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| Titel |
Investigation of the atmospheres of Europa, Ganymede, and Callisto with PEP/JUICE |
| VerfasserIn |
Peter Wurz, Marek Tulej, Audrey Vorburger, Nicolas Thomas, Stas Barabash, Martin Wieser, Helmut Lammer |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079578
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| Zusammenfassung |
| The Particle Environment Package (PEP) suite of instruments has been proposed for the
JUICE mission, which contains sensors for the comprehensive measurements of electrons,
ions and neutrals. One of the instruments for neutral particles is the Neutral and Ion Mass
spectrometer instrument (NIM). NIM is a time-of-flight neutral gas and thermal ion mass
spectrometer and is optimised for exospheric investigations. Full mass spectra (1 – 1000 amu,
m/Δm = 1100) are recorded with high cadence, typically every 100 s, and during flybys even
at 1 s cadence. In a 5-s spectrum the detection threshold is 10-16 mbar (about 1
cm-3).
Various physical processes are acting on the surfaces of Jupiter’s icy moons (Europa,
Ganymede, Callisto) to promote material from the surface into the exosphere. These
are thermal desorption (sublimation), photon stimulated desorption, ion-induced
sputtering, and micro-meteorite impact vaporisation (Wurz and Lammer, 2003; Wurz
et al., 2010). At Europa, sputtering is the most important surface release process
(Johnson et al., 2009), which releases all species present on the surface more or less
stoichiometrically into the exosphere, allowing to derive the chemical composition of the
surface from the exospheric measurements. However, the chemical composition of the
surface is modified by the bombardment of energetic electrons and ions, and the
ultraviolet radiation. For example, species like H2, O2, H2O2 or O3 begin to be
produced in the top surface layer and are later released into the exosphere by various
means. Also, the co-rotation plasma’s electrons and to a smaller extent the UV
photons cause fragmentation and ionisation of molecules at some locations in these
exospheres.
We calculated the expected densities for established and expected species in Jupiter’s icy
moons exospheres. We find that for the planned JUICE trajectories near these moons that
NIM will record most known species because of NIM’s high sensitivity, even in the presence
of the severe radiation environment at Europa. With NIM’s dynamic range of 105 one can
measure even the D/H ratios during flybys. NIM offers the possibility of detection of yet
undiscovered species, with the likely candidates from the non-ice materials Mg, Al, Si, and
Ca, that will help understand the mineralogical composition of the surfaces of the moons.
NIM’s high mass resolution, range and sensitivity are critical in contributing to the
habitability assessment of Europa by being able to investigate localised patchy
regions of the exosphere indicative of sub-surface venting and to resolve chemical
composition. |
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