Gemini South Observes Shape and Origin of Near-Earth Asteroid 2024 YR4

Gemini South Observes Shape and Origin of Near-Earth Asteroid 2024 YR4

April 8, 2025

Astronomers have determined 3D shape and likely origins of house-sized asteroid that could potentially impact the Moon

Using observations from the Gemini South telescope in Chile, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation and operated by NSF NOIRLab, astronomers have constructed a 3D representation of the newly discovered near-Earth asteroid 2024 YR4. The team determined that the unusually-shaped rock is one of the largest objects in recent history that could impact the Moon, and that it likely originated from the main asteroid belt.

2024 YR4 was first detected on 27 December 2024 by the Asteroid Terrestrial-impact Last Alert System (ATLAS). At the time, the asteroid made a close approach to Earth, passing at a distance of just 0.017 astronomical units (approximately 2.5 million kilometers, or 1.5 million miles). Initial uncertainty regarding its trajectory warranted further investigation, leading astronomers to secure critical special Director's Discretionary Time on Gemini South for follow-up observations using the Gemini Multi-Object Spectrograph (GMOS) on 7 February 2025.

In late 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. This potential threat gained international attention among the public and the media. With further analysis, the Earth impact probability then dropped below 1% in late 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, the team of astronomers, led by Bryce Bolin of Eureka Scientific, used the Gemini South telescope in Chile, one half of the International Gemini Observatory, partly funded by the U.S. National Science Foundation and operated by NSF NOIRLab, to capture images of it in multiple different wavelengths. 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.

“Our observations with Gemini South provided a crucial piece of the puzzle in determining 2024 YR4’s characteristics,” says Bolin, lead author of the paper to appear in The Astrophysical Journal Letters. “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.”

This 3D render of asteroid 2024 YR4 was made based on data obtained on 7 February 2025 with the Gemini South telescope. The surface features are artistic interpretation.

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 meters (98–213 feet) [1], 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,” says Bolin.

Based on these orbital characteristics, the team 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.

“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,” says Bolin.

The results of this study demonstrate the power of rapid-response follow-up with ground-based facilities like Gemini South in planetary defense efforts [2], allowing astronomers to quickly assess and categorize newly discovered near-Earth objects.

“Understanding the properties and origins of near-Earth asteroids is proving critical for understanding the risk of collisions between our planet and major bodies in crossing orbits,” says Martin Still, NSF program director for the International Gemini Observatory. “The Gemini telescopes and other astronomical observatories are vital tools for planetary defense.”

More Information

This research is presented in a paper titled “The discovery and characterization of Earth-crossing asteroid 2024 YR4” to appear in The Astrophysical Journal Letters.

The team is composed of Bryce T. Bolin (Eureka Scientific), Josef Hanuš (Charles University), Larry Denneau (University of Hawai‘i at Mānoa), Roberto Bonamico (BSA Osservatorio), Laura-May Abron (Griffith Observatory), Marco Delbo (Université Côte d'Azur; University of Leicester), Josef Ďurech (Charles University), Robert Jedicke (University of Hawai‘i at Mānoa), Leo Y. Alcorn (W. M. Keck Observatory), Aleksandar Cikota (International Gemini Observatory/NSF NOIRLab), Swayamtrupta Panda (International Gemini Observatory/NSF NOIRLab), and Henrique Reggiani (International Gemini Observatory/NSF NOIRLab).

NSF NOIRLab, the U.S. National Science Foundation center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), NSF Kitt Peak National Observatory (KPNO), NSF Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and NSF–DOE Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. 

The scientific community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence of I’oligam Du’ag to the Tohono O’odham Nation, and Maunakea to the Kanaka Maoli (Native Hawaiians) community.

Links

Contacts