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  • [ ♪ Intro ]

  • In places like southern Canada, a glowing, purple ribbon of light sometimes crosses the sky.

  • It's pretty faint, and it sometimes has these green spikes called the picket fence.

  • It's also pretty speedy, moving steadily east to west about six-and-a-half kilometers per second.

  • Citizen scientists and photographers have known about it for a long time,

  • because it keeps photobombing their pictures of auroras.

  • And after years of seeing it, they even gave it a name: Steve, after the scene from the movie Over the Hedge.

  • But they just assumed it was a funny kind of aurora, or at least something similar.

  • Then, in 2016, Steve caught the attention of professional scientists,

  • who realized this streak might be something new.

  • And last Monday, one team published a paper in Geophysical Research Letters with the newest explanation for it.

  • According to their results, Steveis like nothing we've ever seen before.

  • It might be a whole new kind of northern light.

  • Even though citizens scientists kind of named this streak as a joke, scientists decided to roll with it,

  • and they formally called this light the Strong Thermal Emission Velocity Enhancement.

  • Which is pretty amazing.

  • They could immediately tell it was different from normal auroras for a few reasons.

  • First, auroras usually only appear at lower latitudes during periods of especially high solar activity,

  • but STEVE is a consistently lower-latitude event.

  • And its shape and speed don't really match other auroras, which tend to be broader, undulating structures.

  • Plus, auroras tend to be green or red; purple usually only shows up in extreme cases.

  • Because of this, scientists wondered if there was a unique mechanism at play.

  • Earlier this year, one team published the first explanation for STEVE.

  • They suggested it might be caused by something called a subauroral ion drift, or SAID.

  • SAIDs aren't auroras: Instead, they're fast, westward flows of charged gas associated with solar storms.

  • That sounds a lot like our purple streak, but STEVE doesn't only appear during solar storms,

  • and it moves much faster than SAIDs typically do.

  • SAIDs also rarely produce visible light emissions.

  • So in last week's paper, another team took a different approach to the mystery.

  • Since the SAID hypothesis already had some holes in it,

  • the group wanted to see if STEVE could be formally considered an aurora, even if it was an unusual one.

  • Auroras happen when energetic electrons and protons from the Sun precipitate through the Earth's atmosphere,

  • exciting those gases and making them glow.

  • So if STEVE is an auroral event, then scientists should be able to detect these particles when the streak appears.

  • The paper's authors used ground-based and satellite data taken during one of STEVE's 2008 appearances to try and hunt them down.

  • Except, there wasn't much, at least, in the way of energetic particles.

  • So that rules out STEVE as an aurora.

  • That means, at least right now, this purple light is in a class all its own.

  • It's just… a STEVE, probably driven by its own special mechanism.

  • But that doesn't mean we'll stop investigating it.

  • The next steps are to study more STEVE events,

  • since scientists have only really looked at two of them so far.

  • And ideally, that will help us not just understand this light,

  • but how the Sun creates different kinds of auroras in general.

  • While those scientists keep working on that mystery, another team is celebrating a new discovery.

  • According to a paper published in PNAS last Monday,

  • researchers have found direct evidence of water ice on the surface of the Moon!

  • And that could be big news for future explorers.

  • The new discovery was made thanks to Chandrayaan-1,

  • a lunar orbiter launched in 2008 by the Indian Space Research Organization.

  • Its payloads mostly focused on mapping and studying the Moon's composition,

  • and it did some really cool science for almost a year before a communication failure ended the mission.

  • The data for this new paper specifically came from the orbiter's M3 instrument,

  • or the Moon Mineralogy Mapper, which was built by NASA's Jet Propulsion Laboratory.

  • It's a type of spectrometer,

  • which means it measured the wavelengths of light that reflected off the Moon's surface

  • and used them to determine composition.

  • About ten years ago, back when Chandrayaan-1 was still active,

  • M3 found some evidence for water ice on the surface, which was really exciting.

  • But the evidence was pretty indirect, and it wasn't obvious just how much ice there was.

  • Plus, that data included water that was part of hydrated minerals,

  • so it wasn't pure ice or anything.

  • But now, things seem different.

  • This newly-analyzed data directly confirmed the presence of that ice,

  • and it also suggests that at least some of it could be pure water,

  • although more observations would help pin that down.

  • These ice deposits are scattered around the Moon's north and south poles,

  • and a lot of it is in shadowy southern craters.

  • There, it never sees the light of day, thanks to how the Moon is tilted relative to the Sun.

  • That keeps the ice from melting and makes the deposits relatively nice and accessible.

  • So far, we don't really know how all that ice got there or how old it is.

  • But this icy discovery is really promising for future missions.

  • As of right now, NASA is planning to send people back to the Moon,

  • so this ice could potentially become a source of drinking water.

  • But maybe more importantly, if we can split it into hydrogen and oxygen on a large scale,

  • it could also be used for rocket fuel.

  • The Moon could be an interplanetary gas station! Well, someday.

  • There's still a long way to go, but thankfully, that ice doesn't seem to be going anywhere.

  • Thanks for watching this episode of SciShow Space News!

  • And thanks especially to our Patrons who make it possible for us to research new science and create this videos for you.

  • Thank you!

  • And if your name is Steve or Chandrayaan, let us know in the comments, because awesome.

  • [ ♪ Outro ]

[ ♪ Intro ]

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新的北極光 - 科學秀新聞 (A New Kind of Northern Light | SciShow News)

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    林宜悉 發佈於 2021 年 01 月 14 日
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