JANUS: the camera system onboard JUICE. Operational approach and scientific capabilities from operations case studies.

The JUICE (JUpiter ICy moons Explorer) mission was selected in May 2012 as the first Large mission (L1) in the frame of the ESA Cosmic Vision 2015-2025 program and it will be launched in 2022. The mission aims to perform an in-depth characterization of the Jovian system, with an operational phase of about 3.5 years [1]. Main targets for this mission will be the vast Jovian system, including Jupiter itself, its magnetosphere, satellites, rings, neutral gas tori and the complex interplays among all those system components. Detailed investigations of three of Jupiter's Galilean icy satellites (Ganymede, Europa, and Callisto) will be achieved thanks to a large number of fly-bys and 9 months in orbit around Ganymede.

JANUS (Jovis, Amorum ac Natorum Undique Scrutator) is the scientific camera system onboard JUICE [2]. Despite the resource limitations, and the environmental constraints, the instrument architecture and design will be able to satisfy the great variability of observing conditions for its different targets, benefiting from the spacecraft and orbit design to its maximum. The JANUS design has to cope with a wide range of targets, from Jupiter’s atmosphere, to solid satellite surfaces and their exospheres, rings, and transient phenomena like lightning. In order to obtain multispectral observations of scientific targets as well as specific observations in narrow bands, JANUS is equipped with a filter wheel mechanism with 13 wide and narrow-band filters, allowing wavelength coverage in the 340 - 1080 nm range. JANUS will greatly improve spatial coverage, resolution and time coverage on many targets in the Jupiter system. JANUS ground sampling ranges from 400 m/pixel to < 3 m/pixel for the three main Galilean satellites, and from few to few tens of km/pixel for Jupiter and other targets in the Jovian system, such as Io, the minor inner and outer irregular moons, and Jupiter’s rings. JANUS observations of Jupiter’s atmosphere will range from full mapping to regional imaging at spatial resolutions down to 10 km/pix. Global wind fields with accuracies better than 1.0 m/s will be obtained several times during the mission.

Assuming the availability of scientific data volume (during operations about 20% of 1.4 Gbit/day is allocated to JANUS), JANUS observations will fully cover Ganymede in 4 colours with a resolution of about 100 m/pix as a goal, also providing regional DTMs. About 3% of the surface of Ganymede will be covered with a resolution of 10 - 30 m/pix for selected Regions of Interest, using both panchromatic and colour filters, and providing stereo images for the 3D reconstruction of the surface. This will represent dramatic improvements in imaging with respect to Galileo coverage in all the science targets covered by JUICE/JANUS.

In addition to presenting the science goals that we are aiming to achieve during the JUICE science phase, we will show examples of a case study of operations, to highlight how the achievement of science goals is strictly related to the resources available to the instrument.

References: [1] Grasset et al., (2013), PSS, 78, 1-21. [2] Palumbo et al., (2014), EGU conference

Acknowledgements: The activity has been realized under the ASI-INAF contract 2018-25-HH.0. LML acknowledges financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa” award to the Instituto de Astrofısica de Andalucia (SEV-2017-0709) and from project PGC2018-099425-B-I00 (MCI/AEI/FEDER, UE).