Future atmospheric research objectives of missions to the Jovian and the Kronian systems

Icy moons of Jupiter and Saturn are privileged targets in currently developed space missions by several space agencies and in particular ESA, NASA and their partners. One of these missions is ESA’s first large mission in the Cosmic Vision Programme, JUICE [1], which is being developed to address questions regarding the Jupiter system and its satellites, with a focus on the largest moon, Ganymede. The overarching theme for JUICE is the emergence of habitable worlds around gas giants taking into account the requirements involving the presence of organic compounds, trace elements, water, energy sources and a relative stability of the environment over time.

Among other, JUICE will determine the characteristics (composition and dynamics) of the exospheres of the icy moons [2], in particular Ganymede and Europa, with for instance coordinated observations among sets of instruments like UVS, PEP, RPWI, MAJIS, 3GM, J-MAG, JANUS and SWI. The JUICE mission is scheduled to be launched in spring 2023 and arrive at Jupiter in mid-2031 and is foreseen to last nominally for 3 and a half years. JUICE investigations will benefit from current observations by JUNO and will be synergistic to NASA’s Europa Clipper mission. I will describe the foreseen investigations of the tenuous atmospheres of the icy moons around Jupiter.

Cassini explored the dense and organic-laden atmosphere of Titan during several flybys over 13 years [2,3] and also determined the characteristics of the Enceladus plumes. However, new questions have risen and several cold cases [4] remain that will constitute major science objectives for future space missions to the satellites around Saturn, like Dragonfly [5] or an orbiter in the Saturn system or a dedicated Enceladus mission…

In particular, Titan’s atmosphere has not yet revealed all its secrets, in particular for the chemical composition, which should be much more complex than what was detected by Cassini-Huygens. Future in situ measurements will be extremely useful in unveiling this unique complex world. In the meantime, ground-based observations with large telescopes like ALMA, elsewhere in Chile or the ones in Hawaii can help complement the past discoveries.

References:

[1] Coustenis, A., Witasse, O., Erd, C., 2021. The JUICE mission: expectations and challenges. Fall issue of The Bridge on space exploration, Sept. 2021, Vol. 51, issue #3, pp. 41-50.

[2] Coustenis, A., Tokano, T., Burger, M. H., Cassidy, T. A., Lopes, R. M., Lorenz, R. D., Retherford, K. D., Schubert G., 2010. Atmospheres/exospheres characteristics of icy satellites. Space Sci. Rev., 153, 155-184. https://www.nae.edu/260902/The-JUICE-Mission-Challenges-and-Expectations

[3] Coustenis, A., 2021. “The Atmosphere of Titan”. In Read, P. (Ed.), Oxford Research Encyclopedia of Planetary Science. Oxford University Press (August 31). doi: https://doi.org/10.1093/acrefore/9780190647926.013.120

[4] Nixon, C. A., Lorenz, R. D., Achterberg, R. K., et al. (2018). Titan's cold case files - Outstanding questions after Cassini-Huygens. Planetary and Space Science, 155, 50-72.

[5] Barnes, J. et al. (2021). Science Goals and Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander. The Plan. Sci. J., VoL. 2, Issue 4, id.130, 18 pp.