The Core

I've worked with data from X-ray satellites before, and among the many messy things one has to deal with in real data were blocks of time marked SAA. I knew this stood for "South Atlantic Anomaly", but I had only the vague idea that it was a part of the sky that was geomagnetically inconvenient, so that I had to trim it out of my data. The other day I came across a fascinating BBC documentary, titled "The Core":

This documentary talks about the Earth's core and how we're studying it, from seismology to diamond anvils to huge liquid-sodium dynamo experiments. It makes very interesting watching, but I particularly liked that they used the South Atlantic Anomaly as a hook: it caused problems with certain instruments on Hubble, and the documentary is framed as an investigation into why. (More below the jump if you're not worried about spoilers.)


It turns out that the South Atlantic Anomaly is a region of unusually low magnetic field that's been growing and sweeping west under South America for a few hundred years. This weak field allows higher than normal numbers of solar wind protons to get close enough to the Earth to interfere with some satellite observatories. It's not a question of frying the electronics so much as swamping sensitive detectors, but it still means you have to throw out data - or even turn off the instrument - for that part of the orbit.

Interestingly, the South Atlantic Anomaly appears to be the outward manifestation of a change happening in the outer core of the earth. In particular, the field there is (apparently; I don't know how they estimate it) quite complicated, not dipolar at all. What we see has most of the complications smoothed out, but it seems that the South Atlantic Anomaly is a sign that the south magetic pole is wandering and breaking up. Possibly this is a sign that we're headed into a magnetic pole reversal. That would be a matter of hundreds or thousands of years, though, and thankfully there doesn't appear to be a way we can make it worse.

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