How the South Atlantic Anomaly threatens satellites
August 20, 2020 - NASA is monitoring a strange anomaly in Earth’s magnetic field – a vast region of lower magnetic intensity in the skies above the South Atlantic.
A developing phenomenon, known as the South Atlantic Anomaly (SAA), has intrigued NASA for years. The mysterious dip in the Earth's magnetic field that runs from South America and across the South Atlantic to Africa, causes concern because low orbit spacecraft are vulnerable to charged particles from the sun as they pass through it.
The space agency likens the SAA to a "dent" in Earth's magnetic field, or a kind of "pothole in space". It generally doesn't cause concern for life on Earth, but it does for spacecraft like the International Space Station, which periodically pass through the anomaly. The weakened magnetic field exposes craft to high-energy protons emanating from the Sun, which means onboard technological systems can short-circuit and malfunction.
Satellites mainly experience low-level glitches while passing through the SAA, but there is a risk of significant data loss, or even permanent damage. The threat is serious enough for most satellite operators to now routinely shut down their spacecraft before they enter it.
The main contributor to Earth's mysterious magnetic field is an ocean of molten iron forming Earth's outer core, thousands of kilometres below ground. As it swirls around, it generates electrical currents that create Earth's magnetic field.
The field is important to life on Earth because it acts like a shield, pushing away charged particles ejected by the Sun, which could be disruptive if they reached the surface. The field also guides animal migrations and our own compasses.
Scientists believe a huge plateau of dense rock called the African Large Low Shear Velocity Province, located about 2,900km below Africa, disturbs the field's generation, resulting in the dramatic weakening effect – in part aided by the tilt of Earth's magnetic axis.
It is believed the SAA is a recurrent magnetic event that may have begun life 11 million years ago. It is also apparently slowly moving in a north-westerly direction and may even be splitting in two, meaning the future of the SAA is uncertain.