Asteroids have been the stuff of science fiction catastrophes for decades. From classic movies like When Worlds Collide and novels such as Larry Niven and Jerry Pournelle’s Lucifer’s Hammer, to more recent films like Deep Impact and the ludicrously funny Michael Bay popcorn-seller Armageddon. It’s also a real possibility. Ever since the discovery of the colossal Chicxulub impact, which almost certainly wiped out the dinosaurs, the possibility of another impact, if not wiping out humanity but at least giving us a very bad time, has lurked in the background.
Indeed, were it not for the singular good fortune of striking the vast and empty Russian taiga, the Tunguska impact in 1908 could have wreaked untold calamity.
With that in mind, a concerted effort to map the orbits of known asteroids, and their likelihood of impacting Earth, has been underway. Space missions have also tested methods of possibly shunting a dangerous asteroid out of harm’s way. So far, though, nothing has been detected that might pose a real threat.
Until now. In recent weeks, media have reported a ‘city-killer’ asteroid (not big enough to wipe us all out, but certainly to cause massive damage and casualties) on a potential collision course with Earth.
But is it all so much doom porn from a calamity-addicted media? Or are the odds near enough to be concerned about?
Since early this year, the Gemini South Telescope has been tracking YR4, a 40–90m wide asteroid that’s on a ‘near-Earth’ trajectory. In fact, in 2024 it passed at just over twice the distance to the Moon (for perspective, similarly-sized asteroids have passed between the Earth and Moon twice in the past few years). It will be back in 2032.
Currently, NASA puts its odds of impact at one in 67 (down from one in 48 as widely reported even days ago). What would happen if it did impact?
A strike by YR4 could release an energy blast equivalent to 8 megatons of TNT, capable of obliterating an area the size of Washington, as seen in chilling animations taking off online. The asteroid also has a 0.3% chance of hitting the moon as well.
Given what is known about its orbit, astronomers have calculated a likely path of any possible impact. The path begins just above the top of South America (scarily, perhaps,very near the Chicxulub impact, which was, to be fair, a far more gigantic object), across the Atlantic and the midsection of Africa and over the sea south of the Middle East and across India.
Come to think of it, it could be a massive problem-solver.
Meanwhile, [scientist Dr David Rankin] predicts there’s a roughly 0.3 per cent (one in 333) chance of 2024 YR4 hitting the moon […]
Without any atmosphere to slow its approach, the asteroid would slam into the lunar surface at a staggering speed of 31,000 miles per hour (50,000 kilometres per hour).
The collision would unleash an explosion 343 times the size of the atomic bomb dropped on Hiroshima and carve out a crater up to 1.2 miles (2km) across.
Should it hit the moon, it is most likely to land in the region stretching south from the Mare Crisium, a large plain of solidified lava, to the crater Tycho.
This could be concerning since this would place the impact on the side of the moon facing Earth, potentially exposing us to a shower of lunar shrapnel.
Thankfully, experts say that the Earth likely wouldn’t be harmed by any impact which occurs on the moon.
Dr Rankin told New Scientist: ‘There is the possibility this would eject some material back out that could hit the Earth, but I highly doubt it would cause any major threat.’
But what if it really did hit Earth?
The damage caused by an impacting asteroid depends greatly on the exact size and composition of the asteroid. The exact size of 2024 YR4 is still uncertain, but an airburst is a likely scenario for its size range. If the asteroid were to enter the atmosphere over the ocean, models indicate that airbursting objects of this size would be unlikely to cause significant tsunami, either from the middle of the ocean or even nearer shore.
If the asteroid entered the atmosphere over a populated region, an airburst of an object on the smaller side of the size range, about 130–200 feet (40–60 meters) could shatter windows or cause minor structural damage across a city. An asteroid about 300 feet (90 meters) in size, which is much less likely, could cause more severe damage, potentially collapsing residential structures across a city and shattering windows across larger regions.
Well, that’s no fun. Where’s the doom porn in that?
