45th Lunar and Planetary Science Conference (2014) 2094.pdf

JANUS: THE VISIBLE CAMERA ONBOARD THE ESA JUICE MISSION TO THE JOVIAN SYSTEM. P. Palumbo1, R. Jaumann2, G. Cremonese3, H. Hoffmann2, S. Debei4, V. Della Corte5, A. Holland6, L.M. Lara7, J.M. Castro7, M. Herranz7, A. Koncz2, M. Leese6, A. Lichopoj2, D. Magrin3, I. Martinez-Navajas7, E. Mazzotta Epifani8, H. Michaelis2, R. Ragazzoni3, T. Roatsch2, E. Rodriguez7, P. Schipani8, N. Schmitz2, M. Zaccariotto4, M. Zusi8, A. Adriani5, O. Aharonson9, J. Bell10, O. Bourgeois11, M.T. Capria5, A. Coates12, A. Coustenis13, G. Di Achille8, G. Forlani14, S. van Gasselt15, O. Groussin16, K. Gwinner2, J. Haruyama17, E. Hauber2, H. Hiesinger18, Y. Langevin19, R. Lopes20, L. Marinangeli21, W. Markiewicz22, F. Marzari23, M. Massironi24, G. Mehall10, G. Mitri5, S. Mottola2, J. Oberst2, M. Patel6, M.G. Pelizzo25, C. Popa8, F. Poulet19, F. Preusker2, R. Rodrigo7, N. Schneider26, A. Simon- Miller27, K. Stephan2, Y. Takahashi28, F. Tosi5, M. Vincendon19, R. Wagner2. 1DiST, Univ., Napoli, Ita- ly. 2DLR-Inst.Plan.Res, Berlin, Germany. 3INAF-OAPd, Padova, . 4CISAS, Padova Univ., Padova, Italy. 5INAF-IAPS, , Italy. 6CEI-Open University, Milton Keynes, UK. 7IAA-CSIC, Granada, . 8INAF-OAC, Napoli, Italy. 9Weizmann Inst. of Science, Rehovot, Israel. 10ASU, Tempe, AZ, USA. 11Nantes Univ., France. 12UCL-MSSL, London, UK. 13LESIA, Paris Observ., CNRS, UPMC, Univ. Paris-Diderot, Meudon, France. 14Parma Univ., Italy. 15FUB-Inst.for Geosciences, Berlin, Germany. 16LAM, Marseille, France. 17ISAS-JAXA, Sagamihara, Japan. 18WWU Münster, Inst.Planetology, Germany. 19IAS-CNRS, Orsay, France. 20JPL/Caltech, Pasadena, CA, USA. 21ChietiPescara Univ., Italy. 22MPS, Inst.Solar Syst.Res., Lindau, Germany. 23Dept. Astronomy, Padova Univ., Italy. 24Dept. Geoscience, Padova Univ., Italy. 25CNR-IFN, Padova, Italy. 26APS-UCB, Boulder, CO, USA. 27NASA- GSFC, Greenbelt, MD, USA. 28Hokkaido University, Japan.

Introduction: The JUICE ( ICy moons Ex- face of . observations from an orbit- plorer) mission [1] was selected in May 2012 as the er are essential to investigate: (1) its wide range of sur- first Large mission (L1) in the frame of the ESA Cos- face ages which reveals a geologic record of several mic Vision 2015-2025 program. JUICE is now in billions of years; (2) its great variety in geologic units phase A-B1 and its final adoption is planned by late and geomorphical features; (3) its active magnetic dy- 2014.The mission is aimed at an in-depth characteriza- namo; (4) the possible presence of a subsurface ocean. tion of the Jovian system, with an operational phase of The three icy Galilean satellites show tremendous di- about 3.5 years. Targets for this mission will be Jupiter versity of surface features, witnesses of significantly and its magnetosphere, its satellites and rings and the different evolutionary paths. Each of these moons ex- complex coupling processes within the system. The hibits its own fascinating geologic history – formed by main focus will be on the detailed investigation of three competition and also combination of external and in- of Jupiter’s Galilean satellites (Ganymede, Europa, and ternal processes. Their origins and evolutions are con- ), thanks to several fly-bys and 9 months in trolled by factors such as density, temperature, compo- orbit around Ganymede. sition (volatile compounds), stage of differentiation, (Jovis, Amorum ac Natorum Undique volcanism, tectonism, rheological behavior of ice and Scrutator) is the camera selected by ESA to fulfill the salts to stress, tidal effects and interactions with the visible imaging scientific requirements of JUICE. It is Jovian magnetosphere and the space. These interac- being developed by a consortium of institutes in Italy, tions are still recorded in the present surface geology Germany, Spain and UK, supported by the respective wich displays also possible cryovolcanism, widespread Space Agencies (ASI, DLR, Ministerio de Ciencia e tectonism, surface degradation and impact cratering. Innovación, UKSA), with contributions from Co- Other important targets for JANUS observations Investigators also from USA, France, Japan and Israel. are the Jupiter atmosphere, satellite’s exospheres, Jupi- JANUS Science Objectives: The Galilean satel- ter ring system and the minor satellites. lites , Europa, Ganymede and Callisto show an in- Instrument Architecture: In addition to the usual crease in geologic activity with decreasing distance to requirements for a planetary mission, resources con- Jupiter [e.g., 2]. Io, nearest to Jupiter, is volcanically straints, S/C characteristics, mission design and the active. Europa could still be tectonically and volcani- great variability of observing conditions for several cally active today, while Callisto, the outermost Galile- objects place stringent constraints on JANUS architec- an satellite, is geologically inactive but bears witness to ture. Also, a high radiation environment in terms of past processes in the system through its surface fea- total irradiation dose and flux in specific mission phas- tures. Ganymede holds a key position in terms of geo- es has to be considered. Finally, the design has to cope logic evolution because it features old, densely- with a wide range of targets, from Jupiter atmosphere cratered terrain, like most of Callisto, but also wide- and lightning, to solid satellite surfaces, exosphere, spread resurfaced regions, similar to most of the sur- rings, all to be observed in several color and narrow- 45th Lunar and Planetary Science Conference (2014) 2094.pdf

band filters (see preliminary spectral characteristics targets at the minimum distance foreseen by JUICE below) and from low to high ground resolution. A ca- mission design. Only few targets are not resolved. toptric telescope with excellent optical quality is cou- Assuming the available scientific data volume pled with a CMOS detector; filter selection is done (about 20% allocated to JANUS out of 1.4 Gb/day), with a high heritage and redundant mechanism. JANUS observation will cover about a 100% of Gan- Narrowband filters Broadband filters ymede surface in 4 filters at 400 m/pxl sampling. centre/FWHM [nm] centre/FWHM [nm] About 3% of the surface of Ganymede will be covered 590/10 sodium D-lines 650/500 Panchromatic at <24 m/pxl and 60 targeted areas will be observed at 656/10 Hα-line 410/80 violet, UV slope about 3 m/pxl. This will represent a dramatic im- 727/10 methane 450/60 Blue provement with respect to Galileo coverage (figure 2). 760/20 cont 1, geology 530/60 green, bkg Na Stereo imaging at Ganymede is doable at sampling 889/20 methane strong 656/60 red, bkg Hα between 5 and 25 m/pxl and will be obtained by com- 940/20 cont 2, Fe2+ 910/80 NIR 1, Fe2+, Io obs. 1000/150 NIR 2, Fe2+, Io obs. bining nadir and S/C tilted observations. Instrument operations are flexible enough to opti- mize the acquisition parameters with respect to the many different observation conditions that JANUS will face. The instrument design will allow for adjustments in resolution, field of view, signal levels and SNR through binning, windowing and integration time. Up- dated calibration parameters can be applied for on- board data pre-processing. Cold redundancy is imple- mented for all critical electronic parts. Capabilities and Performances: JANUS design > 50x optimizes the use of resources allocated for the JUICE imager in terms of performances and reliability. Anal- yses show that the JANUS design will allow good im- age quality and SNR>100 in almost all observing end- Figure 2: JANUS ground sampling distance and of-life conditions. surface coverage for Ganymede in different mission JANUS will allow orders-of-magnitude steps ahead phases (2 to 7: fly-bys during Jupiter orbits; 8 to 10: in terms of coverage and/or resolution and/or time evo- orbits around Ganymede) compared to Galileo. lution on many targets in the Jupiter system. JANUS For Callisto, assuming only nadir pointing, JANUS spatial resolution ranges from 400 m/pxl to < 3 m/pxl will cover 100% of the surface at ≤ 2 km/pxl, 41 % at ≤ for the three main Galilean satellites, and from few to 1 km/pxl, 14 % at ≤ 400 m/pxl, 6.5% at ≤ 200 m/pxl, few tens of km/pxl for Jupiter and the other targets in and some targets with 4 colors imaging at medium res- the Jovian system (see figure 1). olutions (i.e., ~10 m/pxl). 55% of Europa’s surface can be covered at ≤ 3 km/pxl, 42 % at ≤ 2 km/pxl, 25 % at ≤ 1 km/pxl, 11 % at ≤ 700 m/pxl, 3.2% at ≤ 400 m/pxl, 1.1% at ≤ 200 m/pxl and some targets at resolutions ~ 10 m/pixel. Low to medium-resolution imaging (i.e. km to ~100 m – range) is obtained in four filters. Note that all given numbers are worst case estimations, as raster pointing strategy is under study during the fly-bys in order to increase coverage at higher resolution. Ground sampling at Io will gain 6 to 20 km/pixel with long monitoring time also at NIR wavelengths. The rings and minor satellites can be observed at ~7 km/pxl, while Jupiter’s atmosphere will be observed down to 9 km/pxl. References: [1] Grasset O. et al. (2013) Plan.& SpaceSci. 78, 1-21. [2] Stephan K. et al.(2013) The Science of Solar System Ices, Gutipati & Castillo- Figure 1: ground sampling in km/pxl and image Rogez eds.; Astrophys.&SpaceSci.Libr. 356, 279–367. width in km are compared with the size of different