[LINK] Weekend Magazine (Humour) What's the REAL chance an asteroid will wipe out life on Earth?

[Tom Koltai]

Warning FUD Eliminator.


/Quote [From: http://blastr.com/2011/03/astronomer-whats-the-real.php]

It begins when an amateur astronomer spots something in the sky that
shouldn't be there. A hurried email, a chat over the 'net, and then
confirmation from professional observatories-but a discovery kept secret
from the public. 

In a few weeks' time, an asteroid hundreds of miles across will hit the
Earth, wiping out all life. NASA is notified, and they scramble into
action. A team of astronauts hurriedly trains, launches in the Space
Shuttle, and lands on the rock hours later. They plant a nuclear bomb,
and just barely escape as the explosion vaporizes the killer asteroid
with the Earth hanging hugely in the background.

You've seen this movie, right? I have, in various incarnations,
approximately one bazillion times. Armageddon, Asteroid, Doomsday Rock,
Meteor (actually, two impact movies were made with that title), Deep
Impact ... the details change-maybe it was a comet, or maybe it's a
fighter jet equipped with a laser to blow up the rock-but in the end,
all these movies have one thing in common: they totally screw up how
this would really work. When it comes to preventing an asteroid
impacting the Earth and wiping out all we know and love, Hollywood can't
seem to get it right. From the discovery to the detonation to the
denouement, nothing of reality survives intact.

Let's tackle each issue, point by point, and see where silver screen
storytelling steps off the narrow path of science.

It begins when an amateur astronomer spots something in the sky that
shouldn't be there.

This used to be true: there are thousands of amateur astronomers in the
U.S. alone, and they constantly observe the heavens. But only a few
actually look for asteroids, and it's an inefficient process, scanning
back and forth across the sky. About 20 years ago the robot revolution
hit astronomy; automated hardware and software optimized to look for
moving objects. The vast majority of comets and asteroids are actually
"discovered" by machines now. 

I probably shouldn't mention that one of the professional robotic
networks is called SkyNet [1]. Seriously.

A hurried email, a chat over the 'net, and then confirmation from
professional observatories-a discovery kept secret from the public. 

The first part of this one is close to the truth. Once a potentially
threatening rock is discovered, the physical parameters (coordinates,
orbit shape and so on) are sent to central clearinghouse of this info:
the Minor Planet Center in Cambridge, Mass. The data are checked and
then disseminated to observatories all over the world. If it's a
particularly interesting object-and by "interesting," I mean there's
some chance of "Aiiie we're all gonna die!!!"-then other astronomers
will scramble to observe it and nail down the orbit, confirming or
repudiating any potential impact.

A lot of conspiracy theorists think astronomers would keep something
like this a secret (I get this asked of me all the time). The thing is,
astronomers are a chatty, verbose lot (perhaps you've noticed). If one
discovered an asteroid that really could hit us, the problem wouldn't be
getting an astronomer to talk, the problem would be shutting them up. 

In a few weeks' time, an asteroid hundreds of miles across will hit the
Earth, wiping out all life. 

This part always makes me laugh. Objects hundreds of miles across are
bright. In Armageddon, the asteroid was "bigger than Texas", which is
900 miles across. That's roughly the size of Ceres, the biggest asteroid
in the solar system, and that was bright enough to be discovered in
1801!

Not only that, but space is kinda big. That's why we named it that. So
it takes a long time to move from one part of the solar system to
another. At regular orbital speeds, an asteroid coming in from the main
belt between Mars and Jupiter would take years to get here. Decades. And
that's if it's on a direct course for our blue marble; more likely we'd
find it would pass several times in its orbit before it would hit us.
For example, we know of no objects more than a few miles across that can
hit us in the next century. Don't call Bruce Willis just yet.

Oh, another thing: when something that big and moving that fast hits the
Earth, the resulting explosion is huge. It only takes an object the size
of a house to hit with the energy of a megaton-sized warhead. An object
a mile across would be billions of megatons, thousands of times the
entire world's nuclear arsenal. In at least one movie (yes, Armageddon
again), they mention the explosion will be thousands of times that of a
nuclear weapon. So weirdly, in a movie as completely ridiculously over
the top as that one, the one thing they actually underplay is the actual
danger from the asteroid. 

Brilliant.

NASA is notified, and they scramble into action. A team of astronauts
hurriedly trains, launches in the Space Shuttle, and lands on the rock
hours later.

Well, let's just say NASA isn't exactly nimble. A mission like this
would actually take years to plan and execute ... which, in real life,
they'd have. 

And again, orbital mechanics will not be denied. A trip to an asteroid
would take months. Especially one headed right at us; a rocket would
have to head toward it, swing around and match velocities. That would
take a long time, and a lot more fuel than the Shuttle could carry,
unless it happened to be towing an oil tanker full of liquid hydrogen
and oxygen. That turns out to have engineering difficulties.

They plant a nuclear bomb, and just barely escape as the explosion
vaporizes the killer asteroid with the Earth hanging hugely in the
background. 

This is where the movies really part from reality. First of all,
anything hundreds of miles across-or even just a few-won't get shattered
to smithereens by a nuke. You might carve a chunk out of it, but it
would be like tossing a firecracker at a boulder. In Armageddon, given
the size of the asteroid involved, they'd need a nuke that could
detonate with the same energy output as the sun.

I'm rather glad we don't have a weapon like that. 

Worse, they always seem to shatter the incoming killer rock just as it's
about to hit the Earth, but that won't help. It might even hurt. The
explosive energy of an impact depends on the object's mass and velocity.
Blowing it up doesn't change its speed, and you haven't changed the
mass, either: you've just spread it out a bit. If all the material still
hits, it just spreads the joy-I mean destruction, terror and
death-around a little. Deep Impact, a movie that got a lot of its
science correct, blew it (haha! get it?) on this one.

However, there is a way a nuke might help. Instead of blowing it up on
or in the rock, you detonate it near the surface. The explosion can heat
up and vaporize a layer of material, which would expand violently. That
acts like a rocket, pushing on the asteroid, changing its path. If the
Earth is already looming in the background it's too late for this, but
if you have a few years' warning, then a nuke or two might actually push
the asteroid-or, more accurately, force it to push itself-into a safe
trajectory. 

Even better, one group of engineers and scientists (calling themselves
the B612 Foundation [2] , after the asteroid home of the Little Prince)
has proposed what's called a gravity tractor: a probe with a mass of a
ton or two that can hover over the surface of the killer asteroid. The
gravity of the probe, feeble as it might be, can be enough to pull the
asteroid into different path. Again, given time, this can turn a
potentially extinction-level impactor into just another rock that safely
passes us in the sky.

I'll note I've glossed over a lot of details here, but I hope you get
the picture. At the moment, no asteroid is known to have an
Earth-impacting trajectory, but we're looking. It would take something
about the size of a football field to do us any real damage (and even
then it would be local, not global), and those are hard to see. But our
technology is getting better, and the gravity tug idea-while still
theoretical-is our best hope for preventing us from joining dinosaurs in
some museum in the distant future when marmosets evolve intelligence. 

And as long as we're making movies like Armageddon, I can't necessarily
say that's entirely a bad thing.

Phil Plait has an asteroid named after him-1654347 Philplait-which is in
no danger of ever hitting the Earth, thus foiling his evil plans for
world domination.
/Quote

[1] <http://skynet.unc.edu/> 
[2] <http://www.b612foundation.org/>

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