Sodium Volatilization as a Potential Driver of Activity on Asteroid (3200) Phaethon
Joseph Masiero1, Bjorn Davidsson2, Yang Liu2, Kelsey Moore2, Michael Tuite2 
1Caltech/IPAC, Pasadena, CA, 2NASA JPL/Caltech, Pasadena, CA

Small bodies of the Solar system that contain subsurface volatiles will become active when those volatiles have heated sufficiently to sublimate.  Most cometary objects show activity behaviors consistent with the volatilization of carbon monoxide, carbon dioxide, or water ices.  Other active objects can be traced to impacts or spin up. There are, however, unusual cases of objects showing activity that cannot be explained by these processes.  The active asteroid (3200) Phaethon is one such object, showing brief periods of activity near perihelion and being associated with the Geminid meteor shower dust stream. We present recent results from investigations of the volatility of sodium at temperatures similar to what Phaethon experiences during its perihelion.  We describe our numerical simulations that show the potential for sodium just below Phaethon's surface to be heated sufficiently to volatilize.  We also discuss laboratory experiments heating meteoritic materials to these temperatures to constrain the sodium loss that would be experienced from analogous materials during a diurnal cycle on Phaethon.