Abstract The near-Earth asteroid (NEA) 2024 MK was discovered by the Asteroid Terrestrial-Impact Last Alert System on 2024 June 16, less than two weeks before its close approach to Earth at approximately 0. 76 lunar distance on 2024 June 29. NEAs that would cause significant regional damage upon impact are classified as potentially hazardous asteroids, and 2024 MK belongs to this category. In this study, the linear polarization degree of 2024 MK was measured using the 1. 6 m Pirka telescope at Hokkaido University’s Astronomical Observatory in Hokkaido, Japan, on 2024 June 29 and July 2, at solar phase angles (, Sun–target–observer) of approximately 26^ and 101^. We found that the high linear polarization degree of 2024 MK reached 35% at a solar phase angle of 101^, which is a characteristic typical of C-type asteroids. In contrast, spectroscopic observations conducted by McGraw et al. (2024, ApJ, 977, L25), before and after its close approach to Earth, revealed that 2024 MK exhibits a reflectance spectrum typical of S-type asteroids. We hypothesized that this discrepancy is due to the grain size and/or porosity of the regolith on 2024 MK’s surface. Although 2024 MK is an S-type asteroid, its surface appears to be composed of fine grains, a characteristic likely resulting from space weathering.
Doi et al. (Mon,) studied this question.
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