Friday, November 09, 2007

Why satellites fail over Brazil

The South Atlantic Anomaly

The map above does not represent the most common destination for fleeing Hollywood villains. It’s in fact the South Atlantic Anomaly, a region where the Earth’s inner van Allen radiation belt makes its closest approach to the planet’s surface. The result is that, for a given altitude, the radiation intensity is higher over this region than elsewhere. Brazilians are blessed indeed.
The Anomaly in the radiation belt results from the fact that the planet’s magnetic field is not perfectly aligned with its geographic center and poles. Which means the magnetic field is slightly stronger in the North, and moves around the geographic poles, leaving the area around Brazil and the South Atlantic closer to the radiation belts.

Fortunately, the effects of it over humans on the surface of the planet are not significant. Unfortunately, it’s very relevant to orbiting satellites — the Hubble Space telescope does not take observations while passing through the South Atlantic Anomaly, for instance. Satellite failures are much more common in this stronger radiation zone.

It also affects satellites with humans inside, like the International Space Station. Light Flashes, thought to be produced by radiation directly stimulating the retina of astronauts, are reportedly more common when they are flying through the zone.

As the Anomaly is due to the Earth’s magnetic field, and since it’s always moving — including several complete reversals — it probably danced around the planet for the past billion years. It’s curious indeed that such a “special area” would even exist. And right now, it’s Brazilian.


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