Mapping the Composition of Europa's Surface with the Europa Clipper Surface Dust Analyzer (SUDA)

Introduction: Europa’s surface is a dynamic interface where subsurface materials, radiation-processed surface chemistry, and exogenic inputs converge and are cycled back into the subsurface. Direct sampling of that material is central to assessing Europa’s habitability and evaluating the potential delivery of organic and geochemical species from the interior ocean to the surface¹. The Surface Dust Analyzer (SUDA) onboard Europa Clipper provides a uniquely powerful means of accessing this material through the compositional analysis of individual ice grains lofted from Europa’s surface during flyby using time-of-flight mass spectrometry (TOF-MS). Each particle to be analyzed by SUDA will carry a chemical fingerprint of the surface unit from which it originated, offering a window into the chemical composition of surface regions that cannot currently be directly sampled in situ, including evidence for salts, organics, and other chemical indicators of habitability.

Methods: Successfully interpreting these measurements requires understanding how each detection maps back to its surface provenance. We employ a dynamical modeling framework developed by Goode et al.^2,3 which couples an ejecta cloud model with Monte Carlo simulations of Europa Clipper flybys. For a specified flyby geometry, the local number density of ejecta along the trajectory are computed as a function of time, where SUDA detections are stochastic and are described by a Poisson distribution. At each simulated detection event, particle velocities are drawn from the probability density of the ejecta cloud at the spacecraft location. The resulting vector is then propagated backward under Europa’s gravity to determine the corresponding surface launch point. Repeating this procedure over many Monte Carlo simulations yields a statistical distribution of launch sites for a given flyby, enabling the fraction of detections whose origin lies within a predefined surface region to be computed. Associating features within SUDA’s mass spectra with these launch locations allows chemical compositions determined for individual ice grains to be probabilistically linked to compositionally distinct surface features. This framework provides quantitative measures of both the expected number of detections for a given surface feature as a function of feature size and flyby altitude, and the confidence with which a given chemical composition can be attributed to a particular geological feature.

Acknowledgements: This work was supported by NASA through the Europa Clipper project. 

References: 1. Vance, S. et al. (2023). Space Sci. Rev. 219, 81. 2. Goode, W. et al. (2021). Planet. Space Sci. 208, 105343. 3. Goode, W. et al. (2023). Planet. Space Sci. 227, 105633.