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Brazil Nut Effect Explains Mystery of the Boulder-Strewn Surfaces of Asteroids

Unknown Lamer posted about 3 months ago | from the asteroids-go-well-with-moon-cheese dept.

Space 58

KentuckyFC (1144503) writes When Japan's Hayabusa spacecraft gently maneuvered into a parking orbit around the asteroid Itokawa in September 2005, it conducted a comprehensive photographic survey, the most detailed ever taken of an asteroid. This survey revealed that Itokawa is covered in large boulders that look like ejecta from craters in other parts of the asteroid. But when astronomers added up the total volume of these boulders, it turned out to be greater than the volume of the craters there were supposed to have come from. Other asteroids also show a similarly skewed distribution of large boulders. That has caused some significant head-scratching among astronomers who are at a loss to explain where the boulders come from.

Now an international team has solved the mystery. They say the boulders float to the surface of asteroids in an astrophysical example of the Brazil nut effect. This is the long observed phenomenon in which shaking a mixture of big and small particles causes the larger ones to rise to the top. That's because the shaking creates gaps beneath the large particles that small particles fall into. The result is that the large particles float. The team simulated the shaking effect that collisions between asteroids would produce and say that these vibrations would cause large boulders to float to the surface in a few hours, finally explaining why asteroids have such boulder-strewn surfaces. Problem solved!

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Explains the TV News (4, Funny)

BoRegardless (721219) | about 3 months ago | (#47456751)

Where the biggest nuts rise to the top.

Re:Explains the TV News (4, Funny)

jeffb (2.718) (1189693) | about 3 months ago | (#47456859)

Still does nothing to explain the similar sorting of Slashdot comments, as illustrated in this thread.

Re:Explains the TV News (0)

Anonymous Coward | about 3 months ago | (#47458499)

Yes. Mine is even longer and doesn't make to the top of the thread. I wonder why. Actually it is quite the opposite, with the shorter above. Need to shake that.

Re:Explains the TV News (0)

SQLGuru (980662) | about 3 months ago | (#47457287)

Where the biggest nuts rise to the top.

Politicians, too......

Re:Explains the TV News (0)

Anonymous Coward | about 3 months ago | (#47457661)

The Brazil Nut Effect?

Anyone got any suggestions for a better name?

Re:Explains the TV News (1)

Anonymous Coward | about 3 months ago | (#47458177)

We'll, my grandfather used to call them "nigger-toes", but I don't think that'd go down so well these days....

Re:Explains the TV News (1)

GinRummy33 (629101) | about 3 months ago | (#47461985)

Yes, I grew up hearing this name for them, too. I never knew they even had any other name until I was in my teens, where I eventually heard their real name. Just one of the many old racist words for things that got phased out as the years went by. I can think of several, but I'm not gonna make a list.

Re:Explains the TV News (1)

Anonymous Coward | about 3 months ago | (#47459391)

How about Granular Convection? [wikipedia.org]

Re:Explains the TV News (2)

Will.Woodhull (1038600) | about 3 months ago | (#47462159)

Brazil nut effect is an excellent way to distinguish this process from the superficially similar strawberry effect (which happens in grocery stores where the biggest and reddest strawberries are always visible at the top of the container).

Summary description is not quite accurate (1)

Anonymous Coward | about 3 months ago | (#47458071)

The large boulders rise due to a density disparity. If you take the smallest box that would hold a large boulder, you will find a lot of airspace in it. The same sized box filled with smaller rocks would have less airspace. The larger box is therefore lighter than the smaller box.

This can be experimentally verified by making the large boulders out of a material that is much more dense than the small rocks, such that the cubic density would still be higher for the large boulders, even including the airspace. In this case, the large boulders should sink when the system is shaken.

Re:Summary description is not quite accurate (2)

American Patent Guy (653432) | about 3 months ago | (#47460413)

If a collection of boulders/rocks have the same shape and density (individually), then they will have the same space between them regardless of their size. This is ignoring the conflicts with the walls of your hypothetical box. However, asteroids in space have no walls. Your experiment should not show what you think.

It might be more accurate to say that smaller rocks settle down more readily than larger boulders (in the spaces between), and the effect perceptively "floats" the boulders to the surface.

Oh, THAT Brazil nut effect (1)

damn_registrars (1103043) | about 3 months ago | (#47456847)

I thought this was going to relate to nuts with high amounts of radioactivity.

Re:Oh, THAT Brazil nut effect (2)

K. S. Kyosuke (729550) | about 3 months ago | (#47457375)

I thought it was going to relate it with nuts causing small amounts of player activity.

That's nuts! (0)

Anonymous Coward | about 3 months ago | (#47456893)

...

That's how I clean my cat's litter box. (1)

Rick in China (2934527) | about 3 months ago | (#47456905)

I shake 'er up. The big pieces float to the top. I scoop them out. Brazil nut effect. Asteroid problem solved. It took an international team to sort this out? Come on! :D

Re:That's how I clean my cat's litter box. (3)

gstoddart (321705) | about 3 months ago | (#47456937)

It took an international team to sort this out? Come on!

That's kind of what I was thinking.

I heard about this in Geology class 20+ years ago. It's why farmers fields keep producing rocks, because the bigger pieces move up and work their way to the surface.

I thought this was pretty well understood for quite some time.

Re:That's how I clean my cat's litter box. (4, Informative)

Captain Hook (923766) | about 3 months ago | (#47457027)

But does the process work when the gravity field is tiny? That is what needed to be found out before saying that that is definitely the process at work.

Re:That's how I clean my cat's litter box. (1)

gstoddart (321705) | about 3 months ago | (#47457119)

Intuitively, which we all know is probably wrong, you'd think a smaller gravity would magnify it, no?

The bigger pieces can move more, the smaller pieces still settle.

The mechanism is that the smaller pieces fall down through the cracks between the bigger pieces, and eventually push the bigger pieces upwards.

Yes, it's space, so it's all new ... but I should think the mechanism is pretty universal, and was already widely understood.

Re:That's how I clean my cat's litter box. (3, Insightful)

Captain Hook (923766) | about 3 months ago | (#47457405)

I would have intuitively said the other way around.

Since the gravity is so small I would have expected the motion of the smallest particles to be close to random, perhaps close to Brownian motion if you looked at the system over a long enough period of time.

I guess, even though there isn't much to pull the material together, once a small particle is in a crack or void it is very unlikely to ever escape and so the crack does eventually fill in, it seems to me that the process should exist but be much slower than when compared to the effect in a strong gravity field.

As you said, "Intuitively, which we all know is probably wrong"

Going a little beyond intuitive (1)

Will.Woodhull (1038600) | about 3 months ago | (#47462435)

TFA describes the situation on a dry asteroid.

An asteroid or comet that contains water as well as stone is likely to behave differently. If its ice is melted by impact or increased exposure to sunlight, then frost heaves might cause a faster migration of big stones to the surface than would happen by granular convection. But if the ice is acting as a concrete binding agent, then there will be no frost heaves and no granular convection. Probably on a lot of asteroids both processes will be active.

I'm thinking that determining whether frost heaves or granular convection has been at work is going to be important in figuring out how to deflect any asteroid or comet. I'n guessing this will need to be done on a case by case basis.

Re:That's how I clean my cat's litter box. (4, Funny)

OglinTatas (710589) | about 3 months ago | (#47457565)

Easy enough to check. Send up a can of mixed nuts to the space station and put it in a slow centrifuge. Spin it for a few days then open it up and... shit, someone ate all the cashews and almonds, and reluctantly the peanuts, leaving only the brazil nuts. FAIL.

Re:That's how I clean my cat's litter box. (0)

Anonymous Coward | about 3 months ago | (#47457073)

Yes, because there's more to it than "something similar happens in other completely different situations, let's just assume it' the same cause".

The bothered with those trivial matters like what about the tiny (compared with your farmers field) gravity on an asteroid? How much "shaking" is required and does it match what an asteroid would experience? And so on - you can read the paper.

You'll not it points to the prior work pretty clearly too (as you would expect).

Granular convection and frost heaves (1)

Will.Woodhull (1038600) | about 3 months ago | (#47462311)

There is possibly some confusion in parent post between granular convection and frost heaves.

In New England and other climes that have a winter freeze and spring thaw, the winter freeze pushes rocks upward as the water in the soil expands into ice. In the spring thaw, the ice under the rocks melts from the periphery inward, and slurries of ice water mud fill the voids. As a result, the rocks stay in their higher place as the soil settles back to its spring level.

One of my chores when I was growing up was to help with digging the big and deep holes in the garden next to the emerging boulders that were too large to remove. We'd roll the boulder into the deeper hole and bury it, and be able to use the rototiller and tractor over it for a few years before it would rise again.

Re:That's how I clean my cat's litter box. (2)

Peter Simpson (112887) | about 3 months ago | (#47457261)

I shake 'er up. The big pieces float to the top. I scoop them out. Brazil nut effect. Asteroid problem solved. It took an international team to sort this out? Come on! :D

It's the same in an organization -- shake it up -- the management rises to the top.

Any similarity to a litter box is purely coincidental

Re:That's how I clean my cat's litter box. (1)

GTRacer (234395) | about 3 months ago | (#47459171)

I really hope you're doing this in a well-ventilated area and/or using low-dust litter! But points for ingenuity!

Re:That's how I clean my cat's litter box. (1)

Rick in China (2934527) | about 3 months ago | (#47464141)

Ah - litter box is on a deck outside and I use crystallized cat litter, so there is little to no dust. :D

I thought it would be about opening a Brazil nut (2)

jellomizer (103300) | about 3 months ago | (#47456955)

I never stopped to think if the Brazil nut is on top, but more how the heck do I crack open the shell. A triangle is one of the strongest shapes. The Brazil nut shell is in a nice triangle. Thus my approach is smashing it to pieces, and eating the nut in little fragments.

Re:I thought it would be about opening a Brazil nu (1)

CheezburgerBrown . (3417019) | about 3 months ago | (#47457041)

Jellomizer for president 2016

Of Brazil Nuts and Mexican Waves (1)

sdack (601542) | about 3 months ago | (#47457043)

Wow, the World Cup of Brazil really left a mark all the way into space! Now all I need for today is a scientific article, which explain complex physics by using the Mexican Wave!!

Just buoyancy (2)

NNUfergs (1794256) | about 3 months ago | (#47457055)

Why is this called the "Brazil Nut Effect?" This is just normal buoyancy, science teachers have been doing demonstrations like this for years. You can do the same thing if you put a golf ball in the bottom of a container full of shredded bark and shake it.

Re:Just buoyancy (4, Informative)

Dcnjoe60 (682885) | about 3 months ago | (#47457169)

Why is this called the "Brazil Nut Effect?" This is just normal buoyancy, science teachers have been doing demonstrations like this for years. You can do the same thing if you put a golf ball in the bottom of a container full of shredded bark and shake it.

Because in a can of mixed nuts, the Brazil Nuts are almost always on the top. Thus, the Brazil Nut Effect. It actually has nothing to do with buoyancy which involves mass. It's all about size. Put your golf ball in a container and cover it with marbles and then shake it up. The golf ball will rise to the top as the smaller marbles fall beneath it.

Re:Just buoyancy (0)

Anonymous Coward | about 3 months ago | (#47463097)

Put your golf ball in a container and cover it with marbles and then shake it up. The golf ball will rise to the top as the smaller marbles fall beneath it.

...because the smaller marbles are more dense and thus buoyancy will push the golf ball to the top. Put your golf ball in a container of small plastic balls and shake it up. Does the golf ball fall to the bottom because it is more dense or does it rise to the top because it is larger?

In the case of the asteroid it is likely the materials are the same density so buoyancy cannot explain it. It would be like taking a dimpled hard candy, mixing it with some crushed hard candy and shaking it up.

Re:Just buoyancy (4, Informative)

wonkey_monkey (2592601) | about 3 months ago | (#47457227)

"Normal" buoyancy is about less dense objects floating on top of a fluid. This (granular convection) is about larger objects rising to the top of smaller ones.

As your golf ball example shows, the "floating" object can be denser than the "fluid," which would not be the case in "normal" buoyancy. And there's no upward force being exerted on the objects by the "fluid."

Re:Just buoyancy (4, Informative)

tlhIngan (30335) | about 3 months ago | (#47457443)

Why is this called the "Brazil Nut Effect?" This is just normal buoyancy, science teachers have been doing demonstrations like this for years. You can do the same thing if you put a golf ball in the bottom of a container full of shredded bark and shake it.

Buoyancy is about displacement and density - a buoyant item has less mass than the amount of bulk matter it displaced. Like say, how boats float - the mass of water displaced by a boat is more than the mass of the boat.

The Brazil Nut Effect isn't about buoyancy because it has nothing to do with the Brazil Nut's mass. It's about the observation in a can of mixed nuts, if you give them a shake, the Brazil nut rises to the top. Consistently.

If it was about buoyancy, then it's because the Brazil nut displaces less err, nuts, than the others, but no. You can replicate the effect with many other things - the bigger items rise to the top.

Re:Just buoyancy (2)

sdack (601542) | about 3 months ago | (#47460401)

I believe you are wrong. The mass of objects will certainly play a role in both effects. The Brazil Nut Effect will likely have something to do with the inertia of objects.

The difference when compared to buoyancy will be that with buoyancy you have a calm system, without any energy coming in from the outside, where objects come to a rest. Here the objects will order themselves merely based on their density - their size-to-mass ratio.

While in the Brazil Nuts Effect its the opposite and objects will find themselves exposed to vibrations and shocks. Here the objects with a higher mass also have a higher inertia. The smaller objects will bounce between the more inert objects on fast-changing trajectories, while the more inert and massive objects will have more stable trajectories, because these will only change their trajectory when they hit other massive objects. As a result will the larger, more massive objects travel further than the smaller objects and so end up further out. Therefore will mass and density play a role in the Brazil Nut Effect, too.

The difference will be that one system (buoyancy) is calm without external energy coming in and allowing objects to come together, while the other system (Brazil Nut Effect) sees energy coming in, which shakes up the order of objects and drives objects apart.

Re:Just buoyancy (0)

Anonymous Coward | about 3 months ago | (#47458895)

Guess you failed (massively!) that science class, eh?

Re:Just buoyancy (1)

Nyder (754090) | about 3 months ago | (#47460203)

Why is this called the "Brazil Nut Effect?" This is just normal buoyancy, science teachers have been doing demonstrations like this for years. You can do the same thing if you put a golf ball in the bottom of a container full of shredded bark and shake it.

I don't think you want to call it what my grandma would call Brazilian Nuts. Not very PC.

Re:Just buoyancy (1)

Livius (318358) | about 3 months ago | (#47461707)

Well, not *normal* buoyancy, but Brazil nut is certainly a specialized (I would say obscure) metaphor to choose.

yuk (-1)

Anonymous Coward | about 3 months ago | (#47457109)

nobody likes niggertoes.
they just put them the mix because they waste a lot of space.

Popcorn Effect (0)

Anonymous Coward | about 3 months ago | (#47457231)

Well yeah, every person that goes to movies is well aware of this effect, that is why during the movie you hear the rustle of boxes of popcorn being shaken to bring the large tasty choice kernels to the top.

Re:Popcorn Effect (2)

Bill, Shooter of Bul (629286) | about 3 months ago | (#47458647)

Never thought of that. Probably because I don't like buying popcorn at $5.00 for a small that tastes like wood shavings covered in bromide.

What kind of nut (0)

Anonymous Coward | about 3 months ago | (#47457525)

explains the mystery of why people think we'll be mining asteroids?

Re:What kind of nut (0)

Anonymous Coward | about 3 months ago | (#47462453)

For the Brazil nuts?

It is still just a theory (3, Insightful)

dunkindave (1801608) | about 3 months ago | (#47457619)

My problem with these kind of articles is how they state it as 'case closed'. All this is is a theory of what is happening. Maybe it has a lot of solid science behind it, maybe it is even right, but right now it is still just a theory for us to explain what is happening. Using words like "Now an international team has solved the mystery" makes it sound like there is no debate, this is the answer, and anyone who says otherwise is an idiot. While I am not a scientist, I come close enough, and this fails the scientific method, at least in how the reporting represents it.

OK, I feel better now.

Re:It is still just a theory (0)

Anonymous Coward | about 3 months ago | (#47458223)

+1

As if: Let's not question our politically oriented science or it's conclusions. And perhaps that all is right if we consider we have been lied to for so long we don't have context to draw reasonable conclusions.

Re:It is still just a theory (1)

sdack (601542) | about 3 months ago | (#47462191)

You now make it sound like there is still a need for a debate, but where is your explanation for it? Where is the debate? I do not see you coming up with an explanation as to why there is still a need for a debate. All you really seem to be doing is to express your fear over being called an idiot, but I am fairly certain you will be clever enough to know that insults can never replace a good explanation. The only explanation you are giving is in fact that you are not a scientist.

And yes, it does not only "sound like" as if this is the answer, but it is given as the answer. Quite purposely, consciously, deliberately and intentionally so. It is the f-ing point of a scientist's efforts.

Did you at least read the scientists' explanation of it?

Re:It is still just a theory (1)

Will.Woodhull (1038600) | about 3 months ago | (#47462509)

Mod parent up.

Too many people fall into the trap of mistaking scientific authority for scientific method. A scientist may be an excellent authority in his specialty, but he is still just an authority and is prone to all the kinds of errors of that any man can make. The scientific method with its hypotheses and experiments is the gold standard, and even its results should be rigorously questioned.

A scientist who is not a profound skeptic about just about everything is not really a scientist, but merely an imposter.

Clumping due to Gravity (1)

7bit (1031746) | about 3 months ago | (#47457643)

Odd; My first thought would be that those surface boulders were just the more recent micro-asteroids that were drawn to the larger asteroids gravity. I'm not sure why a more complicated explanation is necessary? But I'm open to learning.

"there were supposed to have come from" - LOL (-1)

Anonymous Coward | about 3 months ago | (#47457735)

American cretins. You can't even write 'they' properly.

And you get REALLY confused when you have to write 'they're', 'their' or 'there'. How the hell is your country still standing?

Re:"there were supposed to have come from" - LOL (1)

HornWumpus (783565) | about 3 months ago | (#47458097)

How the hell is your country still standing?

Your countries thought is good steady footing.

Re:"there were supposed to have come from" - LOL (1)

Bob_Who (926234) | about 3 months ago | (#47469405)

American cretins. You can't even write 'they' properly.

And you get REALLY confused when you have to write 'they're', 'their' or 'there'. How the hell is your country still standing?

We stand on our feet, silly.

It's harder to do that while your head is up your ass.

Your obsessing on typos, homophones, homonyms during a Slashdot banter about Brazil nuts and asteroids is either an emotional disorder or you are from the Land of Trolls that can't walk and talk at the same time.

Hurling vituperative disparagements in grammatically correct English has nothing to do with this story and discussion so please take your meds. .

Another explanation (1)

Anonymous Coward | about 3 months ago | (#47458165)

Another explanation is that the asteroid got showered by a significant amount of other material that was not part of the primary body of the crater making asteroid. Perhaps when a nearby moon or planet exploded like the fictitious planet of Alderan in the popular Star Wars movie A New Hope.

This type of astronomical event would also explain why one side of Mars is the flattest place in the solar system and has a crust thickness of only 1km and the other side hosts the tallest mountains in the solar system and has a crust thickness of 20 km. Also can offer a plausible explanation for why phobos and deimos are not round like one would expect moons to be.

Brzail nut effect? (0)

Anonymous Coward | about 3 months ago | (#47458695)

Is that when you meet up with a hot Brazilian chick but then it turns out she has a monster cock and a bigger ballsack than you?

Back in the day... (0)

Anonymous Coward | about 3 months ago | (#47458767)

This was known as the Cesspool Theory of Managment.

"The big chunks rise to the top."

Mathematical explanation? (0)

Anonymous Coward | about 3 months ago | (#47458769)

Banach-Tarski in action?

spammy post is spammy (0)

Anonymous Coward | about 3 months ago | (#47459033)

What is it with the army of medium.com lovers lately?

Nuts and, Bolts! (1)

MrKaos (858439) | about 3 months ago | (#47463045)

This also explains why all the big nuts and bolts rise to the top of my bolt bucket!

Non-Explanation (1)

Capt.Albatross (1301561) | about 3 months ago | (#47467545)

The apparent discrepancy of the total volume of large boulders being greater than that of the visible craters they have supposedly come from is not resolved by the BNE. In the paper, this paradox is only mentioned in passing, and no definite resolution is offered. No-one seems to have ruled out the possibility that there are additional craters beneath the rubble, or that the excess includes remnants of the impactors. Perhaps there is an assumption that, absent the BNE, the boulders formed by early impacts should now be buried.
     

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