[M-IS18] 惑星火山学

[MIS18-05] CO₂ distribution indicates a recent interaction between the surface and the interior on Europa

*門屋 辰太郎¹、関根 康人¹、小玉 貴則¹ (1.東京科学大学 地球生命研究所)

キーワード：エウロパ、CO2

JWST’s observations reveal that CO₂ accumulates on Europa’s geologically young equatorial terrains, known as Tara Regio and Powys Regio (Trumbo & Brown, 2023; Villanueva et al., 2024). The heterogeneous distribution suggests an endogenic supply of CO₂, implying active surface-interior interactions. However, the timescale of this process remains uncertain. This study employs Monte Carlo simulations to constrain the timescale of the observed CO₂ distribution on Europa. We modeled CO₂ transport via sublimation, ballistic motion, and adsorption, with loss processes including ionization and dissociation. Due to temperature-dependent sublimation rates, CO₂ preferentially migrates poleward, on a timescale of < 10 days. Given CO₂ loss via photoionization induced by solar ultraviolet radiation, the lifetime of CO₂ is estimated to be ~ 4 years (e.g., Trumbo & Brown, 2023). Thus, CO₂ should accumulate at high latitudes before being lost. If this were the case, the JWST observations would have had to occur within 10 days of CO₂ supply initiation, though this scenario is unlikely. This discrepancy suggests that additional CO₂ loss mechanisms, such as ionization and/or dissociation induced by impacts of high-energy particles, may reduced CO₂ lifetimes by at least two orders of magnitude (< 10 days). Under these conditions, CO₂ is lost before reaching high latitudes, leading to steady-state accumulation near equatorial sources, consistent with JWST data. If so, Europa’s CO₂ would dissipate rapidly (~ 10 days) following supply cessation. The observed CO₂ distribution in either scenario strongly suggests ongoing CO₂ eruptions from Europa’s interior.