The odds of a sizable asteroid striking Earth are small, but they’re never zero. Large asteroids have struck Earth in the past, causing regional devastation. A really large asteroid strike likely contributed to the extinction of the dinosaurs. So we shouldn’t be too surprised that astronomers have discovered an asteroid with a better than 1% chance of striking our world. Those odds are large enough we should keep an eye on them, but not large enough that we should start packing bags and fleeing to the hills.
The rock, named 2024 YR4, is somewhere between 40 – 100 meters wide, which would make it a “city killer” asteroid. If it does strike Earth, it wouldn’t decimate human civilization and cause mass extinctions, but it could destroy a heavily populated area if it struck a city, or trigger a tsunami if it struck the ocean. It would back a punch similar to the 1908 Tunguska event in Northern Siberia.
So what is the overall risk of 2024 YR4? The scale most commonly used for asteroid impact risks is known as the Torino Scale. It combines the overall size and relative speed of an object with its odds of impact to assign a number ranging from 0 to 10, where 0 means there is no risk of impact and 10 means it’s time to call Bruce Willis to save us all from extinction. That said, the highest number any asteroid has had on the scale is 4. This was for the asteroid Apophis soon after its discovery, which has now been downgraded to 0.
Currently, 2024 YR4 has a 3 on the scale, which means it “merits attention by astronomers.” It is currently the only object with a number other than 0 on the Torino Scale, and it means a couple of things come into play. The first is that the International Asteroid Warning Network (IAWN) will work to pin down the orbit of the asteroid. Chaired by NASA, the IAWN coordinates with observatories around the world to make detailed observations of 2024 YR4. It will take time to gather enough data. But what will likely happen is that they will determine there is no risk of collision, and 2024 YR4 will be demoted to 0 on the scale.
The second thing initiated is the Space Mission Planning Advisory Group (SMPAG), chaired by the European Space Agency. They have a scheduled meeting next week when there will be some initial discussions about a possible mission to 2024 YR4 to shift its orbit. If we do find there is a real risk of impact, this group would ramp up quickly. But again, this isn’t likely.
Statistically, asteroids the size of 2024 YR4 strike Earth every couple thousand years or so. This is why astronomers track these objects and are constantly looking for more. So even though the odds of an impact are never zero, with planning and preparation we should be able to ensure that any real risk can be mitigated.
