Objectives for Atmospheres and Ring Science for the Jupiter Icy Moons Orbiter

The Solar System Exploration Decadal Survey was made public in draft form in June 2002. It lists 12 key scientific questions, of which 4 are most relevant to the planet Jupiter: 1. Over what period did the gas giants form, and how did the birth of the ice giants (Uranus, Neptune) differ from that of Jupiter and its gas-giant sibling, Saturn? 2. What is the history of volatile compounds, especially water, across our solar system? 3. How do the processes that shape the contemporary character of planetary bodies operate and interact? 4. What does our solar system tell us about the development and evolution of extrasolar planetary systems, and vice versa? The Decadal Survey, which was asked to provide a prioritized list of the most promising avenues for flight investigations, recommended a Jupiter Orbiter with Probes (JPOP) as the highest priority giant planets mission in the New Frontiers line. The goals of that mission are: 1. Determine if Jupiter has a central core to constrain ideas of its formation 2. Determine the planetary water abundance 3. Determine if the winds persist into Jupiter's interior or are confined to the weather layer 4. Assess the structure of Jupiter's magnetic field to learn how the internal dynamo works 5. Measure the polar magnetosphere to understand its rotation and relation to the aurora JPOP was proposed as a high inclination orbiter whose low equatorial perijove enabled it to make detailed measurements of the gravitational and magnetic fields as well as the polar magnetosphere. The probes mainly addressed the water abundance and deep winds. The gravitational field measurement also addressed the deep winds as well as the central core. The JIMO opportunity arose after the Decadal Survey report was written, and is different from the opportunity afforded by a New Frontiers mission. JIMO offers a potential breakthrough in remote sensing: The 1-3 Mbps data rate is 2 orders of magnitude greater than that of previous missions. The circular orbit offers continuous planet viewing during the 3 months between satellite encounters. The 10-30 kW of power offers advantages for radio occultations and other active sensors. In addition, JIMO can carry a probe, which can determine the water abundance, deep winds, and thermal structure to 100 bars. At the Forum on Concepts and Approaches for JIMO in Houston, Texas on June 14-15, 2003, the Atmospheres and Rings Subgroup came up with the following prioritized list of objectives: 1. Composition, structure, chemistry, and dynamics of Jupiter's atmosphere. 2. Composition, structure, and dynamics of icy moon atmospheres. 3. Composition, structure, dynamics, and time variability of the atmosphere of Io. 4. Nature of the interaction between magnetosphere, satellites, and Jupiter. 5. Structure, composition, energy budget, and variability of satellite tori. 6. Structure and particle properties of the Jovian ring system Each objective has several prioritized investigations, and each investigation has a prioritized list of measurements. These will be presented at the meeting. Some of the measurements require a probe; others can be done from the JIMO orbiter. With or without a probe, the JIMO mission can answer fundamental questions about atmospheres, rings, and satellite tori in the Jupiter system.