ISTS 2006-o-2-06V AN OVERVIEW OF THE JUNO MISSION TO JUPITER Richard Grammier Jet Propulsion Laboratory 4800 Oak Grove Drive, MS 301-360, Pasadena, CA 91101-8099 USA (Email: [email protected]) Abstract radiometer for mapping atmospheric composition and dynamics, a dual- Arriving in orbit around the planet Jupiter frequency radio-gravity science system, in 2016 after a five-year journey, the Juno plasma detectors, energetic particle spacecraft will begin a one-year detectors, an ultraviolet investigation of the gas giant in order to imager/spectrometer, a plasma wave understand its origin and evolution by experiment, and a visible camera for determining its water abundance and imaging Jupiter’s poles for the first time. constraining its core mass (Figure 1). In Operations at Jupiter are simple and addition, Juno will map the planet’s repetitive. When the investigation is magnetic and gravitational fields, map its complete, the spacecraft will de-orbit into atmosphere, and explore the three- the planet itself. dimensional structure of Jupiter’s polar magnetosphere and auroras. Contents Abstract 1 1 Overview 1 2 Project Implementation 2 2.1 Science Investigations 3 2.1.1 Origin 3 2.1.2 Interior 4 2.1.3 Atmosphere 5 2.1.4 Magnetosphere 5 3 Mission Design 6 Figure 1: Juno will discriminate among different models for giant planet formation. 4 The Spacecraft 7 5 Conclusion 8 These investigations will be conducted over the course of thirty-two 11-day 6 Acknowledgements 8 elliptical polar orbits of the planet. The orbits are designed to avoid Jupiter’s 1 Overview highest radiation regions. Juno’s goal is to understand the origin and The spacecraft is a spinning, solar- evolution of Jupiter. As a gas giant, Jupiter powered system carrying a complement of can provide a wealth of knowledge that can eight science instruments for conducting help us understand the origin of our own the investigations. The spacecraft systems solar system as well understand other and instruments take advantage of planetary systems being discovered around significant design and operational heritage other stars. from previous space missions. Using a spinning, solar powered Juno’s scientific payload consists of a spacecraft, Juno will produce global maps dual-technique magnetometer, a microwave of the gravity, magnetic fields, and 1 An Overview of the Juno Mission to Jupiter ISTS 2006-o-2-06V atmospheric composition from a unique Atmospheric Composition and polar orbit with a close perijove (closest Dynamics is measured by atmospheric point to Jupiter) (Figure 2). The nominal sounding to pressures greater than 100 32-orbit mission will produce an extensive bars, producing a three-dimensional map of sample of Jupiter’s full range of latitudes the water and ammonia abundances; and and longitudes. Juno will accomplish its determining how deep the belts, zones, and mission through a combination of in situ other features penetrate. and remote observations. The largest structure in the solar system, Jupiter’s polar magnetosphere and its coupling to the atmosphere are explored by measuring auroral emissions, plasmas, fields, waves and radio emissions. 2 Project Implementation The Juno project is implemented as part of NASA’s New Frontier Program, under the leadership of Dr. Scott Bolton, the Principle Investigator (PI) from Southwest Research Institute (SwRI). The day-to-day project management and implementation is delegated to the Jet Propulsion Laboratory (JPL), under the leadership of Rick Grammier, the Project Manager (PM). SwRI and JPL teamed with several companies, universities and other NASA centers to provide the scientific instruments and spacecraft systems. JPL is providing Figure 2: Using a spinning, solar powered the overall management, project spacecraft, Juno will produce global maps of engineering, mission design and navigation, the gravity, magnetic fields, and atmospheric mission operations, payload management, composition from a unique polar orbit with a telecommunications/gravity science system, close perijove. microwave radiometer (MWR) experiment, and part of the dual-technique Juno’s investigations divide into four magnetometer. major themes: Origin, Interior Structure, Lockheed Martin (LM) is the primary Atmospheric Composition and Dynamics, spacecraft contractor and is responsible for and the Polar Magnetosphere. Origin the design, build, and test of the spacecraft discriminates among different models for as well, as the integration of the payload giant planet formation, constraining the instruments. LM also performs mission mass of the solid core by measuring the operations with JPL. gravitational field and determining the The home institution of the PI, SwRI abundance of certain heavy elements provides two of the instruments for the (oxygen and nitrogen) in Jupiter’s polar magnetosphere investigation— atmosphere via microwave observations of Ultraviolet Spectrometer (UVIS) and Jovian water and ammonia. Auroral Distributions Experiment Interior Structure maps the gravitational (JADE)—and manages the science team and magnetic fields with sufficient and the education and public outreach resolution to determine the origin of the program. magnetic field, the core mass and the Goddard Space Flight Center (GSFC) is nature of deep convection. providing the combined magnetometer experiment. Applied Physics Lab (APL) is 2 Project Implementation providing the Energetic Particle Detector sound atmospheric ammonia and water (EPD). The University of Iowa is providing from below the ammonia cloud tops to as the Waves experiment. The visible camera deep as practical. provider has not yet been selected. (The visible camera is not a science instrument and has no scientific requirements associated with it.) 2.1 SCIENCE INVESTIGATIONS 2.1.1 Origin The primary science goal of understanding planetary formation and evolution is directly related to the study of Jupiter’s interior and atmosphere. The mass of Jupiter’s core helps distinguish among Figure 3: Juno’s measurement of O competing scenarios regarding the planet’s discriminates among Jupiter’s formation formation. Jupiter’s water abundance is key scenarios. Abundances of Ar, Kr, Se, C, and S in understanding giant planet formation are well determined on Jupiter at 3x Solar. O and the delivery of volatiles throughout the is not yet determined. Juno determines both solar system (Figure 3). the N and O abundances. The microwave radiometer (MWR) instrument determines the water abundance The number of channels is sufficient to in Jupiter. It maps the water over all fully sample the desired pressure range and latitudes, thus eliminating sampling bias reach below 100 bars. inherent in limited probe measurements. The instrument is based upon a number The instrument consists of six different of previous, Earth-orbiting experiments, antennas, radiometers, and with the most recent heritage to the control/calibration electronics. The MWR Advanced Microwave Radiometer (AMR) uses six frequencies for atmospheric for the Ocean Surface Topography Mission sounding, from 0.6 GHz to 23 GHz (OSTM). (Figure 4). The wavelengths are chosen to Figure 4: Each of the six MWR antennas uses a different frequency from a range chosen to sound atmospheric ammonia and water from below the ammonia cloud tops to as deep as practical. 3 An Overview of the Juno Mission to Jupiter ISTS 2006-o-2-06V band downlink and X- and Ka-band 2.1.2 Interior uplink/downlink. Juno measures the gravity field, magnetic field, and water abundance, to determine the structure of the planet, the nature of deep convection, and the process of magnetic field generation. Juno’s low perijove allows the measurement of the gravity field to a high harmonic degree and unprecedented accuracy. The Juno measurement of the low-order gravitational harmonics, together with microwave data on envelope composition, provide key constraints on planetary structure and the mass of Jupiter’s core (Figure 5). Figure 6: Juno’s precise gravity measurements provide new constraints on Jupiter’s core mass and internal convection. Diamonds represent current knowledge. Triangles show expected tidal responses. The lines show signatures of solid-body (dashed lines) and differential (red line) rotation. By mapping Jupiter’s magnetic field with a resolution exceeding that available for any other planet, including Earth, Juno seeks to understand the origin of planetary magnetic fields. Juno also seeks to detect magnetic- field secular variation in order to image Figure 5: Juno investigates the structure fluid motions at the surface of the dynamo- and convection of Jupiter’s interior by generating region. The experiment reaching through the meteorological layer. A measures the high harmonics of the possible inner “rock” core is shown, surrounded by a “blue” metallic hydrogen magnetic field at small distance, which is envelope and a “yellow” outer envelope of crucial to understanding the dynamo molecular hydrogen, all hidden beneath the mechanism (Figure 7). visible cloud deck. The Magnetometer experiment consists of a pair of fluxgate sensors (FGM) that Juno’s gravity-science experiment measure the three components of the provides data on Jupiter’s internal vector magnetic field, and an orthogonal convection and deep winds (Figure 6). This array of scalar helium magnetometer (SHM) experiment is capable of both X- and Ka- cells that measure the magnitude of the band uplink and downlink. During the field. Both the FGM and SHM are flight mission, the X-band portion is the primary proven