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Title : Magnificent Magnetic Fields
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Magnificent Magnetic Fields

Magnificent Magnetic Fields

earth's magnetic field is one of its most helpful features for us humans not only does it protect us from bearing the brunt of the sun's fury but it's also been pretty useful over the centuries to anyone with a compass trying to get from point a to point b it's mainly generated from the roiling metals deep beneath our feet as they churn they generate electrical currents and those grow into our magnetic field you'd think such a long-lived feature of earth's geology would stay put but well our magnetic field turns out to be pretty indecisive it's a bit of a flip-flopper here's our friend reed who hosts episodes on our space channel to explain how there's something you might not have thought about the magnetic north pole that compasses point two near the geographic north pole is actually the south pole of the earth's magnetic field that's why it attracts the north poles of magnets but that hasn't always been true today's compasses would have pointed south about 1.1 million years ago 

when the geomagnetic north was also a magnetic north pole but then the magnetic poles switched places the magnetic south pole went north and the magnetic north pole went south they swapped again a little less than a million years ago and again about 780 000 years ago giving us today's orientation now if you like doomsday scenarios you might have heard that we're due for another switch that'll make electronics useless and kill us all that's a little extreme and saying that we're due implies that we know a lot about when and why these swaps happen which we really don't the earth's magnetic field comes from electromagnetic induction where iron moving in the outer core generates an electric current with the same physics that power plants use to generate electricity and that electric current creates a magnetic field as molten rock reaches the surface of the earth and cools any iron in it tends to line up with the earth's magnetic field so the iron and solidified lava acts like a time capsule for what earth's magnetic field looked like when it solidified some places like where two tectonic plates have been consistently moving away from each other have had molten rock coming out solidifying for millions of years the farther you get from these divergent plate boundaries the older the iron-filled rocks are and the older the trapped magnetic field is many of these boundaries are on the ocean floor so scientists can measure how the earth's magnetic field has changed over time by bringing sensitive magnetic measuring equipment with them on ships 

across the ocean they first tried it back in the 1950s and 60s and every measurement sense has confirmed the same story there has been a lot of flip-flopping rocks of one age will have magnetic north pointing south just like earth's magnetic field is today but other rocks are backwards magnetic north points north the rocks themselves and the iron trapped inside haven't flipped over or anything so the earth's magnetic field must have reversed over time and it wasn't just once or twice either there have been at least a hundred of these so-called magnetic field reversals in fact there's evidence for reversals going all the way back before the Cambrian period more than half a billion years ago despite these and other measurements like radioactive elements in rocks scientists haven't found much of a pattern in the timing of magnetic field reversals sometimes they happen back to back geologically speaking but other times there are millions of years between them that's one reason it's a little silly to say that we're due for another just because it hasn't happened for around 780 000 years the next one 

might be soon or we could be at the beginning of something like the cretaceous normal super crop a period of about 40 million years without a single reversal or a reversal might have happened more recently than we thought some scientists studying rocks and sediments from the black sea recently found magnetic evidence for a pair of reversals around 41 000 years ago with only a couple hundred years between them but that would be a pretty extreme pair of reversals since we think that a single flip generally takes a few thousand years from beginning to end although there's a ton of variation here too reversals could take hundreds or thousands or tens of thousands of years during a reversal we think that the existing magnetic field generally weakens until it's almost completely gone and then the field gradually builds up in the opposite orientation since the earth's magnetic field helps protect us from some of the most extreme forms of interstellar and solar radiation a reversal would be pretty bad news if it started tomorrow because of all the extra radiation satellites in low earth orbit and electronics down here on the surface might get fried over time and stop working if the power grids go down that could lead to a lot of problems not to mention those kinds of radiation can damage cells so it might cause extra bad sunburns or increased rates of cancers in humans and other living things but it still probably wouldn't be apocalyptic now despite all this research about when reversals happened scientists still 

don't know what causes them they're not sure what has enough energy to affect the earth's core so dramatically changing the way a ton of iron and molten rock are sloshing around in the past it could have been asteroids or comets smacking into earth and sending powerful shock waves through the planet or triggering climate events that changed how its mass is distributed or it could have to do with big chunks of tectonic plates descending into earth's mantle or blobs of magma moving up from the deep mantle and throwing things out of balance but it's hard to find evidence of exactly what's happened in earth's core for the last billion years and our computer simulations can only predict so much with incomplete data sets so geophysicists are still at the guessing stage of science at least for now so we can't always count on north being north and south being south at least these days most of us don't need that information to grow or catch our dinner while we need the magnetic field to protect us from the sun other animals like foxes use it to hunt and here's how we know you might be familiar with the cute pouncing technique many foxes use to hunt mice and voles they'll jump high into the air and come down nearly directly on top of their prey even if that prey is hidden from sight in snow or grassy underbrush this is a tricky hunting technique 

to master because a fox needs to know exactly where their prey is so they can successfully line up their attack and close the distance with that jump scientists know that they're using their big ears to help zero in on their target but some think that they're also using another sense that the foxes are actually hunting using magnetic fields and no this isn't like they've got a built-in metal detector for mice rather they may be sensing the earth's magnetic field in fact foxes might be the first animal we know of to use magnetoreception to gauge the distance to their prey and this sense might be crucial to their pouncing success in a 2011 study of red foxes in europe researchers noticed that when their prey was hidden by vegetation a whopping 74 of successful hunting pounces occurred when the fox was pointed in a northeasterly direction they combed through their data looking for other factors that might bias the direction of attack like the wind or sunny versus cloudy conditions after ruling all that out they proposed that the foxes were using magnetoreception to orient themselves roughly toward magnetic north while they weren't sure how they did make a suggestion for why doing so would be helpful to the fox you see as a fox approaches its prey it will use its other senses to gauge where its target is if they can't see their prey they'll listen for it 

but the fox wants to know exactly where that hidden morsel is to jump the right distance to neatly close the gap the researchers in this study proposed that the fox is searching for where its other sensory cues line up with the angle of the earth's magnetic field that would result in a sort of overlay targeting system the angle of the magnetic field is fixed meaning the fox could basically be using this stable reference point to line up where it thinks its prey is once it matches that angle the fox knows the distance to its prey and can employ the exact same pounce successfully nearly every time it's almost like it has its own biological heads up display basically something in its visual field pinging when it's at the right distance so no matter when or where or what a fox is hunting it pays to have learned just one move to come down right on top of dinner now magnetoreception is actually thought to be fairly common many animals especially 

migratory birds are believed to use the sense for long-distance navigation using it to find the right direction to travel but this would make foxes the only animal thought to use magnetoreception to sense distance scientists have long puzzled over the exact method as to how magnetic fields are sensed research in birds and fruit flies suggest that a chemical reaction in light-sensitive proteins could be the key these proteins are collectively called cryptochromes and foxes have them in their eyes just like birds and some other magnet sensing species so if these proteins are found in the eyes and are sensitive to light what does that have to do with sensing magnetic fields we're not totally sure but there is some evidence for how it might work when a photon of blue light hits a cryptochrome the cryptochrome transfers an electron to a partner molecule this new arrangement leaves each partner with an uneven number of electrons one has an extra electron and one has one fewer and every electron has a property called spin which can be either up or down in the case of our unbalanced pair one of those electrons has an 

up spin and the other has a down spin at the time of the transfer but then they flip back and forth and even wobble now this electron transfer reaction is reversible meaning it can go back the other way but only when the electron spins are opposite but because magnetic fields influence the rates of the electrons flipping between up and down spin and the wobble in that spin a magnetic field could change the rates and products of the chemical reactions too at least this is how it works in theory we know migratory bird eyes contain cryptochromes and that their ability to navigate with magnetic fields may require the presence of light foxes and some other mammals also have cryptochromes in their retinas and they're our strongest candidate for the job of biochemical magnetoreceptor but we still need to show experimentally that cryptochromes form enough of these electron pairs to signal in some way that this way is north and this way isn't and in fact even if cryptochromes are sensitive to magnetic fields at a biologically 

At the relevant level we don't know how that signal would get passed along to the animal's brain so we can't be sure it actually senses anything so while the chemistry and math seem to check out scientists are still working on the biological details of fox's hunting magnet vision still it's no wonder that pounce is a mouse's worst nightmare okay so scientists are probably still working out the biology that helps foxes locate their prey but how would alien foxes find their food because we're not the only planet in the universe and other planetary magnetic fields aren't all set up like ours so here's a look at how that goes down for some of our neighbors with our other friend on scishow space Caitlin here on earth we owe our lives to the magnetic fields surrounding our planet without it charged particles from the sun would crash right into our atmosphere and whisk parts of it off into space, fortunately, earth's magnetic field fends off most of those particles before 

they can do any harm but magnetic fields don't always play the hero other planets relationships with their magnetic fields are complicated and sometimes magnetic fields do more harm than good for example it seems like mars have had it pretty rough as barren as it is today we can tell by its ancient canyons and dried out riverbeds that about three and a half billion years ago water flowed on the surface of mars and that would only have been possible if it had a thick atmosphere putting enough pressure on the water to keep it in liquid form but today its atmosphere is super thin less than one percent as thick as earth's which raises the question where did it go researchers think the answer could have to do with its magnetic field satellite observations of magnetized rock formations on mars suggest that around the time water was flowing on its surface convection in its 

core created what's called a dynamo effect a magnetic field set up by the swirling motion of molten metal the magnetic field would have surrounded the planet and protected its atmosphere just like ours does on earth but for reasons scientists don't fully understand yet mars's dynamo effect stopped around 3.9 billion years ago and switched off its global magnetic field and just like that mars main protection against the sun's charged particles or solar wind vanished but that wasn't the end of the story even now satellites can still detect some very weak magnetism in patches of mars surface that's because over time mars global magnetic field had magnetized rocks on its surface those rocks held onto the magnetism baked into them even when the dynamo effect disappeared and as a result of the magnetization in those rocks mars still has a weak magnetic field today but you might think a weak magnetic field that's better than none when it comes to protecting an atmosphere but in early 2020 a study in the journal of 

geophysical research suggested exactly the opposite the authors used computer models to predict how quickly mars's atmosphere would have escaped from under a strong magnetic field a weak one or none at all as expected in the model with no magnetic field the solar wind gradually swept the atmosphere away over time while a strong magnetic field protected the atmosphere but the fastest loss actually happened in the model with a weak magnetic field see on mars the magnetic field lines are so flimsy that instead of surrounding the planet like they do here on earth the solar wind bends them away from the planet like streamers blowing in the wind this creates a sort of magnetic tail on mars's downwind side unfortunately that doesn't just channel charged particles from the solar wind charged particles from the atmosphere can also drift along magnetic field lines the researcher's computer model showed that oxygen and carbon dioxide ions escaped through the magnetic tail faster than in the scenario with no magnetic field at all and they believe that process is what sped up the loss of mars atmosphere and turned the planet into the barren world it is today so for mars a bit of magnetism was a dangerous thing but that's not always the case like on mercury a weak magnetic field is the whole reason the planet has any kind of 

atmosphere at all the planet is pretty small only about one and a half times the size of our moon and its gravity isn't strong enough to hold onto a proper atmosphere but it actually does have some gases surrounding it they're really sparse and the atmospheric pressure is so low that we can't even measure it but spacecraft have confirmed that there are traces of gas on the planet and that's kind of odd given mercury's weak gravity even that wispy atmosphere should have drifted off into space a long time ago so the only reason it exists today is because there's a process replenishing that gas over time and that has to do with mercury's magnetic field even though at the surface it's only about one percent as strong as earth's mercury's magnetic field is able to deflect some of the solar wind but it can get a little patchy and from time to time its magnetic field lines twist up to form a little bundle called a magnetic tornado these funnels twist out into space and passing particles from the solar wind spiral down them then crash into the 

rocky surface of mercury at about 500 kilometers per second that's fast enough to blast atoms off the surface and replenish some of the particles in its atmosphere in fact without its leaky magnetic field mercury might not have an atmosphere at all so depending on the circumstances weak magnetic fields can play both offense and defense for a planet's atmosphere so now you might be thinking that strong magnetic fields would be more reliable protectors of their planets but that's not always the case when it comes to planetary magnetic fields jupiter is the solar system's undisputed champion even though its core isn't made of molten metals like the rocky planets jupiter's immense gravity creates a liquid core of hydrogen at its center and that generates a powerful dynamo effect in fact its magnetic field is about 200 times bigger than the planet itself that's about 20 times bigger than the sun that gigantic magnetic field steers the solar wind well clear of jupiter millions of kilometers upwind from the planet itself but on jupiter's dark side from time to time that same field delivers a hidden attack on the atmosphere see despite its strength the field doesn't form a perfect sphere around the planet instead as the solar wind blows into it the side facing the sun gets a little 

squashed while the other side gets pulled along with the solar wind giving the planet along magnetic tail in 2007 the new horizon spacecraft flew through this tail on its way to pluto and it found something odd there were blobs of charged gas particles floating down the tail like bubbles being blown in the wind and scientists think those bubbles are a sign that Jupiter's tail is attacking its own atmosphere they seem to form when the magnetic field lines stretching out from the planet reconnect with each other and create closed magnetic loops called plasmoids unfortunately for Jupiter plasmoids can trap chunks of Jupiter's atmosphere inside a kind of like how a soap bubble traps air inside as it forms then those plasmoids drift off down the tail swept along with the solar wind researchers estimate that this process could be whittling away Jupiter's atmosphere at a rate 

of 100 kilograms a second in fact plasmoids are stealing bubbles of gases from many planets including all the other gas giants in our solar system so no matter how strong they are magnetic fields can have a sly streak now not every planet generates its own magnetic field but that doesn't necessarily mean that they're off the hook take venus there's no dynamo effect going on inside the planet so you might think that it would be safe from plasmoids but also wide open to attack from solar wind and incredibly neither one is true when UV light from the sun hits venus it ejects electrons from atoms in its upper atmosphere and that creates a buffer of charged molecules called the ionosphere then when the solar wind collides with this ionosphere it induces a magnetic field around the planet that's because anytime you have moving charged particles they create a magnetic field 

so the particles in the solar wind carry a magnetic field of their own but it also works the other way around a magnetic field also moves charged particles so the magnetic field from the solar wind moves the particles in the ionosphere and when the particles in the ionosphere move they then generate their own magnetic field that induced field push back in the opposite direction to the original one that created it for venus that means that the field in the ionosphere pushes back against the solar wind just like an ordinary magnetic field would and it actually protects venus just like a normal one would too but it also comes with its own problems like Jupiter venus has a long magnetic tail from its induced field and occasionally those field lines reconnect forming plasmoids that snip away parts of its atmosphere just like on Jupiter with all the chaos taking place in the 

atmospheres around the solar system at least here on earth our magnetic field is on our side except when it's not one of the most beautiful effects of our own magnetic field are auroras also known as the northern and southern lights these natural light shows happen when our magnetic field whisks particles from the solar wind toward our planet's poles as they accelerate they radiate light in the visible spectrum creating those gorgeous colorful streaks but as pretty as they are those particles don't always sail harmlessly through the sky sometimes they crash straight into oxygen ions in the upper atmosphere when that happens they often lose their energy and transfer it to the oxygen ion instead speeding it up enough that it can escape the atmosphere and ride earth's very own magnetic tail off into space and that happens more often than you'd think earth loses 90 metric tons of its atmosphere every day to processes like these but while 90 tons sounds like a lot earth's atmosphere contains 5 quadrillion metric tons of gas that's a 5 with 15 

zeros after it so even 90 tons every day isn't going to make a dent for billions of years and by then earth will probably have lots of other problems to deal with so despite the little bit of leakage from our own precious atmosphere we can still rest easy knowing our sturdy dynamo-powered magnetic field is keeping us safe and from what we see around the solar system there's definitely no place like home so there's more than one way to make a magnetic field we can tell from looking at how other planets do it but we could also figure that out without leaving earth because we have more than one magnetic field generating force right here at home aside from our core we've also got the tithes you're likely familiar with the fact that the earth is surrounded by a gigantic magnetic field it keeps us safe from solar radiation and produces beautiful auroras at the poles as a sweet bonus but scientists have also detected a second magnetic field surrounding the earth generated by its surface waters and understanding this second field can not only help us learn more about earth's oceans it may be the key to finding new ones 

farther afield people have known about our planet's primary magnetic field for a pretty long time it's generated by molten metal in the earth's outer core because the electrons in a metal are relatively free to move that means a bunch of electric charge moving around beneath the surface of the planet and flowing charge creates a magnetic field since there's such a huge amount of molten metal in the 2300 kilometer thick outer core of the earth the magnetic field it creates is also huge but it turns out superheated liquid metal isn't the only source of magnetism on this planet any flow of charge in a single direction can create a current and a corresponding magnetic field where there's current there should be a field and it just so happens that our oceans contain a heck of a lot of charge in the form of ions ocean water is salty because it contains minerals like sodium chloride but those minerals dissolve in the water the sodium and the chlorine separate from one another into a positively charged sodium ion and a negatively charged chlorine one and other minerals behave in similar ways the charge from a single ion is minuscule but the oceans contain a lot of salt and when that salty ionic 

water flows through the earth's magnetic field it creates weak electric currents which produce their own weak magnetic field this had actually been predicted as far back as the 1830s but we didn't have the technology to spot the oceanic magnetic field until the 21st century it was in 2018 that the European space agency's swarm satellites detected it for the first time these three satellites orbit the earth and make extremely precise measurements of the magnetic and electric fields surrounding the planet the high level of detail made it possible to distinguish the small oceanic magnetic field from the much larger geomagnetic field this second magnetic field fluctuates with the tides a sure sign that it's coming from the oceans but it's 20 000 times weaker than the main magnetic field so its role in protecting our planet is minimal even so researchers hope that 

studying the field in the future will help us map ocean currents across the globe that'll help us better understand how heat moves around the world ninety percent of all the excess heat generated by humans is absorbed by the oceans so being able to track where that heat is going will help predict the effects of climate change but being able to detect oceanic magnetic fields could also be useful beyond earth faint magnetic signals coming from icy planets and moons could hint at hidden underground oceans researchers have already seen perturbations in Jupiter's magnetic field around its moods Ganymede and io which could mean those moons have internal magnetic fields generated by the underground ocean so this little sibling of a magnetic field is way more than just a curiosity it can help us better understand our own planet and others to boot so the magnetic field that the tides contribute is relatively weak compared to what our core is cooking up 

but even earth's core is no match for the strongest magnetic field in the universe here's caitlin again to tell us more whether you use them to hang pictures on your fridge or they're inside your hard drive the world is full of magnets and sure the magnets in mra machines or particle accelerators are powerful but the strongest magnetic fields are actually scattered throughout the rest of the universe they come from a type of star called a magnetar and they're so strong that getting within a thousand kilometers of one would tear apart your atoms but a magnetar that we'll just call sgr0418 for sure is special it currently holds the title of the strongest magnetic field in the known universe a magnetar is a special kind of neutron star with an extremely strong magnetic field neutron stars form after a big star somewhere between 8 and 15 times the size of the sun has burned up all of its fuel and exploded in a supernova after the explosion all that's left over is the dead super dense core imagine the mass of the sun squeezed into a sphere about 20 kilometers across and you'll get a good idea of how dense neutron stars are everything is packed together so tightly that protons and electrons get fused 

together into neutrons the star might have once been made of carbon or hydrogen or iron but now it's mostly neutrons with a few protons scattered around about one in every 10 neutron stars becomes a magnetar which has a powerful magnetic field that makes it shoot out x-ray bursts every so often astrophysicists aren't positive what causes magnetars to form but one theory is that it requires just the right combination of spin temperature and an existing magnetic field other neutron stars might stay as they are or they could become pulsars rotating stars that emit beams of radiation even regular neutron stars have incredibly strong magnetic fields around a trillion gauss compare that to a standard bar magnet which might have around 100 gauss or even the strongest magnets used in an MRI which are about 30 000 gausses so the magnetic field in a 

regular neutron star is ridiculously strong but magnetars are 10 to a thousand times stronger than that so sgr0418 our record holder for the strongest magnetic field is a thousand times more powerful than many magnetars but the strange thing is we used to think it had an especially weak magnetic field it was discovered in 2009 using the European space agency's xmm newton space telescope and NASA's Chandra x-ray observatory like with any new magnetar discovery the astronomers calculated the magnetic field on the magnetar surface by measuring the change in its spin they calculated that its magnetic field was 6 trillion gauss 100 times lower than a typical magnetar because its surface magnetic field seems so weak astronomers suspected that there was something up with this magnetar so in 2013 they developed a new way to measure it instead of measuring the spin on a normal day they measured it during an x-ray burst instead and this time they found that sgr0418 wasn't a weak magnet at all it's 

actually, the strongest magnetar we've ever seen with a magnetic field of over a quadrillion gauss it turns out that this magnetar behaves a lot differently than other magnetars we've seen while most magnetars have a strong surface magnetic field sgr0418s is weak which is why the normal methods of measurement didn't work instead its strong magnetic field is mostly below the surface where it breaks out during x-ray bursts this magnetar may be so strange because it's much older than other magnetars most only last around ten 

thousand years before their magnetic field is too weak for them to be called a magnetar the sgr0418 is over 550 000 years old and for some reason is still going strong we currently don't know if there are other old magnetars with similar behavior that is with strong internal magnetic fields but weak surface ones but at least now we know how to look for them and how to measure them so who knows maybe someday we'll even find a stronger magnetic field maybe it's a good thing that we don't have a magnetic field so strong that it shoots x-ray lasers out at other planets talk about being a bad neighbor our magnetic field seems to be just the right strength to keep us relatively safe without causing intergalactic strife we love an unproblematic magnetic field and we love space too if you couldn't tell from the episodes we snuck into this compilation there's even more

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