A.J. Tuzzolino

Protons and electrons in Jupiter's magnetic field: results from the University of Chicago experiment on Pioneer 10

Fluxes of high energy electrons and protons are found to be highly concentrated near the magnetic equatorial plane from distances of ~ 30 to ~ 100 Jovian radii (RJ). The 10-hour period of planetary rotation is observed as an intensity variation, which indicates that the equatorial zone of high particle fluxes is inclined with respect to the rotation axis of the planet. At radial distances [unknown] 20 RJ the synchrotron-radiation-producing electrons with energies ≳ 3 million electron volts rise steeply to a maximum intensity of ~ 5 x 108 electrons per square centimeter per second near the periapsis at 2.8 RJ. The flux of protons with energies ≳ 30 million electron volts reaches a maximum intensity of ~ 4 x 106 protons per square centimeter per second at ~ 3.5 RJ with the intensity decreasing inside this radial distance. Only for radial distances [unknown] 20 RJ does the radiation behave in a manner which is similar to that at the earth. Burst of electrons with energies up to 30 million electron volts, each lasting about 2 days, were observed in interplanetary space beginning approximately 1 month before encounter. This radiation appears to have escaped from the Jovian bow shock or magnetosphere.

Saturnian Trapped Radiation and Its Absorption by Satellites and Rings: The First Results from Pioneer 11

Electrons and protons accelerated and trapped in a Saturnian magnetic field have been found by the University of Chicago experiments on Pioneer 11 within 20 Saturn radii (Rs) of the planet. In the innermost regions, strong absorption effects due to satellites and ring material were observed, and from ∼ 4 Rs inwards to the outer edge of the A ring at 2.30 Rs (where the radiation is absorbed), the intensity distributions of protons (≥ 0.5 million electron volts) and electrons (2 to 20 million electron volts) were axially symmetric, consistent with a centered dipole aligned with the planetary rotation axis. The maximum fluxes observed for protons (> 35 million electron volts and for electrons < 3.4 million electron volts) were 3 x 104 and 3 x 106 per square centimeter per second, respectively. Absorption of radiation by Mimas provides a means of estimating the radial diffusion coefficient for charged particle transport. However, the rapid flux increases observed between absorption features raise new questions concerning the physics of charged particle transport and acceleration. An absorption feature near 2.5 Rs has led to the discovery of a previously unknown satellite with a diameter of ≈ 200 kilometers, semimajor axis of 2.51 Rs, and eccentricity of 0.013. Radiation absorption features that suggest a nonuniform distribution of matter around Saturn have also been found from 2.34 to 2.36 Rs, near the position of the F ring discovered by the Pioneer imaging experiment. Beneath the A, B, and C rings we continued to observe a low flux of high-energy electrons. We conclude that the inner Saturn magnetosphere, because of its near-axial symmetry and the many discrete radiation absorption regions, offers a unique opportunity to study the acceleration and transport of charged particles in a planetary magnetic field.

Jupiter Revisited: First Results from the University of Chicago Charged Particle Experiment on Pioneer 11

During the December 1974 Pioneer 11 Jupiter encounter our experiment provided measurements of Jovian energetic protons and electrons both in the magnetic equatorial zone and at previously unexplored high magnetic latitudes. Many of the observations and conclusions from the Pioneer 10 encounter in 1973 were confirmed, with several important exceptions and new findings. We report evidence from Pioneer 11 for protons (∼ 1 million electron volts) of Jovian origin in interplanetary space. In the outer magnetosphere particle intensities at high magnetic latitudes were comparable to those observed in the equatorial zone, and 10-hour variations in particle intensities and spectra were observed at both high and low magnetic latitudes. Therefore, confinement of particles in the outer magnetosphere to a thin equatorial magnetodisc is adequate neither as a description of the particle distribution nor as a complete explanation of the 10-hour variations. Pioneer 11 data support a model in which the intensity varies with a 10-hour period in phase throughout the sunward side of the magnetosphere and is relatively independent of position within the magnetosphere. Transient, highly anisotropic bursts of protons with energies of ∼ 1 million electron volts observed near the orbit of Ganymede suggest local acceleration in some regions of the magnetosphere. In the inner core where particles are stably trapped, a maximum in the high-energy nucleonic flux was again found, corresponding to the Pioneer 10 maximum at ∼ 3.4 Jupiter radii (RJ), which is apparently a persistent feature of, the inner radiation zone. In addition, Pioneer 11 data indicate two more local maxima in the nucleonic flux inside 3.4 RJ, one of which may be associated with absorption by Amalthea, and a maximum intensity at 1.9 RJ more than 20 times that at 3.4 RJ, The flux of relativistic electrons reached a maximum on the magnetic equator at 1.8 RJ, only slightly less its closest approach at 3.1 RJ.

DROPPS: A study of the polar summer mesosphere with rocket, radar and lidar

DROPPS (The Distribution and Role of Particles in the Polar Summer Mesosphere) was a highly coordinated international study conducted in July, 1999 from the Norwegian rocket range (Andoya, Norway). Two sequences of rockets were launched. Each included one NASA DROPPS payload, containing instruments to measure the electrodynamic and optical properties of dust/aerosol layers, accompanied by European payloads (MIDAS, Mini-MIDAS, and/or Mini-DUSTY) to study the same structures in a complementary manner. Meteorological rockets provided winds and temperature. ALOMAR lidars and radars (located adjacent to the launch site) monitored the mesosphere for noctilucent clouds (NLCs) and polar mesosphere summer echoes (PMSEs), respectively. EISCAT radars provided PMSE and related information at a remote site (Tromso, Norway). Sequence 1 (5–6 July) was launched into a strong PMSE with a weak NLC present; sequence 2 (14 July) occurred during a strong NLC with no PMSE evident. Here we describe program details along with preliminary results.

The dust coma of comet P/Halley: measurements on the Vega-1 and Vega-2 spacecraft

The spatial, temporal and mass distributions of coma dust particles for masses > 10−13 g, which we measured with the DUCMA instruments and reported earlier (Simpson et al., 1986a), have been confirmed and extended to reveal additional properties of the dust coma. We have analyzed the inverse square dependence (∝ R −2) of flux with distance R from the nucleus and show that there are well-defined envelope boundaries for the measured range of masses. Regions of enhanced fluxes above these R −2 ‘baselines’ inside these boundaries are identified as dust jets. Of special interest is the giant flux enhancement near closest approach for Vega-1, for which we show that the mass spectrum is similar to the pre-encounter spectra and that there is a smooth rate of rise of intensity over more than four seconds leading into the peak. This is a flux gradient similar to that found for several other much smaller flux enhancements inbound and outbound. The mass dependence of terminal velocities for some jets is consistent with recent predictions, and recurring jets observed by both spacecraft—when traced back to the nucleus—correlate with the active regions predicted by Sekanina and Larson (1986). We have discovered particles with a wide range of masses arriving in clusters or ‘packets’ (i.e., a non-Poisson distribution of dust particles) throughout the regions beyond the envelope boundaries — namely, the fringe regions of the dust coma. These observations suggest the emission from the nucleus of large conglomerates of small particles which gently disintegrate as they travel outward to account for the 10−13 g particles observed beyond the envelope boundaries. Also, dust fluences over the missions have been determined. Finally, we report that both the DUCMA electronics and dust sensors maintained their calibrations and performance throughout the encounters and during the post-encounter interplanetary missions.

A cometary and interplanetary dust experiment on the Vega spacecraft missions to Halley's Comet☆

Abstract An instrument from the University of Chicago which measures the mass and flux of dust particles as a function of time and position in the dust coma of Halleys Comet has been included in the two USSR Vega spacecraft launched 15 and 21 December 1984 for encounters with the comet on 6 and 9 March 1986 respectively. The dust measurements are based on the new detection principle reported by Simpson and Tuzzolino (Nucl. Instr. and Meth. 1985) which employs a polarized polyvinylidene fluoride polymer film (PVDF) and fast electronic pulse techniques. The instrument, called the dust counter and mass analyzer (DUCMA) is described along with its expected performance for the measurement of both cometary and interplanetary dust. Since the electronic PVDF detector signal, resulting from an impacting dust particle of mass m and relative velocity v , is a known function of m and v , measured detector signals at Halleys Comet encounter will directly determine dust particle masses, since v is the known (78 km/s) velocity of the spacecraft relative to the dust particles. DUCMA measures dust particle masses by making use of a single PVDF detector of area 75 cm 2 . The dust mass thresholds selected for the encounter include 3 ranges between 1.5 × 10 −13 and 9 × 10 −11 g, and the integral mass flux above 9 × 10 −11 g. The dynamic range of the instrument counting rates exceeds 5 × 10 4 s −1 for each mass interval and, since the detector remains in calibration even when punctured by large particles, it is expected that the instrument should function properly under the most extreme dust bombardment conditions which could occur during the encounters. The two spacecraft travel around the sun before the March 1986 encounters. Therefore, a search will be undertaken after Venus encounter in June 1985 for possible enhanced streams of interplanetary dust crossing the spacecraft trajectories associated, for example, with known meteor or cometary showers. The opportunity to contribute the dust experiment built and tested by the University of Chicago for the Vega Halleys Comet missions was made possible through the invitation from the USSR Academy of Sciences, Space Research Institute (Moscow) and with assistance from the Max-Planck Institute (Lindau) and the Central Research Institute (Budapest) for arranging this cooperative venture.

Applications of PVDF dust sensor systems in space

Abstract The advantages of ruggedness, no bias requirement, ease of large area sensor construction, high counting rate capability, and space reliability inherent in the Polyvinylidene Fluoride (PVDF) dust sensors which have been under development at the University of Chicago over the last decade have led to PVDF flux/mass/velocity/trajectory systems which have advantages over other systems and are well suited for a variety of dust studies in space. The thermal stability characteristics and flux/mass/velocity/trajectory determining characteristics of PVDF and Vinylidene Fluoride/Trifluoroethylene (PVDF copolymer) dust sensors are described. We summarize the objectives and designs of our earlier VEGA-1/2 comet Halley instruments, a PVDF velocity/trajectory dust instrument for launch on the Advanced Research and Global Observation Satellite (ARGOS) in January 1996, and a PVDF high flux dust instrument for launch on the CASSINI spacecraft to Saturn in October 1997.

Cosmic dust investigations: I. PVDF detector signal dependence on mass and velocity for penetrating particles☆

Our earlier laboratory investigations of polyvinylidene fluoride (PVDF) dust detectors — which we developed for cometary and interplanetary dust studies — were limited to dust mass and velocity ranges of 10−13–10−10 g, and 1–12 km/s, respectively. These measurements established a unique dependence of detector signal amplitude on particle mass and velocity, namely mavb, where a = 1.3 and b = 3.0, respectively, for particles that stopped in thick (e.g. 28 μm) PVDF detectors. We have now extended our dust accelerator investigations to higher dust masses (∼10−9–10−6 g) in the same velocity range so that the dust particles fully penetrate a wide range of PVDF detector thicknesses, including the 28 μm thick detectors we employed for our Comet Halley dust coma measurements. For these penetrating particles we show that the values of a and b are 0.90±0.05 and 1.05±0.05, respectively. We also report, for the first time, the measurement of crater sizes in the detector for these penetrating particles and the correlated detector signal amplitude and pulse shape. From these simultaneous measurements we have proved that the basic response mechanism is irreversible depolarization in the PVDF detector, as we had proposed earlier. These new laboratory investigations also were arranged to determine particle fragmentation and particle (and fragment) velocity after detector penetration by time-of-flight measurements. We discuss the bearing of these studies on our interpretation of measured Comet Halley dust coma mass spectra.

A Large Area Circular Position Sensitive Si Detector

Abstract Circular position sensitive detectors with sensitive areas of 17 cm 2 have been constructed by connecting gold strips on the front surface of a Li-drifted silicon detector to an external resistor network. Detector responses to alpha-particle sources and pulsed-light sources are presented which demonstrate the position and energy response characteristics of the detectors. Measurements with a pulsed-light source equivalent of 140 MeV show that a resolution (fwhm) of 0.19 mm (the width of the gold strips) can be achieved for energy deposits of ∼ 40 MeV. The position resolution (fwhm) obtained from these detectors mounted in a telescope exposed to 95–350 MeV/nucleon 40 Ar nuclei is 0.82 mm for a single detector.

The Space Dust (SPADUS) instrument aboard the Earth-orbiting ARGOS spacecraft: I—instrument description

Abstract The Space Dust (SPADUS) instrument is being carried aboard the Advanced Research and Global Observation Satellite (ARGOS). ARGOS was launched into a circular, sun-synchronous polar orbit at ∼850 km altitude on February 23, 1999 on the Air Force ARGOS P91-1 Mission. The instrument provides time-resolved measurements of dust particle flux, mass distribution, and trajectories, as well as high time resolution measurements of energetic charged particles from the SPADUS Ancillary Diagnostic Sensor (ADS) subsystem, during the nominal three-year ARGOS mission. SPADUS uses Polyvinylidene Fluoride (PVDF) dust sensors developed at the University of Chicago. PVDF sensors have been used earlier on the Vega-1 and Vega-2 missions to Halleys Comet, and are currently being carried on experiments aboard the Cassini spacecraft to Saturn, as well as the Stardust spacecraft to Comet WILD-2. The SPADUS PVDF sensors have a total area of 576 cm 2 , and the SPADUS velocity/trajectory system permits distinction between orbital debris and cosmic (natural) dust, as well as a determination of the orbital elements for some of the impacting particles. The SPADUS instrument measures particle mass over the mass range ∼5×10 −11 g (3.3 μm diameter) to ∼1×10 −5 g (200 μm diameter), and also measures integral flux for particles of mass >∼1×10 −5 g .