Neil deGrasse Tyson – What Asteroid Can Render Us Extinct?

Imagine a world ruled by giant reptiles, where they roam free and dominate the land for over 160 million years. Suddenly, their world is turned upside down by a visitor from space: a monstrous asteroid at least six miles wide crashes into the Earth, unleashing a series of devastating events that wreak havoc on the planet. Earthquakes, tsunamis, volcanic eruptions, and climate catastrophes abound, causing the demise of 75% of all living creatures. The once-mighty dinosaurs, rulers of the Earth, are wiped out. But what if this isn’t just a story from the past? What if it happens again?

As we continue to explore the vast expanse of space, we’ve come to realize that civilization-ending asteroids are not the only threat we face. Countless smaller asteroids hurtle through space, and any one of them could pose a catastrophic threat to our way of life. If you count how many big asteroids there are versus how many small ones, there are more small ones than big ones. When they get really small, we often don’t know they’re around until it’s too late, as they don’t reflect much light. Often, asteroids that come between Earth and the moon are discovered only a few days before they pass by.

This happens several times a year. These house-sized asteroids, if they hit, could explode in the air and level a thousand square kilometers of Earth’s surface. Fortunately, if one of those does hit, it won’t render us extinct, but it could be very damaging for the people living below the impact point.

In 1908, the world witnessed an unforgettable event that shook the foundations of science: the Tunguska event. An explosion flattened an estimated 80 million trees over a vast area of forest near the Tunguska River in Russia. This explosion is attributed to a meteor air burst, where a stony asteroid about 50 to 60 meters in size exploded at an altitude of 5 to 10 kilometers. The asteroid approached Earth at an astonishing speed of around 27 kilometers per second, resulting in a massive impact that generated about a 12-megaton explosion.

As we ponder this phenomenon, the question arises: why do asteroid impacts happen so frequently? Is there a larger force at play governing the movements of these celestial bodies? Once we learned that impacts made a difference in the history of Earth’s life and geology, we became curious about whether there might be another star out there, far away, that is dimmed so we can’t see it. This hypothetical binary star with the sun may have an elongated orbit that takes it through the Kuiper belt, disrupting comets and periodically causing waves of extinction on Earth.

You can look at the extinction record, and while there are big extinctions, there are also smaller episodes. Some have suggested the existence of a twin star, naming it Nemesis, but the numbers didn’t work out because an orbit would be pretty stable, while the extinction periods were not.

A gigantic asteroid named 2019 OK made a close pass by Earth, coming within a mere 40,000 miles of our planet’s surface. This massive space rock, estimated to measure between 195 and 425 feet in diameter, zoomed by us at an incredible speed of 61 times that of a commercial jet. The shocking part is that astronomers had very little warning of its approach, only discovering the asteroid days before its close call.

Now, you may wonder what would have happened if 2019 OK had collided with Earth. This asteroid has been dubbed a “city killer.” To give you some perspective, the asteroid that hit Chelyabinsk, Russia, in 2013 was only 20 meters across, while 2019 OK is estimated to be around 100 meters wide, which is a cause for concern. Although other asteroids have passed closer to Earth in the recent past, none have been as large as 2019 OK, making it a truly unique event that scientists will study for years to come.

According to NASA, an asteroid of this size coming this close to Earth only happens about twice a century, so it’s safe to say we witnessed something extraordinary. However, there is another asteroid named after the Egyptian god of chaos, Apophis, that people worry might come even closer to Earth. Apophis is about 300 meters across, roughly the size of a fully open Rose Bowl. If it were to hit, it would most likely land in the Pacific Ocean, raising a 50-foot tsunami that could devastate the west coast of North America. Fortunately, we would predict when this would happen, allowing us to clear out the west coast and watch the spectacle unfold.

While such an event would not be extinction-level, it could cause significant damage, estimated at a trillion dollars. We know the size of an asteroid that would cause severe disruptions to civilization is about a kilometer across, a little more than half a mile. Such an asteroid could disrupt the food chain and transportation channels, which are vital for modern living. If we consider an asteroid around 10 kilometers in size, similar to Mount Everest, that would be an extinction-level event.

In the vast expanse of space, there lurks a potential danger that could wipe out an entire city or even trigger the end of civilization as we know it. NASA scientists have identified a specific size and distance range that makes any space rock a potential hazard to Earth: measuring at least 460 feet and orbiting within 4.6 million miles (7.4 million kilometers) of Earth. These rocks pose a real threat to our existence, as a collision could unleash unimaginable devastation.

But what about the larger rocks, those measuring at least one kilometer wide? These are the true monsters of space, capable of triggering global climate disasters and bringing about the end of our civilization. So, are we simply sitting on our hands waiting for a disaster to strike? The answer is a resounding no. NASA scientists are hard at work exploring various methods to prevent an asteroid impact.

The first step is to detect any potential threats as early as possible and then slowly deflect them out of harm’s way. The earlier we detect an asteroid, the less we need to deflect it, as the angle accumulates and widens, allowing it to completely miss Earth. The later we act, the more significant the deflection needed to avoid a collision.

One method to deflect an asteroid is to paint one side of it jet black, which would absorb more sunlight than the other side. This difference in radiation rates creates a pressure that pushes the asteroid into a new orbit. Another method involves sending a space probe to park near the asteroid. The gravity will want to attract them to one another, but by firing retro rockets, we can pull the spacecraft a little farther away, creating a gravitational tether that can help measure the effectiveness of the approach.

Over 4.5 billion years ago, as Earth was still taking shape, a colossal object larger than Mars barreled toward our world at breakneck speed. This object was Theia, a Mars-sized planet whose fate was sealed in a momentous crash with Earth. As Theia collided with our planet, it launched a catastrophic salvo of debris into space, which eventually settled into a new celestial body: the moon. Remarkably, this collision did not destroy Earth but fused part of Theia’s core and mantle with our own, remaining hidden for eons.

Experts disagree on whether this was a head-on impact or a glancing blow, but one thing is certain: had anything been alive on Earth at the time, Theia would have wiped it out. However, not all collisions spell doom and destruction. Take the example of the Yarrabubba asteroid, a colossal 4.3-mile-wide behemoth that collided with Earth when the planet was emerging from a global ice age. As the asteroid smashed into ice several miles thick, it released between 100 billion and 5.5 trillion tons of water vapor into Earth’s atmosphere, possibly sparking a greenhouse effect. This warming effect may have melted the ice, sped up the great thaw, and opened the door for new forms of life.