Investigating Europa's Plasma Environment from radar Sounding
Abstract
Investigation of Europa's icy crust from the ocean to its surface and atmosphere is a programmatic goal for the Europa Space Agency (ESA) and the National Aeronautics and Space Administration (NASA), achieved through the future JUpiter ICy moons Explorer (JUICE) and Europa Clipper missions, respectively. The ability to directly probe the subsurface makes radar sounders key instruments of those two missions for ice-ocean detection down to down to several to tens of kilometers deep, sampling the macro-structure and composition of the ice crust.However, radar sounder performance can be degraded by planetary ionospheres along the signal propagation path, affecting the nominal radar vertical resolution and signal-to-noise ratio. Typical vertical profiles of Europa's ionosphere, as measured by Galileo by occultation, can impact the 9-MHz channel of the Radar for Icy Moons Exploration (RIME, onboard JUICE) and the Radar for Europa Assessment and Sounding: Ocean to Near-surface (REASON, onboard Europa Clipper) investigations.We review the current state of knowledge of the Europan plasma environment, its effects on radio wave propagation, and its impact on the performance and design of future radar sounders for the exploration of Europa's ice crust. The severity of these impacts decrease with increasing center frequency and increase with altitude, latitude, and bandwidth. We also explain strategies to correct these impacts based on the extensive heritage from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) and the Shallow Radar (SHARAD) at Mars.Ionosphere correction will be a part of REASON's data processing, providing a Total Electron Content (TEC) data-product for characterization of the Europan plasma environment. Observations from the Hubble Space Telescope reported transient ultraviolet emissions from Europa's exosphere consistent with 200-km high plumes of water vapor venting upward materials from the sub-surface. Plume activity adds neutrals in the exosphere that can in turn be ionized by the incident Jovian magnetospheric flow, creating a plume-induced ionosphere as shown at Enceladus with the Cassini Spacecraft. TEC measured by REASON will address Europa Clipper's plume-search objectives by detecting localized plume-induced plasma-clouds under the spacecraft.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E1286G