An apocalyptic asteroid is on a collision course with our wonderful little planet! What do we do?
Send up some plucky self sacrificing heroes,
or drones, to drill into the thing and blow it to pieces,
or fire off as many nukes as we can to knock the speeding rock off course?
Or is it all just Hollywood nonsense? Is there anything we can actually do?
I’m Stu and welcome to Debunked, where we separate
the truth from the mystery ths and the facts from the misconceptions.
This video is sponsored by Atlas VPN…
We ran a poll to find out what you lovely viewers thought would be the
most likely response to this Doomsday scenario:
Most of you thought blasting it into smaller pieces so that they could
burn up in our atmosphere was the way to go, we’ll find out if our experts agree.
But, before we get stuck into how we might defend ourselves from asteroid annihilation,
it’s worth asking whether there’s a real risk of an interstellar impact in the first place.
There are currently over a million known asteroids and comets. In case
you’re wondering what the difference is between an asteroid and a comet,
and around half of you are, basically,
asteroids are solid rocks made of carbon, metal and silicate materials.
Whereas comets are mostly made of ice and dust,
which is why astronomical boffins refer to them as “dirty snowballs”.
When either of these enter Earth’s atmosphere, we call them meteors.
Most of those asteroids keep themselves to themselves in the asteroid belt between
Mars and Jupiter, and won’t get anywhere near us.
It’s the 30,000 Near Earth Objects (NEOs) that we need to be concerned with.
A Near Earth Object, or N.E.O. is any asteroid or comet whose orbit around the Sun will bring them
within 121 million miles (195 million kilometres) of the Sun. To put that into some perspective,
the distances you can see here are all to scale, but I’ve made the planets 266 times bigger so
you can actually see them. Now in relation to us that means an asteroid or comet must come within
30 million miles (50 million kilometres) of Earth’s orbit to qualify as an NEO.
But don’t worry. If the Solar System were a sandpit, that would
still give NEOs a lot of room to play without knocking over our sandcastle.
That’s why scientists have identified a subcategory of NEOs that they want to
keep a very close eye on - Potentially Hazardous Objects. These are the ones
that will travel within 4.7 million miles (7.5 million kilometers) of Earth and could hit us.
Scientists are particularly concerned with the objects that pass within 240,000 miles (384,000
kilometers) - now this is fully to scale and that is the distance between the Earth and the Moon.
Asteroids get this close several times a month.
But that’s not all. An asteroid has to be a specific size to be classified as a Potentially
Hazardous Object. That’s because, contrary to what news headlines might have you believe,
we actually get hit by asteroids all the time.
Every day, almost 100 tons of asteroids and comets fall to Earth from outer space.
We never notice because most of it disintegrates in our atmosphere.
At night, you might have seen some of this as a shooting star.
These meteors are very small, less than 3 feet (1 metre) in size,
and don’t pose much of a threat unless a fragment lands directly on you.
This is only known to have happened once, on November 30th 1954 in Alabama, when Ann
Hodges was rudely awoken from her sofa nap when a chunk of rock weighing 9 pounds (4 kilograms)
crashed through her ceiling and hit her thigh. Apart from a nasty bruise, Ann was fine.
There are only 110 comets near Earth and none of them pose a threat. But
there are over 2,000 asteroids that are classified as Potentially Hazardous.
So how big does an asteroid have to be before it gets dangerous?
You may remember these videos going viral in 2013.
This meteor was 66 feet (20 metres) across but
exploded with the force of around 25 Nagasaki bombs.
Luckily it burst about 19 miles (30 kilometres) above the earth’s surface,
so it didn’t obliterate the land below. Still, it damaged over 7,000 buildings
in six cities in the Chelyabinsk Oblast in Russia, injuring at least 1,500 people.
A study led by Professor Peter Brown from the University of Western Ontario…
…showed that this kind of impact occurs around three times a year,
but we don’t notice because these meteors come down in the ocean or unpopulated areas.
“But Stu,” I hear you cry, “that’s not terrifying enough! Tell me about the really scary asteroids!”
Well, hold on to your hardhats!
If we travel to Arizona, USA, we’ll find the Barringer Crater. This almighty hole
sits 570 feet or 174 meters deep and its radius stretches nearly 1 mile (1.3 kilometers) across,
this geological giant was made by a meteor just 100 to 160 feet (30 to 50 meters) wide,
and according to NASA, this is the minimum size needed to qualify as a Potentially Hazardous
Object (PHO), because it’s large enough to make landfall instead of burning up in the atmosphere.
So, are any PHOs on their way in the near future? Yes!
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Right, let's get back to that Hazardous Asteroid!
On June 6th 2027, asteroid 1990 MU is currently on course to pass within 3
million miles (5 million kilometers) of Earth. This rock is 1.7 miles (2.8 kilometers) wide.
As NASA’s Planetary Defense Officer, Lindley Johnson, puts it,
“WE DON’T WANT TO GET HIT BY SOMETHING THAT BIG.”
Fortunately, 1990 MU won’t come close enough to hit us.
But if it did, it could wipe out a whole continent.
As Professor Jay Melosh said,
“ASTEROIDS OF ONE KILOMETER OR MORE WOULD RESULT IN CONTINENT-WIDE DEVASTATION,
AND THE DUST INJECTED INTO THE ATMOSPHERE WOULD CAUSE DRASTIC
COOLING AND THE POSSIBILITY OF GLOBAL CROP FAILURES FOR AT LEAST A FEW YEARS.”
Scientists currently estimate there are over
2 million asteroids in our solar system that are as big or bigger than 1990 MU.
But asteroids are the one natural disaster that we can prevent, provided we’re prepared.
“OUR MOST IMPORTANT TASK IS FINDING THEM AND GETTING A FULLER CATALOG OF
EVERYTHING THAT’S OUT THERE, SO WE DON’T GET SURPRISED…
WE TRY TO DETECT ANYTHING THAT MIGHT BE A THREAT YEARS, IF NOT DECADES, IN ADVANCE.”
To do this, NASA formed the Planetary Defense Coordination Office (PDCO) in January 2016.
The PDCO works with observers and space agencies around the world to detect
Near Earth Objects and plan how to deal with ones that might hit Earth.
They’re finding about 500 new NEOs each year on an annual budget of $150 million.
In Hollywood, that’d buy you two Deep Impacts or just one Armageddon.
Detection is key. If we don’t know the asteroids are out there,
we won’t be able to stop them in time. The PDCO says,
“AN ASTEROID ON A TRAJECTORY TO IMPACT EARTH COULD NOT BE SHOT DOWN IN THE LAST
FEW MINUTES OR EVEN HOURS BEFORE IMPACT. NO KNOWN WEAPON SYSTEM COULD STOP THE MASS.”
If the PDCO finds an asteroid with a greater than 1% chance of hitting Earth in the next 50 years,
they’ll warn the government. But unlike the movies, as Professor Grady says…
"IN REAL LIFE, IT IS NOT DOWN TO THE AMERICAN PRESIDENT. IT'S INTERNATIONAL.
ALL THE SPACE AGENCIES AND GOVERNMENTS WORK TOGETHER.”
So what will they do to protect us from an asteroid on a collision course?
Well, Hollywood’s solution of sending nukes is a genuine possibility,
but not in the way you think.
They won’t send a team of astronauts to detonate a warhead.
For one thing, we’d want the nuke to reach the asteroid as
far away as possible from Earth. The PDCO says,
“SOME NEOS COULD BE IN ORBITS THAT ARE ESPECIALLY HARD TO REACH
UNLESS WE FIND THEM MANY YEARS TO DECADES IN ADVANCE OF IMPACT.”
This would mean sending astronauts on a journey that could last years, with no return ticket.
There’s no need to send humans to do a machine’s job.
Furthermore, they won’t actually blow up the asteroid.
Exploding a rock the size of Texas would only create a thousand smaller meteors
that might each destroy a city.
Instead, they’d detonate the warhead near the asteroid, a few hundred meters above its surface.
The X-rays released by the detonation
would superheat and vaporize the top layers of the asteroid. The force of these layers
ejecting from the asteroid would push it onto a new trajectory, away from Earth.
If you’re thinking that it’s risky to send just one nuke to deflect an Earth-destroying asteroid,
you’re not alone. The nuclear cycler method involves a spacecraft carrying
several nukes flying into orbit around an asteroid and releasing several bombs
at controlled intervals to make sure the asteroid is pushed off-course.
However, not all asteroids are solid rock. Some are just big piles of rubble,
and a close explosion might have the same effect as intentionally blasting the asteroid into a
thousand pieces - it could still all crash to Earth and harm thousands or millions of people.
Moreover, this method is politically dodgy. The 1967 Outer Space Treaty says,
“STATES SHALL NOT PLACE NUCLEAR WEAPONS OR OTHER WEAPONS OF MASS DESTRUCTION
IN ORBIT OR ON CELESTIAL BODIES OR STATION THEM IN OUTER SPACE IN ANY OTHER MANNER.”
So to avoid a political minefield,
we could remove the nukes from the nuclear cycler method and employ a gravity tractor.
No, this isn’t a very heavy farm vehicle. It’s a spacecraft that would meet the asteroid and use
its own gravitational pull to gradually change the path of the PHO - like lassoing a charging bull.
If this still sounds tricky, it is. And of course it would only work if
the spacecraft reaches the asteroid well in advance of making impact with Earth.
It also might not work on asteroids larger than 1600
feet (500 meters) across, whose own gravity is just too strong.
Another slowburn way to divert an asteroid is to spray paint it. Not with a Banksy,
but with a thin coating of white paint on one side.
This method uses the Yarkovsky Effect, which describes how a rotating object in space
absorbs thermal radiation faster than it emits that heat. Just like on Earth,
which heats up during the day and cools down at night. The delay in emitting heat means that it
goes out in a different direction from where it was absorbed, creating spin. Over time,
this influences the object’s orbital path. So, by painting one side of an asteroid white
(which reflects heat) and leaving or painting the other side dark (which absorbs heat),
we can encourage the asteroid to spin with more force and move away from Earth.
The main problem with this method is that it would take a very long time to work,
and might need to be done decades or centuries in advance of the asteroid reaching us.
So by the time we knew whether or not the graffiti had worked, it might be too late.
The simplest and most reliable method of deflecting an asteroid is the kinetic impactor.
That’s a fancy way of saying “crash one thing into another”. By sending
satellites to collide with asteroids before they collide with us, scientists hope to slow
them down enough to redirect their paths through the solar system, away from Earth.
This works in theory, but as planetary scientist Dr Patrick Michel says,
"ALL THE MODELS [OF IMPACTS] THAT WE DO ARE BASED ON UNDERSTANDING
OF COLLISION PHYSICS THAT IS ONLY AT LAB SCALE – CENTIMETER-SIZED TARGETS."
That’s why in November 2021, NASA launched the Double Asteroid Redirection Test (DART).
This spacecraft is on its way to make very close contact
with the binary near-Earth asteroid Didymos and its moonlet Dimorphos.
DART will hit or, depending on when you’re watching this, has hit Dimorphos in late 2022,
altering its orbit around Didymos. Dimorphos is 550 feet (170 meters) wide,
and therefore just big enough to count as a Potentially Hazardous Object.
Because it will stay in orbit around Didymos, the PDCO will be able to
easily monitor and measure how well the kinetic impactor method works.
The mission has been carefully calculated because, as Lindley Johnson explains,
“BY CHANGING THE ORBIT OF THE MOON, WE DON’T CHANGE THE ORBIT OF [DIDYMOS].
DIDYMOS IS A POTENTIALLY HAZARDOUS ASTEROID, SO WE DON’T REALLY WANT TO AFFECT ITS ORBIT.
WE DON’T WANT TO ACCIDENTALLY PUSH IT THE WRONG DIRECTION.”
Since Didymos is large enough to destroy a city, let’s hope the mission is a roaring success!
Reassuringly, the odds of a PHO hitting Earth in the next 100 years
are zero. But those odds might change as we learn more.
Currently, planetary defense scientists estimate they’ve only found 40% of PHOs. This is simply
because the smallest ones - which are still city destroyers - are difficult to find.
NASA’s Dr Amy Mainzer says,
“THE SUB-GLOBAL SIZES [OF ASTEROID] THAT ARE CAPABLE OF CAUSING REGIONAL
PROBLEMS - WE STILL HAVE A LOT OF WORK TO DO [ON THEM]… SEARCHING FOR THESE GRAY OR
BLACK ROCKS AGAINST THE BLACKNESS OF SPACE - IT’S JUST A HARD PROBLEM.”
Unfortunately, even the near misses can come back to bite us. The asteroid Apophis is 1,100
feet (340 metres) across and is big enough to hit the Earth with energy equivalent to
1,200 megatons of TNT - 24 times more powerful than the largest manmade nuclear explosion.
Apophis was only discovered in 2004 and on Friday 13th April, 2029, it will come within 20,000 miles
(32,000 kilometres) of Earth - closer than our geosynchronous satellites, and for a bit more
perspective, that’s where our moon is. Luckily it will miss us, but the effect of Earth’s gravity
will alter its orbit so that it might hit us in future - but not for the next century at least.
Of course, the most infamous asteroid is that which was a major factor to
the extinction of all non-avian dinosaurs - around 66 million years ago this asteroid,
known as the Chicxulub Impactor, struck Earth with the blast equivalent of one hundred million
megatons of TNT and caused one of the largest mass extinctions our planet has ever known.
This devastating rock measured roughly 12 kilometers or 7.5 miles across.
To even have a chance of preventing a collision with an astronomical body of that size we would
need to begin implementing countermeasures years in advance. As Professor Monica Grady says,
"PLANET-KILLING ASTEROIDS IMPACT THE EARTH EVERY 50 MILLION YEARS… WITH ANY LUCK,
WE'LL HAVE YEARS TO PREPARE, BUT THEN AGAIN, WE MIGHT NOT."
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