Asteroid 2024 YR4 that has alarmed scientists has arrived to Earth from an unexpected place

A paper has been published on arXiv.org, which provides the first comprehensive assessment of asteroid 2024 YR4, discovered near Earth on December 27, 2024. The article has been prepared for publication in one of the most prestigious astronomical journals, The Astrophysical Journal Letters. Asteroid 2024 YR4 has become the most serious threat to our planet in the entire history of observations of near-Earth objects, so it has attracted unprecedented interest.

An artist’s impression of asteroid 2024 YR4. Image Credit: W. M. Keck Observatory/Adam Makarenko

During the first study of the object 2024 YR4, the degree of its potential danger to the planet increased from 1% to 3%. Since the asteroid could reach 90 meters in size, its fall to the surface of the Earth would destroy all life within a radius of up to 50 km. The collision could have occurred on December 22, 2032 – this is the day on which the asteroid, according to calculations, could dangerously approach the planet to the point of crossing trajectories.

Asteroid 2024 YR4 was observed using multiple ground-based telescopes. In February, the James Webb Space Telescope joined in. It was the latter that allowed the object’s dimensions to be determined more accurately — from 53 to 67 meters. This data is not presented in the published paper: the authors used telescopes from the W. M. Keck and Gemini South observatories. According to their observations, the asteroid’s dimensions are 30–65 meters, which is close to Webb’s data.

Based on the brightness of the asteroid, scientists have concluded that it has an irregular, flattened shape and makes a full rotation in 20 minutes. The asteroid resembles a hockey puck. Its shape indicates its composition and origin: researchers believe that 2024 YR4 is a rocky, not carbon (loose) object. This is important because the choice of method for deflecting an asteroid depends on its structure – ramming a loose body may be ineffective.

Model of the shape of asteroid 2024 YR4 based on photometric measurements

The structure and composition of the asteroid revealed its likely origin, and it surprised scientists. Such objects typically form and reside in the main asteroid belt between the orbits of Mars and Jupiter. Jupiter’s gravity usually shields Earth from such bodies, keeping them within the main belt. However, asteroid 2024 YR4 managed to escape this gravitational protection, causing alarm among both scientists and the public.

Fortunately, new observations allow us to dismiss the threat from 2024 YR4 as insignificant, although the chance of it colliding with the Moon is quite high and exceeds 3%. But this is only to the advantage of terrestrial science. In the event of an impact on the Moon, it will be possible to conduct a valuable seismological experiment to study its interior, as well as in practice, with high accuracy, assess the consequences of an asteroid impact on its surface.