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Lanzerotti, L. J.

Publications and source records attributed to Lanzerotti, L. J..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Ion bombardment of interplanetary dust

It is thought that a fraction of the interplanetary dust particles (IDP's) collected in the stratosphere by high-flying aircraft represent materials ejected from comets. An investigation is conducted regarding the effects of ion bombardment on these particles, taking into account information on ion tracks and carbon in IDP's and laboratory data on charged particle bombardment of surfaces. It is found that the observational discovery of particle tracks in certain IDP's clearly indicates the exposure of these particles to approximately 10,000 years of 1-AU equivalent solar-particle fluences. If some erasure of the tracks occurs, which is likely when an IDP enters the upper atmosphere, then somewhat longer times are implied. The effects of the erosion and enhanced adhesion produced by ions are considered.

Johnson, R. E.↗
NASA NTRS1986

FASAC Technical Assessment Report: Soviet Space Science Research

This report is the work of a panel of eight US scientists who surveyed and assessed Soviet research in the spare sciences. All of the panelists were very familiar with Soviet research through their knowledge of the published scientific literature and personal contacts with Soviet and other foreign colleagues. In addition, all of the panelists reviewed considerable additional open literature--scientific, and popular, including news releases. The specific disciplines of Soviet space science research examined in detail for the report were: solar-terrestrial research, lunar and planetary research, space astronomy and astrophysics, and, life sciences. The Soviet Union has in the past carried out an ambitious program in lunar exploration and, more recently, in studies of the inner planets, Mars and especially Venus. The Soviets have provided scientific data about the latter planet which has been crucial for studies of the planet's evolution. Future programs envision an encounter with Halley's Comet, in March 1986, and missions to Mars and asteroids. The Soviet programs in the life sciences and solar-terrestrial research have been long-lasting and systematically pursued. Much of the ground-based and space-based research in these two disciplines appears to be motivated by the requirement to establish long-term human habitation in near-Earth space. The Soviet contributions to new discoveries and understanding in observational space astronomy and astrophysics have been few. This is in significant contrast to the very excellent theoretical work contributed by Soviet scientists in this discipline.

Lanzerotti, L. J.↗
NASA NTRS1986

Interactions of planetary magnetospheres with icy satellite surfaces

When natural satellites and ring particles are embedded within magnetospheric plasmas, the charged particles interact with the surfaces of these solid bodies. These interactions have important implications for the surface, the atmosphere of the parent body, and the magnetosphere as a whole. Significant erosion of the surface by sputtering, as well as redeposition of sputter ejecta, can occur over geologic time. The surface can also be chemically modified. Sputter ejecta can make important contributions to the atmosphere; sputtering provides a lower limit to the atmospheric column density even for arbitrarily cold satellite surfaces. Sputter ejecta escaping from the parent body can form extensive neutral clouds within the magnetosphere. Ionization and dissociation within these neutral clouds can be dominant sources of low-energy plasma. The importance of these processes is discussed for the satellites and magnetospheres of Jupiter, Saturn and Uranus.

Cheng, A. F.↗
NASA NTRS1985

Does Saturn have rings outside 10 R(s)?

Voyager ion and electron data in the energy range 30-1000 keV as measured by the Low Energy Charged Particle experiment are reviewed to check suggestions based on star occultation data that there are additional tenuous rings of Saturn beyond 10 Saturn radii from that planet. In the Voyager data, there is no convincing evidence for such ring matter. Features in the charged particle fluxes in the regions in question are more readily explained by temporal variations and/or spatial structure unrelated to ring matter, such as the mantle on the dayside and/or detached plasma sheets.

Cheng, A. F.↗
NASA NTRS1985

Latitude dependence of co-rotating shock acceleration

Energetic particle observations in the outer heliosphere (approx 12 A. U.) by the LECP instruments on the Voyager 1 and Voyager 2 spacecraft are discussed that show a definite latitude dependence of the number and intensity of particle enhancements produced by corotating interplanetary regions during an interval when no solar energetic particle events were observed. The particle enhancements are fewer in number and less intense at higher (approx 20 deg.) heliolatitudes. However, the similar spectral shapes of the accelerated particles at the two spacecraft indicate that the acceleration process is the same at the two latitudes, but less intense at the higher latitude.

Gold, R. E.↗
NASA NTRS1985

Interplanetary conditions during 3-kHz radio-wave detections in the outer heliosphere

Plasma waves detected by the Voyager 1 and 2 spacecraft beyond about 12 AU that may be associated with the turbulence expected at the heliopause are interpreted in terms of the characteristics of the interplanetary medium at large heliocentric distances. The low-energy charged-particle environment in the outer heliosphere during the observations of the unusual plasma-wave signals is addressed. The particle data suggest that the outer heliosphere was unusually stable and free of transient shock and particle events for the roughly eight months during the wave observations.

Lanzerotti, L. J.↗
NASA NTRS1985

Measurements of the RF characteristics of earth lightning with the Galileo probe lightning experiment

The results of some measurements of earth lightning made with the functional unit of the Galileo probe RF lightning experiment are presented. The frequency range used is about 100 Hz to 100 kHz. The measurements were carried out in conjunction with simultaneous studies of lightning sources made by the University of Florida lightning research group. It is found that the typical RF pulse duration times are less than 30 microsec, independent of lightning source distance (less than 250 km). It is also found that the time between successive pulses is either quite short (less than 64 microsec), corresponding to the time between intracloud pulses and to the time between bipolar pulses, or occur around 100 ms, corresponding to the time between return strokes in ground discharges. The RF spectra are found to become less steep (relatively more power at the higher frequencies) during an interval of intense, nearby (less than 150 km) storms.

Rinnert, K.↗
NASA NTRS1984

Production of ammonia-depleted surface layers on the Saturnian satellites by ion sputtering

On the basis of laboratory-derived data on the ion erosion of water and ammonia ices, it is suggested that the surfaces of the Saturnian satellites Enceladus, Tethys, Dione, and Rhea could have become enriched with water ice over a reasonable geological time period owing to the preferential erosion of the ammonia by magnetosphere ion bombardment. This mechanism serves as an alternative explanation to other processes invoked for the absence of ammonia spectral features in these satellites.

Lanzerotti, L. J.↗
NASA NTRS1984

Temporal variations in the Siple Station conjugate area

The Siple Station conjugate locations in the Northern Hemisphere are examined for the epoch 1975-1990 according to the predictions of three internal source geomagnetic field models (1GRF 1980, Magsat 1980, Barraclough 1975) and one external field model (Mead/Fairfield) under quiet and disturbed conditions. The conjugate location systematically changes in the interval studied, making it imperative that changes be made in the locations of the Northern Hemisphere geophysical stations during the reactivation of Siple Station in 1985-1987.

Stassinopoulos, E. G.↗
NASA NTRS1984

Sputtering processes - Erosion and chemical change

Laboratory data and models of sputter-induced erosion and chemical alterations in ice films are reviewed and the results are applied to icy grains and satellites exposed to magnetospheric ion bombardment. It is shown that the source of the plasma in the inner magnetosphere of Saturn is likely to be the sputter erosion of the icy objects in this region and the sputter erosion and possible stabilization of the E-ring are considered. Ion-induced polymerization is discussed as a source of the darkened rings of Uranus.

Johnson, R. E.↗
NASA NTRS1984

Measurements of plasma, plasma waves, and suprathermal charged particles in Saturn's inner magnetosphere

The Pioneer 11 and Voyager 1, 2 traversals of Saturn's inner magnetosphere provided direct information on the complex and highly structured distributions of plasma and suprathermal charged particles present in this region. The Voyager wave intruments also yielded absolute electron density measurements in certain inner magnetosphere locations; the wave data were used to evaluate the magnitudes of several wave-particle interactions. The plasma and wave measurements for 24-hr periods centered around closest approach, are summarized, pitch-angle scattering effects possibly associated wtih measured whistler mode turbulence are evaluated, and the effects of wave-particle interactions associated with electrostatic waves are discussed.

Scarf, F. L.↗
NASA NTRS1983

On the plasma conditions at the dayside magnetopause of Saturn

The energy densities epsilon(P) of the low energy ions measured by the Low Energy Charged Particle experiment on Voyager 1 and 2 are compared to the magnetic field energy densities derived from the magnetometer instrument during the crossing of the dayside Saturn magnetopause. The ratios of the proton to magnetic field energy densities are greater than about 0.5 during the Voyager 2 crossing when the magnetopause was at about 18 R(s). During the Voyager 1 crossing of the magnetopause at about 23 R(s), the ratios were about 0.1, although they approached one as the spacecraft entered the region near 18 R(s). The observations show that the dayside Saturnian magnetopause can at times have high beta plasma conditions, similar to the situation found at Jupiter.

Lanzerotti, L. J.↗
NASA NTRS1983

Implications of Voyager data for energetic ion erosion of the icy satellites of Saturn

The possible production of a neutral-particle torus by magnetosphere-particle sputtering of the icy satellites (Enceladus, Tethys, Dione, Rhea) of Saturn is discussed. Particle spectra from the Voyager low-energy-charged-particle experiment are used together with laboratory-derived erosion rates and velocity distributions for the ejected species. An extended torus region in the inner magnetosphere of Saturn is expected, with H2O escape fluxes in the vicinities of the satellites varying from about 2 to 7 x 10 to the 7th mol/sq cm sec for incident protons and from about 6 to 14 x 10 to the 9th mol/sq cm sec if the incident ions are all oxygen.

Lanzerotti, L. J.↗
NASA NTRS1983

Low-energy particles at the bow shock, magnetopause, and outer magnetosphere of Saturn

The characteristics of the dayside bow shock, magnetopause, and outer magnetosphere are emphasized in the present consideration of low energy electrons and protons measured by the Low Energy Charged Particle Experiment during Voyager spacecraft encounters with Saturn. During several of the bow shock crossings, low energy protons were observed streaming from the magnetosphere's dawnside, and in the magnetosheath, the protons were observed to be primarily oriented with pitch angles of about 90 deg. Examination of proton flux distributions suggests that the magnetopause was moving inward with a lower limit speed of 10 km/sec during the Voyager 2 approach to the planet. Intervals of diamagnetic depression observed in the magnetic field energy density during the Voyager 2 encounter nearly coincide with enhancements in the low energy-proton energy density.

Maclennan, C. G.↗
NASA NTRS1983

Plasma ion-induced molecular ejection on the Galilean satellites - Energies of ejected molecules

First measurements of the energy of ejection of molecules from icy surfaces by fast incident ions are presented. Such results are needed in discussions of the Jovian and Saturnian plasma interactions with the icy satellites. In this letter parameters describing the ion-induced ejection and redistribution of molecules on the Galilean satellites are recalculated in light of the new laboratory data.

Johnson, R. E.↗
NASA NTRS1983

The ISPM experiment for spectral, composition and anistropy measurements of charged particles at low energie

The Heliosphere Instrument for Spectral, Composition, and Anisotropy at Low Energies (HI-SCALE) designed to measure interplanetary ions and electrons is described. Ions and electrons are detected by five separate solid-state detector telescopes oriented to give complete pitch angle coverage from the spinning spacecraft. Ion elemental abundances are determined by a telescope using a thin front detector element in a three-element telescope. Experiment operation is controlled by a microprocessor-based data system. Inflight calibration is provided by radioactive sources mounted on closable telescope covers. Ion and electron spectral information is determined using broad-energy-range rate channels, and a pulse-height analyzer for more detailed spectra. The instrument weighs 5.775 kg and uses 4.0 W power.

Lanzerotti, L. J.↗