When you think about the ways the entire
human race might meet its demise, there are
only a few ways we can imagine it going down.
Famine, plague, pestilence, or conventional war
wouldn’t do it; there are simply too many
humans in too many niches that would be
untouched by even the most vile incarnations of
these. But there are two general categories of
ways it might happen:
the possibilities we might bring upon
ourselves, like nuclear war, biotechnology
gone awry, or some type of pollution/
environmental poisoning that renders the
planet inhospitable to human life,
or the possibility that the Universe could
end us naturally, such as from a
catastrophic supervolcano, an incurably
lethal epidemic of disease, or the same
catastrophe that wiped out the dinosaurs: a
massive asteroid strike.
The asteroid belt is filled with rocky bodies of all
different sizes, ranging from dust grains to
pebbles to boulders to mountain-sized objects
and even larger ones: the size of Texas or
greater. Out beyond Neptune, the Kuiper belt is
filled with even more numerous objects made of
a mix of ice and rock, covering the same size
range with even larger ones at the high end, and
the Oort cloud beyond that with a similar
population.
Every 100,000,000 years or so on average, an
object from elsewhere in our Solar System that’s
5 kilometers (3 miles) in diameter or larger
happens to collide with Earth, causing a mass
extinction event significant enough to wipe out
around 50% of the species on the planet,
including practically all of the most dominant
megafaunal species.
Image credit: Wikimedia Commons user
Wilson44691, of the K-T layer, the boundary
between the Cretaceous and Paleogene epochs.
65 million years ago, an event exactly like this
occurred, with a large asteroid striking what is
now the Gulf of Mexico, creating a crater around
a thousand miles in circumference, covering the
Earth in a layer of ash, and bringing the era of
the dinosaurs to an end. Every so often, the
Universe sends us reminders that it’s only a
matter of time before Earth gets hit again with
such an impact: this time, driving not only
human beings, but potentially the vast majority
of mammals to extinction.
In 1908, the Tunguska event leveled an area
about 40 miles in all directions: an airborne
explosion from a meteor caused a tremendous
amount of damage over mostly uninhabited
terrain. That most likely arose from an object
that was only 45 meters (150 feet) in diameter.
More recently, in 2013, a meteor flew over
Chelyabinsk, Russia, injuring over 1,000 people
and causing significant property damage, despite
being only 5% the energy (and about 30% the
diameter) of the Tunguska event. If the meteor
had been about twice a Tunguska-level event, it
could have killed over a million inhabitants of
Chelyabinsk.
Associated Press, of the meteor trail over
Chelyabinsk, Russia, 2013.
Moreover, as we’ve gotten better at monitoring
the upper atmosphere of Earth, including over
the ocean and other uninhabited areas (such as
the Antarctic, as well as much of Russia and
Canada), we’ve discovered that we get about two
10 meter (33 feet) or larger asteroid impacts
every year. Couple that with the fact that we
know city-killer events happen at least every
few millennia, that there are tens of thousands
of city-killer (and larger) asteroids known to be
out there, and that a kilometer-sized asteroid
could end our species, shouldn’t we be
monitoring what’s out there, and shouldn’t we
be prepping the defenses?
The answer to the first question — should we be
monitoring what’s out there — is yes , but not
with the urgency so many advocate. And to the
second question — should we be prepping the
defenses — the answer is not likely . We may get
some very smart, very famous people arguing
counter to this, but even smart people fall prey
to a common human fallacy: risk estimation
when the odds are low but the consequences are
great. There are three things to consider here:
1. Common asteroid strikes. These are the
twice-a-year variety, and realistically, even
if they hit over a populated area, they’re
likely to cause as much property damage as
a modest tornado, and fewer fatalities.
We’re talking millions of dollar in damage,
tops, and we have yet to record an asteroid-
related death here on Earth. So that’s not
consequential.
2. City-killer asteroids. These could be bad.
Tunguska-level events are similar in scale
to the strike that created Meteor Crater
(Barringer Crater) in Arizona. These may
happen as frequently as once per century,
but nearly 90% of the time, they fall over a
completely unpopulated area. Even if they
do happen to be over a large city — like
London, New York or Tokyo — those strikes
will be incredibly rare: only occurring once
every 100,000 years or so.
3. Species-ending strikes. This — if it
happened — would be the big one. All
human life on Earth would end, with a total
of (as of today) around seven billion
human casualties. Even though this only
happens once every 100,000,000 years or so,
the consequences are tremendous.
So with all of this taken into account, what
are your odds of dying in an asteroid strike in
any given year? About 1-in-70,000,000. On
average, that means approximately 100 people
will die of an asteroid strike in a given year:
less than die in earthquakes, tornadoes,
volcanoes, hurricanes, floods or by lightning
strike.
In its quest to map hazardous asteroids and
defend Earth from them, the Sentinel mission
was hoping to raise $450 million, and then
partner with NASA to launch its satellites for
tracking purposes. They’ve fallen well short of
their goal , and NASA is terminating the
partnership indefinitely due to missed deadlines.
Normally, I’ll take any excuse to increase
excitement and funding for space exploration,
but I’m happy to see resources diverted
elsewhere. There’s a whole Universe out there
to explore, and a whole planet that we can all
work to improve. Defending us from asteroids,
from a reasonable cost-benefit analysis, simply
isn’t worth the investment, statistically.
There are real dangers to Earth (and to the
humans on it) facing us today, but asteroids
aren’t one of them. If our species sticks around
for another few thousand years, it will be time
to make that investment. But until then? We’ve
got a planet to save, and an entire Universe to
discover.
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