Formation and Survival of Complex Organic Molecules in the Jovian Circumplanetary Disk

Abstract

Europa, Ganymede, and Callisto are key targets in the search for habitability due to the potential presence of subsurface oceans. Detecting complex organic molecules (COMs), essential for prebiotic chemistry, is crucial to assessing their potential. Though COMs remain undetected on these moons, ESA's JUICE and NASA's Europa Clipper missions aim to fill this gap with their science payloads. This study explores the formation and transport of COMs within Jupiter's circumplanetary disk (CPD), a critical environment for the formation of the Galilean moons. Using a time-dependent model that couples the evolving CPD structure with the dynamics of icy particles of varying sizes and release times, we assess two primary COM formation pathways: thermal processing of ices and UV photochemistry. The results indicate that heating, particularly of NH3:CO2 ices, occurs efficiently before substantial irradiation, making it the dominant pathway for COM formation in the Jovian CPD. However, the relative efficiencies of these two processes are governed by particle density, disk viscosity, accretion rate, and UV flux, which collectively determine drift timescales and exposure to favorable thermodynamic environments. Existing models indicate that Europa's accretion was relatively cold and prolonged, possibly allowing some COMs to survive incorporation, whereas Ganymede and Callisto likely formed under even cooler conditions conducive to preserving COM-rich material. These results highlight the potential inheritance of complex organics by the Galilean moons and offer a framework for interpreting upcoming compositional data from JUICE and Europa Clipper.

Figures (6)

• Figure 1: Temperature profiles of the CPD at $t$ = 50, 100, 150, and 200 kyr of its evolution. The formation of COMs by thermal processing occurs in the temperature range from 80 K (blue dashed line) to 260 K (red dashed line). At 150 kyr of evolution, a cold region appears in the model, with temperatures too low to support COM formation by thermal processing.
• Figure 2: Radial and vertical trajectory of a 100 $\mu$m particle released at one scale height above the midplane of the CPD at the distance of 115 $R_{\rm Jup}$, with an initial release time $t_{\rm 0}$ = 100 kyr, in the case of our nominal model.
• Figure 3: Top four panels: median radial trajectories of 1 $\mu$m, 100 $\mu$m, 1 mm, and 1 cm particles as a function of time in our nominal CPD model. The particles are released one scale height above the CPD midplane at $t_{\rm 0}$ = 50 kyr. Median trajectories are shown at 10 $R_{\rm jup}$ intervals in the midplane, spanning from 5 to 135 $R_{\rm Jup}$ in the CPD. Dotted lines highlight portions of these trajectories that intersect the COM formation zone via thermal processing in the CPD. The horizontal dotted-dashed line indicates the location of $R_c$. Bottom four panels: average irradiation experienced by particles migrating inward within the CPD, shown as a function of time in the nominal CPD model. The two horizontal lines represent the irradiation thresholds discussed in the text, while the dashed curves indicate the fraction of trajectories where CH$_3$OH is in the vapor phase. T22 and B08 refer to the irradiation thresholds experimentally derived by tenelanda2022 and bossa2008, respectively.
• Figure 4: Same as Fig. \ref{['fig:50kyr']}, but with particles released at $t_{\rm 0}$ = 100 kyr.
• Figure 5: Same as Fig. \ref{['fig:50kyr']}, but with particles released at $t_{\rm 0}$ = 150 kyr.