nearly 300° below zero.

[00:00:55]>> [music] >> So, where is this world with rain, rivers, beaches and seas where every single one of them is an imposter?

[00:01:03]It's the strangest familiar place in the solar system and here's the part that should stop you.

[00:01:07]We have already been there.

[00:01:16]Let's clear up the first thing because the title gets it wrong on purpose. The word planet is the bait. What you're standing on is a moon.

[00:01:24]This is Titan, the largest moon of Saturn way out past the asteroid belt about 1 and 1/2 billion kilometers from the sun. It's bigger than the planet Mercury. And out of every moon in the solar system, more than 150 of them, Titan is the only one with a real atmosphere, a thick one.

[00:01:41]Thicker than Earth's.

[00:01:43]Stand on its surface and the air would press on you about 1 and 1/2 times as hard as it does at sea level back home, roughly what you'd feel at the bottom of a swimming pool.

[00:01:51]Above you, a dense orange haze, so complete that for decades we couldn't see the ground through it at all.

[00:01:58]From space, Titan looks like a fuzzy amber marble, a whole world wrapped in smog.

[00:02:03]For a long time, that haze kept its secret. We knew Titan had weather.

[00:02:07]We just couldn't see what the weather was doing.

[00:02:09]And when we finally looked underneath, we found a world running the same machine as Earth.

[00:02:14]Just with the wrong ingredients.

[00:02:19]On Earth, water runs a cycle. The sun warms the ocean. Water evaporates and rises, cools into clouds, and falls as rain.

[00:02:26]The rain fills rivers, the rivers run to the sea, and the whole thing goes around again.

[00:02:31]That cycle is the engine behind almost everything we call a landscape.

[00:02:35]Titan runs that exact same cycle.

[00:02:38]Clouds gather, rain falls. It carves rivers into the ground, pools into lakes, drains into seas, and evaporates back into the sky.

[00:02:46]There's just one swap. On Titan, it is far too cold for water to be a liquid, [music] so water is out of a job. The liquid doing all the work instead is methane. Natural gas. The stuff in the pipe behind your stove. On Titan, methane is [music] the rain.

[00:03:00]And it doesn't rain the way it does here. The air is thick, and the gravity is weak, so the drops grow fat. Nearly a centimeter across, roughly twice the size of the biggest raindrops on Earth.

[00:03:10]And they fall slowly.

[00:03:12]Snowflake slow.

[00:03:14]You could watch a single drop drift down for a few full seconds.

[00:03:17]A planetary scientist put it simply, on Titan, it rains methane.

[00:03:24]But you'd be waiting a long time to see one. Rain on Titan is rare. In any one place, it might be centuries between storms. And then, a downpour heavy enough to darken the ground for weeks. A desert made of fuel that floods once an age.

[00:03:39]And when that rain reaches the sea, this is where it gets genuinely hard to believe.

[00:03:48]Near Titan's North Pole, there are seas.

[00:03:51]Not puddles.

[00:03:52]Seas. The largest is called Kraken Mare, and it is bigger than all five of Earth's Great Lakes put together.

[00:03:58]Its neighbor, Ligeia Mare, is about the size of Lake Michigan and Lake Huron combined.

[00:04:04]In 2013, a passing spacecraft bounced radar off one of them and timed the echo coming back, and for the first time in history measured the depth of a sea on another world.

[00:04:13]Ligeia came back about 170 m deep, deep enough to swallow a 50-story building.

[00:04:19]And every drop of it is liquid methane and ethane, natural gas cold enough to pool like an ocean.

[00:04:25]Stand on that shore and everything betrays you at once. The waves are gas.

[00:04:29]The beach is soot. The bedrock under your boots is water, but frozen at nearly minus 180°. It's harder than most rock on Earth. Nothing you could ever skate on.

[00:04:40]On Titan, water is the mountains.

[00:04:42]Now, a sea of natural gas the size of the Great Lakes tends to raise a very human question. If the whole place is fuel, could we ever use it? The answer is one of the best jokes in the solar system.

[00:04:57]NASA ran the numbers years ago, and they are staggering.

[00:05:01]Titan has hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on Earth.

[00:05:07]Hundreds of times, combined.

[00:05:09]A single one of Titan's larger lakes holds more energy as methane and ethane than all of Earth's proven natural gas.

[00:05:15]The dark dunes around its equator hold hundreds of times more carbon-rich material than every coal deposit on our planet.

[00:05:21]By raw quantity, Titan is the richest fuel depot in the solar system, >> [music] >> a planet-size tank of gasoline.

[00:05:27]And you cannot light a single drop of it because fire needs two things, fuel and oxygen.

[00:05:33]>> [music] >> Titan has an ocean of fuel and almost no oxygen at all. Its air is nitrogen and methane. Strike a match on Titan and nothing happens. Drop a torch into a lake of liquid natural gas and it just sits there cold and dark.

[00:05:45]The greatest fuel reserve we have ever found is a place where a campfire is physically impossible.

[00:05:51]So, the richest energy world in the solar system is useless as an energy source, and it's a billion and a half kilometers away, so nobody's shipping it home, either. For years, that was the whole story, a cosmic tease.

[00:06:03]But lately, scientists have started asking a different question.

[00:06:06]Not how do we bring Titan's fuel to us, but what if we went there and used it on the spot? Because here's the twist. To fly a rocket, you need fuel and oxygen.

[00:06:15]Titan hands you the fuel for free.

[00:06:17]Pump methane straight out of a lake, and the oxygen is locked inside all that water ice lying around as bedrock.

[00:06:23]Crack it apart, and you have the other half.

[00:06:26]Methane and oxygen, that is rocket propellant.

[00:06:30]The same kind our biggest rockets burn today.

[00:06:33]On Mars, making fuel is a grind. You synthesize it out of a thin atmosphere.

[00:06:38]On Titan, you practically dip a bucket in a lake, which is why a serious idea keeps showing up in the research now.

[00:06:43]Titan is a filling station.

[00:06:45]The gas stop at the edge of the solar system.

[00:06:48]>> [music] >> A place a ship could land, tank up, and push on toward Uranus, Neptune, and beyond.

[00:06:53]The fuel you can't burn at home might be exactly the fuel that carries us further from home than we've ever gone.

[00:06:59]And that isn't the first time Titan has quietly made [music] history.

[00:07:02]Cuz and most people have completely forgotten this, we have already landed there.

[00:07:11]In 2005, a small probe named Huygens let go of a NASA spacecraft, fell for 2 and 1/2 hours through Titan's orange haze, and touched down softly on the surface.

[00:07:20]>> [music] >> Let that sit for a second. We have set a machine down gently on the surface of a moon of Saturn. It is still the most distant landing humanity has ever made.

[00:07:30]The only time we've ever touched down anywhere in the outer solar system.

[00:07:32]Nothing has come close since.

[00:07:35]And as it drifted down under its parachute, it took pictures. [music] You can watch them stitched together.

[00:07:40]The haze thinning, a coastline resolving out of the murk, dark channels branching across a pale plane exactly like rivers seen from an airplane window. Then the ground rushing up. And a final photograph from the surface itself, a flat plane scattered with rounded pebble-shaped stones, smooth as if by flowing liquid. Stones of ice on a beach that had clearly recently been wet.

[00:08:01]After a 2 and 1/2 hour descent, >> [music] >> Huygens was down. The first landing in the outer solar system.

[00:08:08]It sent home data for a few hours until its battery went flat and Titan fell quiet again.

[00:08:14]The most extraordinary landing in human history, and it barely left a ripple.

[00:08:18]>> [music] >> We did it once, 20 years ago, mostly forgot.

[00:08:22]But the pictures prove something else.

[00:08:24]That surface is more than alien scenery.

[00:08:27]It might be the most inviting ground in the solar system for one very specific dream.

[00:08:36]Remember those two facts about Titan?

[00:08:38]>> [music] >> Thick air and weak gravity.

[00:08:40]Put them together and something close to magic falls out of the physics.

[00:08:44]Titan's gravity is about 1/7 of Earth's, so everything weighs a fraction of what it does here. And its air is four times denser than the air you're breathing right now.

[00:08:53]Lots of thick air to push against and hardly [music] any weight to lift.

[00:08:58]Which means on Titan a human being could fly. Not in a machine.

[00:09:02]Strap a decent pair of wings to your arms, flap, and according to the actual [music] physics, you'd lift off the ground and glide the way a bird does.

[00:09:09]Something no amount of effort will ever let you do in Earth's thin air under Earth's heavy pull.

[00:09:13]On Titan, it's just an afternoon.

[00:09:16]You'd need the suit, obviously. It's still nearly minus 180°.

[00:09:20]But soaring through an orange sky over rivers of methane on your own two wings is not science fiction out there.

[00:09:27]It's a Tuesday.

[00:09:28]And that same gentle physics is exactly why the next machine we send to Titan won't land and sit still. It's going to fly.

[00:09:39]Here is the last race thing about Titan.

[00:09:41]Maybe the strangest. That orange haze, the thing that hit the surface for so long.

[00:09:46]It's built from complex organic molecules. Carbon-based chemistry forming high in the atmosphere and drifting down like a slow tarry snow.

[00:09:54]And that chemistry looks a great deal like the chemistry scientists believe covered the early Earth before life began.

[00:10:00]Titan may be a frozen snapshot of our own planet's infancy. The raw ingredients of life paused, kept on ice for 4 billion years waiting to be read.

[00:10:09]So, we are going back to read them.

[00:10:12]NASA is building a mission called Dragonfly.

[00:10:15]A nuclear-powered rotorcraft, essentially a car-sized drone with eight blades that will do the exact thing we just said a person could.

[00:10:22]It will fly.

[00:10:23]Hopping from site to site across Titan's dunes, sampling that chemistry, asking whether the building blocks of life ever started assembling themselves out there the way they once did here.

[00:10:33]Dragonfly is a nuclear-powered drone built to fly from site to site across Titan.

[00:10:38]It launches in 2028. It arrives in 2034.

[00:10:43]And when it lifts off Titan's surface for the first time, it'll be the first aircraft humanity has ever flown on another world.

[00:10:49]>> [music] >> So, think back to that beach.

[00:10:52]The slow orange rain, the sea of fuel you can't burn, the ice that plays the part of stone. It looks like the most familiar place imaginable, and it's one of the most alien. A working copy of Earth's machinery run on the wrong chemicals out in the freezing dark.

[00:11:06]The question that's left is the one Dragonfly is flying a billion kilometers to ask.

[00:11:11]Is Titan a dead end, a beautiful frozen accident, or are we looking at a picture of where [music] we came from, and maybe a glimpse of where we're headed next?

[00:11:19]If Titan can hide a whole ocean of fuel in plain sight, the sky right over your head is hiding something, too.

[00:11:26]Tonight, most of humanity looks up and can no longer see our own galaxy.

[00:11:30]And here's what took it.