4

Conclusions

There is compelling science remaining for all of the New Frontiers mission themes and theme subsets considered in this report: Ocean Worlds (both Titan and Enceladus), Trojan Tour and Rendezvous, Io Observer, and LGN. And practically all planetary missions, of any class, may benefit from the significant investments in instrument and technology maturation in the decade since the publication of V&V.

With respect to the statement of task (Chapter 1), for three mission themes or mission theme subsets—Ocean Worlds (Enceladus), Io Observer, and LGN—scientific understanding or external factors, such as programmatic developments or technological advances, have not been sufficiently substantial since the release of the planetary science decadal survey or its midterm review to warrant reconsideration of their inclusion in the NF5 AO. On the contrary, recent scientific discoveries and technological advancements have only increased the compelling nature and technical feasibility of these mission themes or theme subsets. With respect to Io Observer, however, there is an important caveat. If NASA’s exploration of Io proceeds via the selection of the IVO Discovery mission, then based on the IVO Step 1 proposal, inclusion of Io Observer would be redundant scientifically and its inclusion in NF5 would strongly warrant reconsideration.

There are, in contrast, two mission themes or mission theme subsets—Ocean Worlds (Titan) and Trojan Tour and Rendezvous—for which programmatic developments have been sufficiently substantial since the release of the planetary science decadal survey or its midterm review to warrant reconsideration of their inclusion in the NF5 AO. For Trojan Tour and Rendezvous, the preponderance of the science objectives for this mission theme will be addressed by the Lucy Discovery mission. For Ocean Worlds (Titan), the preponderance of the science objectives for this mission theme subset will be addressed by the Dragonfly New Frontiers mission. The committee notes, however, that even assuming Dragonfly’s success, there will remain important and compelling science to be accomplished at Titan, including science related to the subsurface ocean and surface liquid hydrocarbon reservoirs (the second of the two scientific objectives for Titan in the NF4 AO). For programmatic balance, and consistency with the decision rules in V&V, however, Dragonfly’s selection implies that reconsideration of Titan under the Ocean Worlds mission theme is warranted. The evaluation and prioritization of future Titan exploration by the next planetary science and astrobiology decadal survey is a logical next step.

In summary, with respect to all the New Frontiers targets or mission themes considered—Ocean Worlds, Trojan Tour and Rendezvous, Io Observer, and LGN—the key conclusions of this report are as follows:

• Ocean Worlds (Enceladus) and LGN remain compelling mission themes, without any developments suggesting that NASA reconsider their inclusion in NF5;
• The selection of IVO for flight in Discovery 15/16 would represent a programmatic development suggesting that, in that event, NASA reconsider the inclusion of Io Observer for NF5;
• The development of the Lucy mission suggests that NASA reconsider the inclusion of Trojan Tour and Rendezvous in NF5; and
• The development of the Dragonfly mission suggests that NASA reconsider the inclusion of Ocean Worlds (Titan) in NF5, for reasons of programmatic balance.

Last, the committee lauds the list of potential missions for NF5 as robust and scientifically exciting. The NF5 list has, appropriately, extraordinarily compelling scientific mission themes that would, if selected, substantially advance our understanding of the solar system.