How Do We Protect Earth From Asteroids?

How do we protect Earth from asteroids? Divert them with explosives, booster jets, lasers, and various other hardware.

More importantly, we need a huge lead. Especially, to divert an extinction-level asteroid. Easier said than done though. 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. Thankfully though, the chance of a future major collision is low.

But, a monstrous asteroid will one day strike Earth, when you consider cosmic time scales. Thus, we need to prepare for a dinosaur extinction class asteroid, through mastery of deflection techniques. The following are the 5 most popular deflection techniques, which we’ll discuss:

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

To set the stage, we’ll go over asteroids and why they pose a threat.

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 difference is from asteroids forming closer to the sun, where ice doesn’t stay solid.

The small asteroids, properly called meteoroids, strike Earth daily. They measure as small as a grain of sand, to a few meters across. This makes them undetectable until they burn up in our 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.

Large asteroids though, we can easily detect, which is important. Because objects larger than 25 meters can cause serious damage.

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 across and 9,979,000 kg according to NASA. The meteor turned into a fireball in the sky, while raining down pieces to the ground called meteorites.

The result was a monstrous shockwave, causing 1,491 indirect injuries and  7,200 damaged buildings.

What’s more, the size of asteroids isn’t the only concern. The angle of impact and composition is just as critical.

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 would be incomparable.

Important Note: we’ve detected many large objects with orbits near but missing Earth. While new asteroids are constantly found, which can include a humanity-threatening asteroid.

Worst case, we have a year’s warning before a collision. More likely though, we find an object whose collision with Earth is several orbits away. This should give us decades of preparation warning time.

Calculating the impulse to deflect a mega asteroid hurtling towards Earth

Once we discover an asteroid, we can calculate its orbit with great accuracy. Then, compute its potential future collision with Earth 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 reaction time. To make matters worse, the asteroid will strike Earth head-on!

Important Note: Ceres has a diameter of 946 km and a mass of 939 \times 10^{18} kg. For perspective, the moon’s diameter is 3,474.2 km. 

First, we outline our problem parameters.

Earth has a radius of 6,378 km. To avoid impact, we need to deflect the asteroid’s course by 6,378 km. To calculate the Delta-v to avoid impact, we 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 will strike Earth in 365 days, the calculation is 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

Next, using Ceres’ mass, we calculate the total impulse to deflect the asteroid measured in N⋅s.

I list the calculated values in terms of the maximum impulse of a Saturn V rocket. The giant rocket, NASA used in the Apollo program to send humans to the Moon. This will help you wrap your mind around the preposterous calculated figures.

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

So, (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 towards Earth, it’d be game over for humans. We couldn’t do a thing. 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 with 100 years’ advance notice, we still couldn’t do a thing!

But how about the Chicxulub asteroid, which wiped out the dinosaurs?…

Calculating the impulse to deflect a Chicxulub-sized asteroid hurtling toward Earth

Using Wikipedia data, the asteroid is roughly 17 km in diameter with a mass of 6.82×10^15 kg. Doing the same math, we calculate the following total impulses 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

We can’t even divert the smaller dinosaur killer asteroid, if we detect it late. The name of the game is early detection. The earlier we detect a large asteroid barreling toward 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. The Delta-v required for deflection is exponential relative to proximity.

So, even using the total energy consumption by all humans in one year wouldn’t be enough. If a killer asteroid is several weeks away from impact, we’re simply goners.

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. Because the impact energy released is in the form of heat, a shockwave, or both. 

Deflection 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 the asteroid isn’t too big and missiles are an option. For a successful mission, one or both of the following must happen, post missile strike:

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

One other problem is we don’t fully know the internal composition of asteroids. We know even less about a particular asteroid. This makes it even more difficult to predict the direction of the asteroid pieces.

For example, if the asteroid blows up, instead of one rock, countless pieces rain down on Earth. This potential outcome 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. It’s the only way for the debris to separate from the asteroid forever.

This is why you need a VERY strong explosion, to create the necessary escape velocity for the debris. 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. An initial explosion would emit radiation to vaporize one side of the asteroid.

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

Deflection 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 change the orbit of the asteroid by a tiny bit to miss Earth. This is from the gravitational pull between the asteroid and the gravity tractor. The asteroid would accelerate toward the tractor, say a few millimeters per second.

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. And if the spacecraft runs out of fuel to maintain its Delta-v, a second spacecraft will take its place. Then repeat and rinse!

Important Note: a tractor needs to be very close to an asteroid for this mission. This greatly increases the required Delta-v, which increases the difficulty.

Deflection 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. Then the exhaust from the evaporated asteroid’s face would create a force, pushing the asteroid off course.

This technique requires a heck of a strong laser though. Especially, because the laser will compete with sunlight, which endlessly soaks the asteroid’s surface.

Additionally, consider the laser will mount on a spacecraft, traveling near the asteroid. How would we power the laser? Even more, the laser would push itself hard in the opposing direction of the asteroid. Think of a traveling rocket using laser propulsion.

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

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

Deflection Technique #4: drill into the asteroid

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

I can’t emphasize strongly enough, the ridiculousness of the movie physics. For one, the asteroid in the film is roughly 1,000 km in diameter. This is nearly the same size as Ceres, which we did calculations for. Even more mind-numbing, NASA discovers the asteroid 18 days before impact.

For added perspective, let’s 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 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 anchor 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!

Deflection Technique #5: alter the surface of the asteroid

Wrap the asteroid with reflective material, to create a solar sail. This would alter the asteroid’s 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 small asteroids, but it isn’t practical for objects 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, a huge rock is racing toward Earth. Politicians everywhere would scramble and immediately take notice. Next thing you know, the public and all nations are rallying together to find a solution.

And this is precisely why climate change is such a difficult sell. Because it’s such a slowly unfolding crisis, we can’t see its immediate impacts.

Asteroid detection challenges

Some objects are just 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, which can come our way. The best example is Oumuamua. It’s the first interstellar object, which passed by Earth we know about. It measured around 400 meters across and travels 59,000 miles per hour. While our manmade Voyager travels at a speed of around 35,000 miles per hour.

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

Our 5 deflection techniques wouldn’t be effective on this asteroid. Blowing up a pile of rubble isn’t an effective solution.

The unfolding of events on Earth, with an incoming asteroid

Currently, we don’t have a ready-made solution to deflect a large asteroid. But, say we discover a large asteroid hurtling our way and we only have several years to react. The following is how the situation would probably unfold, through various professionals:

  1. Gather hard evidence showing the asteroid is an existential threat
  2. Notify politicians of the eventual asteroid impact
  3. Obtain funding to figure out a solution to deflect the asteroid
  4. Band all nations together, to speed up the deflection project’s design and development
  5. Divert global spending expenditures, to fund the asteroid deflection project
  6. Ensure the deflection solution works on the first try, as there’s no second try
  7. Launch the deflection solution into space toward 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 reach the asteroid

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

Important Note: Earth is a single point of failure. By colonizing Mars, we create redundancy for humanity. Humans from Mars can recolonize Earth if Earth is ever destroyed by an asteroid.

“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 reality, which ended the dinosaur’s run on Earth about 66 million years ago.

In February 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 reminds me of how vulnerable humanity is. Even with all our advanced technology, a big enough asteroid can still wipe us all off the face of the Earth.

Our frailty in the cosmos is truly humbling.

What are your thoughts on an asteroid slamming into Earth? Do you think humanity is 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 wide asteroid?


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