Transcript Exploration of Giant Planet Magnetospheres

Exploration of Giant Planet
Magnetospheres
Fran Bagenal, University of Colorado
• Jupiter Top
Priority
• Polar Regions
• Multi-Spacecraft
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Giant Planet Magnetospheres
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Giant!
Rotation Dominated
Satellite plasma sources
J&S
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Symmetric
~Dipolar
Strong plasma production
Limited solar wind influence
• U&N
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Highly asymmetric,
Highly non-dipolar
Complex transport (SW + rotation)
Multiple plasma sources (ionosphere +
solar wind + satellites)
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Giant Planet Magnetospheres
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
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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
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Giant Planet Magnetospheres
Why not Uranus & Neptune?
• Logical step after Galileo and
Cassini?
• Getting there!
• U&N small, complex, variable
• Main issue of magnetosphereplanet coupling more easily
addressed at Jupiter
• Earth demonstrated necessity
of multi-spacecraft
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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 “indepth investigation-mode”
• Galileo attempted this but
hampered by bits-to-ground
and “old-style” mission
• Accessible by both
spacecraft and earth-based
telescopes
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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
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SMall EXplorer
mission under
study - Earthorbiting UV
telescope to
observe Io, the
torus and Jovian
aurora
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Giant Planet Magnetospheres
Learning 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
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Giant Planet Magnetospheres
“Cheaper, Faster, Better”
Simplest missions “Ulysses-style”
• Spinning
Spacecraft
• No imaging (except
sweeping linear
detectors? UV? Vis/IR?)
• Particles and fields
emphasis
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Full Planetary Missions
• 3-axes stabilized
• Cameras
• Large data rates
Technology Drivers
• Propulsion
• Power
• Communications
• Radiation Protection
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Conclusions:
Study Jovian System in Depth
Priorities for missions
1.
2.
3.
Earth-orbiting UV telescope
Polar Orbiter with fields and
particles instrumentation
Multi-spacecraft missions
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Middle magnetosphere
Io electrodynamics exploration
Solar wind upstream
Magnetotail
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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.
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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.
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Jupiter Polar Orbiter-Scientific Objectives 1
The purpose of JPO would be to explore the polar regions of Jupiter's magnetosphere to answer
the following outstanding questions:
1.
What is the nature and degree of coupling between the magnetosphere, ionosphere and
atmosphere?
2.
What roles do changes in Io's volcanism, the solar wind and the plasmasheet each play in
magnetospheric variability?
3.
What are the compositions and energies of the primary particles that excite auroral
emissions?
4.
What is the cause of the polar-cap auroras at Jupiter?
5.
What is the cause of the brief, super-bright auroral flares occasionally observed in Jupiter's
polar region?
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Jupiter Polar Orbiter-Scientific Objectives 2
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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?
8.
Is there a one-to-one correspondence between auroral emission features and nonthermal
radio emission features?
9.
How is the Io control of the decametric radio emission accomplished?
10. What process creates the long auroral tail observed downstream of the auroral footprint of Io
and perhaps other large satellites?
11. 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.)
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The Io Aurora
Infrared
Ultraviolet
- what accelerates the precipitating energetic particles?
- why does ‘wake’ emission extend half way around Jupiter
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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
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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.
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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
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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
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