In March 2013, the European Space Agency put out a call for the definition of the next cornerstones of the Cosmic Vision process, known as L2 and L3. These missions are planned for launch in 2028 and 2034, respectively, and represent European investments of approximately €1 billion.
Despite the recently-selected Jupiter Icy Moons Explorer (JUICE) being developed for the L1 mission (launch in 2022), the planetary science community was urged to actively participate in this call. There was no shortage of exciting, ambitious and ground-breaking ideas for the exploration of our solar system, addressing themes and questions right at the heart of ESA’s Cosmic Vision. A whole raft of white papers were submitted, several of which were presented at a community meeting in Paris. Ultimately, an X-ray astronomy mission (ATHENA) and a gravitational wave observatory (LISA) were selected as the cornerstone science themes, but the European Ice Giant community were provided with valuable feedback to continue to seek an international mission to these distant worlds.
Senior Survey Committee Report
The 2013 report of ESA’s Senior Survey Committee stated:
“In situ exploration of the icy giant planets would bring major advances in our understanding of these worlds in several respects. First, the study of their internal structure (through radio science, accelerometery and, ideally, a measurement of elemental abundances through mass spectrometry aboard a probe), as well as a study of their satellite properties, could provide key diagnostics concerning the history of these systems. Second, an in-depth study of their atmospheres, ionospheres and magnetospheres, as well as their rings and satellites, will help us understand the physico-chemical processes at work in these two systems. Ideally, comparative planetology could be achieved from similar observations performed on both planets and their environments.
After the success of the Cassini mission, and after the selection of an exploration mission toward the Jovian system, the exploration of the icy giants appears to be a timely milestone, fully appropriate for an L class mission. The whole planetology community would be involved in the various aspects of this mission, including physics of the interior, atmospheric and surface sciences, plasmas physics and dynamics. Several mission concepts could be considered, including orbiters and probes, and would need to be investigated in the next stage.
The SSC considered the study of the icy giants to be a theme of very high science quality and perfectly fitting the criteria for an L-class mission. However, in view of the competition with a range of other high quality science themes, and despite its undoubted quality, on balance and taking account of the wide array of themes, the SSC does not recommend this theme for L2 or L3. Iview of its importance, however, the SSC recommends that every effort is made to pursue this theme through other means, such as cooperation on missions led by partner agencies.”
White papers relevant to the Ice Giants included:
The Science Case for an Orbital Mission to Uranus: Exploring the Origins of Ice Giant Planets
Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun’s planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus’ atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency’s call for science themes for its large-class mission programme in 2013.
Neptune and Triton: Essential Pieces of the Solar System Puzzle
The planet Neptune and its largest moon Triton hold the keys to major advances across multiple fields of Solar System science. The ice giant Neptune played a unique and important role in the process of Solar System formation, has the most meteorologically active atmosphere in the Solar System (despite its great distance from the Sun), and may be the best Solar System analogue of the dominant class of exoplanets detected to date. Neptune׳s moon Triton is very likely a captured Kuiper Belt object, holding the answers to questions about the icy dwarf planets that formed in the outer Solar System. Triton is geologically active, has a tenuous nitrogen atmosphere, and is predicted to have a subsurface ocean. However, our exploration of the Neptune system remains limited to a single spacecraft flyby, made by Voyager 2 in 1989. Here, we present the high-level science case for further exploration of this outermost planetary system, based on a white paper submitted to the European Space Agency (ESA) for the definition of the second and third large missions in the ESA Cosmic Vision Programme 2015–2025. We discuss all the major science themes that are relevant for further spacecraft exploration of the Neptune system, and identify key scientific questions in each area. We present an overview of the results of a European-led Neptune orbiter mission analysis. Such a mission has significant scope for international collaboration, and is essential to achieve our aim of understanding how the Solar System formed, and how it works today.
Scientific Rationale for Uranus and Neptune in situ Explorations
Originally part of a Saturn probe white paper.
The ice giants Uranus and Neptune are the least understood class of planets in our solar system but the most frequently observed type of exoplanets. 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 lack of dedicated exploration missions, our knowledge of the composition and atmospheric processes of these distant worlds is primarily derived from remote sensing from Earth-based observatories and 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 not well understood. Exploration of an ice giant system is therefore a high-priority science objective as these systems (including the magnetosphere, satellites, rings, atmosphere, and interior) challenge our understanding of planetary formation and evolution. Here we describe the main scientific goals to be addressed by a future in situ exploration of an ice giant. An atmospheric entry probe targeting the 10-bar level, about 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 at play in planetary atmospheres. The probe would descend under parachute to measure composition, structure, and dynamics, with data returned to Earth using a Carrier Relay Spacecraft as a relay station. In addition, possible mission concepts and partnerships are presented, and a strawman ice-giant probe payload is described. An ice-giant atmospheric probe could represent a significant ESA contribution to a future NASA ice-giant flagship mission.
The ODINUS Mission Concept: The Scientific Case for a Mission to the Ice Giant Planets with Twin Spacecrafts to Unveil the History of our Solar System
The purpose of this document is to discuss the scientific case of a space mission to the ice giants Uranus and Neptune and their satellite systems and its relevance to advance our understanding of the ancient past of the Solar System and, more generally, of how planetary systems form and evolve. As a consequence, the leading theme of this proposal will be the first scientific theme of the Cosmic Vision 2015-2025 program: What are the conditions for planetary formation and the emergence of life? In pursuing its goals, the present proposal will also address the second and third scientific theme of the Cosmic Vision 2015-2025 program, i.e.: How does the Solar System work? What are the fundamental physical laws of the Universe? The mission concept we will illustrate in the following will be referred to through the acronym ODINUS, this acronym being derived from its main fields of scientific investigation: Origins, Dynamics and Interiors of Neptunian and Uranian Systems. As the name suggests, the ODINUS mission is based on the use of two twin spacecraft to perform the exploration of the ice giants and their regular and irregular satellites with the same set of instruments. This will allow to perform a comparative study of these two systems so similar and yet so different and to unveil their histories and that of the Solar System.
