Geological and Astrobiological Considerations for Narrowband Science Filters on a Landed Multispectral Imaging System on Europa

Jupiter's icy moon Europa is believed to have a significant subsurface liquid water ocean and is therefore a prime target for astrobiology investigations in our solar system. A mission to land on the surface of Europa was the subject of the 2017 report of the Europa Lander Science Definition Team (SDT). Such a lander mission could be a natural follow-on to several flyby and orbital missions currently in development, including NASA's Europa Clipper mission and ESA's Jupiter Icy Moons Explorer mission.

As with other landed missions, a critical part of the science payload would be a multispectral imaging system capable of providing information about the landing location's composition and geology in addition to supporting the operations of other instruments and offering comparison to orbital data. Here, we propose a set of narrowband visible to near-infrared (~400-1100 nm) filters for such an imaging system that could capture key absorption features in a range of possible Europan surface materials. These materials include amorphous and crystalline water ice, hydrated salts (e.g., hexahydrite, epsomite, and natron), hydrated sulfuric acid, irradiated products of other Europan materials, possible silicate and/or meteoritic impactor materials, and potential organic molecules. We convolved measured laboratory reflectance spectra of these materials from numerous literature sources to propose specific filter bandpasses and bandwidths. Convolved data indicate that a multispectral imaging system equipped with at least six narrowband filters could discriminate among many of these various compositions as well as provide detailed color, textural, photometric, and geologic context information to support surface sampling or investigations by other instruments. Our proposed nominal filters centers and half-width at half maximum (in nm) for the full filter set are 380±23, 427±48, 450±18, 490±15, 525±88 (broadband), 555±35, 640±20, 670±30, 725±20, 850±70, 900±20, 1000±50, 1027±35, and 1080±40. We discuss how our recommended filter set is aligned with the measurement requirements and science objectives of the Europa Lander SDT's report. We will rank our recommended filters according to these priorities to accommodate the expected need for flexibility in mission/instrument design and allocated resources.