Exploration of Giant Planet Magnetospheres

1. Exploration of Giant Planet Magnetospheres Fran Bagenal, University of Colorado • Jupiter Top Priority • Polar Regions • Multi-Spacecraft

2. Giant Planet Magnetospheres • Giant! • Rotation Dominated • Satellite plasma sources • J&S • Symmetric • ~Dipolar • Strong plasma production • Limited solar wind influence • U&N • Highly asymmetric, • Highly non-dipolar • Complex transport (SW + rotation) • Multiple plasma sources (ionosphere + solar wind + satellites)

3. Giant Planet Magnetospheres Space Physics Fields Dynamo Local currents Global Electric fields Oscillations Interplanetary Satellites Plasma Production Global transport Radiative cooling Diffusion Waves Plasma instabilities Propagation Particle damping Energetic Particles Acceleration Absorption Charge exchange Radio Emissions Generation Propagation Planetary Interiors Dynamo Convection Conductivity Rotation Induction Planetary Atmospheres Auroral precipitation Auroral heating Ionization Radiative transfer Thermospheric winds Satellite Surfaces Radiolosis Sputtering Satellite Atmospheres Sputtering Heating Ionization Stripping Dust & Rings Charging Transport

4. Giant Planet Magnetospheres Why not Uranus & Neptune? • Logical step after Galileo and Cassini? • Getting there! • U&N small, complex, variable • Main issue of magnetosphere-planet coupling more easily addressed at Jupiter • Earth demonstrated necessity of multi-spacecraft

5. Giant Planet Magnetospheres Why Focus on Jupiter?Again? Still? • Jupiter archetype of rotation-driven magnetospheres (~90% of Tom Hill’s 36 big issues of GPMs relate to Jupiter) • Time to move beyond “exploration-mode” to “in-depth investigation-mode” • Galileo attempted this but hampered by bits-to-ground and “old-style” mission • Accessible by both spacecraft and earth-based telescopes

6. Giant Planet Magnetospheres What can be done from Earth? Ground-based Telescopes Radio Astronomy - synchrotron & auroral emissions Visible - Io, plasma torus (limited) IR - Io volcanoes, Auroral emissions Earth Orbit HST - aurora, Io, torus EUVE, FUSE, CHANDRA…. BUT…. System variable and coupled - need to observe multiple components simultaneously Limited access to telescopes Need in situ measurements

7. SMall EXplorer mission under study - Earth-orbiting UV telescope to observe Io, the torus and Jovian aurora

8. Giant Planet MagnetospheresLearning From Terrestrial Studies Coverage, coverage, coverage… Space & Time Multiple missions • Upstream Solar Wind (from L1) • Middle magnetosphere (Geosynch) • Polar orbits • Magnetotail Ground, Rocket, LEO Studies • Multiple viewpoints • Instrumentation on operational s/c Co-ordination • International Campaigns • ISTP, GGS, etc; • Quiet times & Storms • Prediction - Space Weather

9. Giant Planet Magnetospheres“Cheaper, Faster, Better” • Full Planetary Missions • 3-axes stabilized • Cameras • Large data rates Simplest missions - “Ulysses-style” • Spinning Spacecraft • No imaging (except sweeping linear detectors? UV? Vis/IR?) • Particles and fields emphasis • Technology Drivers • Propulsion • Power • Communications • Radiation Protection

10. Conclusions:Study Jovian System in Depth Priorities for missions • Earth-orbiting UV telescope • Polar Orbiter with fields and particles instrumentation • Multi-spacecraft missions • Middle magnetosphere • Io electrodynamics exploration • Solar wind upstream • Magnetotail

11. Jupiter Polar Orbiter -The Large Print • This is a description of a GENERIC Jupiter Polar Orbiter mission. It has been put together to give a general flavor of the sort of mission that could be flown to address important space physics issues at Jupiter. • It is not the JPO nor Inside Jupiter proposed to Discovery. • It is not the “official” roadmap JPO • Many people are enthusiastic about a JPO mission and contributed material but they are not official co-authors since there was not time for them to critique this presentation. • People from the magnetospheric community who have expressed enthusiasm for a JPO mission (in no particular order): Jack Connerney, Hunter Waite, Tom Krimigis, Tom Hill, Margy Kivelson, Bob Ergun, Barry Mauk, Lou Lanzerotti, Jim Burch, Chuck Carlson, Dave Young, Dan Baker, Don Mitchell, Andy Nagy, John Clarke…. For reference, the Magnetospheres of the Outer Planets conferences held every other year tend to draw about 150 people.

12. Jupiter Polar Orbiter -Background • Remote sensing and spacecraft missions have revealed that Jupiter has a giant magnetosphere which shares gross similarities to the Earth's magnetosphere (bow shock, magnetopause, magnetotail) but Jupiter's strong magnetic field and Io's abundant plasma source produce dramatic differences - the dynamics are dominated by rotation and the variability primarily internally driven rather than driven by the solar wind. • For the magnetospheric plasma to be coupled to Jupiter's rotation, field-aligned currents must flow between the equatorially-confined plasma and the polar ionosphere. The few glimpses of Jupiter's aurora (e.g. provided by HST in UV or ground-based telescopes in IR) show strong emissions presumably associated with particle fluxes which carry these field-aligned currents. • Only the second spacecraft to venture to high latitudes, Ulysses measured strong field-aligned currents as it flew past Jupiter on the dusk side of the planet. Powerful radio emissions and a variety of auroral images (from x-rays to IR) exhibit complex spatial and temporal variability. • To understand the cause-and-effect relationships between magnetospheric and auroral processes we need in situ measurements taken at polar regions. Just as Dynamics Explorer, POLAR and FAST explored Magnetosphere-Ionosphere-Atmosphere coupling at Earth, JPO will elucidate these critical linkages at Jupiter - allowing us to test our understanding of magnetosphere/auroral processes in general through application to a very different planet.

13. Jupiter Polar Orbiter-ScientificObjectives 1 • The purpose of JPO would be to explore the polar regions of Jupiter's magnetosphere to answer the following outstanding questions: • What is the nature and degree of coupling between the magnetosphere, ionosphere and atmosphere? • What roles do changes in Io's volcanism, the solar wind and the plasmasheet each play in magnetospheric variability? • What are the compositions and energies of the primary particles that excite auroral emissions? • What is the cause of the polar-cap auroras at Jupiter? • What is the cause of the brief, super-bright auroral flares occasionally observed in Jupiter's polar region?

14. Jupiter Polar Orbiter-ScientificObjectives 2 • What are the source locations and emission mechanisms of Jupiter's auroral radio emissions? • What are the auroral acceleration processes, and how are they related to the generation mechanisms of radio emissions? • Is there a one-to-one correspondence between auroral emission features and nonthermal radio emission features? • How is the Io control of the decametric radio emission accomplished? • What process creates the long auroral tail observed downstream of the auroral footprint of Io and perhaps other large satellites? • What is the detailed structure of Jupiter's high-latitude magnetic field? (This information is needed for clear interpretation of remotely-observed auroral and radio emision features.)

15. The Io Aurora Infrared Ultraviolet - what accelerates the precipitating energetic particles? - why does ‘wake’ emission extend half way around Jupiter

16. Jupiter Polar Orbiter - Mission 1 Orbit: Polar elliptical orbit (1.1 Rj x ~20 Rj, >80 degrees inclination). The apojove distance is less critical, to be optimized between 20-40 Rj (with longer period orbits lengthening the mission time vs. requiring less mess). The evolution of the orbit will help cover much of magnetosphere. Orbit optimized to get maximum polar coverage with minimum radiation dosage. Spacecraft: Solar powered, chemical propulsion for orbit insertion and corrections, large onboard memory (for accumulating data over the poles/perijove for downloading over apojove). Challenges: propulsion, power, communication, radiation - as with all Jupiter missions

17. Jupiter Polar Orbiter - Mission 2 • Payload: • - plasma, particles, electric and magnetic fields • - UV, IR and/or x-ray remote sensing package - TBD as mass permits • radio science • Cost: ~$350M • Schedule: The fastest trajectory is ~2 years to Jupiter but a Venus flyby may be necessary depending on cost and mass constraints. ~30 orbits over 1 year.

18. Jupiter Polar Orbiter - Which Program? • Discovery? The Discovery program is currently limited to Solar System Exploration. Magnetospheric science is generally not a high priority of planetary science. After the initial exploratory missions (e.g. Voyager) there are often mission conflicts between planetary needs (particularly imaging) and space physics needs - e.g. pointing, spinning, data rates, trajectories, etc. • Midex? Too small. • Space Physics Mission? Ulysses blazed the trail as a small space physics mission - a spinning spacecraft with particles and fields detectors. A Dynamics Explorer type of mission to Jupiter could be achieved with ~$350M

19. Jupiter Polar Orbiter A Space Physics Mission The ultimate test of magnetospheric science comes from applying what we have learned at Earth to other planets