Thermal Evolution of the Phaethon–Geminid Stream Complex

The thermal evolution of the Geminid meteor stream and the Phaethon–Geminid stream Complex (PGC) are summarized. Sodium contents of Geminid meteor streams are altered thermally, perhaps during orbital motion in interplanetary space due to the short perihelion distance of the orbit (q ∼ 0.14 AU). However, the temperature of meteoroids is less than the sublimation temperature of Na in alkali silicates, suggesting that the parent body 3200 Phaethon itself might have suffered from the thermal processing. On the other hand, a breakup event on PGC parent is suggested by the existence of dynamically associated asteroids (Phaethon, 2005 UD and 1999 YC) sharing pristine features (C, B types). A possible mechanism behind the breakup is the sublimation of ice inside the PGC parent due to its thermal evolution. It is tempting to guess that the PGC parent might be evolved dynamically from the outer part of the main asteroid belt where the residence of ice-rich asteroids (main belt comets) into current PGC-like orbit.