Fundamental Technologies

Galileo Spacecraft Pages

Galileo EPD Presentation Abstracts

Stone, S., and T. P. Armstrong, Characterizing Ganymede's Magnetosphere with Energetic Ion and Electron Absorption Signatures, Fall AGU Meeting, Dec. 1999, 1999 Fall Meeting Supplement to Eos, Abstract SM51C-06, 1999.

Abstract (draft): The G2 and G7 flybys of the Galileo orbiter past Ganymede have been analyzed using time-reversed numerical integration of electron and ion trajectories. Accurate numerical values for a magnetic field within a reasonable neighborhood of Ganymede were required for this study. Two magnetic field models were tested. The first, Model I, was the published vacuum superposition model of Kivelson et al. (1996) and the second, Model II, we developed using the magnetometer observations (generously provided by M. Kivelson) and the methods of Choe and Beard to include the contributions of magnetopause and magnetotail currents. After appropriate scaling of Choe and Beard's results for the Earth (and Mercury) the coefficients of the interior and exterior spherical harmonic representations of the field were adjusted to minimize the chi squared deviations between the observed magnetic field and the model. A representation of the magnetopause surface was also derived. Comparisons of the modeled and observed magnetic fields will be shown. Field line tracings will also be displayed. Results of numerical integrations of trajectories predict the times, shapes, and species and energy dependence of absorption features observed with the Energetic Particle Detector. As expected, Model II, which fits the observed field more closely and includes the magnetopause and tail current contributions, explains the observed timing, depth, and shapes of the charged particle absorption features more satisfactorily than does Model I. Tests for the presence of Jovian corotation-generated electric field as well as parallel electric fields within Ganymede's magnetosphere were performed. Results of those tests and implications for magnetospheric interactions will be discussed.

McEntire, R. W., D. J. Williams, B. H. Mauk, E. C. Roelof, S. M. Krimigis, T. P. Armstrong, B. Wilken, J. G. Roederer, T. A. Fritz, and L. J. Lanzerotti, Observations of Energetic Particle Flux Variations During Europa Encounters by the Galileo Energetic Particles Detector (EPD), Spring AGU Meeting, May 1997, 1997 Spring Meeting Supplement to EOS, S292, Abstract SM41D-06, 1997.

Abstract (draft): The EPD instrument on the Galileo spacecraft contains two separate bi-directional telescopes.  The Low Energy Magnetospheric Measurement System (LEMMS) measures the energy spectra of ions above 20 keV (and electrons above 15 keV), while the Composition Measurement System (CMS) measures energetic ion spectra and composition above energies ranging from 80 keV for protons to 10 keV/nucleon for sulfur. This time-of-flight based measurement extends direct composition determination about a factor of ten below equivalent Voyager energy thresholds. We are studying the energetic particle composition and spectra, and the variations in these quantities, from the Io torus to the deep Jovian magnetotail. Preliminary observations are that the individual spectra are best fit by a convected kappa distribution with an additional power-law high energy cutoff. At equal total energy hydrogen is always important, and dominates the intensities in the inner magnetosphere, but beyond 20 to 30 Rj sulfur appears to be the dominant energetic Jovian ion. We will discuss the observations in the context of energetic ion source, transport and energization mechanisms.

Armstrong, T. P., S. Stone, D. J. Williams, R. E. McEntire, S. M. Krimigis, E. C. Roelof, B. Mauk, B. Wilken, J. G. Roederer, T. A. Fritz, and L. J. Lanzerotti, Observations of Ion and Electron Phase Space Densities in the Io Torus Region, Fall AGU Meeting, December 1996, 1996 Fall Meeting Supplement to EOS, F434, Abstract P11A-3, 1996.

Abstract (draft):The Energetic Particle Detector (EPD) aboard the Galileo Orbiter measured the fluxes of protons, oxygen, and sulfur as well as electrons at energies from several tens of keV to several MeV. One approach to inferring sources, losses, and transport of trapped particles is to derive from flux observations versus energy and pitch angle the phase space density (PSD) at selected  available values of the adiabatic invariants. Based on Liouville's theorem, PSDs are expected to be constant along real particle trajectories. Departures from constancy can be interpreted in the framework of transport theories that violate one or more of the invariants. We attempt to identify the processes that account for the depletions of ion and electron intensities in the torus region. Preliminary insights suggest that sources, losses, and transport act differently on different species. We expect to show Galileo results and compare them with available results from Voyager and Pioneer. 

Krupp, N., A. Lagg, B. Wilken, J. Woch, D. J. Williams, E. C. Roelof, B. H. Mauk, R. E. McEntire, S. M. Krimigis, T. P. Armstrong, L. J. Lanzerotti, T. A. Fritz, and J. G. Roederer, New Energetic Particle Observations of the Galileo Energetic Particles Detector (EPD): Ganymede 2 Encounter (G2), Fall AGU Meeting, December 1996, 1996 Fall Meeting Supplement to EOS, F436, Abstract P11A-24, 1996.

Abstract (draft): The Galileo mission provides in situ measurements of the Jovian magnetosphere and especially from the vicinity of the Galilean moons. We report here the first energetic particle observations obtained from the EPD instrument during the second encounter with Ganymede (G2) in August, 1996. During the first Ganymede encounter (G1) the EPD instrument had been turned off.  Signatures in the magnetic field data from G1 led to the conclusion that Ganymede might have a magnetosphere of its own.  This question will be discussed from EPD measurements. Furthermore we will show the calculated flow velocities of ions with different energies as a function of radial distances to the planet and to the moon. 

Williams, D. J., R. W. McEntire, S. M. Krimigis, E. C. Roelof, B. Wilken, T. P. Armstrong, T. A. Fritz, L. J. Lanzerotti, and J. G. Roederer, The Galileo Energetic Particles Detector (EPD): First Observations at Jupiter, 1996 COSPAR Meeting, Birmingham, England, Abstracts, p. 55, 1996. Abstract (draft):

Williams, D. J., R. E. McEntire, B. H. Mauk, E. C. Roelof, S. M. Krimigis, T. P. Armstrong, T. A. Fritz, L. J. Lanzerotti, J. G. Roederer, and B. Wilken, Energetic Particle Distributions and Bidirectional Electron Beams Observed in the Plasma Torus and at Io by the Galileo Energetic Particles Detector (invited), Fall AGU Meeting, December 1996, 1996 Fall Meeting Supplement to EOS, F430, 1996.

Abstract (draft): Intense, magnetic field-aligned, bi-directional, energetic (>15 keV) electron beams were discovered by the Galielo Energetic Particles Detector (EPD) during the spacecraft's close flyby of Io. These beams can carry sufficient energy flux into Jupiter's atmosphere (up to 80 erg cm-2 s-1) depending on assumptions) to produce visible aurora at the footprint of the magnetic flux tube connecting the moon to the planet. Composition measurements through the torus show that the spatial distributions of protons, oxygen, and sulfur are different, with sulfur being the dominant energetic (10) keV/nucleon) ion at closest approach.

Alinejad, N., and T. P. Armstrong, Galileo Observations of Earth's Trapped Radiation, 1995 IUGG Meeting, Boulder, CO, July 1995.

Abstract (draft): The Galileo spacecraft encountered the Earth once on December 8, 1990 (Earth-I) and the second time on December 8, 1992 (Earth-II). These flybys provided an excellent opportunity to evaluate the performance of the Energetic Particle Detector (EPD) and establish analysis procedures in a relatively well-known environment. Further, because Galileo's Earth flyby trajectories were very rapid and nearly radial, the radiation belt measurements provided an excellent ''snapshot" of trapped radiation. The EPD data agree with and extend the familiar radiation belt empirical models established by the National Space Science Data Center. Because of the rapid flyby and the 20 second spin period of Galileo, great care had to be taken to remove time aliasing from the pitch angle distributions. Large anisotropies were also present due to intrinsic density gradients. Spherical harmonics were fit to the pitch and phase distributions in order to obtain fluxes from which phase space densities could be computed. The phase space density is calculated from the fitted data for the particles that conserve the first and the second adiabatic invariants. The extracted phase space density was examined for the steady state one dimensional pure radial diffusion. The results show that there should be other mechanisms besides the pure radial diffusion. We are presently evaluating the data for the multimode diffusion (simultaneous pitch angle and radial diffusion).

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Updated 3/5/10, T. Hunt-Ward
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