Characterizing Enigmatic Phaethon in the UV

(3200) Phaethon is a curious object: just 5 km in diameter, it is a near‐Earth asteroid that shows signs of being active and is the parent body of the Geminid meteor stream. Phaethon is a B‐class asteroid, as is Bennu, the target of the upcoming NASA OSIRIS‐REx mission. As a B‐class asteroid, Phaethon is linked with carbonaceous species and phyllosilicates; both of these types of materials exhibit diagnostic spectral features in the UV, yet Phaethon has not been observed deep in the UV. Phaethon's UV‐visible observations (near 400 nm) suggest spectral variability, spatially and/or temporally. In December 2017, Phaethon will be at its closest approach to Earth in decades. We propose 2 orbits of DD time to observe Phaethon for the first time using STIS deep in the UV to investigate the 400 nm region (potentially diagnostic of phyllosilicates), characterize its spectral shape deeper in the UV (to look for carbon signatures) and to understand the spectral character of Phaethon for better understanding of OSIRIS‐REx target Bennu. UV‐ visible laboratory measurements of candidate materials will be made through our recently‐selected NASA SSERVI program, for comparison with Phaethon STIS data.