14 AUSTRALIAN SKY & TELESCOPE April 2018
FIELD FLIP AHEAD? by Robert NaeyeWe depend upon a global
electromagnetic bubble to protect us
from hazardous space radiation. Is
that invisible field wavering?A
s geologists and mariners have long known, Earth’s
magnetic field is dynamic and ever-changing. The
location of our planet’s north and south magnetic
poles are both wandering, recently by as much as
40 kilometres per year. The strength of Earth’s field varies
significantly from one location to another — in the South
Atlantic Ocean, for example, the field is only half as strong as
the global norm.
Even the familiar north-south polarity is not fixed for all
eternity. The paleomagnetic record clearly shows that our
planet’s field is capable of flip-flopping in such radical fashion
that north becomes south and south becomes north.
In fact, Earth’s magnetic field has weakened overall by
about 9% over the past 175 years. This has led to concern that
our home planet could be heading for one of these polarityMagnetic Field
Evolving
S THREADED EARTH Thanks to churning convection
in its liquid outer core, Earth has a substantial magnetic
field that extends more than 50,000 km into space.Earth’s