How to defend Earth from asteroids Phil Plait
and I want to talk about something kind
of big we’ll start here 65 million years
ago the dinosaurs had a bad day a chunk
of rock six miles across moving
something like 50 times the speed of a
rifle bullet slammed into the earth it
released its energy all at once and it
was an explosion that was mind-numbing
if you took every nuclear weapon ever
built at the height of the Cold War lump
them together and blew them up at the
same time that would be 1 1 millionth of
the energy released at that moment the
dinosaurs had a really bad day
okay now six-mile-wide rock is very
large we all live here in Boulder if you
look out your window and you can see
long speak you’re probably familiar with
it now scoop up long speak and put it
out in space take Meeker Mount Meeker
lump that in there and put that in space
as well and Mount Everest and k2 and the
Indian Peace and you’re starting to get
an idea of how much rock we’re talking
about okay we know it was that big
because of the impact it had and the
crater it left it hit in what we now
know as Yucatan the Gulf of Mexico you
can see here there’s the Yucatan
Peninsula if you recognize kösem el off
the east coast there here is how big of
a crater was left
it was huge give you a sense of the
scale okay there you go the scale here
is 50 miles on top 100 kilometers on the
bottom this thing was 300 kilometers
across 200 miles an enormous crater that
excavated out vast amounts of Earth that
splashed around the globe and set fires
all over the planet threw up enough dust
to block out the Sun it wiped out 75% of
all species on earth now not all
asteroids are that big some of them are
smaller here is one that came in over
the United States
October of 1992 it came in on a Friday
night why is that important because back
then video cameras were just starting to
become popular and people would bring
them parents would bring them to their
kids football games to film their kids
playing football and since this came in
on a Friday they were able to get this
great footage of this thing breaking up
as it came in over West Virginia
Maryland Pennsylvania New Jersey until
it did that to a car in New York now
this is not a 200 mile wide crater but
then again you can see the rock which is
sitting right here about the size of a
football that hit that car and did that
damage now this thing was probably about
the size of a school bus when it first
came in it broke up through atmospheric
pressure it crumbled and then the pieces
fell apart and then did some damage now
you wouldn’t want that falling on your
foot or your head because it would do
that to it that would be bad but it
won’t wipe out you know all life on
Earth so that’s fine but it turns out
you don’t need something six miles
across do a lot of damage there is a
median point between tiny rock and
gigantic rock and in fact if any of you
have ever been to near Winslow Arizona
there is a crater in the desert there
that is so iconic that is actually
called meteor crater to give you a sense
of scale this is about a mile wide if
you look up at the top that’s a parking
lot and those are recreational vehicles
right there so it’s about a mile across
six hundred feet deep
the object that formed this was probably
about 30 to 50 yards across so roughly
the size of Mackay auditorium here it
came in at speeds that were tremendous
slammed into the ground blew up and
exploded with the energy of roughly a
twenty Megaton nuclear bomb a very hefty
bomb this was 50,000 years ago so it may
have wiped out a few Buffalo or antelope
or something like that out in the desert
but it probably would not have caused
global devastation it turns out that
these things don’t have to hit the
ground to do a lot of damage now in 1908
over Siberia near the Tunguska region
for those of you who are
Aykroyd fans and saw Ghostbusters when
he talked about the greatest
cross-dimensional rift and since the
Siberia blast in 1909 where he got the
date wrong but that’s okay it was nice
to know wait
that’s fine I can live with that another
rock came in into the Earth’s atmosphere
and this one blew up above the ground
several miles up above the surface of
the earth the heat from the explosion
set fire to the forest below it and then
the shock wave came down and knocked
down trees for hundreds of square miles
okay
this did a huge amount of damage and
again this was a rock probably roughly
the size of this auditorium that were
sitting in in meteor crater it was made
of metal and metal is much tougher so it
made it to the ground the one over
Tunguska was probably made of rock and
that’s much more crumbly so it blew up
in the air either way these are
tremendous explosions 20 megatons now
when these things blow up they’re not
going to do global ecological damage
they’re not going to do something like
the dinosaur killer did they’re just not
big enough but they will do global
economic damage because they don’t have
to hit necessarily to do this kind of
damage they don’t have to do have global
devastation if one of these things were
to hit pretty much anywhere it would
cause a panic but if it came over a city
an important city not that any city is
more important than others but some of
them we depend on them more on the
global economic basis that could do a
huge amount of damage to us as a
civilization
so now that I’ve scared the crap out of
you what can we do about this all right
this is a this is a potential threat let
me note that we have not had a giant
impact like the dinosaur killer for 65
million years they’re very rare the
smaller ones happen more often but
probably on the order of a millennium
every every few centuries or every few
thousand years but it’s still something
to be aware of well what do we do about
them the first thing we have to do is
find them this is an image of an
asteroid that passed us in 2009 it’s
right here but you can see that it’s
extremely faint I don’t even know if you
can see that in the back row these are
just stars
this is a rock that was about thirty
yards across so roughly the size of the
ones that blew up over Tunguska and hit
Arizona 50,000 years ago these things
are faked their art to see and the sky
is really big we have to find these
things first well the good news is we’re
looking for them nASA has devoted money
to this the National Science Foundation
other countries are very interested in
doing this we’re building telescopes
that are looking for the threat that’s a
great first step but what’s the second
step the second step is that we see one
headed toward us we have to stop that
what do we do you’ve probably heard
about the asteroid Apophis if you
haven’t yet you will if you’ve heard
about the Mayan 2012 apocalypse you’re
gonna hear about Apophis because you’re
keyed into all the doomsday networks
anyway
Apophis is an asteroid it was discovered
in 2004 it’s roughly 215 yards across so
it’s pretty big besides me no bigger
than a football stadium and it’s going
to pass by the earth in April of 2029
and it’s going to pass us so close that
it’s actually going to come underneath
our weather satellites the Earth’s
gravity is going to bend the orbit of
this thing so much that if it’s just
right if it passes through this region
of space this kidney bean-shaped region
called a keyhole the Earth’s gravity
will bend it just enough that seven
years later on April 13th which is a
Friday I’ll note in the year 2036 you
can’t plan that kind of stuff Apophis is
gonna hit us and it’s 250 meters across
so it would do unbelievable damage now
the good news is that the odds of it
actually passing through this keyhole
and hitting us the next go around are
one in a million roughly very very low
odds so I personally am not lying awake
at night worrying about this at all I
don’t think Apophis is a problem in fact
Apophis is a blessing in disguise
because it woke us up to the dangers of
these things this thing was discovered
just a few years ago and could hit us a
few years from now it won’t but he gives
us a chance to study these kinds of
asteroids we didn’t really necessarily
understand these keyholes and now we do
and it turns out that’s really important
because how do you stop an asteroid like
this well let me ask you what happens if
you’re standing on the road and the cars
headed for you what do you do you do
this
right room the car goes past you and we
can’t move the earth at least not easily
but we can move a small asteroid and it
turns out we’ve even done it in the year
2005 NASA launched a probe called Deep
Impact which slammed into slammed a
piece of itself into the nucleus of a
comet comets are very much like
asteroids the purpose wasn’t to push it
out of the way the purpose was to make a
crater to excavate the material and see
what was underneath the surface of this
comet which we learned quite a bit about
we did move the comet a little tiny bit
not very much but that wasn’t the point
however think about this this thing is
orbiting the Sun at 10 miles per second
20 miles per second we shot a space
probe at it and hit it ok imagine how
hard that must be and we did it
that means we can do it again if we need
if we see an asteroid that’s coming
toward us and it’s headed right for us
and we have two years to go boom we hit
it you could try to you know if you
watch the movies you might think about
you know why don’t we use a nuclear
weapon it’s like way you can try that
but the problem is timing you shoot a
nuclear weapon at this thing you have to
blow it up within a few milliseconds of
Tolerance or else you’ll just miss it
and it’s very there are a lot of other
problems it’s very hard to do but just
hitting something that’s pretty easy I
think even NASA can do that and they
proved that they can the problem is what
happens if you you hit this asteroid
you’ve changed the orbit you measure the
orbit then you find out oh yeah we just
pushed it into a keyhole and now it’s
going to hit us in three years well my
opinion is fine ok it’s not hitting us
in six months that’s good now we have
three years to do something else and you
can hit it again that’s kind of
ham-fisted you might just push it into a
third keyhole or whatever so you don’t
do that and this is the part it’s the
part I just love
after the big macho or man we’re gonna
hit this thing in the face then we bring
in the velvet gloves there’s a group of
scientists and engineers and astronauts
and they call themselves the b612
foundation for those who who’ve read the
little prince you understand that
reference I hope little prince who lived
on an asteroid it was called b612 these
are smart guys men and women astronauts
like I said engineers rusty Schweickart
who was an Apollo 9 astronaut is on this
damn dirt and my friend who made this
image works here at Southwest Research
Institute in Boulder on Walnut Street
and he created this image for this and
he’s actually one of the astronomers who
works for them if we see an asteroid
that’s going to hit the earth and we
have enough time and we can hit it to
move it into a better orbit but then
what we do is we launch a probe that has
to weigh a ton or two not doesn’t have
to be huge a couple of times not that
big and you park it near the asteroid
you don’t land on it because these
things are tumbling end over end it’s
very hard to land on them instead you
get near it the gravity of the asteroid
pulls on the probe and the probe has a
couple of tons of mass it has a little
tiny bit of gravity but it’s enough that
it can pull the asteroid and you have
your rocket set up so you can oh you can
barely see it here but there’s rocket
plumes and you basically these guys are
connected by their own gravity and if
you move the probe very slowly very very
gently you can very easily finesse that
rock into a safe orbit you could even
put it in orbit around the earth where
we could mine it although that’s a whole
other thing I won’t go into that
dumb but we’d be rich
so think about this right there are
these giant rocks flying out there and
they’re hitting us and they’re doing
damage to us but we figured out how to
do this and all the pieces are in place
to do this
we have astronomers with telescopes
looking for them we have smart people
very very smart people who are concerned
about this and figuring out how to fix
the problem and we have the technology
to do this this probe actually can’t use
chemical rockets chemical rockets
provide too much thrust
too much push there are the probe would
just shoot away we invented something
called an ion drive which is a very very
very low thrust engine it generates the
force a piece of paper would have on
your hand incredibly light but it can
run for months and years providing that
very gentle push if anybody here is a
fan of the original Star Trek they ran
across an alien ship that had an ion
drive and Spock said they’re very
technically sophisticated they’re 100
years ahead of us with this drive yeah
we have an ion drive now we don’t have
the enterprise we got an ion drive now
Spock so that’s the difference that’s
the difference between us and the
dinosaurs this happened to them it
doesn’t have to happen to us the
difference between the dinosaurs and us
is that we have a space program and we
can vote and so we can change our future
we have the ability to change our future
65 million years from now we don’t have
to have our bones collecting dust in a
museum thank you very much