What, in the end, will signal the end of the world? It’s the question we all ponder, but what could actually happen?

Our Earth is our tiny little haven in this chaotic universe, and it’s by sheer luck we are even here at all. The Little Book of Cosmic Catastrophes (That Could End the World) explores astronomical conundrums, with complex ideas in bitesize, easy to digest segments in three parts.

What makes Earth so special, the beginning of the universe, how everything we know could not have existed at all, the fate of the world if our sun was born a twin, and how Jupiter could have gone from our friend to our foe. In theory, what could happen anytime. From rogue blackholes to deadly gamma ray bursts and alien invasions. And everything from how stars die to statistically predicting the existence of aliens, how our sun will die, our collision course with andromeda and even the end of time. It’s not all doom and gloom though as the book also explores where humans could go next, interstellar travel, and how we might locate Earth 2.0.

In this extract we explore the possibility of an asteroid attack.

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ARMAGEDDON BY ASTEROID

In 1998, one of the greatest sci-fi movies of all time (in my opinion anyway) was released.

The premise of Armageddon is that a giant asteroid is heading straight towards Earth and the only way to survive is to send up a rat pack of oil drillers to plant a nuclear bomb in the asteroid’s core and – you guessed it – blow it up.

Now … although it is an epic adventure and fun to watch, Armageddon is scientifically dubious, at best. Let’s start with the size of the asteroid. In the movie, the killer asteroid was 1000 kilometres wide. If that sounds enormous, it absolutely is! The Chicxulub asteroid, which wiped out the dinosaurs 66 million years ago, was only 12 kilometres wide. If we went head-to-head with an Armageddon-sized asteroid, we wouldn’t stand a chance, even with the nukes.

But what is the likelihood of Earth’s destruction by asteroid? Should you sleep with one eye open and the other on the sky, just in case? The good news is that it is extremely unlikely … but not impossible!

The Solar System is home to at least 3 million individual asteroids. Most of them are stuck in orbit around the Sun between Mars and Jupiter – an area called the asteroid belt. More than a million asteroids seems like a lot compared to just eight planets, but they really aren’t the monsters Hollywood makes them out to be.

Asteroids can be grouped into three main categories: C, S and M types.

C-type asteroids are the most common in our solar neighbourhood, making up about 75 per cent of all asteroids. They contain a large amount of carbon and are often dark in colour, so they don’t reflect large amounts of light, which can make them hard to spot.

S-type asteroids make up 17 per cent of all known asteroids and we suspect they are rich in siliceous minerals. These asteroids reflect light fairly well, and the large ones can be easily spotted with binoculars.

M-type asteroids are probably rich in metal. They probably formed in different regions of the Solar System, but are now mainly found towards the middle of the asteroid belt.

The largest asteroid in the Solar System is Vesta, an M-type asteroid that is 530 kilometres wide. Vesta is so large and bright that it was discovered in 1807 – 39 years before Neptune. (Important side note: the largest object

in the asteroid belt is a dwarf planet named Ceres, but we’ll focus on the asteroid Vesta.) In fact, Vesta is so massive that it contains 9 per cent of all the mass in the asteroid belt. I’m not going to lie to you – if it was flying towards Earth, we probably wouldn’t survive. However, this is next to impossible. For Vesta to head in our direction, the Solar System would need some serious gravitational forces acting upon it. For now, and far into the future, Vesta is safe and sound sitting about 160 million kilometres from Earth.

Unlike Vesta, the vast majority of asteroids are under 1 kilometre in diameter. One of my

favourite fun facts is that if you grouped all the known asteroids together, they would still have less mass than the Moon. You can see why I’m not too concerned about an

Armageddon-level event.

However … that doesn’t mean Earth is completely out of the woods.

Although most asteroids sit between Mars and Jupiter, a small handful live more chaotically. Some never settled into the asteroid belt. Instead, they orbit around the Solar System, weaving in and out of planets. The few that cross Earth’s orbit are called near Earth asteroids (NEAs). These are the ones we need to track as if our lives depend on it, because they very well might.

Currently there are over 30,000 known NEAs. Of these, 8 per cent are further classified as potentially hazardous asteroids (PHAs). To be marked as a PHA, an asteroid must be over 140 metres wide and, at some point, come within 7.4 million kilometres of Earth.

The good news is that, of all the known PHAs, we have only found 153 that are larger than 1 kilometre in diameter. The better news is that most of those large asteroids will not pose any risk to Earth for at least 100 years.

Most?

One PHA is set to have some pretty close calls with Earth in the not-too-distant future. Its name is Bennu – it was named for an ancient, mythological, Egyptian bird that was associated with the Sun, creation and rebirth. The name is fitting because, if Bennu did hit Earth, it really would be a new beginning for whatever life is here.

Bennu is a notable 490 metres wide (40 times larger than the Chicxulub asteroid), so you can be sure that astronomers are always watching it. Our calculations predict the riskiest time to live on Earth will be the year 2054, when Bennu will pass within 5.8 million kilometres of Earth. To put that distance into perspective, it’s 14 times further away from Earth than the Moon is.

Bennu has a 1 in 10,000 chance of accidentally hitting Earth. With those odds, we are probably going to be just fine. But one of the most interesting (and concerning) consequences of the 2054 approach of Bennu is that, even from 5.4 million kilometres away, Bennu will be gravitationally affected by Earth. This will change the asteroid’s orbit permanently, and future close approaches will have a higher chance of impacting Earth.

Astronomers and statisticians love to model potential scenarios. NASA recently said that, in the next 300 years, with multiple close approaches of Bennu to Earth expected, there may be a 1 in 1750 chance that Bennu actually hits Earth. You have a better chance of hitting a bullseye on a dart board blindfolded.

All in all, asteroids can certainly do harm to Earth, as they have in the past, but the likelihood of an asteroid causing the end of the world is next to zero. We see this with the Chicxulub asteroid and the mass extinction of the dinosaurs. The aftermath of the Chicxulub impact wasn’t great, but

it wasn’t the end. Even after catastrophic tsunamis, wildfires and nuclear winters, Earth survived. I’d even argue that Earth actually thrived – after all, we are here. However, it is vital that we are prepared to mitigate any future impact events. Even though Earth would bounce back, humans as a species may not.

Scientists have begun testing systems to move asteroids off dangerous orbits before they get too close. Unlike in Armageddon, they aren’t playing around with nuclear weapons – these would actually do more harm

than good. If we exploded a potentially dangerous asteroid, we might accidentally create an uncontrolled debris field of smaller asteroids that could end up hitting Earth. Not so great. So what can we do instead?

One of the best ideas so far is to perform a “kinetic impact”. This idea is so simple, it’s beautiful. A spacecraft is flown into the potentially dangerous asteroid, and when it impacts, its momentum becomes a kinetic force that slightly alters the asteroid’s orbital path. NASA has successfully tested this idea with the Double Asteroid Redirection Test (DART) mission in 2022.

The DART mission targeted Dimorphos, a moon that orbits the larger asteroid, Didymos. Dimorphos’s orbit is very consistent, giving NASA the perfect opportunity to measure the effect of a kinetic impact in practice. A spacecraft weighing just over half a tonne flew straight into Dimorphos at a speed of 6.1 kilometres per second. The impact was so powerful it shortened Dimorphos’s orbit around Didymos by 32 minutes. It was a promising result, and one we can use to model how much force we would need to target any asteroids that are a bit too close for comfort.