Coustenis, A., Rodrigo, R., Spohn, T., L´Haridon, J. (2020). Editorial to the Topical Collection: Ocean Worlds. Space Science Reviews 216, 4 DOI: 10.1007/s11214-020-00672-z
We are at the beginning of a new era in the exploration of the outer solar system. Spacecraft have already visited each of the giant planets and made detailed observations of their major satellites. In 2017, the Cassini spacecraft ended its highly successful mission in the Saturnian system while the Juno mission has been investigating Jupiter since 2016. The New Horizons spacecraft revealed the Pluto/Charon system in 2015 and is now exploring the Kuiper belt. In parallel, NASA, ESA, and other international space agencies are considering the next major steps in the outer solar system exploration. Among these, the Jupiter Icy moon Explorer (JUICE), the first Large class mission of the ESA Cosmic Vision 2015-2025 campaign currently in development, will explore three satellites of the Jovian system – Ganymede, Europa and Callisto – to study the emergence of habitable worlds around gas giants. NASA is also developing the Europa Clipper mission to explore the eponymous moon of Jupiter through several flybys and investigate the existence and characteristics of a water ocean covered by an ice shell. NASA also recently selected the Dragonfly quadricopter concept as the next New Frontiers mission (NF4) to investigate Titan. In addition, several other proposals with similar objectives and exciting concepts have been or will be submitted to space agencies in response to future calls.