シャドーイング練習: What NASA Found on Io - YouTubeで英語スピーキングを学ぶ
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Out here, deep into space and far away from the sun,
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Out here, deep into space and far away from the sun,
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you might expect everything to be frozen and lifeless.
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And yet, we find images like this,
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captured by one of NASA's most advanced research probes,
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that shows us these bizarre structures seemingly created by a process that is unlike anything we know on Earth.
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Earth.
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Jupiter's moon Io is more alive than any other body in our solar system.
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Its rocky surface is caught up in a raging battle between fire and ice.
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Meanwhile, scientists on Earth have only just begun to uncover the hidden forces that are driving this chaos.
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The Jupiter system is home to nearly 100 officially recognized moons,
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a number that continues to grow as we discover new objects orbiting the giant planet.
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Most of them are very small,
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but four are exceptionally large.
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We call these the Galilean moons,
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as they were first recognized by the 16th century astronomer Galileo Galilei using one of the first telescopes ever made.
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The outer two moons are the largest, Callisto and Ganymede.
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Both are solid orbs of ice and rock with dead, heavily cratered surfaces.
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Second in line is Europa,
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which is made from a thin,
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smooth sheet of ice floating on a vast ocean of liquid water.
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It's one of the most promising locations in the solar system to find extraterrestrial life.
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And then closest to Jupiter is Io,
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just 350,000 kilometers above the clouds of the gas giant,
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not much further than the distance between Earth and our moon,
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and about the same size,
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just a little bigger and heavier.
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Io is actually the most dense moon in our solar system,
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and that's because it's made almost entirely of rock and metal,
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while most of the other large moons out here are made of ice and rock.
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The difference is so extreme
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that Io is believed to have the lowest water content of any known body in the solar system,
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even drier than Mercury, the closest planet to the sun.
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But what really makes Io special is the action on its surface.
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This is the only location outside of the Earth where we know that volcanoes are erupting on a regular basis.
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Io is actually the most volcanically active place in our entire solar system,
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with up to 400 active volcanoes dotting the entire surface of the Moon.
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This discovery was first made by the Voyager 1 probe during its Jupiter flyby in 1979.
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Even from a distance of 20,000 kilometers and using primitive,
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low-resolution cameras, Voyager was able to see nine distinct volcanic eruptions blasting out from the moon's surface.
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These raging lava flows exist in stark contrast to a world that is consumed by a deep freeze.
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Outside of the volcanic zones,
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the surface temperature of Io drops down to negative 130 degrees Celsius.
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We know that the Sun is too far away to contribute any warmth to the Jupiter system,
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so where does all of this heat come from?
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First, we need to appreciate that Io is caught up in a very treacherous location.
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At this close distance to Jupiter,
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it's just far enough away to avoid getting sucked in or even torn apart by the planet's massive gravity.
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But that doesn't mean that Io is in a safe place either.
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The extreme gravity from Jupiter still pulls on the moon's surface hard enough to stretch the rock and distort its shape.
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And then on the other side there are these three other large Galilean moons,
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and they exert their own force of gravity.
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Not nearly as strong as Jupiter,
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but still enough to pull Io in the opposite direction,
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which disrupts its orbit around Jupiter.
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So instead of moving in a circular pattern,
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Io orbits in an oval shape,
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meaning sometimes it's really close to Jupiter and other times it's further away.
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So it never gets an even exposure to that extreme gravity,
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and it cycles back and forth about once every two days,
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constantly being stretched and released and changing shape as it moves along.
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The result is that Io experiences some pretty massive tidal bulging.
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This is the same effect that we see with the ocean on Earth.
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Our own moon has enough gravity to pull up on the water,
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causing high and low tides.
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The rise of the ocean on Earth is only about half a meter on average.
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Different coastal locations will experience varying amounts of tidal change based on their geography,
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but in the middle of the ocean the change is very small.
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On I.O., the gravity of Jupiter does something insane,
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lifting the surface by as much as 100 meters when the two bodies are at their closest distance.
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And that is not just pulling up water,
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That's stretching solid rock and essentially giving the moon itself a slight egg shape.
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All of this stretching and squeezing acts like a pump
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that drives energy into the center of Io and powers all of this volcanic activity.
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But these volcanoes do not function in the same way that we see on Earth.
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If you think about a volcanic eruption,
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you probably imagine a big pointy mountain with lava and ash shooting out from the top.
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These tend to form along areas where tectonic plates collide,
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and force rock up from below the surface.
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I.O doesn't have plate tectonics,
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so lava just tends to erupt from cracks that form as a result of the constant gravitational stretching.
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The initial release of energy can throw lava dozens of kilometers above the moon's surface,
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and above that, a plume of sulfur gas can rise for hundreds of kilometers.
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Sulfur is always present in volcanic activity on Earth as well.
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If you ever see a lava rock that has all of these round holes all over it,
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those are created by trapped pockets of sulfur gas.
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The result of this is a sulfur atmosphere that surrounds Io.
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Depending on the level of volcanic activity at any given time,
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the atmosphere can range from about one-third the density of Earth's to nearly double.
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Most of the sulfur that gets released will eventually settle back down and cover the moon's surface.
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This is what creates the range of vibrant colors that we see from orbit.
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The yellow regions are sulfur that has been crystallized by the low temperatures, essentially snow.
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The white and blue patches are frozen sulfur dioxide that exist in the coldest shadow regions of the moon.
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The green areas are sulfur monoxide which is created by interactions with Jupiter's radiation belt in the upper atmosphere.
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And then, the red areas are hot spots of recent volcanic activity where the sulfur is still being actively heated.
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Going back to what we mentioned earlier,
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volcanic activity on Io does not create mountains or raised shield structures like it does on Earth.
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Instead, after the initial violence of the eruption,
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the moon's surface tends to collapse down and molten rock fills the void to create these giant lava lakes.
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The biggest one is named Lohipatara.
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It's 200 kilometers in diameter,
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and in the center, there's a big island of solidified rock surrounded by an active churning lake of molten rock.
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Now because of all this volcanic activity,
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you might think that Io is composed just like the Earth,
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with a solid crust layer floating on top of a magma ocean.
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But we are pretty sure that's not the case.
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Probes sent to the Jupiter system have been able to measure the gravity field of the Moon,
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and what they notice is a very uneven pull of gravity around the surface.
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That tells us the magma is not evenly distributed,
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it's probably trapped in localized pockets of molten rock
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that are created in the areas that experience the largest amount of tidal flexing.
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So what you end up with are hundreds of separate volcanic engines hidden underground,
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which means every volcano is going to behave a little differently.
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Okay, here's another mystery.
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If volcanoes and plate tectonics aren't creating mountains on I.O.,
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then where did this thing come from?
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This is called Steeple Mountain.
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At somewhere between 5 and 7 kilometers in height,
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it's one of the most iconic views associated with I.O.,
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mostly because it looks a lot like the spire of a church steeple,
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or the Eye of Sauron.
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We are able to see such detailed images like these thanks to data collected by NASA's Juno spacecraft,
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which arrived at Jupiter in 2016 on a five-year mission to study the atmosphere of the gas giant.
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After completing that goal, Juno was repurposed to investigate the four Galilean moons.
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The probe completed two close flybys of Io,
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the first in December 2023 and a second in February 2024,
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coming within 1,500 kilometers of the surface.
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What Juno saw out there is possibly the most unique landscape in our solar system.
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It quickly found that Steeple is actually just one of many tall,
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spiky mountains dotted around the surface of Io.
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The tallest of them rises 18 kilometers,
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or about double the height of Mount Everest.
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And what's really interesting is that unlike Everest,
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these structures on Io are all just kind of lone wolves.
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There are no dense groupings or mountain ranges to be found,
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just these seemingly random peaks stabbing straight up into the air.
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That tells us that these mountains did not form slowly over time.
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Instead, they burst from the ground suddenly,
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like an alien from a guy's chest in that movie Alien.
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Now, we're pretty sure that this is all still linked to volcanic activity,
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just in a very unusual way.
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So earlier, we talked about how the lava flow tends to cause the surface of Io to collapse
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and form these giant lakes.
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The idea is that this downward pressure into the surface actually causes a nearby area of rock to get pushed up.
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Imagine if every time a sinkhole opened on the Earth,
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a new mountain just sprung up right beside it.
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That is kind of what we're looking at here.
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The result would be unlike any mountain you've ever seen before,
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and this is the kind of bizarre natural process that has been playing out on I.O for billions of years,
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with the surface in a constant state of rise and fall thanks to the relentless pull of Jupiter's gravity.
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Sadly though, these images could be the last we ever see of Io.
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With NASA's Juno spacecraft slowly running out of fuel,
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it's set to be replaced by two new robotic explorers of the Jupiter system.
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One is called JUICE, which stands for the Jupiter Icy Moons Explorer.
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It was made by the European Space Agency and launched in 2023.
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When it arrives at Jupiter in 2031,
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JUICE will investigate three of the Galilean moons, Ganymede, Callisto, and Europa.
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Europa, looking specifically at their icy surfaces and hidden oceans of liquid water.
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Then there is NASA's latest deep space probe,
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the Europa Clipper, which launched in 2024 and will arrive at its destination in 2030.
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As you can probably tell from the name,
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this mission is directed specifically at the moon Europa
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and will be primarily looking for signs of alien life in the watery depths below its surface.
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That leaves Io as the odd one out.
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There is no probe heading there any time in the near future,
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and that's not because IO isn't deeply fascinating in its own right,
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it's largely
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because we didn't realize just how interesting the moon was until we saw these Juno images just a couple of years ago.
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Also it definitely doesn't have aliens,
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which automatically drops down to priority level.
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But priorities are changing at NASA.
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There is exciting new leadership coming in,
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there are unprecedented new rocket technologies emerging,
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and sometime in the not-so-distant future,
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we could be studying the deep solar system just as thoroughly as we investigate Mars and the Moon.
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Until then, we'll always have Steeple Mountain.
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このビデオで話す練習をする理由は？
「NASAがイオで見つけたもの」のビデオを利用して話す練習をすることには大きな利点があります。このビデオでは、宇宙、特に木星の衛星イオについての独特な情報が提供されています。具体的なテーマや専門用語が豊富に含まれており、これを通じて学ぶことで、科学英語や自然言語処理のスキルを高めることができます。YouTubeで英語学習をする際、このような興味深い内容を選ぶことは、モチベーションの維持にも役立ちます。
文法と表現の文脈
- “is made from”: この表現は、何かがどのように構成されているかを説明する際に使用されます。例えば、「イオは岩と金属で構成されています」という文脈で使われています。
- “is believed to” : このフレーズは、ある情報が真実であると考えられていることを示します。「イオは水分が最も少ないと考えられています」といった具合に、英語の会話で自然に使用することができます。
- “is caught up in”: これは、何かに巻き込まれている状態を説明する表現です。ビデオでは、イオが木星の重力に巻き込まれている様子が語られています。
- “drops down to”: このフレーズは、温度や数値が下がることを表現する際に便利です。「表面温度はマイナス130度まで下がります」といった文で使われています。
一般的な発音の罠
このビデオにはいくつかの発音の難しい単語やフレーズがあります。特に「volcanoes」（火山）や「Jupiter」（木星）の発音は注意が必要です。これらの単語はスピードが速い会話の中では、正確に発音することが難しいです。また、「active」（活動的）や「scientists」（科学者）といった単語も、しっかりとした発音を心掛けることで、リスニング力やスピーキングのパフォーマンスを向上させることができます。このように、発音の練習も行いながら、ビデオに沿ったシャドースピーチを行うことで、IELTSスピーキング対策にも非常に役立ちます。
シャドーイングとは？英語上達に効果的な理由
シャドーイング（Shadowing）は、もともとプロの通訳者養成プログラムで開発された言語学習法で、多言語習得者として知られるDr. Alexander Arguelles によって広く普及されました。方法はシンプルですが非常に効果的：ネイティブスピーカーの英語を聞きながら、1〜2秒の遅延で声に出してすぐに繰り返す——まるで「影（shadow）」のように話者を追いかけます。文法ドリルや受動的なリスニングと異なり、シャドーイングは脳と口の筋肉が同時にリアルタイムで英語を処理・再現することを強制します。研究により、発音精度、抑揚、リズム、連音、リスニング力、そして会話の流暢さが大幅に向上することが確認されています。IELTSスピーキング対策や自然な英語コミュニケーションを目指す方に特におすすめです。