'City-killer' asteroid that might hit moon has 'unexpected' shape, astronomers say

Scientists have revealed the unusual shape of a large asteroid with the potential to smack into the moon in the year 2032, according to new research.

Asteroid 2024 YR4 sparked a flurry of interest earlier this year after NASA determined there was a chance it could hit Earth. The risk of an Earth impact has since dropped to zero, but there's still a slim chance 2024 YR4 could hit the moon in 2032 — 3.8% likelihood as of early April.

A team of astronomers recently studied the asteroid in more detail using the Gemini South telescope in Chile. The researchers found that 2024 YR4 likely came from the asteroid belt between Mars and Jupiter and has an unusually flat, disk-like shape, similar to a hockey puck, according to a statement released by the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory (NOIRLab).

"This find was rather unexpected since most asteroids are thought to be shaped like potatoes or toy tops rather than flat disks," study lead author Bryce Bolin, a research Scientist at Eureka Scientific, a California-based astrophysics and astronomy research corporation, said in the statement.

The researchers posted their findings to the preprint database arXiv, and will soon publish them in The Astrophysical Journal Letters.

Related: 'Just the tip of the iceberg': Why risky asteroids like 2024 YR4 will pester Earth for decades to come

Astronomers discovered the asteroid 2024 YR4 in December 2024, hence the "2024" in its name. In February, the likelihood of 2024 YRY hitting Earth in 2032 rose to 1 in 32, or 3.1%, which was the highest impact probability NASA had ever recorded for a space object of 2024 YR4's size or larger.

However, astronomers always expected the threat level to drop once they learned more about 2024 YRY's trajectory. Within days, the likelihood plummeted to effectively zero, and has a 0.00078% chance of hitting Earth in 2032 at the time of writing. However, there remains a risk for the moon — not that the asteroid would significantly damage the moon even if it does hit.

For the new study, researchers captured images of the space rock at different wavelengths of light. The team used 2024 YRY's pattern of light output over time, or lightcurve, to study the asteroid's shape, composition and orbital characteristics, according to the statement.

From the rock's reflective pattern, the researchers concluded that 2024 YR4 is likely an S-type asteroid, which means it is rich in silicates — a class of minerals that includes quartz. The team also determined that the asteroid is rotating very fast, about once every 20 minutes, and estimated its size to be 98 to 213 feet (30 to 65 meters) wide, according to the study.

Researchers have been trying to accurately calculate the size of 2024 YR4 since its discovery, and this latest approximation is similar to previous estimates. Recent data from the James Webb Space Telescope suggested it could be slightly larger, 174 to 220 feet (53 to 67 meters), Live Science previously reported.

2024 YR4 is one of the largest objects in recent history with the potential to strike the moon, according to the statement. Back when there was a rising likelihood of 2024 YR4 hitting Earth, it was dubbed a potential "city killer" because it was large enough to wipe out a major city.

While unlikely, a lunar impact would provide researchers with an unprecedented opportunity to study how the size of an asteroid relates to the size of the crater it creates, according to the statement.