演講資訊

摘要：

The size distribution of fragments is one of the few observables that records how a small body breaks up, yet it is usually measured in only one size range, by one technique, for one process. In this talk I combine three of our recent studies that cover fragments from sub-millimetre to centimetre sizes and three different modes of disruption. (1) Lunar impact flashes. Twenty flashes observed during the 2018 and 2025 Geminids reveal centimetre-sized meteoroids from (3200) Phaethon, with an excess of large particles (mass index s = 1.76 ± 0.17). (2) A meteor cluster. Twenty-four meteors observed over Hawai'i in 2021 came from a meteoroid that broke up gently (ejection velocities < 1 m/s) about five days before entry. (3) Hypervelocity impact experiments. At ~7 km/s⁻, high-speed spectroscopy measures the size, spin and temperature of hot sub-millimetre ejecta. Their size distribution (q = 1.70) matches the NASA breakup model for space debris but is much shallower than that of the boulders on Itokawa, Ryugu and Bennu. I discuss to what extent this sequence reflects the fragmentation mechanism (cratering, thermal stress, catastrophic disruption) rather than observational selection, regolith burial or later evolution. I also discuss what joint observations, such as lunar impact flash and meteor monitoring from Taiwan and Japan, could add.