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Titel |
Plasma IMS Composition Measurements for Europa and the Other Galilean Moons |
VerfasserIn |
Edward Sittler, John Cooper, Richard Hartle, Alexander Lipatov, Paul Mahaffy, William Paterson, Nick Pachalidis, Mike Coplan, Tim Cassidy |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250038137
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Zusammenfassung |
NASA and ESA are planning the joint Europa Jupiter System Mission (EJSM) to the Jupiter
system with specific emphasis to Europa and Ganymede, respectively. The Japanese Space
Agency is also planning an orbiter mission to explore Jupiter’s magnetosphere and the
Galilean satellites. For NASA’s Jupiter Europa Orbiter (JEO) we are developing the 3D Ion
Mass Spectrometer (IMS) with two main goals which can also be applied to the other
Galilean moons, 1) measure the plasma interaction between Europa and Jupiter’s
magnetosphere and 2) infer the 4Ï surface composition to trace elemental [1] and significant
isotopic levels. The first goal supports the magnetometer (MAG) measurements,
primarily directed at detection of Europa’s sub-surface ocean, while the second gives
information about transfer of material between the Galilean moons, and between the
moon surfaces and subsurface layers putatively including oceans. The measurement
of the interactions for all the Galilean moons can be used to trace the in situ ion
measurements of pickup ions back to either Europa’s or Ganymede’s surface from the
respectively orbiting spacecraft. The IMS instrument, being developed under NASA’s
Astrobiology Instrument Development Program, would maximally achieve plasma
measurement requirements for JEO and EJSM while moving forward our knowledge of
Jupiter system composition and source processes to far higher levels than previously
envisaged.
The composition of the global surfaces of Europa and Ganymede can be inferred from the
measurement of ejected neutrals and pick-up ions using at minimum an in situ
payload including MAG and IMS also fully capable of meeting Level 1 mission
requirements for ocean detection and survey. Elemental and isotopic analysis of potentially
extruded oceanic materials at the moon surfaces would further support the ocean
objectives. These measurements should be made from a polar orbiting spacecraft about
Europa or Ganymede at height ~ 100 km. The ejecta produced by sputtering of the
surfaces of Europa and Ganymede has been shown to be representative of the surface
composition [2,3]. Level 2 science on surface geology and composition can then be
further enhanced by addition of the following: 3D Ion Neutral Mass Spectrometer
(INMS), 3D plasma electron spectrometer (ELS), and hot plasma energetic particle
instrument.
The measurement approach is to alternate between times measuring pickup ions and
times measuring plasma and magnetic field parameters along the spacecraft trajectory. By
measuring the pickup ion energy, arrival direction and mass-per-charge, the ion can be traced
back along the ejection trajectory to the approximate area of origin if the 3-D electric field
and magnetic field are known. In situ observations of plasma flow velocities and vector
magnetic fields can be used to determine the local convective electric field (E = -VXB) along
the spacecraft trajectory. By combining this information with models of the magnetospheric
interaction with Europa [3,4], one can generate 3D maps of the electric and magnetic field
and compute the trajectories of the pickup ions back to the surface or exospheric
points of origin. In the case of Ganymede there is the additional complexity of
its own internal dipole magnetic field, while Io’s volcanic activity introduces the
complexity of a highly structured denser atmosphere. Callisto with its less globally
extended exosphere will have a simpler interaction than for Europa (i.e., more like our
moon). We will discuss these differences in light of the above proposed technique.
Finally, the INMS observations and neutral exosphere models are needed to estimate
production rates of pickup ions. The hot plasma measurements are needed to correct for
sputtering rates which can be time dependent and electron plasma observations for
electron impact ionization rates. Instrument characteristics, field-of-view requirements,
modes of operation and effects of radiation on instrument functionality will be
discussed.
1. Cassidy, T. A., Johnson, R. E., Tucker, O. J., 2009. Trace constituents of Europa’s
atmosphere. Icarus 201, 182-190.
2. Johnson, R. E., et al., Europa (ed R. Pappalardo et al.), Univ of Arizona Press, in press,
2009.
3. Schilling, N., Neubauer, F. M., Saur, J., 2008. Influence of the internally induced
magnetic field on the plasma interaction of Europa. Journal of Geophysical Research (Space
Physics) 113, 3203.
4. Lipatov, A. S., Cooper, J. F., Paterson, W. R., Sittler, E. C., and Hartle, R. E., Jovian’s
plasma torus interaction with Europa: 3D Hybrid kinetic simulation. First results, submitted
to Plan. Sp. Sci., 2009. |
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