Fundamental Technologies

Cassini MIMI Pages

Cassini MIMI AGU Abstracts Co-authored by Fundamental Technologies Personnel:

N. Krupp, E. Roussos, T. P. Armstrong, C. Paranicas, D. Mitchell, S. M. Krimigis, G. H. Jones, K. Dialynas, N. Sergis, and D. Hamilton, Discovery of a Transient Radiation Belt at Saturn, Fall AGU Meeting, 2008.

Radiation belts have been detected in situ at five planets. Only at Earth, however, has any variability in their intensity been heretofore observed, in indirect response to solar eruptions and high altitude nuclear explosions. The Cassini spacecraft's MIMI/LEMMS instrument has now detected systematic radiation belt variability elsewhere. We report three sudden increases in energetic ion intensity around Saturn, in the vicinity of the moons Dione and Tethys, each lasting for several weeks, in response to interplanetary events caused by solar eruptions in the year 2005. However, the intensifications, which could create temporary satellite atmospheres at the aforementioned moons, were sharply restricted outside the orbit of Tethys. Unlike Earth, Saturn has almost unchanging inner ion radiation belts: due to Saturn's near-symmetrical magnetic field, Tethys and Dione inhibit inward radial transport of energetic ions, shielding the planet's main, inner radiation belt from solar wind influences.

K. Ogasawara, S. Livi, D. G. Mitchell, and T. P. Armstrong, Properties of High-Energy Electrons at Dawnside Magnetosheath: Cassini Observations During the Earth Swing-by 1999, Fall AGU Meeting, 2008.

We report on the energetic electrons of the magnetospheric origin at the night side magnetosheath using the Low-Energy Magnetospheric Measurement System (LEMMS) aboard the Cassini spacecraft during the Earth swing-by maneuver on 17 August 1999. LEMMS is able to identify the energy and incidence direction of energetic ions and electrons with energies of a few tens of keV to several tens of MeV. The spacecraft was traveling with a velocity of 9 Earth radii (RE) per hour and made rapid transversals of the terrestrial magnetosphere. The spacecraft was outbound over the dawn magnetopause at approximately 10:50 UT at the last time, investigating through the magnetosheath afterward. LEMMS identified 6 electron bursts ranging at least up to 100 keV from X = -70 to -95 RE. These electron streams were away from the general magnetopause position along the magnetic field line. Those features were consistent with former works on the energetic particles in the magnetosheath [e.g. Sarafopoulos et al., 1999]. In this study, taking advantage of the uniqueness of the position in the distant dawnside magnetosheath and the fast snapshot during the swing-by, we discuss the source of these electrons and probability of the event compared to the ion bursts.

T. P. Armstrong, J. Manweiler, N. Krupp, A. Lagg, S. Krimigis, S. Livi, D. Mitchell, E. Roelof, C. Paranicas, and D. Hamilton, Observation of the Spectrum and Angular Distribution of Trapped Protons in Saturnís Inner Magnetosphere: Implications for Sources, Transport, and Loss, Fall AGU Meeting, December 2005, EOS Trans. AGU, 86(52), Fall Meet. Suppl., Abstract P43A-0951.

The Cassini MIMI investigation carried a set of solid state detectors designed in part to resolve the shape and magnitude a local minimum in the flux of energetic protons at about 10 MeV reported from the Voyager 2 flyby in 1981. Preliminary results from Cassini Saturn Orbit Injection (SOI) show that this reported feature of the proton spectrum has persisted throughout the region within Dione's orbit . We will report the fluxes, pitch angle distributions, and phase space densities along with our estimates of source and loss processes of Saturnian trapped protons. Further, we will attempt to reconcile our results with those from Voyagers 1 and 2 and Pioneer 11, especially regarding the inner "CRAND" source.

E. Roussos, N. Krupp, G. H. Jones, A. Lagg, J. Woch, C. Paranicas, D. G. Mitchell, S. M. Krimigis, M. K. Dougherty, W. H Ip, and T. P. Armstrong, Electron Microsignatures from the Saturnian Satellites: Cassini MIMI/LEMMS Observations, Fall AGU Meeting, December 2005, EOS Trans. AGU, 86(52), Fall Meet. Suppl., Abstract P43A-0955.

Since the Saturn Orbit Insertion in July 2004, Cassini has performed numerous crossings of Saturn's inner moons L-shells at various longitudinal distances from the moons. The Low Energy Magnetospheric Measurement System (LEMMS) has detected a significant number of absorption features, referred to as microsignatures, in the lowest energy electron channels (20-200 keV). The detections occur mainly in the vicinity of Tethys and Dione L-shells, while microsignatures from Enceladus, Rhea and Mimas are less frequent. From the analysis of these features we present: (i) estimates of the radial diffusion coefficient in Saturn's radiation belts as a function of L and energy, including for the first time their dependence on local time, (ii) the region of influence that the electric fields and energetic events (e.g. injections) have on the electron drift shells and (iii) the implications for the unique interaction characteristics of each moon with Saturn's magnetospheric plasma. Data from the recent close flybys of Tethys, Dione and Rhea are also briefly discussed.

N. Krupp, A. Lagg, J. Woch, G. H. Jones, E. Roussos, S. M. Krimigis, S. Livi, D. G. Mitchell, E. C. Roelof, C. Paranicas, D. C. Hamilton, T. P. Armstrong, and M. K. Dougherty, Global Structure and Dynamics of the Kronian Magnetosphere: Cassini Results, Fall AGU Meeting, December 2005, EOS Trans. AGU, 86(52), Fall Meet. Suppl., Abstract P43A-0949.

Since July 2004 the Cassini spacecraft is in orbit around Saturn providing in-situ measurements of the Saturnian magnetosphere. Several magnetospheric regions could be identified including the intense radiation belts and ring current regions in the inner magnetosphere as well as the equatorial plasma sheet and the regions close to the outer boundaries of the magnetosphere from which the global structure as well as the dynamic of the Kronian magnetosphere can be studied. Using the energetic particle measurements from the MIMI instrument as well as the magnetic field measurements from the MAG instrument onboard Cassini we will discuss the derived pitch angle distributions, electron and ion energy spectra and periodicities in magnetic field components and particle parameters in various regions. Some of the results are (1) asymmetry in the particle fluxes between the day and night sector at comparable distances; (2) highly varying particle fluxes as a consequence of large-scale dynamic processes in the equatorial plasma sheet; (3) field-aligned bi-directional electron fluxes in the outer part of the Kronian magnetosphere with correlation to the Saturnian aurora; (4) variations of the magnetic field components and electron fluxes with the planetary rotation period pointing to a magnetic anomaly inside the planet or pointing to corotating structures in the Saturnian magnetotail; (5) injections and corotating structures in Saturn's magnetotail as a consequence of dynamical processes.

Krupp, N., S. Livi, S. M. Krimigis, T. P. Armstrong, A. Lagg, D. G. Mitchell, I. Dandouras, and D. C. Hamilton, First Results of the Energetic Particle Detector MIMI/LEMMS Onboard the Cassini Spacecraft during Earth Flyby, Fall AGU Meeting, Dec. 1999. Abstract SM32B-08.

We present results from the Low Energy Magnetospheric Measurement System (LEMMS) which is a part of the Magnetospheric Imaging Instrument (MIMI) onboard the CASSINI spacecraft The data were obtained during the Earth encounter in August 1999. LEMMS is designed to measure the angular and spectral distribution of energetic ions and electrons in the energy range between 20 keV and roughly 20 MeV. The instrument is mounted on top of a turntable allowing measurements from all directions within a scan plane. During the Earth flyby this scan plane was basically perpendicular to the ecliptic plane. The collected data of LEMMS allows us to investigate the energetic particle environment along the spacecraft trajectory through the Earth radiation belts providing a snapshot of the momentary state of the magnetosphere. We show a detailed analysis of the energetic particle spatial distributions and energy spectral shapes in that region of the magnetosphere.

Livi, S., S. M. Krimigis, T. P. Armstrong, D. G. Mitchell, I. Dandouras, N. Krupp, A. Lagg, H. Sommer, S. Jaskulek, and D. C. Hamilton, The Low Energy Magnetospheric Measurement System (LEMMS) Onboard the Cassini Spacecraft, Fall AGU Meeting, Dec. 1999. Abstract SM32B-09.

LEMMS is one of three detector systems of the Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft to study charged particles in the Saturnian magnetosphere and in the interplanetary space. Particles measured with LEMMS are analyzed by the particle type (ions or electrons) and their incidence energy. They are counted into various energy channels in the energy range between 0.02 and roughly 20 MeV. LEMMS consists of two telescope systems, a low and a high energy end. Particles incident on the low-energy telescope are first separated by an internal magnet, and then analyzed with solid state detectors at various positions. The high-energy head consists of a stack of solid state detectors where ions and electrons are distinguished by logic conditions between several electronic thresholds of the detectors. The whole assembly in mounted on top of a programmable turntable which in addition to allow the determination of the incidence direction of the particle within the scan plane. In combination with the other two detector systems of MIMI, namely a Charge Energy Mass Spectrometer (CHEMS) and an Ion and Neutral Camera (INCA), LEMMS is a very powerful tool to investigate the overall configuration and dynamics of Saturn's magnetosphere, and its interactions with the solar wind and its satellites.

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Updated 12/22/08, T. Hunt-Ward