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  • This Episode is sponsored by the Ridge.

  • Go to ridge.com/space and use promo code "SPACE" to get 10% off your next order.

  • [♪ INTRO]

  • It's been 50 years since humans last walked on the Moon,

  • but that doesn't mean we've stopped exploring our closest neighbor.

  • Countries from all over the world have sent robotic missions to study it,

  • but none has been as important, or as successful, as NASA's Lunar Reconnaissance Orbiter.

  • NASA launched the mission, often called LRO, in 2009 as part of its Vision for Space Exploration program.

  • This was a long-term plan designed to guide the U.S. space program

  • after the loss of the space shuttle Columbia.

  • The goal with LRO wasn't just to do science, but to pave the way for a new era of human exploration.

  • And while we have yet to send people back to the Moon, we can definitely say the LRO has succeeded.

  • The things it's teaching us about our closest neighbor are transforming the way we think about the Moon,

  • and the information we're learning from it will make it much easier for future astronauts.

  • So, in honor of all it's done so far, and to celebrate its 10th birthday,

  • let's look back at three of LRO's biggest accomplishments.

  • For one, this mission showed us that the Moon is not as dry as we used to think.

  • When researchers examined lunar rocks brought back by the Apollo astronauts,

  • they turned out to be almost completely waterless; way drier than rocks found on Earth.

  • That painted a picture of a pretty arid Moon.

  • But some scientists suspected that frozen water

  • might be hiding out in the Moon's deepest craters, which the Apollo program didn't visit.

  • Those spots are so deep that they've never seen sunlight,

  • and can have surface temperatures colder than Pluto, just 35°C above absolute zero.

  • Temperatures like that are too cold for water to sublimate away,

  • and they make it possible for ice to survive in the vacuum of space.

  • But just because water could exist on the Moon didn't mean it had to be there.

  • To find out more, LRO's companion mission, called LCROSS, took one for the team.

  • It sent part of its rocket to smash into the Moon's Cabeus crater,

  • sending a plume of surface debris into space.

  • Then, the LCROSS spacecraft and LRO studied the light from this material

  • as it passed in front of the Sun, and researchers later found that

  • the plume was full of grains of mostly-pure water ice.

  • They pronounced this craterwetter than the Sahara.”

  • That might not sound very impressive, but it showed us that ice can accumulate on the Moon,

  • and that this supposedly-arid place has pockets full of frozen water.

  • Someday, that water could be used to help astronauts on the Moon's surface.

  • But even if not, it's still pretty amazing that it's up there.

  • That's not the only thing LRO has uncovered in hidden ice, either.

  • In 2016, scientists published another big discovery made by the orbiter: the Moon's ancient poles.

  • Besides finding ice at today's poles,

  • LRO found ice deposits offset by about 200 kilometers in opposite directions.

  • If you draw a line between them, it passes directly through the Moon's center.

  • Researchers interpreted this arrangement as evidence of the Moon's old poles,

  • meaning the Moon used to spin on a different axis.

  • Which isn't unheard of in the solar system, but still feels downright weird to think about.

  • Models show that that axis shifted around 3 billion years ago,

  • most likely as mass moved around deep below the surface.

  • This process was slow.

  • The poles drifted only around 2 centimeters every century,

  • but that was enough to knock the Moon off kilter by about 5°,

  • like if Earth's axis shifted from the South Pole to Australia.

  • As sunlight leaked into the once-shady areas, some of that old polar ice probably evaporated,

  • but the rest traced out the path of the moving axis for us to uncover billions of years later.

  • Besides being cool, this finding is also significant because

  • it helps us understand when the inside of the Moon was molten,

  • which is important for studying how the Moon changed and evolved.

  • I mean, it doesn't give us a very specific estimate, but you have to start somewhere!

  • Finally, although LRO is meant to study the Moon,

  • it's actually taught us a lot about the entire solar system.

  • For instance, it took enough images for scientists to create a detailed,

  • billion-year-long timeline of large asteroid impacts on the Moon.

  • And this January, scientists reported that that timeline revealed something strange:

  • Asteroid collisions seem to have more than doubled around 290 million years ago.

  • While that's interesting by itself, that also tells us something surprising about Earth.

  • Scientists have known for a while that Earth has surprisingly few craters older than 300 million years,

  • but they'd always assumed that the craters had just eroded away.

  • Now, LRO is telling us that these aren't just gaps in the record,

  • there were simply fewer impacts back then than the period that followed.

  • Scientists still don't know exactly what happened 290 million years ago,

  • but one idea is the sudden bombardment might point to

  • large collisions in the asteroid belt between Jupiter and Mars.

  • Whatever it was, though, the scars on the Moon point to some major event in the distant past.

  • And figuring out what it was would help us continue to understand

  • how the solar system has changed over its lifetime.

  • Also, on a much broader note, cratering rates on the Moon are also used

  • to determine the ages of surfaces all around the solar system.

  • Like, when scientists first saw Pluto's smooth surface,

  • they assumed it was young because it doesn't have as many craters as the old lunar surface.

  • So the more we understand about the Moon's craters,

  • the more we can infer about all the other objects out there.

  • Of course, even though LRO has taught us so many specific things over the last decade,

  • it isn't valuable just because of those discoveries.

  • LRO is especially important because it lives around the Moon.

  • That means that, if scientists find something interesting,

  • they can ask questions and get answers without having to wait for a new mission,

  • which is pretty unusual in planetary science.

  • Also, as much as space exploration is always pushing new horizons,

  • LRO has shown us that there are still endless things to explore right here in our neighborhood.

  • And even closer to home, sometimes we get bogged down

  • with all the stuff we carry around, and we need to trim down.

  • We all carry around useless stuff.

  • Random receipts, hotel room keys, spent gift cards.

  • The Ridge helps you carry less, but also, have what you need.

  • They help you streamline your life by turning the things you carry,

  • like backpacks, phone cases, and wallets into tools for better living.

  • The Ridge wallet has over 30,000 5-star reviews.

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  • Get 10% off today with free worldwide shipping by going to ridge.com/space,

  • that's ridge.com/space, and use the codeSPACE”.

  • You can find the link in the video description.

  • And if you check them out, it also supports us too, so thanks!

  • [♪ OUTRO]

This Episode is sponsored by the Ridge.

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B1 中級

過去十年中最大的月球發現。 (The Biggest Moon Discoveries of the Last Decade)

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    林宜悉 發佈於 2021 年 01 月 14 日
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