Observation Objectives
Satellite Working Group
KEY QUESTIONS
The UVS and EUV satellite observations during the Jupiter tour will answer
several key questions related to the state of evolution and the surface
composition of the Jovian satellites. The observational goals and strategies
detailed below, combined with the Galileo's capabilities based upon the Phase
II flight software, will permit observations which can answer these questions.
The UVS and EUV satellite observations will determine the composition, or
upper limits to the number density, of the neutral atmosphere of the
Galilean satellites and the Io neutral cloud. The UVS observations will
also determine the excitation mechanisms and escape rates of the satellite
atmospheres. In addition, the UV albedo, when combined with the visible and
infrared spectra, will determine surface composition and particle size.
Observation Goals
The UVS and EUV satellite observations will be conducted during each Jovian
orbit with the exception of the non-targeted fifth-orbit (J5). The principal
goal of these observations will be to answer these key scientific questions
as well as to support the Satellite Working Group observations where possible.
Observation Strategy
Observations which will address the science questions are based upon the
detailed observation descriptions below. UVS and EUV observations can be
grouped into two general science area categories. These are 1) Volitile
Escape; and 2) Surface Albedo and Composition observations. The categories
are described below where the capitalized acronyms are the six-character
observation names.
1) Volitile Escape observations will search for atomic spectral lines
(H,O,C,N), molecular bands (OH,CO,CO2+), and neutral clouds (SO2,SO,O,S,K,Na)
to determine the altitude near the Jovian satellites. These measurements will
enable an understanding of the excitation mechanisms and the escape rates
to determine the state of evolution of the Jovian satellites. The measurement
set used to obtain this information consists of the BRTLMB, DRKLMB, ECLIPS,
NRLCLD and SPNSCN observations.
2) Surface Albedo and composition observations will extend the surface
scattering property measurements into the ultraviolet (1600A - 3200A) and
extreme ultrviolet (500A-1300A) wavelengths. The data retrieved will provide
information about particle size and absorption properties of the surface
materials at resolutions and phase angles which cannot be obtained from Earth.
The data will also be used to supplement and complement the NIMS surface
property measurements. The measurement set used to obtain this information
consist of the GLOBAL, MAPPNG, PHASE and SPNSCN observations.
3) Additional data is required through AACS-provided pointing information
for all realtime and recorded observations. These data are provided through
the realtime science formats and the recorded low-rate science ancillary data
packets.
SWG Measurement Set Priorities
The UVS and EUV measurment sets are listed by acronym and fully described
below. The recorded observations reflect the agreements made between
discipline working groups as to the bits-to-ground and tape track allocations.
The realtime observations include high priority UVS activities (designed to
minimize the bits-to-ground and tape track allocation resources) and will use
realtime bits-to-ground during the encounter period.
Orbit JA/J0:
No UVS or EUV satellite observations are planned.
Orbits G1-E11:
BRTLMB - UVS Satellite Bright Limb Drift Observations
DRKLMB - UVS Satellite Dark Limb Drift Observations
ECLIPS - UVS Satellite Eclipse Observations
GLOBAL - UVS Satellite Global Observations (ride-along with NIMS team)
MAPPNG - UVS Satellite Mapping Observations (ride-along with NIMS team)
NRLCLD - UVS Io Neutral Cloud Observations
PHASE - UVS Satellite Phase Coverage Observations
SPNSCN - EUV Callisto Spin Scan Image Observations
Recorded:
1) BRTLMB
Objective: Measure the altitude distribution of the volatiles near the
sub-solar point to determine the escape rates from the Jovian satellites
when the atmosphere is in full solar illumination.
Strategy: Near the satellite closest-approach, position the UVS field-of-view
(FOV) approximately 1 satellite-radius off the satellite sub-solar point and
allow the spacecraft motion to carry the FOV onto the body surface. Once this
has completed, reposition the UVS FOV to ~1000 Km off the satellite sub-solar
point and allow the spacecraft motion to carry the FOV onto the body surface.
Orbits: Ganymede - G1, G2; Callisto - C3, C10; Europa - E11.
2) DRKLMB
Objective: Measure the altitude distribution of volatiles off the dark limb to
determine the particle impact excitation emission rates from the Jovian
satellites.
Strategy: Near the satellite closest-approach, position the UVS field-of-view
(FOV) on the surface of the dark limb and allow the spacecraft motion to
carry the FOV to approximately 1 satellite-radius off the satellite surface.
Orbits: Ganymede - G1, G2; Callisto - C3, C10; Europa - E11.
3) GLOBAL
Objective: Extend the surface scattering property measurements into the UV
(1600A - 3200A) in concert with the NIMS measurements to infer information
about particle size, and refractive and absorption properties of the surface
materials.
Strategy: Ride-along with the NIMS Ganymede and Callisto global observations.
Cover the satellite surface at the highest resolution available within the
allocated downlink bits and tape.
Orbits: Ganymede - G1, G7; Callisto - C3, C9, C10.
4) MAPPNG
Objective: Extend the surface scattering property measurements into the UV
(1600A - 3200A) in concert with the NIMS measurements to infer information
about particle size, and refractive and absorption properties of the surface
materials.
Strategy: Ride-along with several NIMS Ganymede and Callisto high resolution
observations. Cover the satellite surface at the highest resolution available
within the allocated downlink bits and tape.
Orbits: Ganymede - G1, G8; Callisto - C9.
5) SPNSCN
Objective: Characterize Callisto's surface and aeronomic properties by
measuring the EUV surface albedo (He,O2,H) and local atmospheric resonance
line wavelengths (H,He,O,Ar,S,C).
Strategy: Record EUV data for approximately 15 RIMS centered on the time when
Callisto will cross the EUV FOV at 90 deg. cone.
Orbits: Callisto - C3, C10.
Realtime
6) ECLIPS
Objective: Characterize the change in the lower atmospheric UV airglow
emissions as Io and Europa enter and exit eclipse. Determine if the source of
the change is due to: 1) a change in the lower atmospheric composition as it
cools (ie. SO2 condesation); or 2) a potential change in the excitation
mechanism if solar excitation is dominant over particle impact.
strategy: Monitor the satellite for one hour prior to ingress, one hour after
ingress, one hour before egress, and one hour after egress utilizing the UVS
10bps realtime capacity.
Orbits: Io - all, Europa - all.
7) NRLCLD
Objective: Determine the composition and time variation of the ionized Io
neutral cloud (SO2,SO,O,S,K,Na) to assist in the modeling of the Io plasma
torus and Io's atmosphere.
Strategy: Monitor the emissions from the Io at various distances from the
satellite for a total of four hours per orbit.
Orbits: Io - all.
8) PHASE
Objective: Observe Io and Europa in the 1600A to 3200A wavelength regions at
phase angles not obtainable from the Earth to supplement and complement the
NIMS surface property measurements.
Strategy: Observe Io and Europa at various phase angles throughout the tour
utilizing the UVS 10bps realtime capability.
Orbits: Io - all, Europa - all.