Measurements of the solar wind as Cassini approaches Saturn
will be coordinated with observations of the Jovian aurora from Cassini, HST,
and possibly Gallileo, in order to establish the role of solar wind dynamic
pressure and magnetic field in generating and controlling auroral dynamics.
Observations can be repeated for the Kronian aurora to establish comparative
aspects.
Solar wind observations will establish the properties of the Jovian bow
shock and upstream magnetosheath. Observations can be repeated at Saturn to
establish comparative aspects.
Begin detailed studies of solar wind properties in the outer solar system
(part of systematic studies between 5 and 10 AU).
Cassini Unique Science:
The Cassini approach trajectory gives a long period in the upstream solar wind
in which to make correlated observations of the aurora. No other currently planned
mission will carry out these observations. The CAPS sensors are far more capable than
corresponding GLL sensors. Only Cassini will be able to provide high quality
comparative science at Jupiter and Saturn.
The Cassini trajectory gives more time for observing upstream Jovian phenomena
than previous missions. CAPS sensors have wider coverage of the appropriate particle
phase space than previous missions and will be able to detect leakage of Jovian particles
into the upstream region. Only Cassini will be able to provide high quality comparative
science at Jupiter and Saturn.
CAPS will be the only instrument travelling between 5 and 10 A.U. that is capable
of detailed high resolution velocity measurements of the solar wind. It is unlikely
that this opportunity will occur again.
Scientific Importance:
Jovian aurora is presumed driven by convective motions of plasma in the Jovian
magnetosphere. Convection is controlled by both Jovian rotation and solar wind
pressure. Existing MHD models show this coupling. Coordinated measurements with CAPS
would provide ground truth to help establish physical processes driving aurora.
Intercomparison with similar observations at Saturn will advance comparative
magnetospheric science.
CAPS has higher time resolution (x 24), angular resolution (x 3), energy coverage
(up to 50 keV vs. 6 keV), and mass resolving capabilities than did Voyager PLS.
Comparative Cassini observations of the bow shock, magnetosheath, and magnetopause of
Jupiter and Saturn will yield far more detailed insights into formation and
intercomparison of plasma shocks and boundaries.
Cassini is likely to be the only misson that will permit continuous detailed
monitoring of the evolution of the solar wind between 5 and 10 AU.
Observation Geometry and Pointing:
Beginning at C/A - ~ 3 months up to C/A + TBD, orient the S/C so that the solar
direction lies between the S/C -X and -Y axes and within
±30°of the S/C
XY plane.
All coordinated auroral observations will have to allow for solar wind
propagation effects between Cassini and Jupiter where:
Tlag »
dC-J/VSW
Typical fluctuations (~ ± 40%) in
VSW will lead to uncertainties in estimating the time lag and lead to the
necessity for somewhat wider CAPS observing slots to bracket imaging observations.
HST observations will consist of 3 each 45 min. observations separated by 45 minutes for
a total of 3.75 hours.
Observation Resources:
Duration:
Campaign mode: ~ 6 hours (2 kbps)
Routine: 2 hours
Frequency:
Routine: approximately 24 hours apart
No. repetitions:
Routine: daily
Data volume:
Campaign mode: 5.4 MB
Routine: 1.8 MB
TLM mode:
S&ER-3
Preparation for Saturn:
All 3 CAPS observations are identical to their counterparts at Saturn.
Although none of the operations appear to be very complex at this time, early
application of the observing methodology will nonetheless act as a pathfinder for
all CAPS-involved operations at Saturn.
Jupiter observations form a large subset of the early (SOI - 2 years) CAPS
operations. Success at Jupiter will simplify and reduce the cost of early CAPS science
operations at Saturn.
Note: Following Jupiter closest approach Cassini will be travelling along the
duskside flank of the magnetosphere. Fluctuations in solar wind pressure and magnetic
field are expected to cause the bowshock, magnetosheath, and perhaps the magnetopause,
to engulf the Cassini trajectory thereby enabling the following objectives. Moreover,
prolonged contact with the dusk flank of the magnetosphere is almost certain to offer the
opportunity for direct observation of Jovian plasma.
Obtain comprehensive distribution function and morphological observations of the
Jovian bowshock and magnetosheath. It may also be possible to observe the magnetopause
and plasma boundary layer as well as discrete parcels of Jovian plasma. Use observations
as ground truth for theory and simulation of plasma flow past the magnetosphere.
Observe Jovian plasma (ions) entrained from within the magnetosphere to augment
Gallileo and Voyager plasma composition measurements.
Cassini Unique Science:
CAPS multi-sensor measurement capabilities and the length of time that Cassini will
be in the vicinity of the bowshock and magnetosheath provide a unique opportunity.
Studies will be more detailed and extensive than previous missions and can be conducted
under a much wider variety of solar wind conditions because of prolonged contact with the
boundaries. (GLL trajectories are transverse rather that longitudinal w.r.t.
magnetosheath.)
If blobs of Jovian plasma are found, CAPS sensitivity and mass resolution will permit
the first detailed compositional analysis of Jupiter’s thermal magnetospheric plasma.
Scientific Importance:
Measurements up to now have been piecemeal, taken during inbound/outbound
trajectories (P10, V1, V2, Ulysses) or with instruments that are much less capable than
CAPS. CAPS can obtain a self-consistent set of measurements that will advance
understanding about plasma interactions (both fluid and kinetic) with rapidly rotating
magnetospheres over a wide range of plasma flow conditions.
Composition of Jovian thermal plasma is not well determined. CAPS can easily resolve
ion species (including multiple charge state species) associated with oxygen, sulfur
(32/34), potassium and related molecules (e.g., S2+ and
SO2+). Measurements will serve as ground truth for Jovian models
(e.g., Bagenal, 1994) and as tracer measurement for origin of any parcels seen at
Cassini. This will constrain global MHD models of Jovian magnetosphere.
Observation Geometry and Pointing:
Beginning at ~ C/A out to C/A + ~ 30 days, orient the S/C so that the solar direction
lies between the S/C -X and -Y axes and within ±
50°of the S/C XY plane.
Observation Resources:
Duration:
4 hours (4 kbps)
Frequency:
1/day (no particular time)
No. repetitions:
Every day
Data volume:
7.2 MB/day
TLM mode:
S&ER-3
Preparation for Saturn:
All observations are the same as those that will be carried out as part of the global
plasma survey of the Kronian magnetosphere. Early application of the CAPS operations and
data reduction methods at Jupiter will serve as a pathfinder for the Saturn tour, e.g.,
in building observation modules/templates.
Extend measurements of Interstellar Ion (II) composition from 5 AU out to 10
AU. Near 5 AU, build on the measurements of Ulysses. Note: Fluxes are extremely
weak---long observing times are required.
Cassini Unique Science:
Measurement has never been performed. Cassini is the only mission in the
foreseeable future that will carry instruments with sufficient sensitivity and resolution
to make these measurements.
Scientific Importance:
Neutral atoms from interstellar gas and dust grains enter the solar system and
are photoionized and picked-up (accelerated) by the solar wind. Measurements of
interstellar ions yield information on the composition of interstellar material, its
distribution, and its infall into the solar system.
Observation Geometry and Pointing:
Carried out throughout Jupiter flyby period. Geometry independent.
Observation Resources:
Duration, frequency, number of repetitions:
Observations can ride along with any other instrument observations and are
additional to the CAPS observations I and II already listed (solar wind & Jovian
plasma). This separate request is for additional, nearly continuous, operations at an
average of 0.25 kbps for 20 hours per day.
Data volume: 2.25 MB/day
Telemetry mode: S&ER-3
Preparation for Saturn:
Early test of the implications of continuous survey mode desired by
particles and fields instruments. Early implementation and test of ultra-compressed
CAPS data modes.
