The exploration of carbon-to-oxygen ratios has yielded intriguing insights into the composition of close-in giant exoplanets, giving rise to a distinct classification: carbon-rich planets, characterized by a carbon–to–oxygen ratio ≥ 1 in their atmospheres, as opposed to giant planets exhibiting carbon–to–oxygen ratios close to the protosolar value. In contrast, despite numerous space missions dispatched to the outer solar system and the proximity of Jupiter, Saturn, Uranus, and Neptune, our understanding of the carbon-to-oxygen ratio in these giants remains notably deficient. Determining this ratio is crucial as it serves as a marker linking a planet’s volatile composition directly to its formation region within the disk. This article provides an overview of the current understanding of the carbon-to-oxygen ratio in the four gas giants of our solar system and explores why there is yet no definitive dismissal of the possibility that Jupiter, Saturn, Uranus, or Neptune could be considered carbon-rich planets. Additionally, we delve into the three primary formation scenarios proposed in existing literature to account for a bulk carbon-to-oxygen ratio ≥ 1 in a giant planet. A significant challenge lies in accurately inferring the bulk carbon-to-oxygen ratio of our solar system’s gas giants. Retrieval methods involve integrating in situ measurements from entry probes equipped with mass spectrometers and remote sensing observations conducted at microwave wavelengths by orbiters. However, these methods fall short of fully discerning the deep carbon-to-oxygen abundance in the gas giants due to their limited probing depth, typically within the 10–100 bar range. To complement these direct measurements, indirect determinations rely on understanding the vertical distribution of atmospheric carbon monoxide in conjunction with thermochemical models. These models aid in evaluating the deep oxygen abundance in the gas giants, providing valuable insights into their overall composition.

Recent observations of Jupiter's atmosphere showing unexpected depletion of ammonia below the ammonia cloud-forming region has brought up the question of whether a single point measurement below the cloud decks in a giant planet atmosphere can provide sufficient information to answer fundamental science questions. We outline here the science questions that can only be answered by in situ observations in the giant planet atmospheres, many of which are location invariant. These questions are identified in the recent planetary science decadal survey as high priority for answering over the next decade. We evaluate the implications of the ammonia observations at Jupiter for the specific measurements needed and demonstrate that they do not invalidate single point measurements made to answer these questions.

The main objective of this chapter is to present an overview of the different areas of key technologies that will be needed to fly the technically most challenging of the representative missions identified in chapter 4 (the Pillar 2 Horizon 2061 report). It starts with a description of the future scientific instruments which will address the key questions of Horizon 2061 described in chapter 3 (the Pillar 1 Horizon 2061 report) and the new technologies that the next generations of space instruments will require (section 2). From there, the chapter follows the line of logical development and implementation of a planetary mission: section 3 describes some of the novel mission architectures that will be needed and how they will articulate interplanetary spacecraft and science platforms; section 4 summarizes the system-level technologies needed: power, propulsion, navigation, communication, advanced autonomy on board planetary spacecraft; section 5 describes the diversity of specialized science platforms that will be needed to survive, operate and return scientific data from the extreme environments that future missions will target; section 6 describes the new technology developments that will be needed for long-duration missions and semi-permanent settlements; finally, section 7 attempts to anticipate on the disruptive technologies that should emerge and progressively prevail in the decades to come to meet the long-term needs of future planetary missions.

The primary objective of this chapter is to present an overview of the different key technologies that will be needed in order to fly the technically most challenging of the representative missions identified in Chapter 4 (the Pillar 2 Horizon 2061 report, Lasue et al., 2021). It starts with a description of the future scientific instruments which will address the key questions of Horizon 2061 described in Chapter 3 (the Pillar 1 Horizon 2061 report, Dehant et al., 2021) and the new technologies that the next generations of space instruments will require (Section 2). From there, the chapter follows the line of logical development and implementation of a planetary mission: Section 3 describes some of the novel mission architectures that will be needed and how they will articulate interplanetary spacecraft and science platforms; Section 4 summarizes the system-level technologies needed: power, propulsion, navigation, communication, advanced autonomy on-board planetary spacecraft; Section 5 describes the diversity of specialized science platforms that will be needed to survive, operate, and return scientific data from the extreme environments that future missions will target; Section 6 describes the new technology developments that will be needed for long-duration missions and semipermanent settlements; finally, Section 7 attempts to anticipate some of the disruptive technologies that should emerge and progressively prevail in the decades to come to meet the long-term needs of future planetary missions.

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>The ice giants Uranus and Neptune are the least understood class of planets in our solar system, while planets of their size, the most frequent among exoplanets, represent a common outcome of planet formation. Presumed to have a small rocky core, a deep interior comprising ~70% heavy elements surrounded by a more dilute outer envelope of H2 and He, Uranus and Neptune are fundamentally different from the better-explored gas giants Jupiter and Saturn. Because of the dearth of missions dedicated to their exploration, our knowledge of their composition and atmospheric processes is primarily derived from a single Voyager 2 flyby of each, complemented by subsequent remote sensing from Earth-based observatories, including space telescopes. As a result, Uranus's and Neptune's physical and atmospheric properties remain poorly constrained and their roles in the evolution of the Solar System are not well understood. Exploration of ice giant systems is therefore a high-priority science objective as these systems (which link together the magnetospheres, satellites, rings, atmosphere, and interior of these planets) challenge our understanding of planetary formation and evolution. In this context, the US planetary science decadal survey report recently recommended the launch of a flagship mission towards the Uranian system in the early 2030s. This mission would be composed of an orbiter aiming at exploring the Uranian system as a whole and a descent probe to directly sample the giant’s atmosphere.</p> <p>Measurements to be made with a probe can be defined as Tier 1, representing threshold science required to justify the probe mission, and Tier 2 representing valuable science that significantly complement and enhance the threshold measurements, but of themselves are not sufficient to justify the mission. Tier 1 measurements comprise atmospheric noble gas abundances including helium, key noble gas isotope ratios, and the thermal structure of the atmosphere. Instrumentation required to achieve the Tier 1 measurements include a mass spectrometer, a helium abundance detector, and an atmospheric structure instrument comprising both sensors for pressure, temperature, a Tunable Laser System and atmospheric acoustic properties (speed of sound). Tier 1 science can be achieved with a probe making measurements near one to several bars. Tier 2 science includes measurements of key isotopic ratios, the abundances of atmospheric condensables and disequilibrium species, atmospheric dynamics, the net radiative flux transfer profile of the atmosphere, and the location, composition, properties, and structure of the clouds. To achieve all the Tier 2 science objectives requires a probe descending through at least ten bars carrying the full Tier 1 suite of instruments as well as a nephelometer, net flux radiometer, and an ultrastable oscillator to enable Doppler wind tracking of the probe throughout descent.</p> </div> </div> </div>

Exploring planetary atmospheres uncovers important information as to how our solar system formed and evolved. While remote sensing is extensively used, some crucial observations require in situ measurements by an atmospheric probe. Given their scientific importance, probe missions to Saturn, Uranus, and Neptune are under consideration for the coming decades. In anticipation of future probe missions, the software tool Visualization of the Impact of PRobe Entry conditions on the science, mission and spacecraft design (VIPRE) was developed as proof-of-concept to facilitate selection of probe entry locations. Currently, there is no analytical way to identify which interplanetary trajectory from thousands of feasible launch opportunities is optimal for a considered mission concept. The search and decision process for that solution is complex and relies on the intuition of mission designers, who focus on a subset of trajectories to make the trade space manageable. The idea of VIPRE is (1) to generate a multidimensional data cube showing relevant engineering and science parameters simultaneously for thousands of trajectories, and (2) to visualize the data for all entry sites over the body's envelope. VIPRE lays a foundation to make available the data for browsing in a 3D visualization to identify the best family of solutions for a given mission. This paper introduces the validated and verified core algorithms of VIPRE, published on GitHub Probst. VIPRE serves as a basic framework to be used and extended for different purposes. The paper further presents the motivation for the development and algorithms; it explains the computation and data visualization strategy; and gives a list of suggested functionalities to extend and further develop VIPRE to fully leverage its potential.

The ice giants Uranus and Neptune are the least understood class of planets in our solar system, while planets of their size, the most frequent among exoplanets, represent a common outcome of planet formation. Presumed to have a small rocky core, a deep interior comprising ∼70% heavy elements surrounded by a more dilute outer envelope of H2 and He, Uranus and Neptune are fundamentally different from the better-explored gas giants Jupiter and Saturn. Because of the dearth of missions dedicated to their exploration, our knowledge of their composition and atmospheric processes is primarily derived from a single Voyager 2 flyby of each, complemented by subsequent remote sensing from Earth-based observatories, including space telescopes. As a result, Uranus's and Neptune's physical and atmospheric properties remain poorly constrained and their roles in the evolution of the Solar System are not well understood. Exploration of ice giant systems is therefore a high-priority science objective as these systems (which link together the magnetospheres, satellites, rings, atmosphere, and interior of these planets) challenge our understanding of planetary formation and evolution. Here we describe the main scientific goals to be addressed by future in situ exploration of an ice giant's atmosphere. An atmospheric entry probe targeting the 10-bar level, approximately 5 scale heights beneath the tropopause, would yield insight into two broad themes: i) the formation history of the ice giants and, in a broader extent, that of the Solar System, and ii) the processes governing the structure and composition of planetary atmospheres. The battery-powered probe would descend under parachute to measure composition, structure, and dynamics. In our favorite scenario, an Ice Giants orbiter performing a comprehensive exploration of the system would be used to deliver the probe to the atmosphere and to relay its data back to Earth. Following the successful architecture of the Cassini-Huygens mission, we envision that the probe would be delivered by ESA and the orbiter by NASA, with possible technical contributions of one Agency to the other's platform, on the basis of technical and programmatic considerations. The science payloads of the two platforms would be shared between NASA and ESA members states on the basis of scientific merit and technical/funding resources.

The Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission described herein has been selected for flight to Venus as part of the NASA Discovery Program. DAVINCI will be the first mission to Venus to incorporate science-driven flybys and an instrumented descent sphere into a unified architecture. The anticipated scientific outcome will be a new understanding of the atmosphere, surface, and evolutionary path of Venus as a possibly once-habitable planet and analog to hot terrestrial exoplanets. The primary mission design for DAVINCI as selected features a preferred launch in summer/fall 2029, two flybys in 2030, and descent-sphere atmospheric entry by the end of 2031. The in situ atmospheric descent phase subsequently delivers definitive chemical and isotopic composition of the Venus atmosphere during an atmospheric transect above Alpha Regio. These in situ investigations of the atmosphere and near-infrared (NIR) descent imaging of the surface will complement remote flyby observations of the dynamic atmosphere, cloud deck, and surface NIR emissivity. The overall mission yield will be at least 60 Gbits (compressed) new data about the atmosphere and near surface, as well as the first unique characterization of the deep atmosphere environment and chemistry, including trace gases, key stable isotopes, oxygen fugacity, constraints on local rock compositions, and topography of a tessera.

Understanding the formation and evolution of the solar system and the formation of the giant planets is constrained by inherent limitations in the capabilities of remote sensing. In situ exploration of planetary atmospheres provides key measurements not possible from remote observations, remarkably demonstrated at Jupiter by the Galileo probe, where key measurements included the determination of noble gas abundances and the precise measurement of the Jupiter helium mixing ratio. In this paper, we describe the primary scientific goals to be addressed by future in situ exploration of the ice giants Uranus and Neptune, placing in situ explorations of the gas giants, including the Galileo probe and a future Saturn probe, into a broader solar system context. An ice giant atmospheric entry probe reaching 10 bars would provide insight into both the formation history of the solar system and the giant planets, and the structure and composition of, and physical processes at play within ice giant atmospheres. An entry probe as an element of a future ice giant flagship mission would descend under parachute to measure the abundances and isotopic ratios of the noble gases, D/H in H2 and 13C/12C, and the thermal structure and dynamics from the upper atmosphere down to the deepest region from which the probe is able to return data, perhaps 10-20 bars or more. Probe data would be returned to Earth using a Carrier Relay Spacecraft as a relay station. The relay spacecraft, particularly if it is an orbiter with a suite of remote sensing instruments, can significantly enhance the science return from the probe; remote sensing provides the global context from which to understand the probe's local measurements of weather and cloud properties. One or more small atmospheric probes could represent a significant ESA contribution to a future NASA New Frontiers or Flagship Ice Giant mission.

Background: Miranda is the innermost and smallest of the classical Uranian satellites, with a ~470-km-mean-diameter [1]. This satellite has a geologically complex and highly deformed surface, highlighted by regions of tectonically resurfaced terrain with low crater densities, termed “coronae” and a large system of normal fault scarps up to 8 km in height making up the “Global Rift System,” present within the cratered terrain (Figure 1) [2,3]. Verona Rupes, the 340 Degree Chasma, and the South Pole Tangent Chasma are part of the Global Rift System [3], along with numerous smaller scale faults and fractures across the cratered terrain.

This paper describes atmospheric entry and descent probe missions in the atmospheres of the ice giants, Uranus and Neptune, targeting a minimum depth at the 10-bar level.In situ exploration of ice giant atmospheres addresses two broad themes: i) the formation history of the ice-giant planets and their role in the evolution of the solar system, and ii) the structure, dynamics, and processes in their atmospheres.An ice giant probe descending under parachute can measure abundances of key atmospheric constituents, deep thermal structure, dynamics, and processes, with data returned to Earth by a Carrier Relay Spacecraft.An atmospheric probe is an essential element of a possible future NASA Ice Giant New Frontier or Flagship mission.

In the pursuit of deciphering the formation of our solar system, the exploration of the compositional and dynamical structure of planetary atmospheres with entry probes plays a crucial role. A probe's measurements provide insight into an atmosphere's deeper composition and dynamical processes not accessible via remote sensing, providing key information on the origin and possible migration of planets during early formation phase. A planetary entry probe mission has been in discussion in several Planetary Science Decadal Surveys, one to Saturn has been identified as a mission of highest priority in the current one 2013-2022, and a mission to Uranus and/or Neptune carrying a probe is being considered as a Flagship mission in the next one spanning 2023-2032. In the development of such missions, the probe approach and delivery trajectory is a critical element to mission success, including ring avoidance, and targeting of highly desirable regions in the atmosphere, while balancing other requirements such as providing an optimal communication geometry between the probe and the relay spacecraft while meeting the mission's science objectives. Due to the complexity of the problem, mission concept studies are usually limited to the investigation of a limited number of specific trajectories and probe delivery opportunities to a very small, pre-defined range of latitudes while leaving a huge trade space unexplored. The tool VAPRE (Visualization of Atmospheric PRobe Entry conditions) has been developed to enable a fast and wide-range evaluation of entry conditions for planetary probes, spanning the complete range of latitudes for each of the three planets. VAPRE allows a rapid assessment of feasible entry sites by evaluating a large number of arrival trajectories based on their hyperbolic arrival velocities with respect to parameters such as the flight path angle and the relative entry velocity of the probe at the entry interface point. VAPRE facilitates the mission design process by combining the evaluation of technical feasibility and science value for the investigated scenarios to assess potential entry sites. VAPRE is developed in the framework of IPED (Impact of the Probe Entry zone on the trajectory and probe Design), which is a two- to three-year research study to investigate both the impact of interplanetary and approach trajectories on the feasible range of entry sites as well as on probe design, considering Saturn, Uranus, and Neptune as target bodies. In this paper we fully demonstrate the functionalities of the VAPRE tool on a case scenario for a mission to the Ice Giants. The presented research was supported by an appointment to the NASA Postdoctoral Program (NPP) at the Jet Propulsion Laboratory (JPL), California Institute of Technology, administered by Universities Space Research Association (USRA) under contract with National Aeronautics and Space Association (NASA). © 2020 All rights reserved.

The innovative Saturn Ring Skimmer mission concept enables a wide range of investigations that address fundamental questions about Saturn and its rings, as well as giant planets and astrophysical disk systems in general. This mission would provide new insights into the dynamical processes that operate in astrophysical disk systems by observing individual particles in Saturn's rings for the first time. The Ring Skimmer would also constrain the origin, history, and fate of Saturn's rings by determining their compositional evolution and material transport rates. In addition, the Ring Skimmer would reveal how the rings, magnetosphere, and planet operate as an inter-connected system by making direct measurements of the ring's atmosphere, Saturn's inner magnetosphere and the material owing from the rings into the planet. At the same time, this mission would clarify the dynamical processes operating in the planet's visible atmosphere and deep interior by making extensive high-resolution observations of cloud features and repeated measurements of the planet's extremely dynamic gravitational field. Given the scientific potential of this basic mission concept, we advocate that it be studied in depth as a potential option for the New Frontiers program.

In situ atmospheric measurements are a high priority for any future Flagship mission to the Ice Giants; however, most current mission concepts only include a single atmospheric entry probe in their designs. To maximize science returns and provide redundancy at a marginal cost, different mission architecture options are explored to deliver multiple atmospheric probes to Uranus. A methodology is developed for the consistent and generalized design of each architecture, integrating interplanetary trajectories, science orbits, probe entry and descent trajectories, telecommunication and data transfer performances, and to a certain extent, risks. A baseline single-probe mission is first designed using this methodology. Then, different architecture options to add a small secondary probe to this baseline mission are explored one by one and compared with each other and the original baseline mission. During the design of these different architectures, it is found that operational conflicts and data transmission capabilities are key drivers for the mission design and render some configurations infeasible. Comparisons are then made on the impact to the baseline single-probe mission, and it is determined that an additional 30 kg probe can be delivered to Uranus for a total mass penalty of under 100 kg. The dependence of probe mission design on the selection of interplanetary trajectory is also explored and is shown to have a significant impact on the design of the mission and its potential for success.

The composition of outer planet atmospheres holds fundamental clues to understanding the formation and evolution of the solar system. Measurements of noble gas abundances and key isotope ratios help constrain formation models, and along with measurements of atmospheric structure and dynamics they reveal formation and evolutionary processes [1], [2]. These enable conclusions about giant planet formation and possible migration during the epoch of solar system formation. With the Galileo Probe laying the foundation of in situ atmospheric measurements of the outer planets by exploring Jupiter, entry probe missions to Saturn, Uranus and Neptune are essential to complete the picture of how our solar system evolved to its present state. During the development of entry probe missions, the interplanetary and probe approach trajectory, as well as the selection of the entry interface zone, are critical elements to mission success. Both elements are driven by considerations such as spacecraft safety (e.g. avoiding rings), while balancing science and engineering requirements at the same time (e.g. highly interesting science and entry zone vs. optimal communication geometry between probe and relay spacecraft). Due to the complexity of the problem, there is no analytical solution for finding the ‘best’ trajectory. Instead, one relies on the experience and intuition of mission designers to select a few possible interplanetary trajectories, which are then explored in detail to see how they meet science and engineering requirements. This approach leaves a huge trade space unexplored and may find a local, rather than a global optimum trajectory for the mission. We are addressing this gap by developing a software tool called VAPRE (Visualization of Atmospheric PRobe Entry Conditions for different bodies and trajectories) [3], [4] that allows us to explore those previously unexplored trade spaces. VAPRE can process thousands of trajectories, significantly more than in the currently common mission design processes. Due to its flexible architecture, VAPRE can be adapted and extended to accommodate new science and engineering constraints for different or similar mission scenarios. In our talk, we will present an example of how the tool can be used to design a flyby mission to a giant planet that delivers an atmospheric probe considering opportunities between 2028 and 2042.

<p>Planetary atmospheric winds, waves, tides, and turbulence represent a tie-point between planetary structure and processes, including atmospheric thermal and energy structure, cloud location and properties, and atmospheric composition and compositional gradients. The only direct means by which dynamics of an ice giant atmosphere can be measured along the probe descent path is via radiometric tracking of an ice giant entry probe. Additionally, measurements on an orbiter of the strength of a probe telecom signal can be used to provide the abundance of microwave absorbing molecules along the probe relay signal raypath, expected to be primarily ammonia (NH<sub>3</sub>) or hydrogen sulfide (H<sub>2</sub>S).</p> <p> </p> <p>Doppler tracking of a descent probe has been demonstrated with the Galileo probe at Jupiter and the Huygens probe at Titan. By including an ultrastable oscillator on both the transmit and receive sides of the probe telemetry relay signal, the time variation of the measured relay signal frequency provides a measure of wind speeds (via the Doppler effect). and the signatures of atmospheric waves, convection, and turbulence. In addition, other probe dynamical effects such as pendulum motion under the parachute, probe spin, and aerodynamic buffeting can be retrieved from careful analysis of the probe telecom signal Doppler residuals. Measurements made on board the orbiter of the time-varying received signal strength would provide a profile of microwave absorbing molecules along the probe radio signal raypath, complementing composition measurements made the probe mass spectrometer.</p> <p> </p> <p>The scientific objectives, measurement requirements, and expected measurement accuracies of the profile of zonal winds and atmospheric absorption will be discussed in this presentation, with a preliminary attempt to quantify the effect of uncertainties in the reconstruction of the probe descent and carrier overflight trajectories.</p>

More than 85% of the 23 investigations developed by VEXAG are largely accomplished via a NF mission centered on a variable-altitude balloon (aerobot) supported by a science/comm orbiter. Circling Venus >15 times over ~90 days, the aerobot repeatedly visits 52–62 km alts as it semi-continuously samples a host of environmental & surface parameters.