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