3:30 PM - 5:00 PM
[PCG19-P06] Europa's surface composition uncovered by the plasma irradiation experiment for NaCl samples
Keywords:Europa, Icy satellite, plasma irradiation experiment, tenuous atmosphere
Jupiter’s icy moon Europa potentially has the interior water ocean with the habitable environment for life. Elemental and molecular compositions of Europa's surface materials tell us that of the interior ocean because the materials may be transported between the ocean and surface. Europa's surface materials are continuously irradiated with Jovian plasmas, UV, and micrometeorites from the space. The irradiated energy drives the space weathering process. In particular, Jovian plasmas are dominant energy sources of the space weathering at Europa. Europa’s materials are sputtered from the surface by the plasma irradiation and create the tenuous atmosphere. The residual un-sputtered surface material may change in the elemental and molecular compositions by the irradiation. However, since this process comprises complex physics and chemistries that are hard to theoretically estimate, it has been a big unsolved problem to quantitatively associate the tenuous atmosphere with the surface compositions accompanying the space weathering.
Here we present the laboratory experiment that quantitatively associates the tenuous atmospheric sputtering with the surface composition at Europa for the first time. We also measured the number of the sputtered Na and Cl particles by the mass spectrometer during the irradiation experiment. We irradiated energetic H2+,O2+ ions and electrons at 10 keV with a fluence of 5e+18 /cm2 to NaCl samples to model the sputtering by Jupiter’s plasma irradiation to Europa’s surface materials. We found that the electron more efficiently sputters Europa’s surface than the ions under Europa’s environment. For example, the total Na production rate by the hydrogen and oxygen ion irradiations is estimated to be 1.1e+6 /cm^2/s, while that by the electron irradiation is to be 2.7e+5 /cm^2/s. We also found that the yield of Cl (8.7e-1 /incident particle) is greater than that of Na (2.8e-2 /incident particle). These results suggest that the surface NaCl is decomposed predominantly by the electron irradiation and forms the resultant tenuous atmosphere, while on Europa’s surface Na is concentrated more effectively than Cl because of the small volatility of Na.
We estimated the column density of Europa’s Na atmosphere by our 0-dimensional atmospheric model with constraints on the sputtering yield obtained by our irradiation experiment. The estimated column density is found to be comparable with that estimated by the ground-based telescope observation of Na atmosphere (Brown and Hill 1996), which corresponds to the total Na atmospheric mass of 770 kg.
Our Na atmospheric model assumed 100% NaCl on Europa’s surface. The estimated column density is consistent with the ground-based observational one, which suggests a high concentration of NaCl on Europa’s surface. The interior ocean brain is likely concentrated during the upwelling process or by the space weathering after geysering to the surface.
We are currently extending the Na atmosphere model to 1-3 dimensions to estimate the spatial distribution of the Na rarefied atmosphere, taking into account particle motion under Europa gravity. We plan to constrain the surface NaCl concentration with higher accuracy by estimating the Na rarefied atmosphere distribution with the developed model and comparing it with actual atmospheric distribution observations [Brown and Hill 1996], using the irradiation experiment results of this study as boundary conditions. This presentation will present the current status.
Here we present the laboratory experiment that quantitatively associates the tenuous atmospheric sputtering with the surface composition at Europa for the first time. We also measured the number of the sputtered Na and Cl particles by the mass spectrometer during the irradiation experiment. We irradiated energetic H2+,O2+ ions and electrons at 10 keV with a fluence of 5e+18 /cm2 to NaCl samples to model the sputtering by Jupiter’s plasma irradiation to Europa’s surface materials. We found that the electron more efficiently sputters Europa’s surface than the ions under Europa’s environment. For example, the total Na production rate by the hydrogen and oxygen ion irradiations is estimated to be 1.1e+6 /cm^2/s, while that by the electron irradiation is to be 2.7e+5 /cm^2/s. We also found that the yield of Cl (8.7e-1 /incident particle) is greater than that of Na (2.8e-2 /incident particle). These results suggest that the surface NaCl is decomposed predominantly by the electron irradiation and forms the resultant tenuous atmosphere, while on Europa’s surface Na is concentrated more effectively than Cl because of the small volatility of Na.
We estimated the column density of Europa’s Na atmosphere by our 0-dimensional atmospheric model with constraints on the sputtering yield obtained by our irradiation experiment. The estimated column density is found to be comparable with that estimated by the ground-based telescope observation of Na atmosphere (Brown and Hill 1996), which corresponds to the total Na atmospheric mass of 770 kg.
Our Na atmospheric model assumed 100% NaCl on Europa’s surface. The estimated column density is consistent with the ground-based observational one, which suggests a high concentration of NaCl on Europa’s surface. The interior ocean brain is likely concentrated during the upwelling process or by the space weathering after geysering to the surface.
We are currently extending the Na atmosphere model to 1-3 dimensions to estimate the spatial distribution of the Na rarefied atmosphere, taking into account particle motion under Europa gravity. We plan to constrain the surface NaCl concentration with higher accuracy by estimating the Na rarefied atmosphere distribution with the developed model and comparing it with actual atmospheric distribution observations [Brown and Hill 1996], using the irradiation experiment results of this study as boundary conditions. This presentation will present the current status.