Moon-Threatening Asteroid Has Weird Shape, Scientists Say

Forbes

09-04-2025

Asteroid 2024 YR4's star has faded when it comes to the general public, but scientists are pumped to be learning more about it. The space rock reached celebrity status earlier this year when initial data showed it had a small chance of striking Earth in 2032. Further observations ruled out the scary scenario—but the moon is still in play. Now we know more about the famous asteroid.
Scientists teamed up to study the asteroid and discovered some surprising information about its possible origin and shape. 'Studying this asteroid was vitally important in understanding the population of Earth crossers that have the potential to be Earth impactors and are poorly understood,' said astronomer Bryce Bolin of Eureka Scientific in a statement on April 8. Bolin is the lead author of a paper on the asteroid set to be published in 'The Astrophysical Journal Letters.'
Bolin and his colleagues used the Gemini South telescope in Chile to image the asteroid. 'Detailed analysis of the asteroid's lightcurve (pattern of light output in time) allowed the team to determine its composition, orbital characteristics and 3D shape,' the United States National Science Foundation National Optical-Infrared Astronomy Research Laboratory said.
The asteroid likely came from the solar system's main asteroid belt, a region between Mars and Jupiter. It's quite the hot hangout for asteroids, with NASA estimating it contains between 1.1 and 1.9 million asteroids larger than 0.6 miles in diameter—and many more smaller ones. 'We are a bit surprised about its origin in the central main asteroid belt, which is a location in the asteroid belt that we did not think many Earth-crossing asteroids could originate from,' said Bolin.
The asteroid has a fast rotation of only about 20 minutes. The data shows YR4 has a shape reminiscent of a hockey puck. That qualifies as another surprise. 'This find was rather unexpected since most asteroids are thought to be shaped like potatoes or toy tops rather than flat disks,' Bolin said.
The W. M. Keck Observatory in Hawaii also got in on the asteroid fun and contributed data to the team's paper. Keck's ability to see in infrared helped the researchers study the asteroid's composition. It's likely made of solid rock. Larger asteroids are often called 'rubble piles' since they're conglomerates of rock fragments. Asteroid YR4 may have once been a boulder on one of those larger asteroids.
Whether an asteroid is solid or a rubble pile makes a difference when it comes to planetary defense. That's crucial information that could help with planning a mission like NASA's DART test. DART involved crashing a spacecraft into an asteroid to alter its orbit.
Asteroid 2024 YR4 was first spotted in December. There had been some uncertainty about the asteroid's size, but NASA's James Webb Space Telescope turned its powerful instruments on the rock and found it measured in at about 200 feet wide, roughly the size of a 15-story building. That's within the initial estimates of between 130 and 300 feet wide.
At one point, early observations suggested 2024 YR4 had a 3.1% chance of impacting Earth. As more data came in, researchers revised that down to near zero. However, the asteroid now has a 3.8% chance of impacting the moon on Dec. 22, 2032. Don't worry about the moon, though. 'In the small chance that the asteroid were to impact, it would not alter the moon's orbit,' NASA said in a statement on April 2.
If YR4 does smack into the moon, it will be a thrilling time for astronomers. It would 'provide an unprecedented opportunity to study the relationship between the size of an asteroid and the size of its resulting impact crater—a previously unknown quantity,' NOIRLab said.
Researchers aren't done with YR4 yet. Webb is set to check it out again in late April or early May, even as the asteroid becomes too far away and too faint for ground-based telescopes to make observations.
Asteroid 2024 YR4 is no longer a big mystery. Its composition, size, shape and origin are better understood. We can also breathe a sigh of relief that it won't be barreling into our planet in 2032. The moon, however, may need to brace for impact. We'll know even more as scientists continue to study the space rock.