Inside the Boardroom with Alan Bagley - SETI Institute

Astrobiology
Magnetic Field Reversal
The Andromeda Galaxy
NASA/JPL-Caltech/NOAO
Here Comes
Andromeda
by Laurance Doyle
Looking at the last term of the Drake Equation, we see that it relates to the lifetime
of technological civilizations – how long they last as technological (meaning
interstellar communicating) entities. The three biggest considerations for
our civilization at the moment could be characterized as a) getting along with
each other, b) getting along with the environment, and c) staying technologically
alert for large-scale concerns from space.
Some dinosaurs were bipedal, had opposable claws, and were pretty intelligent—so
why didn’t they, for example, invent space travel Well, that’s a topic for another essay.
Meanwhile, let’s stick to a few of the things we might want to deal with “out there” at
various times in the future, from a few thousand to a few billion years from now.
The Earth’s magnetic field is thought to
be generated by a dynamo effect – that is,
the movement of charged particles in its
huge iron and nickel core as it spins. Other
planets have magnetic fields also, and there
seems to be some relationship between the
strength of the magnetic field and the size
and spin rate of the magnetic core. Jupiter,
with a huge core and a 10-day rotation
period, generates a massive magnetic field,
for example, and spacecraft sent there have
to be specially built to withstand this intense
field. You may remember the science
fiction movie Outland with Sean Connery
stranded in a mining colony on Io, one
of Jupiter’s moons. However, Io would be
uninhabitable since the magnetic field of
Jupiter causes a 5 million ampere electric
current to flow through it.
However, magnetic fields can also be
helpful. They can protect the inhabitants
of the planet from high energy particles
from, for example, the solar wind. (Yes, the
Sun has a wind component, one that can
be used to power solar-sail spacecraft in the
near future.) When the high energy particles
from the Sun encounter the Earth’s
magnetic field, they are deflected toward
the poles, causing beautiful auroral “curtains”
of color as they hit the atmosphere.
Without the magnetic field of the Earth,
these high energy particles could do damage
to biology on Earth.
When rocks containing magnetite cool
from volcanoes or are baked (as in clay pottery),
they record the direction of the magnetic
field of the Earth at the time of cooling.
It turns out, from examining rocks of
various ages, that the Earth has reversed its
magnetic field many times – the last about
750,000 years ago (the average being about
every few hundred thousand years). Recent
measurements of ancient pottery and other
evidence suggest that the Earth’s magnetic
field may be declining – perhaps getting
ready for an overdue reversal. This could
take place within the next couple of thousand
years. If the Earth’s magnetic field is
just beginning to reverse, it would certainly
be important for us to protect ourselves
from the high energy particles of the solar
wind and of space. It would not be as devastating
an event as, for example, a comet
impact, but it does indicate that we do not
have the luxury of indulging in another
Dark Age over the next thousand years
or so. If civilization is to maintain itself,
we need to be on our technological “toes”
pretty much from now on.
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SETI Institute Explorer