An asteroid identified late last year is attracting significant public attention as predictions of its potential collision with Earth in less than eight years have increased. Two weeks ago, Ars reported on the asteroid, named 2024 YR4, citing data from NASA’s Center for Near Earth Object Studies, which estimated a 1.9 percent chance of the asteroid impacting Earth in 2032. Recent calculations have raised this figure to 3.2 percent. Although this probability remains low, it is notable.
The possibility of an asteroid, several tens of meters in diameter, striking the planet is concerning. Such an impact could create localized destruction similar to the Tunguska event of 1908, which flattened approximately 500 square miles (1,295 square kilometers) of Siberian forest.
To explore the changing odds provided by NASA and the potential threat posed by 2024 YR4, Ars consulted Robin George Andrews, author of the book “How to Kill an Asteroid.” The timing of this book’s publication coincides purposefully with current events.
When asked why the likelihood of impact is increasing, Andrews explained that the asteroid’s orbit has not been precisely determined due to the limited number of observations. However, as the asteroid moves away from Earth, some telescopes continue to monitor it, gradually refining the understanding of its orbital path around the sun. Although the likelihood has fluctuated, it has generally risen because uncertainties about the asteroid’s actual orbit have diminished, while Earth remains within this zone of uncertainty. As uncertainty decreases, Earth occupies a larger percentage of the remaining probable area, thus increasing the impact odds for now.
Andrews equated the orbit to a beam of light emitted from the asteroid, which narrows as the orbit is better understood. If Earth stays within this beam, it appears proportionally larger. Over time, with additional observations, Earth is expected to fall outside this trajectory, reducing the impact probability to zero. Conversely, the chance could approach 100 percent if other predictions prevail.
Regarding the asteroid’s potential for destruction, Andrews noted that any damage would be confined to an area about the size of a city. If the impact happens in an isolated part of the ocean or a desert, the consequences could be negligible. However, a direct hit on a city could cause extensive damage or destruction.
The asteroid’s mass is a critical factor in determining its impact potential. If the asteroid’s size is on the smaller margin of estimates, around 40 meters, its impact might resemble that of a small nuclear explosion in the atmosphere. At this size, unless it is predominantly composed of iron, the asteroid would likely disintegrate upon entering the atmosphere, resulting in an airburst. Such an explosion could cause substantial structural damage near the impact zone, while minor to moderate damage could occur over a wider area. An asteroid measuring 90 meters in diameter would release significantly more energy, akin to a large nuclear detonation, causing severe damage to a major city and destroying the area directly beneath the explosion.
