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  • [ ♪ Intro ]

  • Sometimes, it just feels like life would be easier if the days were a little longer.

  • You'd have more time to spend with family or sleep or start another YouTube channel.

  • But the next time you're wishing for a few more hours, you can be thankful you weren't

  • around 1.4 billion years ago.

  • Thanks to our good friend the Moon, days on Earth were around six hours shorter back then.

  • These results were published on Monday in the Proceedings of the National Academy of Sciences.

  • And while this is something we've known before, what's special is the model the

  • researchers created to confirm it.

  • It allows them to look deep into the early history of the solar systemand it could

  • have a lot more to teach us.

  • Researchers are always trying to understand the processes that shaped the early Earth,

  • and for good reasons.

  • Besides helping us figure out our origin story, it can also help us understand other worlds

  • in the solar system and beyond the solar system.

  • One way we can study the Earth's climate specifically is through processes called Milankovitch cycles.

  • They track things like a planet's rotation rate, how it wobbles on its axis, and how

  • tilted and circular its orbit is.

  • All of those things affect how much direct sunlight a planet gets.

  • And on Earth, these factors add up to produce a cycling of warming and cooling on a ten-thousand

  • to one-million year time scale.

  • To be clear, though, they do not mean climate change isn't also happening and that it

  • isn't also caused by humans.

  • Because it is.

  • Researchers can track Milankovitch cycles in the geologic record, in things like isotope

  • ratios, rocks, and ice cores.

  • Still, these methods aren't very reliable for really old samplesespecially those

  • older than around 50 million yearsso it's hard to look into the distant past.

  • There's also a lot we don't know about Earth's orbit and its relationship to other

  • planets from back then, so it's difficult to extrapolate climate cycles from that alone, too.

  • That's where this new model came in.

  • By combining geologic evidence with our knowledge of orbital mechanics, this team was able to

  • bypass a lot of those limitations.

  • As a result, they got one of our clearest looks yet into the early solar system.

  • They used a technique broadly called Bayesian statistics or Bayesian inference, which is

  • wildly important to modern science.

  • It's used in particle physics and hydrogeology and cell biologyyou name it, you can Bayesify it.

  • Basically, you start with some initial model, calibrate it to data, then update your model.

  • Over time, you get an increasingly precise and probable explanation for whatever phenomena

  • you want to explain.

  • Kinda like the scientific method, but with statistics!

  • This new model covers things like the shape of Earth's orbit and its gravitational interactions

  • with the planets out to Saturn.

  • But it also gave a special focus to how the Moon affects Earth's climate and behavior.

  • Among other things, it showed that, thanks to the Moon, our days were a little under

  • 19 hours long 1.4 billion years ago!

  • Admittedly, though, this isn't really surprising.

  • Thanks to evidence from ocean models, we've known for a while that interactions between

  • Earth and the Moon have been steadily slowing our rotation rate.

  • But this new model was able to confirm that just using rock formations!

  • This helps show how well-calibrated it is for those distant time periods.

  • And it means we can apply it in ways we can't with other methods.

  • More data would make it even more accurate, but right now, it can reach back in time really well.

  • Now, we can start using it to get a better understanding of Earth's early history and

  • habitability, and the dynamics of the early solar system!

  • Where would planetary science be without computers?

  • Where would any of us be?

  • Meanwhile, on the other side of our little neighborhood, there's more news from Pluto!

  • Because even though it's been almost three years since the New Horizons fly-by, we're

  • still learning more about what a lot of people thought would be a boring dwarf planet.

  • One of the major initial discoveries New Horizons made was that Pluto has an atmosphere.

  • And this led scientistsand all the rest of us nerdsto wonder whether the atmosphere

  • had any effect on Pluto's topography.

  • Wind can erode rock into all kinds of neat shapes, and sculpt big ol' sand dunes like

  • in the Sahara.

  • And now, thanks to an article published in Science last Friday, we know there are dunes

  • on Pluto, too!

  • Except, of course, they're very different from the ones we've got here.

  • First, their composition is different.

  • Earth's dunes are made of little particles of rockmostly quartzy stuff.

  • But Pluto's are made of methane.

  • On Earth, methane is a gasspecifically, an odorless part of your fart gas.

  • And also the natural gas that people frack for, if you want a different comparison.

  • But come on.

  • Fart dunes.

  • Pluto is so cold that methane is solid there, and there's a whole bunch of it existing

  • in little particles.

  • Now, we know that they make up some lovely, ripply dunes on Sputnik Planitia, the west

  • half of Pluto's heart.

  • These dunes also form differently from ours.

  • The dwarf planet's atmosphere is a lot thinner than Earth's, so it can't carve out dunes

  • just by whipping across the methane plains.

  • Instead, researchers think the process could be driven by day/night atmospheric cycles.

  • Just like water vapor in Earth's atmosphere condenses and freezes to form dew and frost,

  • nitrogen gas in Pluto's atmosphere condenses and freezes at night.

  • Then, in the morning, it sublimates and turns back into gas.

  • As it does, it could puff up a bunch of methane sand, which would get caught in Pluto's winds.

  • And suddenly, you'd have 1001 Plutonian Nights.

  • Or something.

  • Another cool thing is that, based on their surface features, the authors of the paper

  • could also tell that these dunes have formed recently.

  • Or at least, within the past 500,000 years, which is very recent for objects like planets.

  • That means these processes may be going on right now on Pluto's surface!

  • Which is way more dynamic and exciting then most people expected when New Horizons launched.

  • And in case you were curious

  • Yes, they figured this out with the help of a model, too.

  • Thanks again, computers.

  • And thank YOU for watching this episode of SciShow Space.

  • If you want to celebrate your love of science with the whole universe, we've added to

  • our finds on SciShowFinds.com.

  • Just today we're adding fossilized Mesosaur Teeth and Ammonite Pairs.

  • As well as thiswandering wombpin inspired by our SciShow video on Hysteria.

  • I'm also excited that we are adding more trilobite fossils, because we sold out of

  • those, and more copies of the book that made me love geology: The Story of Earth by Robert Hazen.

  • There's a bunch of good stuff on there right now that we love and have selected for you

  • to check out.

  • And just like last time, these are all available until we run out.

  • So go to SciShowFinds.com to get your own celebratory artifact of our edgeless universe.

  • [ ♪ Outro ]

[ ♪ Intro ]

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B1 中級

地球曾經有19個小時的一天(冥王星也有沙丘!)。 (Earth Used to Have 19-Hour Days (and Pluto Has Dunes!))

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    林宜悉 發佈於 2021 年 01 月 14 日
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