Phew,
that was close! A colossal asteroid just came by. It narrowly missed the
Earth -- and smashed up the moon instead. Well, no reason to be cheerful. For
without the moon, we could be just as doomed.
Just look at that moon. Isn’t it
lovely? But beware: the moon isn’t just there to entertain us. Without the
moon, we could be doomed.
There’s always the small but alarming possibility that some dreadful
cataclysm takes out the moon. Some billions of years ago, this almost
happened. On one terrible day, a vast comet struck the moon, carving out
what’s now known as the biggest impact crater of the entire solar system:
the Aitken Basin, a huge, 2,500 kilometers wide scar on the moon’s South
Pole.
Ok, but what’s the
big deal?, you ask.
Well, not too many
people know this, but the moon is what keeps our planet stable. Without it, we
would find ourselves on a hostile rollercoaster world. Our planet would
go berserk.
For one thing, the
moon tugs at the oceans. This gives us the tides. No moon, and the floods
would immediately be about 2,5 times lower -- some minor tidal motion would
remain, because the Sun pulls at the oceans, too.
The consequences would be dramatic. Many fertile deltas would dry up.
Other areas would become permanently inundated. There would be all kinds of
changes to nature. All over the world, people would face droughts, famines,
diseases and wars.
And to cheer you up a
little more: that’s not the worst part.
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Swing
It Out: The moon and the Earth are locked into a twin system, much
like an athlete about to hurl a hammer.
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Crucially, the moon
also stabilizes the axis around which the Earth rotates. You could compare the
Earth-moon system to an athlete swinging a hammer around. Take a good look at
the picture on the right. Now, ask yourself: what would happen if the rope
suddenly snapped? You get the idea: the athlete would fall over.
Exactly the same
thing would happen to the Earth if you took away the moon. Right now, our
planet rotates at an axis that is tilted about 23 degrees. It has always
roughly been that way. But without the moon, the Earth’s rotational axis
would slowly drift off, because of the pull of the other planets -- especially Venus
and Jupiter. So one moment you’re in Africa; the next, you’re on the North
Pole!
In
the long run, this would
cause massive, unpredictable and abrupt climate shifts. The Earth would
heat up, freeze up, and heat up again. One moment, your nose freezes off in a
massive Ice Age. The next moment, you find yourself sweating your eyeballs
out, in a period of soaring heat.
Even worse, our planet could tip over and ‘lie on its back’ for some
millions of years (or longer). One half of the globe would be in constant
sunlight, while the other half would be plunged into everlasting darkness --
and in cold.
We’d have a two-sided planet. And to be honest, you probably don’t want to
live on either side. The southern half would become a barren, waterless, roasted desert world. The northern half would be an equally barren,
dry, ultra cold ice world.
Ok,
so you decide to live in between the sunny and the icy side. There, you
might find a small zone with good old days and nights, and mild temperatures.
But there’s a downside: the region will be harassed by HUGE, everlasting
storms. With temperature differences like that, there would be massive flows
of air between north and south.
And actually,
that’s not even the biggest concern. For chances are the
massive, abrupt climate shifts will at some point kill our world altogether.
With the moon gone, our world could become a lifeless, dead planet in the end.
The sweeping climate shifts could at some point disrupt the Earth’s
atmosphere for good. This
is probably what happened to Mars (once watery and friendly, but now as dead
as a doornail). Mars indeed tilts like a drunken athlete: it tips over to
about 60 degrees!
And
that’s not everything. When the moon gets smashed up or knocked off
course by a super big asteroid, it’ll probably rain debris on Earth for many
years. For years, we’d have to wear hard hats
- only to find that hard hats don’t help against big, incoming chunks
of moon rock falling down on our world.
Howling
at the moon
Still, there’s some
good news, too.
According to some
doom prophets, without the moon, our planet would start spinning wildly, like a whipped top. A day and night on Earth would last only an
estimated four to eight hours. And we would have HUGE, apocalyptic storms, tens to even hundreds
of times stronger than anything ever seen on Earth, and each one of them
lasting many years. Cities and forests would
be flattened, agriculture would become impossible.
But
fortunately, the doom prophets saying this have got it all wrong.
The moon has slowed down the rotation of our
planet for
good. The moon puts the brakes on our planet, because the tides serve like a
sort of ‘counter weight’. Over the billions of years, this has slowed down
the rotation speed of the Earth. But if some rogue black hole suddenly snatched
away the moon, our planet wouldn’t suddenly start to whirl. It would in fact
even slow down some more, because of the Sun’s pull.
Another often heard,
but wrong, horror scenario is that the moon is about to leave us
for good.
Indeed, the moon IS
leaving us. Very, very slowly, it creeps away from us, inch by inch, year by
year. The moon flies off at the speed at which fingernails grow: 3,8
centimeters per year.
But that
doesn’t mean the moon will be lost in space eventually. Calculations
show that in about 15 billion years time, the moon’s orbit will stabilize at
a distance of about 640.000 kilometers. If you looked up from our planet, you would notice
that the disk of the moon was much smaller than it is now -- only about three
quarter its present size.
Not that you would be
here looking at the moon. Within 5 billion years or so, the Earth will become
a dead, inhabitable world because the Sun has swallowed us by then -- but
that’s another story.
So all in all, next
time you see that lovely moon up there, better be grateful. For now, things
are just right the way they are. No sweeping storms, no ice ages, no falling
over of the Earth. Let’s hope it’ll stay like that for some time.
(A big celestial
thanks to dr. Frank Israel (Leiden University) for technical advise)
