he once warm planet began to dry
up. Its sprawling riverbeds vanished.
Most of the vast oceans that painted
its surface blue evaporated. What was left
turned to ice. A lush, potentially habitable
world was transformed into an arid, dusty
wasteland. This is not some apocalyptic script
from a Hollywood movie, but the significant
climatic change endured by our neighbouring
planet Mars some four billion years ago.
Our suite of orbiting satellites and
trundling rovers has revealed modern Mars
to be a shadow of its former self. It once
boasted a thick, warming atmosphere that
permitted liquid water to flow across its
surface. In fact, the infant Mars may well
have resembled our own planet and a similar
fate may await us too.
Of course, something catastrophic must
have happened to change the Martian climate
PHOTO: ITTIZ/WIKIPEDIA, NASA, SCIENCE PHOTO LIBRARYso dramatically. While the exact cause remainsunclear, some have pointed the finger at Mars’s
current lack of a magnetic field. Instruments on
board passing spacecraft have revealed that, like
our planet today, Mars was once surrounded by
a giant magnetic bubble. However, it switched
off about four billion years ago – around the
same time that temperatures on the Red Planet
took a nosedive.
Without a protective magnetic cocoon,
Mars’s atmosphere would have been laid bare
to the onslaught of the solar wind, a constant
stream of charged particles produced by the
Sun. Over time, the solar wind would have
stripped away all but a tiny fraction of the Red
Planet’s gas blanket. If life did ever get started
on Mars once, it is likely to be long extinct,
fried by the intense radiation from the solar
wind. Also, with no atmosphere to keep the
planet warm, the water vanished.
The same thing could happen to us. Our
planet still has its magnetic defences. But forhow much longer? Measurements of the
strength of Earth’s magnetic field suggest
that it too is in rapid decline. Its strength has
dropped 10 per cent in the last 300 years alone.
It is diminishing at a greater rate now than
at any time in the past 5,000 years. If it keeps
falling at its current rate, estimates state that it
will be gone in a few thousands years.North becomes south
Yet such a dramatic drop might not be
the harbinger of a complete, Mars-like
eradication of our magnetic shield. It could
be a sign that it is about to do something
else, something it has done many times
before: flip. Such a reversal would eventually
see compass needles point south instead of
north. While the field reverses – a process that
can take thousands of years – the magnetic
field would be so messy that there wouldn’te
st
h has
rs alone.
han
keepsMars could
have lost its
liquid water and
atmosphere when
its magnetic
field diedPOLE REVERSAL
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