The NASA Roadmap to Ocean Worlds

Abstract

In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to “identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find.” The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists.

Holistic Approach for Studying Planetary Hydrospheres: Gibbs Representation of Ices Thermodynamics, Elasticity, and the Water Phase Diagram to 2,300 MPa

“…As a common molecular species in our cosmic neighborhood (Hanslmeier, ), water ice polymorphs at high pressures in planetary interiors could be the most abundant “mineral group” in the Universe. A focus on potentially habitable hydrospheres of icy moons, small bodies such as Pluto and Ceres, and ocean exoplanets (Sotin & Tobie, ; S. Vance & Brown, ; B Journaux et al, ; Baptiste Journaux et al, ; Noack et al, ; Kite & Ford, ; Unterborn et al, ; Hendrix et al, ) motivates an interest in thermodynamic properties of water and ices in the <200 MPa range. For example, the presence of an insulating layer of high‐pressure ice between the deep ocean and the underlying silicates on large water‐rich planetary bodies has been identified as a potential bottleneck for habitability, as it could limit nutrient transport (Léger et al, ; Noack et al, ; Baptiste Journaux et al, ; Kite & Ford, ).…”

Overview and perspectives of Astrobiology

“…现代火星地表环境恶劣, 但其地下可能 具有支持类似于地球微生物等生命形式生存的条件, 当前对火星宜居环境和生命的探索已逐渐从地表转入 地下 [78] . 太阳系内的一些冰卫星, 如木卫二、木卫三、木 卫四、土卫二、土卫四和海卫一等, 在其表面冰层以 下可能存在液态的海洋, 具有一定的宜居性 [29] . 在这些 冰卫星中, 木卫二和土卫二尤为引人关注.…”

Exo-Ocean Exploration with Deep-Sea Sensor and Platform Technologies

“…L iquid water is present in the form of vast extraterrestrial oceans (i.e., exo-oceans) on various icy moons of our solar system (NASEM, 2018;Hendrix et al, 2019;Kamata et al, 2019). Five icy moons have been confirmed as ocean worlds, namely, three satellites of Jupiter (Europa, Ganymede, and Callisto) and two of Saturn (Enceladus and Titan, the latter with an exo-ocean below a thick hydrocarbon layer; Iess et al, 2012).…”