There’s something inherently dramatic about space rocks hurtling toward Earth. Just check out movies like Armageddon or Don’t Look Up. So it’s no surprise that when scientists recently detected a new asteroid on a potential collision course, the doomsday gears started turning.
In fact, I wouldn’t be surprised if 65 million years ago one dinosaur turned to another and mumbled, “Is it just me Rex, or is that rock getting a little bit too close for…?”
The latest orbital object to get this treatment is the blandly named asteroid 2024 YR4, a chunk of rock between 40 and 90 meters wide, which has a 2.3% chance of impacting Earth on December 22, 2032.
You’re right to think that this number sounds small, but FYI it’s recently been upgraded from a 1.3% or a one-in-77 chance, to this now one-in-43 chance. This makes 2024 Y4 the highest known risk of any asteroid in modern tracking history.
So while we might not need to send Ben Affleck and Bruce Willis out there just yet, it could be good to keep them on speed dial.
How do we know if an asteroid will hit?
Predicting asteroid trajectories isn’t just a case of pointing a telescope and drawing a straight line. The calculations are deeply mathematical, involving a wide range of disciplines including celestial mechanics, probability theory, and chaos dynamics.
In trying to calculate where an asteroid might be eight years from now, mathematicians will use:
Celestial Mechanics (thanks Kepler and Newton!): Kepler’s laws of planetary motion and Newtonian physics can help determine an asteroid’s long-term elliptical path around the Sun.
N-body Simulations: But once you get multiple objects all exerting gravitational forces upon each other, the maths gets remarkably tricky. You might have seen the Netflix hit The 3-Body Problem. Well, it’s named after the phenomena whereby even adding a third object to a celestial model makes the results exponentially harder to obtain.
Since gravitational forces from the Sun, Earth, our moon and other planets can all tug at an asteroid’s course, the best we can do it to get supercomputers to run simulations considering all of these complicated effects over time.
Monte Carlo Simulations: Astronomers might then model millions of possible future paths, each with slightly different starting conditions, to quantify impact probabilities. Run a few million simulations, check how many slam into Earth, and you get your percentage risk.
Uncertainty and Chaos Theory: As if the task wasn’t already hard enough with all these complicated systems of equations at play, even the smallest of uncertainties in the initial measurements you plug into the system can lead to wildly different outcomes over years or decades.
If you’ve heard of ‘chaos theory’ - this is it. Changing the assumed initial speed of an asteroid, or it’s mass or angle of approach, by even a fraction of a percent, may over a few years lead to different paths millions of kilometres apart.
This is why initial probabilities often change over time as more observations refine the asteroid’s trajectory.
In other words, what looks like a 2.3% impact chance today may drop to zero or rise once we gather more data. In the worst-case scenario, we might not be ‘certain’ of an upcoming impact until it is imminent.
How often does space rock actually hit Earth?
Despite the alarm bells, Earth gets pelted by space debris all the time; it’s just usually too small to matter. Consider the following:
100+ tons of dust and tiny meteors hit Earth daily.
Every year, a few car-sized asteroids burn up in the atmosphere.
Every century or so, a Tunguska-style explosion happens, flattening a region up to perhaps the size of a city.
Every few million years, a planet-changing impact occurs – like the one that wiped out the dinosaurs.
That’s why NASA and the European Space Agency track thousands of objects on a possible trajectory to Earth, ensuring that the big ones don’t take us by surprise.
So should we be concerned about 2024 YR4?
For now, probably not. The asteroid’s current risk corridor stretches across the Pacific, South America, and parts of Asia, but millions of further observations and calculations will refine its trajectory.
If the danger remains high, that’s when Hollywood comes a knocking. Planetary defence agencies could explore options like nukes, kinetic impactors, or gravitational tractors – all serious strategies in Earth’s anti-asteroid arsenal.
Until then, astronomers will keep watching the skies. And as for Mr Affleck – well Benny boy, I’d keep hitting the gym. Just in case.
The Torino Scale: The asteroid threat level system
Scientists love a good scale. A simple way to clarify by number how serious something is. You’ve heard of the Richter Scale (earthquakes) and maybe Def-Con 1 (the highest level of US military readiness). But when it comes to ranking the threat of an asteroid impact, we use the Torino Scale.
The scale combines the likelihood of an impact with the predicted energy involved in a collision. And it goes a little something like this;
0 (no hazard): Routine space debris, no risk.
1 (normal): A near-Earth object (NEO) passing close but unlikely to hit.
2-4 (meriting attention): Possible impacts, warranting continued observation.
5-7 (threatening): The asteroid has a real impact probability - serious discussions start here.
8-10 (certain collision): If a 10-class asteroid (massive and almost certain to hit Earth) is coming, you might have to kiss civilization goodbye.
Asteroid 2024 YR4 currently sits at Torino Scale 3, meaning it’s the highest-ranked threat on record, but still in the 'probably fine' category.
Adam’s top 5 mega meteor impacts in Earth’s history
1. The Moon-Forming Impact (4.5 billion years ago): A Mars-sized planet (Theia) slammed into early Earth, blasting debris that formed the Moon.
2. The Chicxulub Impact (66 million years ago): The dinosaur killer; a 10-kilometre-wide asteroid smashed into Mexico, triggering global climate chaos.
3. The Sudbury Basin Impact (1.85 billion years ago): A 250-kilometre-wide crater in Canada - one of Earth’s largest impact sites.
4. The Vredefort Impact (2 billion years ago): The largest known impact crater on Earth (South Africa), 300 kilometres wide.*
5. The Tunguska Event (1908): A mystery explosion over Siberia, flattening 2,000 square kilometres, likely caused by a 40-metre-wide asteroid exploding in the atmosphere.
* The science isn’t settled here yet and there are several sites on Earth where scientists think meteorites may have impacted, they just need further evidence. And one of them, The Deniliquin Structure in NSW may well be the largest ever! If the impact zone - now buried deep underground and rumoured to have been part of the Hirnantian mass extinction event which wiped out 85% of all life on Earth around 445 million years ago - is confirmed, it will come in at a whopping 520 kilometres wide. This would be 1.5x bigger than the Vredefort Impact.
That’s all from me for now. If you'd like more geeky fun, please check out my other newsletters below, or connect with me on LinkedIn and/or X.
Yours in nerdiness,
Adam
Comments