Telescopes around the world are currently trained on a building-sized asteroid hurtling in Earth’s direction, in an effort to try to understand whether it might hit us. Our current best guess is that this object, called 2024 YR4, has a 1-in-43 chance of striking in 2032, the highest risk of any known asteroid. But what does that number really mean, and when should we start panicking?

Astronomers are continuously tracking thousands of asteroids as they move through our solar system. This information is then collated at the Minor Planet Center,…