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Imagine you're standing on a primitive Earth,

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billions of years ago.

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Oh, wow.

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It's not the peaceful blue planet we know today, though.

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It's a wooden world.

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Really?

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Yeah.

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Yeah.

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And it's constantly being bombarded

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by asteroids and planetoids.

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Yikes.

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It's chaos, like a cosmic demolition derby,

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where planets are basically billiard balls

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smashing into each other.

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That's a pretty intense picture.

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Well, welcome to Cosmos in a Pod, the space and astronomy

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series.

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Please like, comment, share, and subscribe.

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Today, we're diving deep into the solar system's wild past.

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Exciting.

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We're going to explore how those giant impacts shape

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the planets and moons we see today.

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Those collisions weren't just fender benders.

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We're talking impacts so powerful

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they could shatter planets, tilt them on their axes,

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even create entire moons.

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So let's start at the very beginning.

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What was the early solar system like?

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Well, picture this.

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A swirling disk of gas and dust left over

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from the sun's formation.

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OK, I can see it.

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Over millions of years, gravity pulled those particles

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together, forming bigger and bigger clumps.

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Like a snowball effect.

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Exactly.

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These clumps became planetary embryos,

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some the size of our moon, others as big as Mars.

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So those embryos were the building blocks of the planets.

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Precisely.

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But the solar system was a crowded place.

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These embryos were constantly moving around,

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colliding with each other.

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It was a chaotic dance, and collisions were inevitable.

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And I'm guessing those collisions weren't exactly

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gentle.

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Definitely not.

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Picture two planetary embryos each

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traveling at tens of thousands of kilometers per hour,

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smashing into each other.

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Wow.

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The energy released would be unimaginable.

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It would melt rock, vaporize oceans, and fling debris

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into space.

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Sounds more like a science fiction movie than reality.

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It does, but it's how our solar system formed.

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And these impacts were crucial in shaping the planets.

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So the inner solar system, with Mercury, Venus, Earth,

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and Mars, was especially chaotic.

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Exactly.

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And that chaos led to the formation

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of the moon, the most familiar object in our night sky.

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It's hard to believe the moon, with its gentle light,

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is a result of a cataclysmic event.

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It is, but the evidence points to a giant impact.

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Picture a young molten earth being

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struck by a Mars-sized protoplanet named Theia.

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Theia, like the mother of the moon goddess

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in Greek mythology.

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Precisely.

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The name is fitting because this impact,

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about 4.5 billion years ago, was a head-on collision that

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changed Earth forever.

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Wow.

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The impact was so powerful that it

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ejected a massive amount of molten rock and debris

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into orbit around Earth, forming a ring.

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And from that ring, the moon was born.

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Exactly.

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Over time, gravity pulled the debris together.

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It cooled and solidified.

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And eventually, it formed the moon we see today.

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So a single event, billions of years ago,

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had a huge impact on our planet.

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It did.

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It affected the length of our day and the stability

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of our climate.

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To name a few.

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Incredible.

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It shows how interconnected everything

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is in the universe.

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It really does.

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And speaking of interconnectedness,

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let's move on to Mercury.

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Mercury.

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The smallest planet and the closest to the sun.

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What makes its story so unique?

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Well, Mercury is an oddball.

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It's incredibly dense for its size.

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Its iron core makes up about 85% of its volume.

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That's much larger than any other planet.

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So what explains that oversized iron core?

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The leading theory is that Mercury

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wasn't always this small.

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It was once much larger, maybe twice its current size.

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But then, early in its history, it

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experienced a catastrophic impact.

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Imagine a massive object slamming into Mercury

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and stripping away its outer layers.

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So Mercury was essentially left with just its core

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and a thin crust.

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That's right.

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It's a shell of its former self.

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It makes you wonder what Mercury could

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have been like if it hadn't suffered that impact.

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It's a fascinating thought.

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But the story of impacts doesn't stop there.

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The inner solar system went through an even more chaotic

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period.

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You mean a time when asteroids were raining down

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on the planets.

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Exactly.

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And it all started with the ice giants Neptune and Uranus

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as they moved through the early solar system.

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So they caused problems for the inner solar system.

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You could say that.

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This period, called the Late Heavy Bombardment,

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saw a huge increase in asteroids hurdling

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towards the inner planets, including Mercury.

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It was a time of constant bombardment.

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And Mercury, being the closest to the sun,

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probably took the biggest hit.

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Absolutely.

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Imagine standing on Mercury during that time.

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The sky would be filled with asteroids.

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Impacts would shake the planet to its core.

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One of the most impressive scars from this period

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is the Cholorus Basin, a massive crater

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over 1,500 kilometers wide.

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1,500 kilometers?

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That's huge.

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It gives you an idea of the scale of those impacts.

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And the impact that formed Cholorus

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was so powerful that it created a jumbled terrain

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on the opposite side of Mercury.

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It's like a cosmic battlefield.

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That's a great way to put it.

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And speaking of battlefields, let's talk about Uranus.

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Uranus, the ice giant that's tilted on its side,

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what could cause that?

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Another giant impact.

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But this one knocked Uranus over.

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Picture a massive object, maybe an icy super Earth,

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slamming into Uranus billions of years ago.

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So it's like Uranus was in a cosmic T-bone collision.

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It was an event of unimaginable scale.

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But unlike Earth, Uranus didn't gain a large moon

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from the impact.

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Really?

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Yeah.

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Impactor probably shattered within Uranus's atmosphere.

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Instead, Uranus ended up with a unique system

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of rings and moons, all orbiting on the same tilted plane

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as the planet.

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So we've seen some dramatic impacts,

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from a moon-forming collision to a planet-tilting one.

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What else is there?

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Well, let's head to the outer solar system, to Pluto.

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Pluto, the dwarf planet that captured our hearts.

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Yes.

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And one of Pluto's most captivating features

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is Sputnik Planitia, a vast heart-shaped nitrogen glacier.

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Pluto's heart of ice.

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How did that form?

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Another giant impact, of course.

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Scientists think that billions of years ago, a large object

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struck Pluto, creating a basin that filled with nitrogen ice

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and became Sputnik Planitia.

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So Pluto's heart is actually a scar from a collision.

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Exactly.

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And there's more.

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Underneath that icy heart, Pluto

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might have a subsurface ocean.

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An ocean on Pluto.

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That seems impossible.

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It might sound strange, but there's evidence.

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One clue is Pluto's wobble, its true polar wander.

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Pluto wobble.

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Yes.

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It suggests a large mass beneath the surface,

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dense enough to shift Pluto's balance.

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And that dense mass could be a subsurface ocean.

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Liquid water is denser than ice, so it could cause

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Pluto to reorient itself.

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Wow, I never knew that.

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And there's more.

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The presence of ammonia in Pluto's system is another clue.

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Ammonia, like the cleaning product.

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Yes.

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It acts as an antifreeze, allowing water to stay liquid

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at very low temperatures.

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So even though Pluto is freezing,

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the ammonia might be keeping the ocean from freezing solid.

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That's amazing.

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It's like Pluto's moon, Charon, is

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helping to keep its heart warm.

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That's a poetic way to put it.

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And this ocean on Pluto changes our understanding

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of where liquid water and maybe even life might exist.

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It opens up a whole new frontier of exploration.

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It does.

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These hidden oceans beneath the ice

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could be protecting life from the harsh conditions of space.

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So the solar system is full of surprises.

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Absolutely.

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We should never underestimate the power of nature.

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And speaking of surprises, let's go back to the inner solar

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system to explore Mars.

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Mars.

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What surprises does the red planet have in store for us?

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Well, Mars has a fascinating impact history, too.

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And one impact in particular stands out.

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I'm ready.

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Tell me more.

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So before the break, we were talking

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about that hidden ocean under Pluto's surface.

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Yeah, an ocean on a world so far from the sun.

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It's pretty amazing to think about.

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It really makes you rethink where

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we might find the ingredients for life, huh?

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It does.

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And the evidence for that ocean is strong, too.

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You remember how we talked about Pluto wobbling?

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You mean that true polar wonder thing?

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Exactly.

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Pluto seems to reorient itself over time.

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And that suggests there's something massive

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under the surface, something dense enough

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to throw Pluto off balance.

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And you're saying that dense mass is probably the ocean.

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Right.

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Liquid water is denser than ice.

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So a big subsurface ocean could be pulling on Pluto

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gravitationally and making it reorient itself.

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That's what we're seeing with that true polar wander.

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Wow, it's crazy how something we can't even see

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can affect a whole planet.

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It really shows how everything's connected, even in space.

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And the wobble isn't the only clue, either.

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We've also found ammonia in Pluto's system.

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Ammonia?

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Like the stuff in cleaning products?

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What does that have to do with an ocean?

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Well, ammonia works as an antifreeze.

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It keeps water liquid even at really low temperatures.

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Ah, I get it.

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So even though it's super cold on Pluto,

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the ammonia could be preventing the ocean from freezing solid.

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Exactly.

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Nature finds some pretty clever ways

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to keep water liquid even in the most extreme places.

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It makes you wonder what's in that ocean.

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Is it just water, or is it more like a salty brine?

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Maybe it even has organic molecules.

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Scientists are trying to figure that out.

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Based on what we got from the New Horizons mission,

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we think it's probably very salty, maybe even saltier

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than Earth's oceans.

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A salty ocean on Pluto.

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It's like something out of science fiction.

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It is pretty wild.

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But let's zoom out for a second and think

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about what this means for the solar system as a whole.

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OK, so what does Pluto's ocean tell us

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about the bigger picture?

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It really changes our understanding of where water,

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and maybe even life, could exist.

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We used to think that liquid water was limited

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to the inner solar system.

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Yeah, like Earth and Mars?

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Right.

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But Pluto shows us that water might be much more common,

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even in the outer solar system, where it's super cold.

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So maybe there are more oceans out there

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just waiting to be found.

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It's a whole new frontier.

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And those oceans, hidden under the ice,

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might be protecting life from the harsh radiation

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and freezing temperatures of space.

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It's like the ice is a shield.

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A cosmic incubator.

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Exactly.

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Those hidden oceans could be full of life,

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evolving in ways we can't even imagine.

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That's an incredible thought.

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Nature is always full of surprises.

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And speaking of surprises, let's go back

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to the inner solar system and look at Mars.

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Mars.

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What surprises does the red planet have?

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Mars has had a really interesting history

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with impacts, too.

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And there's one impact that really stands out.

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OK.

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I'm all ears.

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Tell me about it.

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OK, so before the break, we were talking about those giant

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impacts on Mars.

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Yeah, Mars has had a wild ride when it comes to impacts.

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And one of the most impressive scars

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is Hellas Planitia, this huge impact basin

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in the southern highlands.

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Hellas Planitia.

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That's one of the biggest impact craters in the solar system,

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right?

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It is.

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It's massive, over 2,300 kilometers across.

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And it's eight kilometers deep.

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Eight kilometers.

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That's like, what, almost twice as deep as the Grand Canyon?

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It gives you a sense of just how powerful these impacts were.

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The thing that hit Mars to make a crater that big

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must have been enormous, probably hundreds

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of kilometers wide.

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It's almost impossible to imagine the kind of energy

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released by an impact like that.

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It must have been a truly planet-shaking event.

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And Hellas Planitia isn't just a cool feature to look at.

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It might also tell us something about what Mars

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was like a long time ago.

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What do you mean?

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What can a crater tell us about the past?

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Well, scientists think that Hellas Planitia might have once

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been a giant lake, maybe even an ocean.

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The basin is really deep.

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And there are signs of ancient shorelines.

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So you're saying that Mars, even though it's dry and dusty

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now, might have had huge amounts of liquid water

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billions of years ago.

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That's the idea.

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It's pretty exciting to think about.

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And the impacts on Mars didn't stop billions of years ago,

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either.

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There's evidence of much more recent ones,

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even within human history.

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Wait, recent impacts.

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You mean like since humans have been around.

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Exactly.

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In two years 18, a NASA orbiter spotted a brand new impact

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crater in Valus Marineris, that enormous canyon system on Mars.

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So Mars is still getting hit by space rocks today.

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It is.

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Not as often as in the past, thankfully.

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But it's a reminder that our solar system is constantly

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changing.

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And things can happen out there that we need to be aware of.

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It's a little scary, but also really cool to think about.

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It makes you realize how important

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it is to explore space and understand

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what's happening out there.

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Exactly.

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And by studying the impact history of planets like Mars,

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we get a better understanding of what shaped our solar system.

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We've seen how impacts have created moons, tilted planets,

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and maybe even created environments

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where life could exist.

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It's been an amazing journey.

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It really shows you the power of these cosmic events.

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Well, that's all the time we have for today's deep dive

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into the solar system's wild past.

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Don't forget to subscribe to Cosmos in a Pod

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and check out our YouTube channel for more cosmic

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adventures.

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Keep looking up at the night sky and wondering

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about what's out there.

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Until next time.