On the in-situ detectability of Europa's water vapour plumes from a flyby mission

TL;DR

This study assesses the potential for in-situ detection of Europa's water vapor plumes during flyby missions, demonstrating that even low flux plumes can be detected with high confidence using current instrumentation.

Contribution

It introduces a Monte Carlo simulation approach to evaluate the detectability of Europa's water plumes and analyzes the influence of plume geometry and background separation.

Findings

Detection of low flux plumes is feasible with high signal-to-noise ratios.

Plume geometry does not significantly affect detectability.

Separation of plume signals from exospheric background depends on exosphere density knowledge.

Abstract

We investigate the feasibility of detecting water molecules (H2O) and water ions (H20+) from the Europa plumes from a flyby mission. A Monte Carlo particle tracing method is used to simulate the trajectories of neutral particles under the influence of Europa's gravity field and ionized particles under the influence of Jupiter's magnetic field and the convectional electric field. As an example mission case we investigate the detection of neutral and ionized molecules using the Particle Environment Package (PEP), which is part of the scientific payload of the future JUpiter ICy moon Explorer mission (JUICE). We consider plumes that have a mass flux that is three orders of magnitude lower than what has been inferred from recent Hubble observations (Roth et al., 2014a). We demonstrate that the in-situ detection of H2O and H2O+ from these low mass flux plumes is possible by the instruments with large margins with respect to background and instrument noise. The signal to noise ratio for neutrals is up to ~5700 and ~33 for ions. We also show that the geometry of the plume source, either a point source or 1000 km-long crack, does not influence the density distributions, and thus, their detectability. Furthermore, we discuss how to separate the plume-originating H2O and H2O+ from exospheric H2O and H2O+ . The separation depends strongly on knowledge of the density distribution of Europa's exosphere.