NASA
Is Tracking a Vast, Growing Anomaly in Earth's Magnetic Field
NASA is actively monitoring a strange anomaly in Earth's magnetic field: a
giant region of lower magnetic intensity in the skies above the planet,
stretching out between South America and southwest Africa.
This vast, developing phenomenon, called the South Atlantic Anomaly, has
intrigued and concerned scientists for years, and perhaps none more so than
NASA researchers. The space agency's satellites and spacecraft are particularly
vulnerable to the weakened magnetic field strength within the anomaly, and the
resulting exposure to charged particles from the Sun.
The South Atlantic Anomaly (SAA) - likened by NASA to a 'dent' in Earth's
magnetic field, or a kind of 'pothole in space' - generally doesn't affect life
on Earth, but the same can't be said for orbital spacecraft (including the
International Space Station), which pass directly through the anomaly as they
loop around the planet at low-Earth orbit altitudes.
During these encounters, the reduced magnetic field strength inside the anomaly
means technological systems onboard satellites can short-circuit and
malfunction if they become struck by high-energy protons emanating from the
Sun.
These random hits may usually only produce low-level glitches, but they do
carry the risk of causing significant data loss, or even permanent damage to
key components - threats obliging satellite operators to routinely shut down
spacecraft systems before spacecraft enter the anomaly zone.
Mitigating those hazards in space is one reason NASA is tracking the SAA;
another is that the mystery of the anomaly represents a great opportunity to
investigate a complex and difficult-to-understand phenomenon, and NASA's broad
resources and research groups are uniquely well-appointed to study the
occurrence.
"The magnetic field is actually a superposition of fields from many current
sources," explains geophysicist Terry Sabaka from NASA's Goddard Space
Flight Centre in Greenbelt, Maryland.
The primary source is considered to be a swirling ocean of molten iron inside
Earth's outer core, thousands of kilometres below the ground. The movement of
that mass generates electrical currents that create Earth's magnetic field, but
not necessarily uniformly, it seems.
A huge reservoir of dense rock called the African Large Low Shear Velocity
Province, located about 2,900 kilometres (1,800 miles) below the African
continent, disturbs the field's generation, resulting in the dramatic weakening
effect - which is aided by the tilt of the planet's magnetic axis.
"The observed SAA can be also interpreted as a consequence of weakening
dominance of the dipole field in the region," says NASA Goddard
geophysicist and mathematician Weijia Kuang.
"More specifically, a localised field with reversed polarity grows
strongly in the SAA region, thus making the field intensity very weak, weaker
than that of the surrounding regions."
While there's much scientists still don't fully understand about the anomaly
and its implications, new insights are continually shedding light on this
strange phenomenon.
For example, one study led by NASA heliophysicist Ashley Greeley in 2016
revealed the SAA is drifting slowly in a north-westerly direction.
It's not just moving, however. Even more remarkably, the phenomenon seems to be
in the process of splitting in two, with researchers this year discovering that
the SAA appears to be dividing into two distinct cells, each representing a
separate centre of minimum magnetic intensity within the greater anomaly.
Just what that means for the future of the SAA remains unknown, but in any
case, there's evidence to suggest that the anomaly is not a new appearance.
A study published last month suggested the phenomenon is not a freak event of
recent times, but a recurrent magnetic event that may have affected Earth since
as far back as 11 million years ago.
If so, that could signal that the South Atlantic Anomaly is not a trigger or
precursor to the entire planet's magnetic field flipping, which is something
that actually happens, if not for hundreds of thousands of years at a time.
Obviously, huge questions remain, but with so much going on with this vast
magnetic oddity, it's good to know the world's most powerful space agency is
watching it as closely as they are.
"Even though the SAA is slow-moving, it is going through some change in
morphology, so it's also important that we keep observing it by having
continued missions," says Sabaka.
"Because that's what helps us make models and predictions."
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