Comprehensive Study of Near-Earth Asteroid 2024 MK: Testing Planetary Encounters as a Source for Surface Refreshing

Abstract Near-Earth object 2024 MK was discovered on 2024 June 16, less than 2 weeks before it made a sub-lunar-distance close approach. This close approach provided an ideal opportunity to determine how planetary encounters affect asteroid surfaces in preparation for the numerous missions to (99942) Apophis during its close approach in 2029. We collected spectroscopic data before and after its close approach to determine if planetary encounters induce spectral changes due to surface refreshing. We used NASA’s Infrared Telescope Facility’s (IRTF) near-infrared spectrometer SpeX prism mode (0.7–2.5 μ m) to observe 2024 MK pre and postapproach. We also observed the asteroid before its close approach using Las Cumbres Observatory’s FLOYDS visible spectrometer and after its close approach using IRTF’s SpeX long-wavelength cross-dispersed short grating mode, resulting in full spectral coverage from 0.32 to 4.2 μ m. 2024 MK is an S-type asteroid that is compositionally most analogous to an L-ordinary chondrite. Spectral analysis of the 3 μ m region indicates no surficial water or hydroxide within the level of noise. Band parameter analysis of the pre and postapproach data shows the planetary encounter did not induce any significant spectral changes, suggesting that surface refreshing did not occur on a measurable scale. Similar studies of other targets at smaller encounter distances are required to determine if the lack of spectral changes on 2024 MK indicates it was not close enough to Earth to affect its surface or if the spectral similarity pre and postapproach instead indicates planetary encounters do not cause surface refreshing.