Utilizing the Gemini Multi-Object Spectrograph (GMOS) aboard the Gemini South telescope, astronomers have established that the recently identified near-Earth asteroid 2024 YR4 represents one of the most substantial celestial bodies encountered in recent history with the potential for lunar impact. Evidence strongly suggests its genesis lies within the Solar System’s principal asteroid belt. These groundbreaking revelations are slated for publication in the esteemed 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.
The celestial object, designated 2024 YR4, was initially detected by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on December 27, 2024.
At the juncture of its discovery, the asteroid executed a close transit of Earth, maintaining a proximity of merely 0.017 AU (astronomical units).
By January 2025, precisely one month subsequent to its identification, 2024 YR4’s projected trajectory surpassed the 1% probability threshold for a future Earth impact, as established by the International Asteroid Warning Network (IAWN), with a potential collision date set for December 22, 2032. Subsequent rigorous analysis, however, recalibrated the probability of an Earth impact to below 1% by February.
Although the asteroid is anticipated to bypass Earth during its current transit, a residual probability, albeit small, persists for a potential collision with the Moon.
Driven by an interest in thoroughly characterizing this now prominent asteroid, Eureka Scientific astronomer Bryce Bolin and his associates employed the Gemini South telescope to procure imagery of 2024 YR4 across a spectrum of electromagnetic wavelengths.
An in-depth examination of the asteroid’s lightcurve afforded the research team the capability to ascertain its constituent materials, orbital parameters, and three-dimensional morphology.
“The observations obtained with Gemini South were instrumental in furnishing a critical component for discerning the attributes of 2024 YR4,” stated Dr. Bolin.
“Investigating this particular asteroid proved profoundly significant in advancing our comprehension of the population of Earth-crossing bodies that possess the potential for impact and are, as yet, inadequately understood.”
The data aggregated from the lightcurve analyses indicate that 2024 YR4 is most probably an S-type asteroid, implying a composition predominantly rich in silicates.
The reflective signature further suggests an approximate diameter ranging from 30 to 65 meters (98 to 213 feet), positioning it as one of the larger entities in recent memory with a potential for impacting the lunar surface.
While remaining improbable, should an impact with the Moon occur, the asteroid would present an unparalleled opportunity to scrutinize the correlation between an asteroid’s dimensions and the resultant crater size—a hitherto unquantified relationship.
The investigative process also unveiled that the asteroid exhibits a highly accelerated rotation period, approximately one revolution every 20 minutes, in addition to an unconventional, flattened shape akin to a hockey puck.
“This discovery was rather unanticipated, given that the prevailing hypothesis is that most asteroids are shaped more like potatoes or spinning tops rather than flattened discs,” commented Dr. Bolin.
Based upon the ascertained orbital characteristics, the astronomical researchers have concluded that 2024 YR4 most likely originated from the main asteroid belt, with a substantial likelihood of its current near-Earth orbit being a consequence of gravitational perturbations induced by Jupiter.
Its retrograde spin orientation suggests a potential inward migration from the inner regions of the main belt, thereby contributing to our growing knowledge base concerning the evolutionary pathways of diminutive asteroids and their trajectories towards Earth-crossing orbits.
_____
Bryce T. Bolin et al. 2025. The discovery and characterization of Earth-crossing asteroid 2024 YR4. ApJL, in press; arXiv: 2503.05694v2
