TRS-1

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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
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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

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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

Planet Gas Ice Rock Total Mass (MEarth)
Earth 0 0 100 1
Jupiter/Saturn 95 4 1 200
Uranus/Neptune 10 65 25 15
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As of February 2011
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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.
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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?
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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!
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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

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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 planets 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

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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
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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
objects natural resonances form curving
patterns. Different interior structures yield
different patterns. (Courtesy F.-X. Schmider)
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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 Surveys
Uranus Flagship mission
Simulated DI images for Uranus
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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

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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

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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

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Questions?