00:00Beneath the frozen surface of Uranus's moon, Ariel, something massive may be hiding an ocean more than 100 miles deep.
00:09That's 40 times deeper than the Pacific Ocean.
00:12And it's been sealed up under ice for billions of years, waiting to be discovered.
00:18So Uranus is this pale blue gas giant way out there, the loner planet that never gets much attention.
00:25But recently, scientists turned their telescopes and computer models toward one of Uranus's 29 known moons, Ariel.
00:33Compared to its sisters and brothers, Ariel's got quite a unique personality.
00:39When the Voyager 2 spacecraft flew by in 1986, it caught some photos showing an oddly smooth surface peppered with craters, fractures, and valleys.
00:50Those details might not sound exciting until you realize what they mean.
00:54This moon was geologically active, moving, cracking, and reshaping itself like Earth does.
01:02That's rare in the outer solar system, where most moons are just frozen popsicles, quietly spinning around their planet.
01:09When scientists studied those fractures, technically called grabins, they found something strange.
01:16The pattern of these cracks looks exactly like what happens when there's pressure building underneath the surface, like a balloon stretching before it pops.
01:26It's as if something deep inside Ariel was pushing outward, warping, and breaking the crust.
01:32The most logical culprit would be a subsurface ocean, which was once warm enough to push against the icy layers above it.
01:39An ocean sealed under miles of ice, hidden for billions of years.
01:46So, how would something so far from the Sun even have liquid water?
01:51Well, Ariel's orbit isn't perfectly circular, but slightly oval, which scientists call eccentric.
01:58That means, as it circles Uranus, the gravitational pull changes a little each time.
02:05The constant tugging stretches and flexes the moon's interior, creates friction, and voila, generates heat.
02:13Combine that with natural radioactive decay inside the rocky core, and suddenly, you've got enough warmth to melt ice deep below the surface.
02:22So, Ariel might have been making its own geothermal spa out there in the middle of nowhere.
02:29Scientists modeled its interior structure, and found that the stress the tidal forces were causing could have kept liquid water stable for millions, maybe even billions of years.
02:40Even cooler, or warmer in this case, is that traces of that ocean may still exist.
02:46Ariel's icy shell shows features that look recent, geologically speaking.
02:52That means the moon hasn't been completely frozen for all eternity.
02:57Beneath those fractures, there could still be small pockets or thin layers of liquid water.
03:03And this brings up the most exciting part.
03:07Water means potential life.
03:09Every time scientists find signs of liquid water somewhere in the solar system, they start whispering that question we all secretly love.
03:18Could something live there?
03:20Sure, Ariel's no tropical resort.
03:22But remember, on Earth, we've found microbes thriving near hydrothermal vents at the bottom of our oceans, living off chemicals, not sunlight.
03:31If Ariel once had similar vents pumping heat and minerals into its ocean, it could have easily hosted its own microscopic residence.
03:42And if there was an ocean there once, it could still have salt in its interior.
03:47Scientists believe salts and ammonia could act like antifreeze, keeping the water liquid longer.
03:53So even though the surface temperatures dropped to minus 351 degrees Fahrenheit, the inside could stay cozy enough for water to remain unfrozen.
04:05Now, before you start packing for Uranus, let's remember this is a moon orbiting a gas giant that's about 1.8 billion miles away from us.
04:15Visiting it isn't as simple as booking a plane ticket.
04:18Voyager 2 is the only spacecraft that's ever gotten even close, and that was almost 40 years ago.
04:25We have better photos of Mars' sand dunes than we do of most Uranian moons.
04:30So, for now, scientists rely on clever modeling, telescope data, and a lot of patience.
04:37Still, this discovery is big.
04:39For decades, we've looked at moons like Jupiter's Europa or Saturn's Enceladus as the best representatives of the ocean world category.
04:49They're icy, they have subsurface oceans, and scientists have actually detected water plumes jetting into space from them.
04:57But now, Ariel joins the club.
05:00If we ever send another mission to Uranus, Ariel would be a prime target for exploration.
05:05Now, another destination worth checking out is Saturn's moon, Mimus.
05:11Scientists have always thought it was just a frozen rock ball.
05:15But it might be hiding a whole ocean underneath its surface, and a future spacecraft could find it.
05:22Researchers have been mapping how thick the moon's icy crust is.
05:26And those maps help them figure out how old this ocean could be and where the ice is thinnest.
05:32That's the jackpot spot for future missions to check for liquid water.
05:37Mimus doesn't look like a typical ocean world.
05:40When you look at Europa or Enceladus, you can literally see the cracks and crevices in their icy shells.
05:47Mimus looks smooth and quiet, almost like a cue ball in space.
05:52The craters look permanent, carved in rock rather than ice.
05:56Nothing about it screams ocean world.
05:58But a few years ago, data from NASA's Cassini spacecraft started telling us otherwise.
06:05Cassini, the probe that gave us our best tour of Saturn and its moons,
06:10kept sending back info that didn't quite make sense unless Mimus had liquid water under all that ice.
06:17The more Cassini's data rolled in, the more it looked like there might be a newborn ocean
06:23hiding under 12 to 19 miles of solid ice.
06:27Scientists used models, originally made for Europa, to figure out how heat moves through Mimus's icy shell.
06:34They wanted to know how thick it was, how much heat it could trap, and whether it could melt ice below.
06:41And they found that once melting starts on Mimus, it doesn't stop.
06:47It accelerates, and really quickly.
06:49All that melting ties back to Mimus's orbit.
06:52The moon doesn't orbit Saturn in a perfect circle.
06:55Its path gets a little stretched.
06:58That oval shape means the moon gets pulled and squeezed by Saturn's gravity as it orbits.
07:04The same way the moon's gravity gives us tides here on Earth, Saturn's gravity tugs on Mimus.
07:10But instead of water tides, it's flexing solid ice.
07:14And that flexing creates heat.
07:16So, at some point, something kicked Mimus into a slightly weirder orbit.
07:22Maybe a collision or a gravitational nudge from another moon.
07:26The inside of Mimus heated up, melted some of its ice, and created an ocean under the surface.
07:33But then, gravity slowly started to pull Mimus's orbit back into a circle again.
07:38When it does that, the heating will stop, and eventually, the ocean will freeze all over again.
07:45So, basically, Mimus is in its warm, ocean-having phase right now.
07:51Computer models show that the orbital change probably happened just 10 to 15 million years ago.
07:57That's nothing in space-time.
07:59It also turned out that the heat on Mimus doesn't move in a simple straight line.
08:04It kind of loops and twists, depending on how thick the ice is.
08:08Which means finding this ocean won't be easy.
08:12But it's not impossible.
08:14Studying possible ocean worlds, and the ones of which we already know for sure,
08:19like Europa and Cetalus, Titan, and Callisto, is crucially important for us down here on Earth.
08:25Every time humans find liquid water somewhere new,
08:29we're basically discovering another version of the one thing that made us possible.
08:35Earth's oceans gave birth to everything alive, including us humans.
08:40When scientists learn how Europa's or Cetalus's oceans stay liquid without sunlight,
08:46they learn something about Earth's deep-sea vents, about heat and balance.
08:50When they model Titan's chemistry, they're basically looking at what Earth might have been like before life began.
08:58So maybe life isn't that rare.
09:01And one day, a probe will dip into the icy ocean of Europa with NASA's Europa Clipper,
09:07or scoop up water from Cetalus's geysers and find something.
09:12Even a single living cell.
09:14And when that happens, it'll rewrite everything we think we know about life.
09:19It'll also remind us we're not the center of the story,
09:23but just one chapter in a universe full of water.
09:27That's it for today.
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