[0:02]There's a region of our planet that no human being has ever visited.
[0:10]No one has ever seen this place. Yet what happens here affects every one of us, every day of our lives. It's 2,000 miles beneath our feet, the Earth's molten core. Here, a vast ocean of liquid iron generates an invisible force. The Earth's magnetic field. It's what makes our compasses point north, but it does a lot more. It helps to keep the Earth a living planet. Our neighbors, Venus and Mars, have only weak magnetic fields, which means they're unprotected from the deadly radiations sweeping through the solar system. The Earth, on the other hand, exists within a vast magnetic cocoon. A force field that for billions of years has sheltered us on our journey through space.
[1:21]But now, scientists have made a startling discovery. It seems there's a storm brewing deep within the Earth. A storm that is weakening our vital magnetic shield.
[1:47]The Earth's magnetic field has been our protector for millennia, and now it appears it's about to go away.
[1:56]The Earth's magnetic field is getting weaker rapidly. We cannot guarantee that the magnetic field of the Earth is still meant to be there a thousand years from today. Is our invisible shield about to disappear? The question is not if that's going to happen, it's when that's going to happen.
[2:23]And what will happen if it does?
[2:28]Up next, on Nova, Magnetic Storm.
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[3:51]Searing heat, crushing pressure, and a billion trillion tons of molten iron. These are the conditions at the center of the Earth. This is the Sparrow's Point blast furnace for Bethlehem Steel Corporation, and this is as close to the environment of the Earth's core as we have here on the surface of the Earth.
[4:21]Buried beneath nearly 2,000 miles of solid rock, the Earth's core is inaccessible to geophysicists like Peter Olson. Halfway to the center of the Earth, we reached the true heart of the Earth, the Earth's core. An immense molten sphere of liquid iron, and that's where the Earth's magnetic field is generated.
[4:47]But recently, scientists have detected a dramatic change in the Earth's magnetic field. The core's ability to generate the field seems to be faltering. Today there's something very strange is going on with the Earth's magnetic field. Its strength is rapidly decreasing, so fast that at the current rate it will last only into the next millennium. It seems the Earth's magnetic field is rapidly fading, a puzzle that is challenging scientists around the globe.
[5:28]It's quite surprising how little is understood about the Earth's magnetic field and how it's generated. It was a very intriguing problem, something that was screaming out for an answer. I've often wished I could see the magnetic field. I'm motivated by the mysteries that are there. As scientists grapple with the complexities of the magnetic field, they realize that what is happening at the center of the Earth could change our world for generations to come.
[6:03]Magnetism is something we're all familiar with.
[6:23]When the magnets are turned over one way, they don't want to go together. And when you flip them over, they want to come together and stay together. But this mysterious force is not just a curiosity. Magnetism, a close relative of electricity, lies at the heart of most modern technology, everything from power stations to the television you're watching now. And in fact, the Earth itself is a gigantic magnet. While we are constantly aware of the pull of gravity, most of the time, we are oblivious to the other force the Earth generates, the magnetic field.
[7:20]Magnetic field extends is really huge. The biggest thing really we have on Earth. The magnetic field is created deep in the Earth's core. It streams out near the South Pole, loops around the planet, and then runs back into the core near the North Magnetic Pole.
[7:48]This is the Earth's protective force field. Without it, we'd be in trouble. It protects us against radiation from space.
[8:00]It's a little bit like being in the pod here. This shields us from the weather on Earth, the magnetic field of the Earth shields us from space weather and space radiation. Space weather is nasty. The winds that blow through the galaxy are winds of radiation, some of the most harmful from distant exploding stars.
[8:28]But there is another source which is much nearer, which is our sun. The sun itself is a thermonuclear furnace. And this flings off huge amounts of dangerous material in very large explosions.
[8:46]In some cases, it's about the same mass as Mount Everest actually coming towards us.
[8:53]Every few hours, the sun ejects billions of tons of electrically charged particles, the solar wind. Often, the Earth lies directly in the path of this onslaught. But magnetism deflects charged particles. This means that the solar wind is unable to penetrate the Earth's magnetic shield, and so flows harmlessly around the planet. The only visible signs of this drama far above our heads are the northern and southern lights, produced when solar particles trapped in the Earth's magnetic field are dragged through the atmosphere toward the poles.
[9:43]Now, we're lucky on the Earth, we have the magnetic field which deflects the particles and protects us. But if we lost the magnetic field, there would be nothing to stop the radiation bathing the whole of the atmosphere, and the effect would be much more dangerous. But just how dangerous? What would be the ultimate consequences for planet Earth if the magnetic field were to disappear altogether?
[10:16]The answer has become clear only recently. And we have lift off of NASA's Mars Global Surveyor, as America begins its journey back to the red planet.
[10:31]In 1996, NASA sent a satellite to Mars. Mars has been a difficult planet to get to with spacecraft. Even after 16 missions by US and Russia and so on, we still did not know whether Mars had an intrinsic magnetic field or not. It was this long-standing question which Mario Acuna and his team from NASA hoped finally to settle. What they actually uncovered was considerably more significant. Nature had big surprises for us, beyond our wildest expectations. Hidden in the history of Mars lay the connection between magnetism and life. And here is where we developed our expensive toys, our instruments.
[11:25]This is our lab.
[11:29]Mario is one of the world's leading experts on extraterrestrial magnetic fields. He has sent instruments to measure them all over the solar system. This one went to Jupiter, Saturn and beyond, this is Voyager 1 and 2. This one went to Mercury with Mariner 10. This one went around the orbit of the sun, this one went through Comet Halley, for example.
[11:53]To measure magnetic fields, Mario uses a technique which was discovered a century and a half ago. The simplest way to measure a magnetic field is with a little magnet like we have here. That has been mounted in such a way that it can move freely in three dimensions. And this magnet, because magnetic field is a force field, will align itself with the Earth's magnetic field in this case, in this direction that we have here, which is actually going into the core at an angle of 70 degrees here, and pointing north. So that gives us an idea of the direction of the field. And you can see that if I perturb this magnet just slightly, how fast it recovers the original position, gives us indication of the strength of the magnetic field. So is very weak for the Earth. And if I use a strong permanent magnet, then we see that our test magnet moves much faster. So if I make this magnet work against a spring, I get an idea of not only the direction of the field, but also how strong it is. In the Mars Global Surveyor satellite, the instruments are electronic, rather than mechanical, but the principle remains the same. A tiny electromagnet, which works against a magnetic spring.
[13:35]As Mars Global Surveyor started to send back data, it soon became clear to Mario and the team that today, Mars has no overall magnetic field.
[13:49]But the satellite also detected signs indicating that that had not always been the case. We found these huge magnetic fields in the crust, and all of a sudden a completely unexpected and unknown planet, in a sense, emerged.
[14:07]Although there was no magnetism coming from the core of Mars, strangely, large areas of the surface were strongly magnetized. The Martian crust is mainly made of frozen lava, a remnant of the time when Mars was covered with volcanoes. And there is a way volcanic rocks can get magnetized when they form.
[14:34]If molten rock cools in a strong magnetic field, iron-based minerals in it can pick up that magnetism, and the resulting solid rock will itself be magnetic. So, the fact that there was magnetism in the Martian crust proved that when the lava first erupted, Mars must have had a global magnetic field.
[15:02]And not only that, at an intensity which is 20 to 30 times that of the Earth. Mario's team now knew that Mars had once had a magnetic shield, which it must at some point have lost.
[15:49]Gradually, the atmosphere and oceans of Mars mysteriously disappeared.
[15:59]The puzzle was where did the water go? What process could have caused the loss of water?
[16:06]Mario realized that two dramatic events in the early history of Mars might lead him to the answer.
[16:43]And that was odd, because the huge impacts must have melted the crust, and as it cooled again, the rock should have become magnetized by the strong Martian magnetic field. Yet, there was no trace of magnetism in Hellas and Argyre.
[17:00]Which immediately meant that they were formed after the magnetic field of Mars has ceased to exist.
[17:10]And the estimate is that these impacts took place more than 4 billion years ago.
[17:18]4 billion years ago is when Mars was beginning to lose its water and atmosphere. Though not all scientists agree with him, Mario is convinced that the timing is not just a coincidence. If we shut down the magnetic field, then the solar wind has direct access to the atmosphere of Mars. Then we have a process which is equivalent to the erosion in a desert. The wind blows and it blows the sand away. In this case, the sand are atmospheric particles. Slowly but surely, the atmospheric gases, which includes water, are carried away and are lost to Mars. The loss of its magnetic shield could well have meant death for the red planet. Exposed to the wind of radiation from the sun, over millions of years its atmosphere was gradually blown away, leaving the sterile world we see today.
[18:22]If we were to turn off the Earth's magnetic field, the same process would occur. The atmosphere of Earth would be exposed to the erosional effects of the solar wind, and it would be slowly carried away. The fate of Mars suggests that without the protection of its magnetic shield, the Earth could also become a dead planet. Which makes it all the more disturbing to learn that our own magnetic field is fading so rapidly.
[19:00]Evidence of that decline has come from a surprising source.
[19:09]People have been making pottery for thousands of years. Archaeologists study pots to learn about ancient cultures. But these vessels have another story to tell. Pottery acts just like a magnetic tape recorder. It records the Earth's magnetic field when the pottery's first made.
[21:24]And of course, if the field's very strong, then the pot's strongly magnetized, and if the field's very weak, then the pot's weakly magnetized. By examining pottery from prehistory to modern times, John has discovered just how dramatically the field has changed in the last few centuries. When we plot the results from the ceramics, this is what we see: gentle changes as we come forward in time over 12,000 years, a gentle rise, and then a rapid fall as we come towards the present day.
[22:01]The rate of change is higher over the last 300 years than it has been for any time in the past 5,000. It's going from a strong field down to a weak field, and it's doing it very quickly. In 300 years, the field has fallen 10%, and the rate of decline is increasing. In just a few centuries, it could be gone altogether. So is the Earth going the way of Mars? There's only one place to look for an answer, the inaccessible region where the field is generated, the Earth's core.
[52:26]No one has ever experienced a magnetic reversal.
[53:57]But on Nova's website, get a sneak preview of what the night sky will look like when it happens. Find it on pbs.org.
[54:50]Nova is a production of WGBH Boston.
