Abstract
Hypervelocity impacts on anhydrite (CaSO4) induce degassing of SO2. Degassed SO2 is released into the atmosphere of planets and is thought to play an important role in controlling the surface environment of planets. For example, sulfate aerosols produced from SO2 were thought to block the sunlight and invoke the mass extinction at 65 Ma Cretaceous/Tertiary boundary (K/T boundary). However, it is suggested that these SO2 back-reacts with CaO into CaSO4 (i.e., SO2+1/2O2+CaO->CaSO4) in impact-induced vapor clouds soon after degassing. In this case, the amount of SO2 released into the atmosphere decreases.
Impact-induced vapor clouds larger than the atmospheric scale height cool by adiabatic expansion and reach the temperature-pressure state where the back-reaction of SO2 and CaO is thermodynamically possible. However, if the reaction rate is slower than the cooling rate of vapor clouds, the back-reaction is inhibited kinetically.
In this study we determine the reaction rate of the back-reaction SO2+1/2O2+CaO->CaSO4. Then, we compare the reaction rate and the cooling rate of the impact-induced vapor clouds to examine whether the back-reaction really occur. The results show that the back-reaction occurs in K/T-scale vapor clouds and that more than 40% of SO2 are consumed.
