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I have noticed lately that future missions by NASA and ESA are targeted towards the moons of Jupiter and Saturn. They mention that they might be a possibility of life; the icy moons they are focusing on are Europa and Titan.

Examples of these missions are the Europa Clipper mission, the Dragonfly mission to Titan, and the JUICE mission.

I was wondering what are the main driving factors that has lead to start projects and missions to the icy moons? Not necessarily the ones I mentioned but why is there a sudden interest to the icy moons? (e.g., is it driven by the search for life? Or is it following the water?)

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    $\begingroup$ The mission pages describe the motivations, in the case of Europa Clipper it is "NASA's Europa Clipper will conduct detailed reconnaissance of Jupiter's moon Europa and investigate whether the icy moon could harbor conditions suitable for life." If that is not what you are looking for you may need to be a bit clearer. $\endgroup$ – GdD Jan 24 at 14:48
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    $\begingroup$ @GdD I meant in general, not necessarily the mentioned missions. I edited the questions. $\endgroup$ – John Jan 24 at 16:19
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    $\begingroup$ @GdD I am actually asking why are we exploring the icy moons. Not space. $\endgroup$ – John Jan 24 at 16:32
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    $\begingroup$ @GdD if a commonality among stated scientific motivations for icy moon-bound missions is the search for life, then it seems that that would be a concise, definitive, and completely fact-based answer. All closing does is blocks people from posting additional high-quality answers. There are two answers already, clearly others found the question quite answerable. $\endgroup$ – uhoh Jan 24 at 22:08
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    $\begingroup$ I don't think there is a sudden interest in visiting icy moons. The interest has always been there, it's just that now we have (or are close to having) the technology to do so with reasonable funding, and funding that isn't being directed to higher priority missions. $\endgroup$ – jamesqf Jan 26 at 3:19
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The icy moons are of interest for exploration as part of the overall "follow the water" strategy of exploration that NASA (and others) have been exploring for some time. The "where else can water be found" is a major question in e.g. the US Planetary Science Decadal Survey (which is a community-driven consensus document which outlines the questions of interest and the mission priorities for the next decade), ESA's Cosmic Vision 2015-2025 and the NASA Planetary Science "Big Questions" overview.

The "Roadmaps to Ocean Worlds" team (public overview here) laid out the goals of the ocean worlds program in 2018 and the overview graphic sets out the motivations and the path forward: investigation roadmap for exploring Ocean Worlds So the main targets are Europa, Ganymede and Callisto (icy moons of Jupiter) and Enceladus and Titan (icy moons of Saturn) with other "honorable mentions" for Mimas, Triton and Pluto and Ceres as detailed a little more in this NASA JPL infographic. Most of these destinations are in the "Characterize Oceans" and "Assess Habitability" stages of needing new missions, instruments and data to guide the future search for life.

Ocean Worlds destinations were added, somewhat controversially at a late stage, to the NASA New Frontiers 4 competition for mid-size missions (cost cap ~$900M; NASA New Frontiers program page) which was subsequently won by the Dragonfly mission which will go to Saturn's icy moon of Titan. Europa is the target of the NASA Europa Clipper mission which has followed a separate path of development, in some part at the urging of former Representative John Culberson, and ESA's JUICE - JUpiter ICy moons Explorer -mission, which will study Ganymede, Callisto and Europa (along with Jupiter itself)

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The motivation is the growing understanding, from the Voyager, Galileo and Cassini probes, that these icy moons (I'd throw in Enceladus) are geologically active with sub-surface oceans of liquid water, along with the realization (from studying the Earth's ocean vents and deep biosphere) that life can be sustained from the energy of geologic processes, not just the solar energy impinging on the surface.

The combination of liquid water and available energy beneath the surface of these moons make them an intriguing place to look for extraterrestrial life.

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    $\begingroup$ To seek out new life and new civilizations. $\endgroup$ – Mazura Jan 25 at 19:02
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    $\begingroup$ The search for life is the goal that makes headlines. But from a biology perspective, these worlds are still interesting if they don't support life, because they tell us what potential building blocks for life were likely to be available on earth before life emerged - a question that's difficult to answer on earth, and whose answer would rule out some theories on the origins of life. $\endgroup$ – James_pic Jan 27 at 11:38
  • $\begingroup$ @James_pic And if you don't find any life there... water is quite useful for any attempts at space colonization, in-situ refuelling etc. $\endgroup$ – Luaan Jan 27 at 12:44
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One of the reasons is that the Cassini mission ended on September 15, 2017, and Juno around Jupiter isn't exploring its moons, as far as I'm aware.

So currently we have nothing around Saturn and Jupiter that would explore any of its moons.

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