Name: 地球は19時間の日を持っていた（そして冥王星は砂丘を持っている！）。 (Earth Used to Have 19-Hour Days (and Pluto Has Dunes!))
Uploaded: 2021-01-14T10:30:27.000Z
Duration: 6 min 22 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

程度の副詞

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

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

It allows them to look deep into the early history of the solar system — and it could

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

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

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

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

Still, these methods aren't very reliable for really old samples — especially those

older than around 50 million years — so 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.

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

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

It's used in particle physics and hydrogeology and cell biology — you 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

Kinda like the scientific method, but with statistics!

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

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

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?

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 scientists — and all the rest of us nerds — to wonder whether the atmosphere

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

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

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

Earth's dunes are made of little particles of rock — mostly quartzy stuff.

On Earth, methane is a gas — specifically, an odorless part of your fart gas.

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

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

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

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.

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.

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

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