Kind: captions
Language: en
this video was sponsored by kiwiko
more about them at the end of the show
on february 15 2013 over chelyabinsk
russia
an asteroid heavier than the eiffel
tower slammed into the atmosphere
and then 30 kilometers above the ground
it exploded
this violent event was brighter than the
sun
but so high up that it was silent
for a full 90 seconds after the blast
which only made the devastation worse so
you see all these videos of people
looking look at what was that they see
the
smoke trail in the sky oh that's amazing
and then
you know just when you think nothing's
gonna happen the shock wave hits
it blows out the windows thousand people
got glass in their face in their eyes
because they're looking through the
windows
the shockwave damaged thousands of
buildings and injured
1500 people
what makes the chelyabinsk incident kind
of embarrassing
is that the very same day scientists had
predicted that an asteroid would make a
close
flyby of earth and they were right
16 hours after chelyabinsk a similar
sized asteroid
known as duende came within 27 000
kilometers of earth's surface
that's closer than satellites in
geosynchronous orbit
but while they correctly predicted this
close approach
they completely missed the unrelated
asteroid that exploded over russia
and the truth is this happens all the
time we're really not that good at
detecting asteroids before they hit us
since 1988 over 1200 asteroids bigger
than a meter have collided with the
earth
and of those we detected only five
before they hit never with more than a
day of warning
with all our technology and all the
telescopes across the earth
not to mention the ones in space why do
we struggle to detect
dangerous asteroids before they strike
what are the chances
that a big asteroid will hit wiping out
most
if not all life on earth and
if we saw one coming what could we do
about it
[Music]
asteroids are the leftover debris from
when our solar system formed
four and a half billion years ago rocks
and dust clumped together into molten
protoplanets
inside heavy elements metals like
iron nickel and iridium sank into the
core
leaving lighter silicate minerals on the
surface
some of these protoplanets grew into the
planets we know today
but many more collided with each other
breaking into pieces
these pieces continued orbiting the sun
and smashing into each other and
breaking into even smaller fragments
these became the asteroids which is why
some of them are rocky loose
conglomerates of
gravel-sized rocks called rubble piles
and others from the cores of
planetesimals
are mostly metal so this
is this is an iron meteorite
and essentially it's the piece of a core
of a small
planetary body like basically a small
planet
that formed four and a half billion
years ago
differentiated so the core material fell
out
and then this thing was smashed apart by
a collision with another asteroid
that's the oldest thing you'll ever see
most of the asteroids have stable orbits
between mars and jupiter
in the main asteroid belt but some
have made their way closer to earth and
these are known as
near-earth objects they are of greatest
interest to
us because of the threat they pose in
his last book
stephen hawking considered an asteroid
impact to be the greatest
threat to life on earth but
finding asteroids is difficult for
several reasons
most are spotted by ground-based
telescopes so what you do is you take
a sequence of pictures one two three one
two three four and you look for
essentially a moving dot and it's moving
because it's orbiting around the sun
whereas the stuff far away the stars and
galaxies are not
but you have to look carefully asteroids
are
not very big they range from meters up
to
kilometers in size and in the vast
expanse of space
rocks like that just don't stand out and
even the small ones can be damaging
the chelyabinsk meteor was only around
20 meters in diameter
roughly the width of two school buses
plus asteroids are rough and dark
they only reflect around 15 of the light
that hits them
so our best chance to see them is when
they're fully illuminated by the sun
and that's why over 85 percent of the
near-earth asteroids we've detected
were found in the 45 degrees of sky
directly
opposite the sun this is called the
opposition effect and
it means there are likely more
near-earth and potentially hazardous
asteroids
that haven't been detected yet any
asteroid
approaching from the direction of the
sun just
can't be seen this is exactly what
happened
with chelyabinsk
so far we have detected and cataloged
a million asteroids the vast majority of
which
are in the main asteroid belt but
24 000 are near earth objects
ones that we need to keep a particularly
close eye on
because even once you've detected an
asteroid it's hard to tell
if it will hit the earth so if you just
discover an object
and you only have data from a few days
then you can't really
tell where it's going to go because
you're trying to take this little
arc of motion and predict it far into
the future so what you need is
observations over years and years
but even if you have perfect
observations of an asteroid
there's kind of a fundamental limit to
how far in the future you can predict
and that's because a couple of effects
but one is that you know
they're not just orbiting the sun with
no other influence
all of the planets have gravity and all
of the planets are pulling
on near-earth asteroids and can change
the orbit
significantly so there is something
called dynamical chaos which basically
means
after a certain amount of time you don't
know where the asteroid is going to be
and in practice what that means is we
can't do any work
more than 100 years in the future so the
maximum time you can predict
with any accuracy at all where a body
will be is about 100 years
and this is pretty important because we
know with
certainty if one does hit the results
will be
dramatic
this is behringer crater in arizona it's
named after mining engineer
daniel behringer who was the first to
suggest
it was formed by a meteorite impact the
prevailing view even up until the 1950s
was that it was created by volcanic
activity
but behringer was convinced it was the
site of an iron meteorite
impact so in 1903 he
staked a mining claim and began drilling
for the metallic
meteorite which he believed to be worth
more than a billion
1903 dollars yeah so people are
motivated by money right so they thought
hey we can get some iron for free
basically so they started to drill
in the bottom of the crater and found
nothing
and then they started to do other
exploratory drills and this went on for
years and
decades they started to drill sideways
somebody said you know maybe it came in
from an angle which it did
and maybe the iron is is not under the
middle but maybe it's
over there under the wall so he was
doing drilling if you go there you can
see the drills now
he was drilling around the wall he found
nothing so what they didn't realize is
when you have
an impact at high speed it's not like
you're throwing a stone
into a brick wall you know and it makes
a hole and sticks in there
or just bounces off it's explosive it's
like totally explosive so the kinetic
energy of the projectile comes in
maybe 30 kilometers per second the
kinetic energy of the projectile is big
enough to completely vaporize the
projectile turns it into a gas
and that gas is super hot and super high
pressure and it explodes and it blows
out the crater
so the projectile doesn't really exist
after the impact i mean little pieces
can survive
but this 50 meter body was basically
obliterated so he was looking for
something that
did not exist he spent 27 years
mining the crater drilling down to a
depth of over 400 meters
but what he was searching for had
vaporized on impact
50 000 years earlier the 50-meter
asteroid
not that much bigger than chelyabinsk
released
the energy equivalent of 10 megatons of
tnt
that's over 600 times the energy of the
hiroshima bomb so
the thing that most closely resembles a
meteorite impact
is a very large nuclear explosion
this is the actual size of the t-rex
skull and i thought
this is such a cool thing i got to have
it so i bought the t-rex
[Applause]
the dinosaurs were wiped out by a 10
kilometer sized
asteroid that hit about 65 million years
ago so
above the critical size which is
probably a couple of kilometers
uh an impactor delivers so much energy
that it has a global effect
[Music]
so essentially it launches a whole bunch
of debris
into sub-orbital trajectories so the
ejector goes around the earth
falls back into the earth all over even
on the other side of the planet from
where the impact occurred
and what that means is the whole sky
lights up with
wall-to-wall meteors
so you can imagine the sky turning from
you know a nice
blue day like today into essentially
a red hot glow like being inside a
toaster oven
[Music]
so the first effect of this impact apart
from the initial blast
near where the actual impact occurred
the first effect is the sky
turns into a great source of heat and it
cooks everything on the ground so these
guys were basically
cooked cooked alive cooked alive as they
were walking around
the only animals that had a chance were
the ones living in tunnels
under the ground or maybe um in the
water
they were able to to come back and take
over without having to deal with the
dinosaurs as a
major obstacle what are our chances that
earth gets hit
by a another 10 kilometer or bigger
asteroid
in your lifetime assuming you live to be
a hundred years old you have a 10
kilometer impactor like the kt
extinction event every 100 million years
or something like that
so the probability of getting it in one
year is one in 100 million so you have
one in a million chance of dying from
a 10 kilometer impact but because we
know that there are no
10 kilometer impactors with a path that
intersects the earth
for the next 100 years your chance of
dying from that is actually zero
so work done already has reduced that
down you know from one in a million to
to nothing
so the good news is there won't be
another dinosaur style extinction event
in our lifetimes
but there are exponentially more
asteroids of smaller sizes
for every 10 kilometer asteroid there
are roughly a thousand
one kilometer asteroids and they're
still capable of doing
a lot of damage one or two kilometers
is capable of causing local but massive
damage so that means
you know instead of wiping out the
entire world
you would wipe out the equivalent of
some
european country like france or germany
to mention
two of my favorites so you would
obliterate those countries
with the impact of a one or two
kilometer sized body
do we know about all the one to two
kilometer
bodies that could hit us we think that
we know 90 something percent maybe 98
of those bodies have been identified
and we have their orbits and we can make
reasonable predictions for the next
10 years or something about where
they'll be
and we seem to be okay at the moment but
you know
uh what about the ones that are just a
little bit less than a
kilometer what about the ones that are
800 meters that's still pretty
pretty savage if it hits and this is
possibly where the greatest threat of
asteroids remains
a few hundred meters is large enough to
obliterate a large city
but small enough that we haven't
detected them all yet
we're missing a lot of hundred meter
sized projectiles
and those guys are big enough to cause
substantial damage on the earth
depending on where they hit
so it could destroy a city yeah it would
knock down the buildings in the city
it would cause city-wide fire and
if it hit the ground it would throw up
ejecta
that would come back down and rain on
the ground would be high-speed ejector
that would obliterate a 100 kilometer
zone
around it and this could happen tomorrow
well it could yeah
[Laughter]
if we saw a big one coming
what's our best bet for i mean could we
do anything about it what would we do
about it
is there anything we can do to actively
no there's nothing we can do
i was on a committee that looked at that
okay like 10 years ago what could we
what could we do one option would be to
try to bomb it
it's a standard thing we don't know how
that would work out
even when you got it there and even if
you could explode it on the surface
or in the surface it's not clear what
you would do because typically what
happens is you
blow up a body and the fragments move
out they expand out but not very quickly
and then gravity pulls them back
together again so it would reform
as a rubble pile if it was not already a
rubble pile to begin with which it
probably would be because of past
impacts
so blowing up a rubble pile is something
that we don't really know about
another idea is you could attach you
could be all gentle and attach
a rocket to the asteroid and just try to
push it aside let's nudge it aside
instead of trying to blow it up let's
just push it gently aside
so that it deflects it and it doesn't
hit the earth the trouble is
when you work out the numbers none of
the rockets that we have can push it
around enough you would have to keep the
rockets
attached to the surface which we don't
know how to do remember it's a rotating
body
for centuries to have a significant
effect on the motion of the asteroid so
forget
bombs forget attaching rockets
ablating the surface basically you boil
the surface with a laser
we don't have any lasers powerful enough
and probably can't make lasers powerful
enough to do that from the earth we
would have to take the lasers to the
object which is even more difficult
the idea that you could wrap an asteroid
in cooking foil aluminum cooking foil is
another nice one that may be a good one
the best one
but it still doesn't really work because
we don't know how to do that
we don't have a way to launch enough
cooking foil
to wrap up an asteroid and change its
radiative properties which would itself
move the asteroid around so the truth is
to be honest we do not
have a way now to deflect
a kilometer-sized asteroid at all
that could destroy a country yeah we
just don't have a way
10 kilometers 10 kilometers is
absolutely a thousand times more
hopeless
so when when we discussed this you know
we we had all these grand ideas oh we
could do this and this and none of them
worked we came down to the most basic
idea well
maybe if we could figure out where the
asteroid is going to hit like which city
is it going to
explode over we can evacuate that city
and then we looked at the history of
city evacuations and we looked at cases
you know where
for example you have like a week's
warning where some
hurricane system is going to come in and
flood a city
and an evacuation uh just doesn't work
either
and the reason is very very simple like
going into a city there are not that
many
freeways if you have millions of people
trying to get on a freeway
the first time a car breaks down you you
block that freeway
so instantly you have millions of people
trying to get out of the target zone
and and they won't be able to because
all of the roads will be
instantly blocked so again even that
even evacuation of a city is probably
the most
hopeful thing that we could try to do
even that's really really difficult
because of the large numbers of people
involved
what i think all reasonable people would
conclude is
let's do the thing that we can do first
so let's look for them
let's do the surveys let's build the
telescopes let's put this telescope in
space that will be
a major contribution to understanding
the threat from the asteroids
and then when we find a particular
object
that looks especially dangerous then we
can focus on it
we can focus everything we have on it
and we can begin to think seriously and
with real motivation
about ways to deflect it
now if you're concerned about the world
ending in an asteroid impact
let me set your mind at ease there are
many
other potential global catastrophes
summarized in this
map of doom made by my friend dom over
at domain of science
so if you want to see which of these
horrible scenarios is likeliest to be
our downfall
well go check out the video on his
channel
my oldest now knows how to do the
sponsor message
do you want to say it this episode is
sponsored by kiwico
very good kiwi co creates awesome
projects and toys
to get kids making they offer eight
subscription lines for kids of
all ages all the way down to newborns
and with the holidays right around the
corner kiwi co is the perfect gift idea
as a parent i know that lots of gifts
get unwrapped and played with for a
little while
but then kids lose interest but a kiwi
co-crate subscription will keep kids
engaged
learning and making throughout the year
now i use their crates with my sons
and they are a lot of fun while also
being educational
and i want my kids to see learning as a
form of play and kiwico really helps me
do that
plus all the supplies you need come
right in the box so you never need
to run out to the store now here i built
a
perpetual calendar a reminder that each
passing day
brings the chance of an asteroid impact
for viewers of this video kiwico is
offering 50 off your first
month of any crate just go to kiwico.com
veritasium50 and i'll put that link down
in the description
so i want to thank kiwiko for sponsoring
veritasium and i want to thank you
for watching