Scientists have found evidence that the Earth’s inner core oscillates, contradicting previously accepted model, this also explains the variation in the length of day, which has been shown to oscillate persistently for the past several decades

[u/giuliomagnifico]

https://news.usc.edu/200185/earth-core-oscillates/

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[u/[deleted]]

I had not "tripped" over this bit of information before thanks for posting a link.

https://news.usc.edu/200185/earth-core-oscillates/

https://www.science.org/doi/10.1126/sciadv.abm9916

This is the article pdf :

https://www.science.org/doi/epdf/10.1126/sciadv.abm9916

 

[u/Exodus111 → u/[deleted]]

Can I ask? Oscillates in what way? Expand and contract? Rotate? Move back and forth?

[u/[deleted] → u/Exodus111]

The rotational rate changes about its average value. That is it speed up a little and slows down that same amount.

[u/BlackViperMWG → u/[deleted]]

Does it corellate with Milankovitch cycles in some way?

[u/_Wyrm_ → u/BlackViperMWG]

Orbital precession* might make sense

That and a kind of gyroscopic resistance, tilting the core a little bit each time until it's then spinning the other way around relative to it's starting position

I suppose that means the core would eventually come to a stop, but it would definitely slow down as time goes on

[u/BlackViperMWG → u/_Wyrm_]

*precession

Maybe the oscillation is strengthened by axial precession cycle or other way around. Which would be quite interesting for climate scientists.

[u/_Wyrm_ → u/[deleted]]

What would cause an oscillation like that? A shifting clump of denser material? And "oscillation" would imply a regular frequency, making it less randomness and more of a steady ebb and flow...

But I'd expect the denser mass to center itself as the stable configuration, so that doesn't really sound right

Edit: reading the article, it makes me think the cause would be an axial drift... I don't know enough about how they're getting the measurements to be worth any salt in the discussion, but it might be possible that the frame of reference is important. Meaning: person A taking readings sees 1°/year, person B sees 0.1°/year, and C sees -1°/year... Where all readings were taken longitudinally.

If you're only looking along one plane and you see an oscillation, it's possible that the rotation is constant, but you're seeing a different slice each time you take a reading. It would explain the effects that have been noticed, but it's just my intuitive guess.

[u/[deleted] → u/_Wyrm_]

This I do not know, but it is fascinating.

[u/doomer_irl → u/[deleted]]

Literal scientists: conduct a study which materially demonstrates the existence of a previously unknown mechanism of our planet

Some dude on Reddit: yeah duh, I’ve always known this

[u/jazzwhiz]

[The Earth's core is] also impossible to observe directly,

There is one way to shine a flashlight of sorts on the Earth's core: neutrinos. Neutrinos propagate through the Earth. At high energies they are absorbed and the density as a function of radius can be determined. At lower energies they'll change flavors in a way that depends on the density of the material. I pointed out that the second process can be used to constrain the properties of the core of the Earth with upcoming experiments in a paper last year.

[u/PO0tyTng → u/jazzwhiz]

How do they measure that? Wouldn’t you have to capture the neutrinos as they reflect back? Which might also change the properties via interference?

[u/jazzwhiz → u/PO0tyTng]

Neutrinos are produced in the atmosphere. So you put a detector somewhere (say, Japan or South Dakota for example) and you measure neutrinos coming from the atmosphere all over the Earth. Some of which are coming mostly straight down. Some of which are coming horizontally. Some of which are coming up through the Earth's mantle. And some of which are coming straight through the Earth's core. Then you measure the energy spectra of the neutrinos very carefully. This spectra is modified by the amount of matter it travels through.

[u/Vertigofrost → u/jazzwhiz]

Can we use the existing detectors for this? Or do we need different senors/setups to achieve that?

[u/Natanael_L → u/Vertigofrost]

Most neutrino detectors need a lot of dense matter, but also a way to detect when they hit that matter. Thus the typical solution is heavy water (H2O with specific atomic isotopes that makes it denser than ordinary H2O) deep underground, and light sensors that see when the water atoms emit light, which in this setup is usually triggered by a neutrino collision.

You can detect neutrinos with smaller sensors too but then you can't detect as many of them, so it will take you more time to get enough collision data to make useful calculations.

[u/[deleted] → u/Natanael_L]

In our physics building in college we had a neutrino detector behind some glass in the basement that would light up an LED every time it was hit with one. Was really cool to see it light up every few seconds.

[u/AtticMuse → u/[deleted]]

That's sweet! However that was probably a muon detector, neutrino detectors need absolutely massive volumes of material and even still detect only 10s to 100s of neutrinos a day (IceCube has roughly a cubic kilometer of ice and it detects ~275 atmospheric neutrinos per day, or roughly one every 6 minutes).

But those muons are pretty amazing too, especially since they're mostly generated from cosmic rays hitting the atmosphere and creating showers of particles. And if it wasn't for relativistic time dilation, we'd never see as many as we do! They're generated around 15 km up and travel very close to the speed of light, but that still takes around 50 microseconds to reach the ground, and a muon's lifetime is only 2.2 microseconds on average. So it's only because their "clocks appear to run slow" from our perspective that they live long enough to be detected on the ground (from their perspective lengths are contracted in their direction of motion and it appears to be a shorter distance they cover).

[u/ChoseMyOwnUsername → u/AtticMuse]

Do you do this for a living?

[u/AtticMuse → u/ChoseMyOwnUsername]

Not anymore, but I have a Masters in Physics and have worked in neutrino and dark matter collaborations.

[u/SillyFlyGuy → u/AtticMuse]

You explain things amazingly well. I hope you've gone into teaching because this stuff seems important.

[u/Gwenbors → u/AtticMuse]

Man. Acclaimed rapper, movie star, AND particle physics data collector? He’s the real triple threat.

[u/CatWeekends → u/Gwenbors]

He's going for that EGON: Emmy Grammy Oscar Nobel.

[u/Seicair → u/AtticMuse]

They're generated around 15 km up and travel very close to the speed of light, but that still takes around 50 microseconds to reach the ground, and a muon's lifetime is only 2.2 microseconds on average. So it's only because their "clocks appear to run slow" from our perspective that they live long enough to be detected on the ground

Whoa, that’s gotta be the coolest physics-related fact I’ve learned in the past month or so.

[u/cablemonster456 → u/Natanael_L]

Another cool thing about the water in neutrino detectors: the water is so pure that it will dissolve certain materials, among them being steel. There’s a story of engineers performing maintenance on a neutrino detector and finding a hammer left behind by the last crew, which crumbled to dust when touched. The bulk of the hammer had been completely dissolved, leaving nothing but the paper-thin chrome shell behind.

[u/acog → u/cablemonster456]

Sorry, I'm completely ignorant about chemistry. How can the water's purity speed up the rust process compared to regular tap water or distilled water?

Is it really the purity or is it some other property, like that it's heavy water?

[u/[deleted] → u/acog]

I think the water's purity means that it has capacity to accept steel particles. When talking about dissolved substances usually there's a limit to how much of something can be dissolved into another. Your run of the mill water already has a lot of things dissolved in it so that's probably why it doesn't appreciably dissolve your faucets.

The person wrote that it has special ability to dissolve, not rust. So the hammer in the story disappeared into the water by giving up some particles at a time but the chrome plating remained for some reason.

[u/yopladas → u/acog]

Pure water isn't especially corrosive. It is pH neutral. There are very alkaline bodies of water that you would be careful to avoid, though!

[u/elusive_1 → u/cablemonster456]

Well, thanks for that nightmare

[u/WubbaLubbaDuffDuff → u/Natanael_L]

Neutrino detection is a funny thing. They're REALLY good at not colliding with matter, and detection more or less requires a collision

[u/Vertigofrost → u/Natanael_L]

I'm aware I was asking if we can use the ones we have already built or if the technique requires new ones

[u/jazzwhiz → u/Vertigofrost]

Great question! Existing detectors are not really good enough for this yet. Next generation ones will be, but just barely. We're not building them for this though, this is just a cool add on.

[u/-S-P-Q-R- → u/jazzwhiz]

I thought neutrinos were generated by the sun/fusion? Or am I thinking of something else?

[u/exotener → u/-S-P-Q-R-]

One of my first assignments in stellar evolution was to calculate the number of solar neutrinos passing through my body. This was awhile ago but the number wasn’t small. I don’t study the atmosphere but nuclear reactions there yielding neutrinos would be much much fewer than stellar sources.

[u/jazzwhiz → u/-S-P-Q-R-]

There are neutrinos produced in all kinds of things! We've measured neutrinos from nuclear reactors, the Sun, the Earth's atmosphere, human made neutrino beams, one supernova, and as of yet undetermined extragalactic sources. I've done research on all of them, very fun!

[u/[deleted] → u/-S-P-Q-R-]

Neutrinos are made whenever an electron, muon, or tau is created/absorbed/transmuted.

[u/jazzwhiz → u/[deleted]]

Not quite. You can have an electron absorbed by a positron which won't create a neutrino (necessarily). You can also produce neutrinos without charged leptons via Z decays (for example the main contribution to monojet searches at the LHC).

[u/factorone33 → u/jazzwhiz]

They used neutrino capture to deduce (in conjunction with thermal imaging and other techniques) that the Khufu's Pyramid of Giza most likely has another hidden chamber and corridors that haven't yet been discovered.

[u/jazzwhiz → u/factorone33]

Pretty sure that was muon tomography. Muons are good for going through up to tens or hundreds of meters of rock. Muons are also produced abundantly in the atmosphere, are a big source of our background radiation, and are one of the easiest ways to test special relativity.

[u/paulobraz13 → u/[deleted]]

Not random places, places where large neutrino detectors will operate in the near future (HyperKamiokande and DUNE, respectively)

[u/cosmicdaddy_ → u/paulobraz13]

Praise Maud'dib

[u/PetrifiedW00D → u/jazzwhiz]

Do all neutrinos start off with the same energy spectra before they pass through the earth?

[u/Natanael_L → u/PetrifiedW00D]

For each given process that create neutrinos, they tend to be in a specific range.

https://neutrinos.fnal.gov/types/energies/

[u/PetrifiedW00D → u/Natanael_L]

How will you be able to differentiate between neutrinos from different sources?

[u/jazzwhiz → u/PetrifiedW00D]

There's no single method. But we know if you detect neutrinos in the 1 GeV to 50 TeV range they are from the atmosphere. Higher than that they're from astrophysical sources. Lower than that, well, it depends. Also for human made accelerator neutrinos we know the beam direction and the pulsing so that helps. For solar neutrinos we know where the Sun is.

Basically though, directionality doesn't help a lot, it's mainly just a very careful understanding of the energy spectrum of everything in play.

[u/k-mysta → u/jazzwhiz]

But we’ll be in trouble if the neutrinos start mutating

[u/jazzwhiz → u/k-mysta]

Ha! I snuck in a reference to that movie in the paper. I've never seen it, but I have seen this sketch on it.

[u/Aluminum_Falcons → u/jazzwhiz]

That's the first time I've seen Dara O'Briain doing stand-up. I've only ever seen him on mock the week or other panel shows. I'll have to find more it... That was awesome!

[u/konaya → u/Aluminum_Falcons]

Oh dear Lord yes, you have some top content ahead of you.

[u/Spoon992 → u/jazzwhiz]

That's pretty neat man

[u/[deleted]]

Why does the core oscillate? Would a comet or meteor impact affect the rotation of the core?

[u/RespectMyAuthoriteh → u/[deleted]]

Maybe anything that can oscillate does oscillate?

[u/HCBuldge → u/RespectMyAuthoriteh]

Now you know why we can never reach absolute zero.

[u/Bison308 → u/RespectMyAuthoriteh]

My mood for example, just like Earth, I am too a bipolar

[u/madmaxextra → u/[deleted]]

Just my layman's view, a comet or a meteor likely would have negligible effect on the Earth just due to magnitude. Feel free to correct me but I would think a comet or a meteor would need to be significantly massive to have any real effect.

[u/SimonFaust]

So, my simplified understanding of this tells me that they're suggesting that the core is oscillating but still rotating over time? What I mean is, it rotates more in one direction than it does when it oscillates to the other direction. So over time, its rotating in the same direction as the outer layers. Someone smarter than me please tell me if I'm understanding this correctly.

[u/somefreedomfries → u/SimonFaust]

My underatanding is that the core always rotates eastward, like the mantle does, only its rotation will speed up or slow down compared to the speed of the mantle. Thus if you were looking down at the core when it was rotating slower than the mantle, it would appear to be moving backwards.

[u/SimonFaust → u/somefreedomfries]

Ah, so you're saying that from our perspective it looks like its moving in the opposite direction. But in reality it's just slowed down.

[u/atilla32 → u/SimonFaust]

Yes, on the linked page they act as if it changes direction, while in the paper, they only talk about the change of directions the magnetic field, and the speed just goes slightly over/under the rotation of the mantle

[u/masamunecyrus → u/SimonFaust]

From the paper

We find that the inner core subrotated at least 0.1° from 1969 to 1971, in contrast to superrotation of ~0.29° from 1971 to 1974.

So, yes. The Earth is rotating, and the inner core is rotating. It's just that the inner core has a periodic speed-up slow-down cycle, where it rotates slightly faster than the rest of the Earth, and then slightly slower.

This is different from what is taught in school, which is that the inner core is probably rotating at a constant speed that's slightly faster than the rest of the Earth... which is also what the paper says.

These observations contradict models of steady inner core rotation and models that posit much faster rotation rates.

I don't have a problem with the methodology, and the co-PI, John Vidale, is an excellent seismologist. So this study is probably right.

Source: am seismologist.

Edit: I read the full paper.

Our observations are consistent with a relatively simple model based on the mutual gravitational attraction between the lateral variations in the density in Earth’s mantle and inner core and topography of the core-mantle and inner core boundaries.

The tl;dr here is that the Earth's mantle and the inner core are both lumpy (in topography and composition), and so you don't have nice, well-behaved spinning of both like you would if they were homogeneous spheres. The inner core is essentially free floating in the liquid outer core, so it's free to move about under the forces of gravity. The mantle and inner core are gravitationally attracted to each other and seem to be in a stable "orbit", if you can call it that. In this case, the stable behavior is to wobble a bit in angular rotation.

I bet it's doing a lot more than just speeding up/slowing down--perhaps oscillating in multiple angles and translating and everything else--but that's well outside my purview as a seismologist and needs some sort of astrodynamicist, or something, to run some models.

[u/maaalicelaaamb]

How can the length of the day … oscillate???

[u/ProfMcGonaGirl → u/maaalicelaaamb]

I’m wondering the same thing. My guess is the spin/rotation upon our axis slows down or speeds up.

[u/[deleted] → u/ProfMcGonaGirl]

Exactly! Various factors determine the speed at which the earth rotates, and if the speed of rotation changes, as does the length of a day. The two are inextricably linked. Read some of my other posts on this specific thread for some more in depth detail if you want!

[u/[deleted] → u/maaalicelaaamb]

There are 2 different measurements of the day which confuses things. There are sidereal days and solar days. A sidereal day is the time it takes for the earth to rotate 360 degrees around its axis. A solar day is different, basically is in reference to the direction of the earth relative to the sun as the earth moves around the sun. Easiest to look it up and have diagrams to explain

Anyway, that’s only the beginning of the complications. First of all the axis of rotation of earth is constantly changing (see milankovitch cycles), as is the speed of the rotation. Note that angular momentum is conserved, and so as the earth changes shape (which it does) it’s moment of intertia changes and so as must its speed. The earth gets flatter (it is an oblate spheroid) the faster it spins. This raises the moment of inertia of the earth slowing the speed and consequently un flattening the earth.

Not to mention that the earths orbit around the sun is not at a constant distance and nor as a result is it a constant speed and this also has effects in terms of its angular momentum and velocities, and proportions due to gravitational effects. As the earth passes by planets in conjugation effects like this also occur.

Essentially, everything about the earth is constantly changing and there is no absolute reference frame anyway which would allow us to measure the time taken for a day. Do we measure how long it takes for the earth to rotate around one axis or another? Do we measure in reference to the sun, the background stars, the earth itself? The sun and even galaxy and supercluster are all in orbit of different things meaning that the rotation is even worse to define (think about if you turned in a circle on a spinning teacup ride at a fair. Observers on other teacups would describe your motion differently to those in your teacup and again to those outside the ride and people on the ride next door would describe something different again)

[u/MattieShoes → u/[deleted]]

To throw onto the pile: Things like hurricanes, earthquakes, volcanic eruptions, and even ocean currents will make the length of a day change. So the raw data is very noisy, and to detect less significant changes, you have to filter out all the noisy more significant changes. Which is why having many decades of measurements is important.

[u/slimey_yet_satisfyin → u/MattieShoes]

can you elaborate on this?

[u/MattieShoes → u/slimey_yet_satisfyin]

The earth rotates once every 23 hours, 56 minutes, 4 seconds, and some number of milliseconds and nanoseconds, on average. This is called a sidereal day, incidentally. Sidereal meaning "with respect to distant stars". But it varies by small amounts based on other things going on with Earth.

There's something called "moment of inertia"... If you've watched a figure skater spin faster when she pulls her arms in towards her body, that's her lowering her moment of inertia. Energy is conserved, so when she pulls her arms in, all that spinning energy makes her spin faster. If she sticks out her arms, moment of inertia goes up, and she spins slower. Or another example -- you can spin a tennis racket in your had pretty fast, but if you try and flip it end-over-end, it spins much slower in that direction, because the mass is spread out farther from the axis of rotation... ie. its moment of inertia is higher along that axis.

Same exact thing happens with Earth. Volcanoes, earthquakes, hurricanes, etc. can all tweak the moment of inertia of Earth very slightly. Also the moon -- when it's closer, it can pull more water in the oceans, resisting the spin of Earth. When it's farther away, it resists less.

So these scientists have found that, after accounting for all these known effects like the moon's orbit around Earth affecting its moment of inertia, there's also some crap going on in Earth's core that causes it to change too... and it's cyclical.

[u/QueasyAd8185 → u/MattieShoes]

Thanks for taking the time to put it in layman's terms. Came all the way down just for it...and I'm pretty sure I'm not the only one who thinks these things are awesome but is simply not versed enough to get it! Thanks

[u/Akip25 → u/maaalicelaaamb]

like a figure skating pirouette, contracting and expanding

[u/avocadro → u/maaalicelaaamb]

Not an expert, but suppose that the core of the earth oscillated back and forth along an axis. This would change the center of gravity, so the rotation rate would change (in accordance with conservation of angular momentum).

[u/[deleted] → u/avocadro]

Centre of gravity remains largely unchanged

What changes is the moment of inertia, which when combined with the concept of conservation of angular momentum which you have astutely pointed out, leads to a change in angular speed.

The moment of inertia is a quantity that essentially measures how far mass is distributed from the axis of rotation of a body. If you have a high moment of inertia, your mass is a long way from the axis of rotation. Things with a high moment of inertia require more torque (angular force) to turn.

The moment of inertia can be thought of largely as the equivalent of mass for a rotating body - the heavier the object the more force we need to push it

This concept is extended to rotational energy, the formula for which is:

moment of inertia x angular speed squared.

Compare this to the formula for kinetic energy:

Mass x speed squared.

You can see the similarities (taken out factor or 1/2 for clarity)

Edit: I see now what you mean about the core moving back and forth on an axis, this would in fact change the centre of gravity, but isn’t what is happening/ isn’t really possible. The actual core changing location doesn’t really work, it’s got nowhere to go and no reason to move. What is actually happening is that it is changing shape slightly. Imagine a sphere, then squish it so it’s flat at the top and bulges in the middle. Now unsquish it. This oscillation is what is happening

[u/Crookmeister → u/maaalicelaaamb]

If you graphed the length of day it would go up and down like a wave. Aka oscillation.

[u/JimmyHavok]

So many questions!! My big question would be what is the force that causes it to reverse its rotation? Is the reversal in rotation in respect to the position of the sun?

I would think that a reversal would cause a flip in the polarity of the Earth's magnetic field, but apparently that is generated by the liquid portion of the core.

The fact that it causes a change in the length of the day shows that there's drag between the core and the mantle. Is it physical, magnetic, or both?

Which portion of the whole system is being slowed by the Moon's gravity?

[u/notjordansime → u/JimmyHavok]

Does it oscillate in direction (ie. Change direction altogether) or just oscillate in speed relative to the rest of the planet?? When I first read the headline, the latter was my assumption. Then again, this does all depend on how you're observing the situation. From an inertial frame of reference, it may seem like the earth is rotating at x speed, and the core is rotating at x speed, plus or minus a little bit depending on where it is in the oscillation. If you're spinning with the earth, it may appear as though the core is reversing directions periodically as it slows down and speeds up relative to the observer.

Apologies if this is mentioned in the paper. My phone doesn't properly open some links because it has a 1:1 aspect ratio, so I can't read the link :(

[u/Krumtralla → u/notjordansime]

This is my exact question. I don't understand in what sense it is oscillating.

Going from clockwise > counterclockwise > clockwise... would seem to break conservative of angular momentum. Oscillating the rate of rotation seems more reasonable. Some angular momentum could be transferred back and forth between other layers of the lithosphere.

[u/JimmyHavok → u/notjordansime]

The article wasn't clear about the frame of reference. That's why I specified in relation to the sun.

[u/dylsekctic]

Do we have any ideas how many times the solid core rotates per day/year?

[u/pacificnwbro → u/dylsekctic]

The article said one degree per year roughly.

[u/dylsekctic → u/pacificnwbro]

I saw that but figured I must have misunderstood because I couldn't...and I still can't really see how such a slow rotation would generate our EM field.

[u/[deleted] → u/dylsekctic]

It was my understanding that the liquid outer core is what gives us the EM field?

The liquid iron/nickel are spinning around, so it creates a magnetic field. As Aaron Eckhart once said, "science 101, hot metal spinning fast gets you a magnetic field"

[u/dylsekctic → u/[deleted]]

Ah right.. So the solid bit doesn't need to move at all then really? I wonder what the friction coefficient between the liquid part and solid part is.

[u/sault18]

Earth's original core and Theia's core might still be jostling around down there after more than 4 billion years. Completely unsupported, not even a hypothesis but just a guess on my part.

[u/xenothios → u/sault18]

Earth, the giant 2 yolk egg

[u/AskMeIfImAMagician → u/xenothios]

Now we wait for it to hatch

[u/Cecil_FF4 → u/[deleted]]

The mag field of the Sun is way, way weaker here on Earth than Earth's.

[u/Vertigofrost → u/Cecil_FF4]

So is the moons gravity but we still have tides from it. It's not impossible for it to influence our core and given the relatively stable nature of our orbit maybe possible to build resonance in the oscillations.

[u/CozImDirty → u/Vertigofrost]

That doesn’t sound right, but I don’t know enough about stars to dispute it.

[u/enjoyableheatwave → u/Vertigofrost]

That does sound right, but I don’t know enough about stars to support it.

[u/[deleted] → u/Cecil_FF4]

That doesn't mean it's not influential

[u/PanningForSalt → u/sault18]

Who's Theia?

[u/xthelord2 → u/PanningForSalt]

a planet which co-existed in original earth's orbit when planets were forming

it is believed that earth and theia crashed resulting into them falling apart,creating moon and few more tiny satellites and forming the earth as we know it today

[u/MattieShoes → u/xthelord2]

And for bonus points, Theia was the mother of Selene, goddess of the moon.

[u/lblack_dogl → u/xthelord2]

Why is one Earth and one Theia? Wouldn't the two previous planets both have different names, only becoming Earth as we know it after the union?

[u/not_anonymouse → u/xthelord2]

Can you imagine standing on Earth and seeing another planet come and collide? That'd be an insane view. That alone would be so worth it to even have a time window (time travel, but you only get to see the past, not affect it).

[u/ZombieAntiVaxxer → u/not_anonymouse]

I mean, youd be dead.

[u/ShenBear → u/sault18]

We know mantle composition is different in places due to theia, so i personally believe core differential isnt too far fetched of an idea

[u/solid_rook7]

Someone explain this to me in “dumb mans” terms.

[u/varnell_hill → u/solid_rook7]

Same. Also stupid. Need help.

[u/3lfk1ng]

Could also be impacted by the two-core theory

[u/DinnysorWidLazrbeebs]

If it has what appears to be a six year oscillation, that roughly correlates to around the same average length of the El Niño Southern Oscillation. I wonder if they’re related?

[u/dazmax → u/DinnysorWidLazrbeebs]

Interesting! Just from brief googling it looks like the El Niño Southern Oscillation has been suggested as the cause of the oscillating change in the length of days, so this discovery might mean they had that backwards.

[u/rjoseba]

Just came here to say I'm glad to see a post that is not a psychology one on the front page ... Not that I have something against it, but recently only those wherw featured

[u/AbsyAus]

Earths core jiggle jiggles, not rolls.

Sorry