The Discovery and Characterization of Earth-crossing Asteroid 2024 YR₄

Abstract We describe observations and physical characteristics of Earth-crossing asteroid 2024 YR 4 , discovered on 2024 December 27 by the Asteroid Terrestrial-impact Last Alert System. The asteroid has semimajor axis a = 2.52 au, eccentricity e = 0.66, inclination i = 3 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 41, and a ∼0.003 au Earth minimum orbit intersection distance. We obtained g -, r -, i -, and Z -imaging with the Gemini South/Gemini Multi-Object Spectrograph on 2025 February 7 and Y and J imaging with the Keck/Multi-Object Spectrometer for Infrared Exploration on 2025 February 12. We measured a g − i spectral slope of 13% ± 3%/100 nm and color indices g −​ r = 0.70 ± 0.10, r − i = 0.25 ± 0.06, i − Z = −0.27 ± 0.10, and Y − J = 0.41 ± 0.10. 2024 YR 4 has a spectrum that best matches R-type and Sa-type asteroids and a diameter of ∼30–65 m using our measured absolute magnitude of 23.9 ± 0.3 mag and assuming an albedo of 0.15–0.4. The lightcurve of 2024 YR 4 shows ∼0.4 mag variations with a rotation period of ∼1170 s. We use photometry of 2024 YR 4 from Gemini and other sources taken between 2024 December to 2025 February to determine the asteroid’s spin vector and shape, finding that it has an oblate, ∼3:1 axial ratio and a pole direction of λ , β = ∼ 42 ∘ , ∼−25 ∘ . Finally, we compare the orbital elements of 2024 YR 4 with the near-Earth object population model and find that its most likely sources are resonances between the inner and central Main Belt.