How Do We Protect Earth From Asteroids?

How do we protect Earth from asteroids? We can use explosives, booster jets, lasers, and other techniques. But these methods aren’t proven.

The most important thing is to have a huge lead time to divert an extinction-level asteroid. This is easier said than done though.

In fact, a study from Cardiff university states,

The sun’s movement through the Milky Way regularly sends comets hurtling into the inner solar system — coinciding with mass life extinctions on earth, a new study claims. The study suggests  a link between comet bombardment and the movement through the galaxy.

So even if we’re diligent in our asteroid detection, a large object could still surprise us out of nowhere. Crazy, right?!

Thankfully, these events are rare, and the chance of a major collision is low in the near future. But the point is, Earth WILL one day get hit by a monstrous asteroid when you consider cosmic time scales. So we, humans, need to prepare for a dinosaur extinction class asteroid. This requires us to master asteroid deflection techniques.

Each currently proposed deflection technique has shortcomings though, which I’ll go over. The following  are the 5 most common techniques:

  1. Blow up the asteroid
  2. Tether a spacecraft in the asteroid’s gravitational space
  3. Blast the asteroid with a laser
  4. Drill into the asteroid
  5. Alter the surface of the asteroid

Before we go over these techniques, let’s discuss asteroids and why they pose such a threat. This will set the stage for the discussion on the deflection techniques.

The threat from asteroids

meteor crater in arizona
Arizona’s Meteor Crater

Asteroids come in all shapes and sizes. Also, they’re quite different than comets in composition.

Asteroids commonly consist of rocky-type materials and metals. Whereas comets consist of ice, dust, and some rocky material. This is because asteroids formed closer to the sun, where ice wouldn’t remain solid.

Now, small asteroids, properly called meteoroids, hit Earth every day. They’re as small as a grain of sand to a few meters across. Given their small size, we can’t detect them until they hit Earth. But they’re not harmful since they burn up in the atmosphere.

According to NASA,

Space rocks smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth’s atmosphere and cause little or no damage.

Larger asteroids for the most part we can easily detect, which is so important. Because once an object gets larger than 25 meters, there’s a reason for concern.

To illustrate, on February 15th, 2013, a small asteroid entered Earth’s atmosphere near the skies of Chelyabinsk, Russia. It was only roughly 18 meters and 9,979,000 kg according to NASA. The meteor turned into a fireball in the sky, yet it rained down pieces to the ground called meteorites. It also generated a monstrous shockwave!

This incident caused 1,491 indirect injuries and damaged about 7,200 buildings.

What’s more, the size of asteroids isn’t the only concern. The angle of impact and composition are all critical variables in an impact too.

Imagine an asteroid made of ice brushing over the ocean. Now, think about an asteroid made of iron directly slamming into rocky terrain at a 90° angle. The difference between the two impacts is night and day.

Important Note: we’ve detected many large objects with orbits near Earth. But so far, each of their orbits misses Earth.

We find new asteroids all the time though. The possibility does exist we find a large asteroid that could threaten humanity. The asteroid may have an orbit that aligns with Earth. 

Worst case, we’d have maybe a year’s warning before the collision. More likely though, we’ll find an object whose collision with Earth is several orbits away. This would probably give us decades of warning time to prepare. 

Calculating the impulse to deflect a mega asteroid hurtling towards Earth

One thing we know a lot about is the orbit of asteroids. Once we discover an asteroid, we can calculate the orbit with great accuracy. Using computers, we can compute an Earth impact many years in advance.

BUT, what if we don’t have an advance warning? Also, what if the asteroid is freakishly large?!

In this simplified case study, I’m going to assume several worst-case impact scenarios. Imagine an asteroid the size of Ceres heads towards Earth and we have little to no time to react. To make matters worse, the asteroid will hit Earth head-on!

Important Note: Ceres has a diameter of 946 km and a mass of 939 \times 10^{18} kg.

For added perspective, the moon has a diameter of 3,474.2 km. 

Before we calculate, let’s outline our problem parameters.

Earth has a radius of 6,378 km. So, to avoid the impact, we need to deflect the course of the asteroid by 6,378 km. To calculate the Delta-v to avoid impact, we’ll use the simple velocity equation.

velocity = distance / time

Important Note: Delta-v is a change in velocity. If you’re driving 40 mph and speed up to 80 mph, your delta-v is 40 mph. 

With rockets, Delta-v is how much speed a rocket achieves by burning its entire rocket fuel load.

If the asteroid was going to impact Earth in 365 days, the calculation would be the following:

6,378,000 meters / (365 days x 24 hours x 60 minutes x 60 seconds) = 0.2 m/sec

Now, we do the same calculation for the following impact windows of time:

  • 1 day: 73.8 m/sec
  • 10 days: 7.4 m/sec
  • 365 days: 0.2 m/sec

Using the mass of Ceres, we now can calculate the total impulse to deflect the asteroid measured in N⋅s.

I’m also going to list the calculated values in terms of the maximum impulse of a Saturn V rocket. This is the giant rocket that NASA used in the Apollo program to send humans to the Moon. This will allow you to wrap your mind around the preposterous calculated figures.

According to Wikipedia, the Saturn V rocket has a specific impulse of 2.58 km/sec. Also, it has a gross weight of 2,290,000 kg.

Thus, (2,580 m/sec) x (2,290,000 kg) = 5.9 \times 10^{9} N⋅s. The following is the calculated total impulse to divert the asteroid in our timeframes:

  • 1 day: 73.8 m/sec requires 6.93 \times 10^{22} N⋅s or 11,745,762,711,864 Saturn V rockets
  • 10 days: 7.4 m/sec requires 6.95 \times 10^{21} N⋅s or 1,177,966,101,695 Saturn V rockets
  • 365 days: 0.2 m/sec requires 1.88 \times 10^{20} N⋅s or 31,864,406,780 Saturn V rockets

In short, if an asteroid the size of Ceres barrels right towards us all of a sudden, it’d be gameover for humans. We couldn’t do anything. But what if we had 1 full century to prepare, or 36,500 days?

  • 36,500 days: 0.002 m/sec requires 1.88 \times 10^{18} N⋅s or 318,644,068 Saturn V rockets

Even still, with 100 YEARS advance notice, we couldn’t do a thing!

Thankfully, it’s very unlikely an asteroid the size of Ceres will come our way. Plus, we’d undoubtedly detect it far in advance.

Now, let’s do the same calculation, but for an asteroid sized equal to the Chicxulub asteroid? This is the asteroid that ended the age of dinosaurs.

Calculating the impulse to deflect a Chicxulub sized asteroid hurtling towards Earth

Using Wikipedia data, the asteroid is roughly 17 km in diameter with a mass of 6.82×10^15 kg. Let’s now do the same math to calculate the total impulse for deflection.

  • 1 day: 73.8 m/sec requires 5.03 \times 10^{17} N⋅s or 85,254,237 Saturn V rockets
  • 10 days: 7.4 m/sec requires 5.05 \times 10^{16} N⋅s or 8,559,322 Saturn V rockets
  • 365 days: 0.2 m/sec requires 1.36 \times 10^{15} N⋅s or 230,508 Saturn V rockets
  • 36,500 days: 0.002 m/sec requires 1.36 \times 10^{13} N⋅s or 2,305 Saturn V rockets

Even the smaller dinosaur killer asteroid we can’t divert if we detected it late. Thus again, the name of the game is early detection. The earlier we detect a large asteroid barreling towards us, the better chance we have to survive.

Also what’s evident, the closer an asteroid is to impact, the more energy we need to divert it. In other words, the Delta-v required to deflect an asteroid is exponential.

To illustrate, even using the total energy consumption by all humans in a year isn’t enough. If a killer asteroid is several weeks away from impact, we’re simply done for.

Important Note: a concentrated short blast on Earth’s crust is the most dangerous. It’ll cause nuclear winters, endless volcanic activity, and heavily polluted skies. Plus, whatever else results from the impact. 

The impact energy released is either in the form of heat or a shockwave or both. The question for scientists becomes, would heat or a shockwave cause more damage?

Technique #1: blow up the asteroid

asteroid approaching earth

Fire missiles at the asteroid. Because blowing things up is always an awesome choice.

Let’s assume firing missiles is possible, given the asteroid isn’t too big. To pull this off, you need to be sure after the asteroid blows up, the result is a combination of the following:

  • The pieces burn up once they reach Earth’s atmosphere
  • The pieces divert away from Earth and they don’t hit Earth several years later

One other problem is that we don’t fully know the internal composition of asteroids. We know even less about a particular asteroid. Thus, it makes it even more difficult to predict what will happen to the pieces of an asteroid hit by missiles.

For example, if the asteroid blows up, instead of one rock, countless pieces could rain down on Earth. This reality alone makes explosives a last-choice option.

Important Note: debris from explosions won’t just sail off into space. The debris needs to reach the escape velocity of the asteroid’s gravitational field. This is the only way for the debris to separate from the asteroid forever.

This is why you need a VERY strong explosion to create the escape velocity for a large part of the debris. To point out, at a far enough distance, the debris wouldn’t recombine due to the weak gravity and lack of time. 

Vaporize the asteroid

The other option is to detonate nuclear weapons at a short distance away from the asteroid. The initial explosion would emit radiation that’d engulf one side of the asteroid. This radioactive energy would vaporize parts of the asteroid.

Then the secondary explosion would eject the vaporized part of the asteroid. The vaporized material would then hopefully forever separate from the asteroid’s gravitational field. But, any large broken parts of the asteroid probably wouldn’t reach escape velocity.

What’s more, the explosion could help change the asteroid’s orbit, depending on the size.

Technique #2: tether a spacecraft in the asteroid’s gravitation space

meteor shower striking earth

Send a heavily massed vehicle called a gravity tractor, next to the asteroid.

With enough advance notice, we can potentially change the orbit of the asteroid by a tiny bit. This happens because of the gravitational pull between the asteroid and gravity tractor.

Imagine changing the velocity of the asteroid by a few millimeters per second. The gravitation would make the asteroid accelerate towards the tractor.

For this mission, we’d use spacecraft with high specific impulse thrusters. The spacecraft would use a bit of thrust to avoid falling into the asteroid. Then, if the spacecraft runs out of fuel to maintain its Delta-v, a second spacecraft will take its place. Then repeat and rinse!

Given enough advance notice, this would deflect the asteroid’s orbit to miss Earth.

Important Note: a tractor needs to be very close to an asteroid. This greatly increases the required Delta-v, which isn’t ideal. 

Technique #3: blast the asteroid with a laser

end earth apocalypse asteroid impact

Use a probe with a laser to evaporate a part of the asteroid. The exhaust from the evaporated asteroid part would then create a tiny force. This could push the asteroid off course.

For this technique, you need a heck of a strong laser though. Especially because the laser needs to compete with sunlight. Sunlight endlessly soaks the surface of asteroids.

But what if we mount the laser onto a spacecraft and get near the asteroid?

For one, how would we power this laser? Secondly, the laser would push itself hard in the opposing direction of the asteroid. Think of it like a rocket with laser propulsion.

Important Note: the “mirror bee” concept is a potential option. A whole swarm of small spacecraft carrying mirrors would travel towards the asteroid. 

The mini spacecraft would aim reflected sunlight at one location on the asteroid. The heating would cause vaporization creating propulsive jets. 

Technique #4: drill into the asteroid

For those who saw the Hollywood movie Armageddon, you know exactly what I’m talking about. The film was mesmerizing. But at the same time, you felt stupid as you watched what unfolded on screen.

I can’t emphasize strongly enough, how ridiculous the movie physics is. For one, the asteroid in the film is around 1,000 km. That’s near the same size as Ceres, that we did calculations for. What’s more mind-numbing is that NASA discovers the asteroid 18 days before impact.

For added perspective, let’s take a look at the movie analysis done by physics students in England.

To split the asteroid, they calculated you need 800 trillion terajoules of energy. While the total energy of the most powerful bomb, “Big Ivan,” is only 418,000 terajoules. So, we’d need to make a bomb that’s 2 billion times more powerful.

Good luck!

Another big slip-up is, how will the drill press against the asteroid without gravity?

If the drill isn’t firmly pressed, the drill bit will only scratch the surface versus boring in. Then throw in the fact there’s no air, so we can’t create an air vacuum to hold the drill down.

The obvious solution is to drill the legs of the drill into the asteroid to hold it down. But what if there’s nothing for the drill to grab onto? Maybe the asteroid consists of only loose material.

I can go on and on. The point is, the film was nothing more than fun entertainment!

Technique #5: alter the surface of the asteroid

Wrap the asteroid with reflective material. The reflecting material would act as a solar sail.

Also, you can coat the asteroid with material to again alter its orbit through reflected radiation. Radiation pressure provides a small thrust in the radial direction. Then the Yarkovsky effect provides an even smaller transverse thrust.

This technique may work on smaller asteroids. But, it’s not practical for objects that are miles in diameter.

What are we actually doing to prepare for an asteroid impact?

asteroids near earth

I’m always surprised how little hard science exists for asteroid detection and diversion. Asteroids are huge existential threats to humanity. Yet, so much global funds go to beef up militaries and other “trivial” activities. In the grand scheme, what’s more important?

The point is, we’re not doing as much as we possibly can to protect Earth.

And I get it. Trying to sell the public on asteroid detection and deflection is outright difficult. It’s only if we know for certain one is hurtling our way for a head-on collision, it’s an easy sell.

Imagine NASA broadcasts to the world that a huge rock is racing towards Earth. Politicians everywhere would then scramble and immediately take notice. In return, all the necessary dominos would fall into place. For example, the public and all nations would rally together without hesitation.

This is exactly why climate change is such a difficult sell. Because it’s such a slowly unfolding crisis, we can’t see its immediate impacts. But a massive rock from outer space that’d kill all humans is a frightening palpable event.

Asteroid detection challenges

The problem is, some objects are very difficult to detect. Imagine an object with a long orbital period with a high velocity in the inner solar system. We’d easily be able to detect it coming our way.

But, there are other objects not even in the Sun’s orbit that can come our way. The best example is Oumuamua. It’s the first interstellar object that passed by Earth that we know about. It measured around 400 meters across, and it travels 59,000 miles per hour. For added perspective, our manmade Voyagers travel at speeds of around 35,000 miles per hour.

What I’m getting at is, we need to better observe the space around us. We can then avoid surprises, outside of an object traveling from interstellar space.

Important Note: not all asteroids are large solid rocks. For example, (29075) 1950 DA is an asteroid that could one day hit Earth. It’s not solid, rather a pile of rubble.

So, our 5 deflection techniques wouldn’t be too effective. Blowing up a pile of rubble isn’t a solution.

The unfolding of Earth events with an incoming asteroid

Currently, we don’t have a ready-made solution to deflect a large asteroid.

BUT, let’s just say we discover a large asteroid hurtling our way and we only have several years to react. The following is how the situation would presumably unfold:

  1. Gather concrete evidence that the asteroid is an existential threat
  2. Notify politicians of the eventual asteroid impact
  3. Get funding to figure out a solution to deflect the asteroid
  4. Global spending habits will change to fund the astroid deflection project
  5. Band all nations together to speed up the deflection project’s design and development
  6. The deflection solution needs to work on the first try as there’s no testing phase
  7. Launch the deflection solution into space towards the incoming asteroid

NASA believes we need significant advance notice to deflect a reasonably sized asteroid. According to NASA,

Even throwing a lot of resources at it, you would be talking 4 or 5 years to mount a deflection mission.

I believe we need MUCH more time than 5 years. We need to consider the following:

  • Several years to perfectly map the asteroid’s orbit to intercept it
  • Few years to prepare the mission
  • Roughly a year to open a launch window to travel to the asteroid
  • Several years to get to the asteroid

What I’m getting at is, we need to better observe the space around us. We can then avoid surprises, outside of an object traveling from interstellar space.

Important Note: Earth is a single point of failure. If we colonize Mars one day, we’d create redundancy.

We’d then protect humanity from a rare event that may be tens of thousands of years away. Because one day, a Ceres size rock may hurtle towards us. On Earth, we’d be sitting ducks, and our advanced technology couldn’t do a thing.

But planet redundancy would allow the human experiment to continue. After a large impact, humans from Mars can then recolonize Earth. 

“How do we protect Earth from asteroids?” wrap up 

A monster asteroid striking Earth seems like a page straight out of science fiction. But, it’s a very real reality that ended the dinosaur’s run on Earth about 66 million years ago.

In February of 2018, the B612 Foundation stated,

“It’s 100 percent certain we’ll be hit by a devastating asteroid, but we’re not 100 percent sure when.”

All of this just reminds me of how vulnerable humanity is on our small blue marble. Even with all our advanced technology, a big enough asteroid can wipe humans off the face of the Earth. One level higher, look up into the night sky at all the stars to be further humbled.

Currently, I believe our best bet is using nuclear weapons. But from the calculations I did for Ceres, you can see how small scale we are even in our own solar system. Our largest nuclear bombs would be like tiny pops with little to no impact.

BUT, at least, smaller objects, which are more abundant, we can divert IF we plan ahead.

So, we as humans need to band together and not only live in the present. We need to avoid the same fate as the dinosaurs. In other words, we need to increase the funding for the study and deflection of asteroids.

What are your thoughts on an asteroid slamming into Earth? Do you think humanity is ready and prepared to deflect a large asteroid if we have a 100-year warning window? What do you think is the best technique to deflect a 1 km asteroid?


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