JUICE flybys at Europa: context for MAJIS observations

We report here about the currently foreseen scientific activity of the MAJIS instrument during the two planned JUICE flybys of Europa in 2032. MAJIS [1] (Moon and Jupiter Imaging Spectrometer) is a two-channel imaging spectrometer onboard JUICE, covering the spectral range 0.5-5.55 μm, splitted in a VISNIR channel (0.5-2.36 μm, <4.6 nm sampling) and a IR channel (2.27-5.55 μm, <7 nm sampling). This work has been developed in the framework of an inter-instrumental planning exercise carried on by ESA in 2022/23 to establish the best scientific and technical strategy to be adopted by the JUICE spacecraft during its low-altitude encounters with the Jovian satellite. Although the final JUICE trajectory is still subject to change (version Crema 5.0 [2] has been used), and several details of the actual observations are pending, the overall framework of the operations is well established and able to give an idea of the possible scientific constraints and outcomes for MAJIS. The two Europa flybys are expected to be rather similar in terms of overall geometry, but almost specular about equator, enabling a good complementary coverage of both northern and southern hemispheres. Only the first one has been studied in detail and discussed here. Due to favorable illumination conditions, the flyby inbound leg is mainly devoted to surface studies. A first almost full coverage of the trailing hemisphere for all latitudes below 45°N, including some slant view of the southern polar cap, can be obtained at lower resolutions (3-10 km/px), during the initial flyby phase.A wider surface coverage can then be achieved at medium spatial resolution (1-2 km/px), encompassing a wide portion of Europa’s darker trailing hemisphere. The 150 μrad IFOV will also enable MAJIS to acquire multispectral images of the Europa surface at high resolution (110-300 m/px) in small postage stamps distributed along narrow tracks (about 80 x 1800 km), near the closest approach. While current evaluations make them cover mid latitudes linear features (a region around Cadmus and Minos Lineae, ~160°E,45°N), the precise location of these high-res tracks might change significantly as a consequence of trajectory adjustments.  A search for thermal anomalies can be performed during the outbound flyby leg, when the spacecraft mostly flies over the night (leading) hemisphere. The rest of the outbound is devoted to limb observations at different latitudes, with vertical resolution changing from 1.1 to 10 km/px. The high solar phase angle encountered in this section (~140°) is optimal for searching eventual active plumes thanks to the high forward scattering efficiency of small ice particles in the MAJIS spectral range. The region covered by such limb observations should also be compatible with the location of plumes reported in literature [3,4,5].   References [1] Poulet et al., 2023, Submitted to Space Science Review. [2] ESA SPICE Service, JUICE Operational SPICE Kernel Dataset, DOI: 10.5270/esa-ybmj68p. [3] Roth et al.,2014, Science, 343, 171, DOI: 10.1126/science.1247051. [4] Sparks et al.,2016, ApJ,829,121, DOI: 10.3847/0004-637X/829/2/121. [5] Jia et al.,2018, Nature Astronomy, 2, 459, DOI: 10.1038/s41550-018-0450-z.   Acknowledgments This work has been developed under the ASI-INAF agreement n. 2023-6-HH.0.