Synergistic Science with an

1. Synergistic Science with an Entry Probe and Carrier Vehicle at Uranus Thomas R. Spilker, SSSE Mark D. Hofstadter, JPL Neil Murphy, JPL 10th International Planetary Probe Workshop San Jose, CA, USA 2013 June 19

2. Topics • Why is Uranus important? • High-priority science objectives at Uranus • Studying the interiors of stars & planets • Giant planet normal mode seismology • Combining Doppler imaging and atmospheric entry probes • Summary

3. Why is Uranus Important? • Uranus and Neptune represent a distinct class of planet, commonly referred to as “Ice Giants.” • Definitions • Gas: H2 and He. • Ice: Things which could be solid or gas in the solar nebula, such as H2O, CH4, NH3. (We do not believe these species are present as solid ice in Uranus and Neptune today.) • Rock (or metal): Things that were solid almost everywhere in the solar nebula. • Clues to solar system formation: materials, processes, time scales • Approximate Composition as a Percentage of Mass

4. As of February 2011

5. Why Uranus? – The Concise Answer I) The Ice Giants are a distinct and important type of planet about which very little is known. II) Ice Giants may be the most abundant type of planet in our galaxy. III) Uranus is the most accessible ice giant, and is also the most challenging to our understanding of planetary interiors, energy balance, formation, and evolution.

6. Why Uranus? – The Concise Answer I) The Ice Giants are a distinct and important type of planet about which very little is known. II) Ice Giants may be the most abundant type of planet in our galaxy. III) Uranus is the most accessible ice giant, and is also the most challenging to our understanding of planetary interiors, energy balance, formation, and evolution. Follow the water?

7. Why Uranus? – The Concise Answer I) The Ice Giants are a distinct and important type of planet about which very little is known. II) Ice Giants may be the most abundant type of planet in our galaxy. III) Uranus is the most accessible ice giant, and is also the most challenging to our understanding of planetary interiors, energy balance, formation, and evolution. Follow the water? -- Oh, there it is!

8. High-Priority Uranus Science Objectives GOALS • Understand Ice Giant formation, evolution, and their current state in our solar system, and implications for exoplanets • Understand the materials, processes, and time scales involved in formation of our solar system

9. High-Priority Uranus Science Objectives Based on the PSDS and Reviews Since its Release • Highest Priority • Determine the internal structure: bulk composition and density profile • Determine the noble gas abundances • Determine the isotopic ratios of H, C, N, and O • Secondary • Determine atmospheric zonal winds and dynamics • Determine atmospheric composition and structure • Understand the structure of the magnetosphere & internal dynamo • Determine the planet’s heat budget (absorbed solar vs. emitted IR) • Determine atmospheric thermal emission, structure, and variability • Measure the magnetic field, plasma, & currents to determine how the tilted/offset/rotating magnetosphere interacts with the solar wind and upper atmos • Determine the geology, geophysics, composition, and interior structure of large satellites

10. Studying the Interiors of Stars and Planets Techniques Available • Gravity field measurements • Distribution of mass in the planet • Acoustic (seismic) wave propagation • Propagation constants of the media traversed • Magnetic field structure and variability • Structure and dynamics at the dynamo generation boundary • Small-scale structure in a crust • Neutrino flux measurements • Useful for nearby stars (we have one) At Earth, geologists and geophysicists use gravity for studying the crust, seismic for studying the interior

11. Studying the Interiors of Stars and Planets Normal-Mode Oscillations as a Probe of Interior Structure Schematic of standing waves forming within a celestial body. Low-order waves (purple) sample the entire body, while higher-order waves (red) probe shallower levels. Representation of standing acoustic waves in the atmosphere of Jupiter, with blue indicating regions of rarefaction, and red areas of compression. Note the differing radial, zonal, and meridional wavelengths. (Courtesy P. Gaulme) A k-omega plot. It shows the power spectrum (reds having the most power, blue the least) as a function of oscillation frequency in time (omega, on the y-axis) versus spatial frequency (horizontal wavenumber, k, along the x-axis). The object’s natural resonances form curving patterns. Different interior structures yield different patterns. (Courtesy F.-X. Schmider)

12. Studying the Interiors of Planets Normal-Mode Oscillations as a Probe of Interior Structure • Giant Planet normal mode seismology • Emerging field – so far, observed only at Jupiter • Doppler Imager (DI) instrument and technique • Measures atmospheric motions using Doppler shifts of reflected visible-wavelength solar lines • Data can be acquired at any distance allowing full-disk images of the planet • Can also measure atmospheric winds and other dynamics A DI instrument addresses two of the highest-priority goals of the Decadal Survey’s Uranus Flagship mission Existing Doppler instrument operated at South Pole Simulated DI images for Uranus

13. Combined DI and Entry Probe at Uranus A Powerful Combination • Addresses many high-priority science objectives • ALL the highest-priority objectives • Interior structure, noble gas abundances, isotopic ratios • Several of the secondary objectives, including the first two • Zonal winds and dynamics, atmospheric composition and structure • Synergistic measurements • Probe: • Measures depth of reflecting layers • Shallow measurements of T, r profiles • In situ turbulence, dynamics measurements • DI: • Imaging for probe entry site context • Global view of atmospheric dynamics

14. Combined DI and Entry Probe at Uranus Naturally Compatible • Entry probe and DI data need not be taken simultaneously • DI data best taken some distance from the planet for full-disk images • Acquired long before closest approach • No DI constraints on near-close-approach trajectory or pointing • Orbit insertion not needed (nor proscribed) for either investigation • Flyby spacecraft could optimize trajectory and pointing for probe data relay • Clean interfaces allow practical partnering options • Examples: contributed probe or descent module • Potential for ANY planetary mission class • NASA planetary programs: Discovery, New Frontiers, Flagships • Would require GFE RPS (2) and Atlas-class launch vehicle

15. Summary • Uranus is an important destination for planetary science • The DI technique can provide critical interior structure information without orbiting the subject planet • A mission combining DI and an atmospheric entry probe could address all the top-priority Uranus science objectives • There is potential to fly such a mission in any planetary mission class • Clean interfaces support practical partnering options

16. Questions?