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  • Is there water on the Moon

  • The obvious answer seems to be No. because during a day

  • on the Moon, which lasts 2 earth weeks,

  • the temperature on the lunar surface

  • gets up to 123 degrees celsius,

  • which would be enough to boil away any water

  • if the Moon had an atmosphere like Earth,

  • which it doesn't.

  • And the reason that it doesn't

  • is because the Moon's gravity is weak,

  • just a sixth of Earth's gravity, which means

  • it can't hold onto light fast moving

  • molecules like water. Anything going

  • faster than 2.4 kilometers per second

  • the Moon's escape velocity is gone.

  • But that might sound pretty quick, but at any

  • given temperature there are always a

  • small number of molecules going

  • significantly faster than the average.

  • On the Moon

  • these molecules flap into space and then

  • other molecules take their place until

  • all the light fast moving molecules

  • are gone.

  • Plus, since the Moon has a very weak

  • magnetic field, there's little to protect

  • the lunar surface from the solar wind.

  • That's the stream of charged particles

  • coming from the Sun. These particles can

  • effectively blast molecules from the

  • surface of the Moon into space.

  • In fact that's how Mars lost most of its atmosphere.

  • So in short, if the Moon ever

  • had any water, it should be long gone by now.

  • And this appeared to be confirmed by

  • the Moon landings. Rock samples brought

  • back by Apollo astronauts

  • contained virtually no hydrated minerals.

  • Some water was detected but it was assumed

  • just to be terrestrial contamination

  • rather than actual Moon water, because

  • seals on some of the sample-return

  • containers were damaged by the gritty moondust.

  • But in 2009 a very different

  • picture emerged, when scientists

  • intentionally crashed part of a rocket

  • into the surface of the Moon.

  • It was going two point five kilometers per second

  • on impact, making a crater 25 meters wide

  • and 4 meters deep.

  • That injected 10,000 tons of material

  • with half of it making high enough to be lit

  • by the Sun. That allowed cameras on an

  • orbiting spacecraft, to look for the

  • emission lines of water in the dust.

  • And what did they find ?

  • The water emission lines were bright.

  • Scientists estimated that five

  • point six percent the mass of the

  • objective debris was water.

  • but how is this possible? Where did the

  • water come from and hadn't remain

  • on the Moon?

  • Well strangely enough, there are actually

  • three different sources of lunar water.

  • To understand the first source, you just

  • have to look at where they crashed that

  • rocket into theMmoon. Now it's a

  • misconception that the Moon has

  • a dark side.

  • Although the same side always faces earth,

  • all sides of the Moon do receive

  • sunlight.

  • However, at the poles there are some

  • craters which due to their location and depth,

  • are always in shade. They're called

  • but permanently shadowed regions.

  • Now since they never see the Sun,

  • these craters are some of the coldest places

  • in the whole solar system, colder than

  • the surface of Pluto. They can reach

  • negative 249 celcius. And it is here that

  • scientists decided to crash that piece

  • of rocket. Since the permanently shadowed

  • regions maintain such a consistently low

  • temperature, they act as cold traps

  • places where volatiles like water

  • remained frozen as ice.

  • But, where the water come from in the first place?

  • Well, from water containing comets

  • and asteroids that have struck the Moon over time.

  • Any water molecules that found

  • their way to the permanently shadowed regions

  • would be trapped there. Forever.

  • as ice but this is not the only source

  • of water on the Moon.

  • In a lunar samples from Apollo 15 and 17,

  • scientists found tiny glass beads. These beads were formed

  • back when the Moon was still

  • volcanically active. Fire fountains

  • launch droplets of lava into space, where

  • they cooled rapidly and then fell back

  • to the surface. In 2007 these beads were

  • sliced in half and tested for water.

  • The results showed significant amount of

  • water with concentrations highest in the

  • middle of the beads, and this indicates

  • that the water must have been trapped there

  • during the initial eruption, rather

  • than leaching in due to contamination

  • once those beads were back on earth.

  • Now, this water came from the interior of

  • the Moon. So the Moon must have contained

  • water to begin with, which kind of makes sense

  • considering the Moon is likely a

  • piece of Earth that broke off billions

  • of years ago in an impact with a mars-sized

  • body.

  • The third and final source of water

  • on the Moon is : Water created on the Moon

  • surface from the reaction of oxygen and hydrogen.

  • Now, the source of oxygen is easy.

  • Oxygen makes up

  • 45 percent of the lunar surface

  • mostly bounded oxide mineral. But where

  • do you get the free hydrogen? The answer

  • is in the solar wind, which is constantly

  • bombarding the Moon surface with protons.

  • These can react with oxygen, to form

  • hydroxide, and ultimately water.

  • This water can then drift over the surface of

  • the Moon until either flys off into space,

  • or it lands in the cold traps and becomes ice.

  • So there is water on the Moon.

  • And this is important because

  • it means that future missions can take

  • advantage of this valuable resource.

  • Not only for Moon colonists to drink and

  • grow crops, but also for processing into

  • rocket fuel. If you can make your own

  • rocket fuel on the Moon, that

  • dramatically reduces the challenges and

  • cost of space travel. For a long time we

  • used to think the Moon was completely dry.

  • But now we know that hypothesis is all wet.

  • Big news! I have a brand new channel

  • called Sciencium, posting videos in this format.

  • So if you enjoyed this video,

  • you should go check out that channel

  • and subscribe to it.

  • the more of you who do, the more videos I will make

  • over there. Now, making this new channel

  • was made possible by Google's making and

  • science initiative, team that seeks to

  • inspire people to learn more about

  • science and pursue their science goals.

  • And of course none of this would be possible

  • without your support on patreon.

  • so I want to thank you for supporting me,

  • and I want to thank Google for making it

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  • goals and make a new channel all about

  • awesome discoveries in science.

  • So if you click on this link,

  • I will see you over on the new channel.

Is there water on the Moon

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月に水? (Water on the Moon?)

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    林宜悉 に公開 2021 年 01 月 14 日
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