An Emerging Planetary Science Community ---------------------------------------------- Space agencies and academic institutions that are establishing JUpiter ICy moons Explorer (JUICE) [@2006ExA....26..197R], and ESA’s Characterizing Exoplanet Satellite (CHEOPS) [@CHEOPS] have begun to form a Planetary Science Community. This community will provide technical and science expertise in three main areas: [**Target Selection:**]{} - [**JUICE.**]{} JUICE will be a NASA mission, with the launch scheduled for the early 2020’s. Its primary goal is to explore the giant Jupiter Moon system Ganymede, Callisto, Europa and Io. The mission is expected to also provide important information regarding the structure and dynamics of gas giant atmospheres and jovian interiors. - [**CHEOPS.**]{} This ESA mission will be launched in the same year as JUICE, scheduled for the first half of 2020. Its science goals are focused on providing targets for both radial velocity measurements and transit timing experiments. [**Target Characterization:**]{} - [**JUICE/CHEOPS.**]{} Once the planet or moon is discovered the second phase of a JUICE/CHEOPS mission will begin. While the mission would not perform its own detailed mission the characterization of the target will most certainly require a large portion of the mission’s time. The focus of such a mission will not be in the identification of potential habitability or biosignatures, but rather how can we best characterize the environment to determine if it is worth using resources to search for biosignatures. Possible targets for this effort include Titan and perhaps the Galilean moon Callisto (though it is unclear if such a mission would be approved). These missions should be scheduled around the JUICE launch, though it is unclear if such an early mission would be possible or funded. The possibility of a follow-up mission, scheduled around an already launched JUICE, would be much more feasible. - [**Biosignature Hunting:**]{} This is the effort to search for potential biosignatures in outer system objects. Targets will be identified by ongoing exoplanet surveys such as TESS [@Ricker2014] and the ESA Gaia mission. More sophisticated characterization missions will be necessary to properly characterize a biosignature producing environment. This characterization can only be performed after a biosignature has been discovered or suspected. [**Triage/Retrieval:**]{} - [**CHEOPS.**]{} CHEOPS was developed to search for biosignatures on Jupiter satellites, though a potential mission extension to study other targets has been discussed [@Wong2016]. CHEOPS is also beginning to develop tools for in-situ space chemistry. CHEOPS will perform a limited search for biosignatures with the help of an automated tool [@Crespin2013] in the final years of its mission. CHEOPS was conceived of as a mission dedicated to the search for biosignatures, and may be the only mission capable of performing a full biosignature search given the difficulty in finding and testing the required technology. - [**JUICE.**]{} JUICE will search for a biosignature via its remote sensing instruments, but it will also be able to characterize a candidate environment using remote sensing techniques. In both cases, the spacecraft will need to make decisions about the optimal approach to investigate a given target. Because the JUICE mission architecture is not tightly tied to those planning a biosignature survey it would be possible for another mission, such as a follow up mission or a precursor, to fly to explore the environments that are detected and found to be chemically interesting. Because of the tight link to JUICE’s data flow, a mission that would receive data products from the JUICE mission will need to have access to detailed mission-level plans. - [**Cryo/Mars2020.**]{} The goal of these missions is to better characterize the composition and potential habitability of Titan, Europa and Enceladus. These missions should be scheduled around an already launched JUICE mission. [**Advanced Technology Development:**]{} - [**JUICE/CHEOPS.**]{} While JUICE and CHEOPS can be used to test a wide variety of potentially interesting technologies, the possibility of a follow up mission (e.g. CHEOPS 2 or JUICE 2) makes this more difficult. Some technology development for JUICE and CHEOPS will be performed through the ExoMars program, the first European planetary surface mission (ExoMars Trace Gas Orbiter, TGO), and the second (ExoMars Rover, Rosalind Franklin). Beyond technology development, JUICE and CHEOPS will provide valuable in-flight demonstrations of critical technologies to enable future biosignature searches. JUICE should provide some tests of the potential for exozodiacal cloud identification and characterization using photometry, and CHEOPS should provide demonstration of atmospheric characterization via transit spectroscopy. A follow up mission can then use this data for design purposes and develop key technologies for a future biosignature search. Beyond JUICE/CHEOPS and other missions like it, the next mission generation may well involve missions that are dedicated to biosignature searches. One example of such a mission could be something like NASA’s Discovery Program, though NASA requires that most of the funding for such missions be provided by the team performing the science and does not generally allow missions to be led by non-NASA entities. In some cases, small teams of potential proposers may be able to self-fund their proposal in order to conduct a mission, though this would almost certainly limit their ability to acquire the data necessary for a robust investigation. One example would be an autonomous mission that is limited to performing transit photometry on targets identified in an independent survey (e.g. Gaia, TESS, LSST). The development of biosignature detection techniques will continue on current mission for the coming decade. CHEOPS, JUICE and other missions will likely be important pathfinders and are designed for such purposes. CHEOPS should be used to test technology for a JUICE-type mission [@Crespin2013], while JUICE will be used to confirm promising findings with larger telescopes and further characterize the environments. The JUICE and CHEOPS missions will also provide both photometry and spectroscopy from different angles, enabling more complete characterization of the exoplanet-hosting planets’ host stars, which is important for biosignature searches. Once it becomes clear that CHEOPS has identified a promising exoplanet that is more likely to have an Earth-like planet around it, CHEOPS may be well suited to find and study those planets. After those planets have been identified, a more extensive survey for biosignatures could be done. The JUICE mission, CHEOPS, and similar future space missions will likely discover targets that will be studied using in-situ measurements on the ground, such as CHEOPS’ own work on Jupiter’s stratosphere and thermosphere, or future missions searching for biosignatures on planets (or moons). For more distant objects that are inaccessible to current instruments on the ground, missions like JUICE and CHEOPS may need to be followed up by satellites like the proposed TPF-C mission, though this would have to be tested beforehand. The exact configuration of these missions will be determined in the future, but it is likely that NASA/ESA will not approve another follow-up mission, meaning that they will have to rely on the data that is available in the archives. A future Biosignature Search Campaign and Technology Demonstration mission may involve a lander or rover system, which could potentially be hosted by the Moon or in orbit around the Earth. We see great benefit in continued investment into the development of these missions. They will provide a significant resource for exoplanet exploration, and are likely to lead to some unexpected discoveries that can potentially be made only in space. In particular, the development of exoplanet atmospheres instrumentation may be accelerated by these missions. Furthermore, the discovery of Jupiter’s ring-moon system may be possible only due to the advanced technology and data products provided by these missions. Future work may find the exoplanet characterization in a JUICE-like mission will be limited to those of short orbital period, thus making a rover-based mission more useful than its current spacecraft based mission architecture. As more observations become available, particularly for the targets that do not have a gas giant planet or a small terrestrial planet orbiting them, it is increasingly likely that we will have some exoplanet systems that will challenge some of the theories in exoplanet research. JUICE/CHEOPS will not necessarily discover habitable worlds that have biosignatures, but it may well provide some exciting new insights and data products that could be leveraged to help answer that question. Additionally, while it is expected that most of the science community will be in agreement on the need to pursue exoplanet characterization using other methods (particularly ground-based spectroscopy), the exact composition of the exoplanet-hosting planets may be in contention. A ground-based biosignature detection mission should be able to test these competing hypotheses. CHEOPS will likely not have enough resolving power to detect biosignatures, though this is expected to improve in the future. CHEOPS would have some possibility of detecting biosignatures for nearby hot-Jupiters and gas giant moons, or provide valuable upper limits to the population of hot-Jupiters that may have an Earth-like environment. As these missions are proposed and defined, however,