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Two days ago, Ferrebeekeeper wrote about Earth’s magnetic field, an underappreciated invisible force-field which keeps the planet habitable by preventing solar wind from blowing away our atmosphere and oceans (we need those!). Long ago, Venus and Mars seemingly had liquid oceans and nice atmospheres, but something went wrong (?) with their magnetic fields a billion or so years ago, and just look at them now (tuts censoriously). But maybe we shouldn’t be so quick to judge our neighbors…Five hundred and sixty-five million years ago, the Earth underwent a magnetic crisis too.
Geologists have been studying fragments of plagioclase and clinopyroxene from the ancient continental shield of Canada to learn about the state of the planet’s magnetic fields in the ancient past. As they form, these crystals trap tiny magnetized iron fragments in place like the needles of little compasses. Scientists can thus study the deep history of the magnetosphere. As they studied magnetic crystals that were formed 565 million years ago, they found some troubling things: half a billion years ago, the Earth’s magnetic field was over 10 times weaker than what it is today. Additionally the poles were rapidly fluctuating between north and south at an unexpected rate.
A closer reading of all of this suggests that 550 million years ago the Earth’s magnetic field nearly collapsed! (for a look at what that means, just walk around Mars). Life was saved because the solid nickel iron core of Earth nucleated from the molten core at that time. Instead of a field collapse, our magnetic field became much stronger as the spinning solid inner core and the convection cycles of the molten outer core worked together to form a super geodynamo. Coincidentally, 541 million years ago is familiar to paleontologists as the inception of the Cambrian explosion, when multitudinous animal life forms appeared on Earth. It is such an important point that it divides the Phanerozoic (filled with mushrooms, megafauna, liverworts, and Roman centurions) from the Proterozoic (billions of years of bacterial soup). Just a coincidence?
In 2016 the Japanese Space Agency launched a quarter-of-a-billion dollar x-ray observatory named Hitomi into Earth orbit. The craft’s mission was to study extremely energetic processes at the far reaches of the universe. It was hoped that the data Hitomi provided would allow astronomers to understand how the large scale structures of the universe came into being (how galactic superclusters form, for example). The satellite initially worked perfectly, but, within 38 Earth days, the spacecraft was lost: a failure of attitude control sent it into an uncontrolled spin which caused critical structural elements to break apart.
The full story of what destroyed Hitomi is perhaps of greater immediate interest to living beings on Earth than how the meta-structures the universe came into being. When everything went wrong for the ill-fated space observatory it was passing over the southern part of the Atlantic ocean. For spacefarers, this region of the Van Allen Belt is analogous to what the Bermuda Triangle or the Namib Skeleton Coast is for sailors: it is a haunted and dangerous stretch of space. Astronauts who travel through it report strange phantasmagorical dots and streaks in their vision, even when they close their eyes. The Hubble Space Telescope does not make observations when it passes over the south Atlantic. Controllers turn off its delicate systems. The region is known to the world’s space agencies as “the South Atlantic Anomaly.” Hitomi was not its first victim–it is surmised that the South Atlantic Anomaly was responsible for the failures of the Globalstar network satellites way back in aught seven.
The existence of the South Atlantic Anomaly was known long before that. It was discovered in 1958 by Explorer 1, the first American satellite (which was equipped with a Geiger counter). Perhaps the Soviets would have discovered the anomaly by means of Sputnik, but, because the Cold War made scientific cooperation difficult, Australia did not hand over Sputnik data to the Soviets until later. Suffice to say, the South Atlantic Anomaly is an anomaly in the Van Allen Belt, the torus-shaped field of charged particles which are held in place by the magnetic field of Earth. Earth’s magnetosphere is important. Billions of years ago, Mars and Venus seem to have been exceedingly Earthlike, with water oceans and convivial atmospheres. But neither Mars nor Venus has a magnetosphere and their oceans have perished and their atmospheres have changed into monstrous things….although we don’t know exactly what happened on either of our neighboring planets (and the present priorities here on Earth are to make Michel Dell and Howard Schultz as rich as possible at everyone else’s expense, not, you know, to understand what planetary scale forces could make worlds uninhabitable).
Um, at any rate, the magnetic field of Earth is created by the mysterious processes beneath our feet at the center of the planet. The Earth’s inner core is believed to have two layers: an outer core of molten iron and heavy metals and an inner core of solid iron nickel alloy. The inner core is about 70% of the volume of the moon and it is nearly as hot as the surface of the sun with an estimated temperature of (5,430 °C) or 9806 °F, but the molten outer core is only as hot as the surface of an orange star (2,730–4,230 °C; 4,940–7,640 °F). Within the outer core, eddy currents form in the superheated metal. The complex relationship between these currents, the spinning planet, and the two core layers creates a geodynamo which produces the planet’s magnetosphere which in turn captures the particles which make up the Van Allen Belts. However, the eddy currents cause the magnetic poles to invert every few hundred thousand years (we are currently overdue for such a flip). The South Atlantic Anomaly is a manifestation of the “weather” in the molten outer core of Earth–a prelude to the magnetic polar flip. First generation spacecraft used solid state components and had big ungainly robust circuitry. Additionally they were hardened against radiation. Some of today’s craft make use of delicate & elaborate microcircuitry which is prone to failure when struck by esoteric radiation particles. This is how what happens far beneath our feet influences what happens to craft in outer space.
ferrebeekeeper 