Thermal decomposition as the activity driver of near-Earth asteroid (3200) Phaethon

Near-Earth asteroid (3200) Phaethon exhibits activity during its perihelion passage at 0.14 au from the Sun and is the likely parent body of the annual Geminid meteor shower. Its low albedo and featureless B-type reflectance spectrum indicate a primitive composition, but a definitive meteorite analogue is currently indeterminate. Here we analyse a mid-infrared emissivity spectrum of Phaethon and find that it most closely matches the Yamato group (CY) of carbonaceous chondrites. The CY chondrites experienced aqueous alteration and recent thermal metamorphism in which extreme temperatures caused mineral decomposition, resulting in the production of gas species. Temperatures within Phaethon during its close approach to the Sun are conducive to the thermal decomposition of carbonates, iron sulfides and phyllosilicates that release CO 2 , S 2 and H 2 O gas, respectively. Spectral detection of these minerals strongly implies that gas release from mineral decomposition is capable of triggering dust ejection. The planned flyby of Phaethon by the DESTINY + spacecraft in 2028 will allow us to verify this hypothesis.