Astronomers using the Gemini Multi-Object Spectrograph (GMOS) on the Gemini South telescope have determined that the recently-discovered near-Earth asteroid 2024 YR4 is one of the largest objects in recent history that could impact the Moon, and that it likely originated in the Solar System’s main asteroid belt. Their findings will be published in the Astrophysical Journal Letters.
This image of 2024 YR4 was captured with the Gemini South telescope in Chile, one half of the International Gemini Observatory, partly funded by NSF and operated by NOIRLab. Image credit: International Gemini Observatory / NOIRLab / NSF / AURA / M. Zamani.
2024 YR4 was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on December 27, 2024.
At the time, the asteroid made a close approach to Earth, passing at a distance of just 0.017 AU (astronomical units).
In January 2025, one month after its discovery, 2024 YR4 rose above the International Asteroid Warning Network (IAWN) notification threshold of 1% probability of a future impact with Earth, projected for 22 December 2032. With further analysis, the Earth impact probability then dropped below 1% in February.
While the asteroid will miss Earth during this encounter, there remains a few percent chance it could hit the Moon instead.
Interested in characterizing the now famous asteroid, Eureka Scientific asrtonomer Bryce Bolin and colleagues used the Gemini South telescope to capture images of 2024 YR4 in multiple different wavelengths.
Detailed analysis of the asteroid’s lightcurve allowed the team to determine its composition, orbital characteristics and 3D shape.
“Our observations with Gemini South provided a crucial piece of the puzzle in determining 2024 YR4’s characteristics,” Dr. Bolin said.
“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.”
The information gathered from the lightcurves indicates that 2024 YR4 is likely an S-type asteroid, meaning it has a composition rich in silicates.
The reflective pattern also suggests a diameter of about 30-65 m (98-213 feet), making it one of the largest objects in recent history that could impact the Moon.
While it remains unlikely, if it does impact the Moon the asteroid will 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.
The analysis also revealed that the asteroid has a rapid rotation period of approximately one rotation per 20 minutes, as well as an unusual hockey-puck-like shape
“This find was rather unexpected since most asteroids are thought to be shaped like potatoes or toy tops rather than flat disks,” Dr. Bolin said.
Based on these orbital characteristics, the astronomers determined that 2024 YR4 most likely originated from the main asteroid belt, with a high probability of being perturbed into its current near-Earth orbit by gravitational interactions with Jupiter.
Its retrograde spin direction suggests it may have migrated inward from the central main belt region, adding to our understanding of how small asteroids evolve and reach Earth-crossing trajectories.
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Bryce T. Bolin et al. 2025. The discovery and characterization of Earth-crossing asteroid 2024 YR4. ApJL, in press; arXiv: 2503.05694v2
