Engineering topics

Richardson, John D.

Publications and source records attributed to Richardson, John D..

At least 19 records

DOE OSTI2024

The Effects of Turbulence on Heliosheath Ions and Implications for Energetic Neutral Atoms

The distribution of ions in the heliosheath—the region between the heliospheric termination shock and the heliopause—is important for understanding remote observations of energetic neutral atoms (ENAs). The ion distributions were estimated previously based on hybrid simulations of the heating and evolution of solar wind and interstellar pickup ions across the solar wind termination shock, but these estimates only provide the distributions near the shock. In this work, we use self-consistent hybrid kinetic simulations to investigate the effects of turbulence on ion distributions in the heliosheath. The simulations are compared against Voyager observations, constraining the feasible amplitude and compressibility of turbulence. We find that the heating due to turbulent dissipation can lead to a significant increase in the temperature of thermal solar wind ions. Both turbulent velocity fluctuations and the heating of solar wind ions increase the charge-exchange source for ENAs at low energies (around 100 eV), where current ENA models underpredict observations by more than an order of magnitude. However, the effects of turbulence are likely not strong enough to fully explain these discrepancies.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2010

Layered Model for Radiation-Induced Chemical Evolution of Icy Surface Composition on Kuiper Belt and Oort Cloud Bodies

The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environments. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Interactions of surface irradiation, resultant chemical oxidation, and near-surface cryogenic fluid reservoirs have been proposed to account for Enceladus cryovolcanism and may have further applications to other icy irradiated bodies. The diversity of causative processes must be understood to account for observationally apparent diversities of the object surfaces.

Cooper, John F.↗

NASA NTRS2010

Layered Model for Radiation-Induced Chemical Evolution of Icy Surface Composition and Dynamics on Kuiper Belt and Oort Cloud Bodies

The diversity of albedos and surface colors on observed Kuiper Belt and Inner Oort Cloud objects remains to be explained in terms of competition between primordial intrinsic versus exogenic drivers of surface and near-surface evolution. Earlier models have attempted without success to attribute this diversity to the relations between surface radiolysis from cosmic ray irradiation and gardening by meteoritic impacts. A more flexible approach considers the different depth-dependent radiation profiles produced by low-energy plasma, suprathermal, and maximally penetrating charged particles of the heliospheric and local interstellar radiation environment. Generally red objects of the dynamically cold (low inclination, circular orbit) Classical Kuiper Belt might be accounted for from erosive effects of plasma ions and reddening effects of high energy cosmic ray ions, while suprathermal keV-MeV ions could alternatively produce more color neutral surfaces. The deepest layer of more pristine ice can be brought to the surface from meter to kilometer depths by larger impact events and potentially by cryovolcanic activity. The bright surfaces of some larger objects, e.g. Eris, suggest ongoing resurfacing activity. Cycles of atmospheric formation and surface freezeout can further account for temporal variation as observed on Pluto. The diversity of causative processes must therefore be understood to account for observationally apparent diversities of the object surfaces.

Cooper, John F.↗

NASA NTRS2006

Heliosheath Space Environment Interactions with Icy Bodies in the Outermost Solar System

The Voyager 1 and 2 spacecraft are exploring the space environment of the outermost solar system at the same time that earth-based astronomy continues to discover new icy bodies, one larger than Pluto, in the transitional region outward from the Classical Kuiper Belt to the Inner Oort Cloud. Some of the Scattered Disk Objects in this region periodically pass through the heliosheath, entered by Voyager 1 in Dec. 2004 and later expected to be reached by Voyager 2, and out even beyond the heliopause into the Very Local Interstellar Medium. The less energetic heliosheath ions, important for implantation and sputtering processes, are abundant near and beyond the termination shock inner boundary, but the source region of the more penetrating anomalous cosmic ray component has not yet been found. Advantageous for modeling of icy body interactions, the measured heliosheath flux spectra are relatively more stable within this new regime of isotropic compressional magnetic turbulence than in the upstream heliospheric environment. The deepest interactions and resultant radiation-induced chemistry arise from the inwardly diffusing component of the galactic cosmic ray ions with significant intensity modulation also arising in the heliosheath beyond Voyager 1. Surface gardening by high-velocity impacts of smaller bodies (e.g., fragments of previous KBO collisions) and dust is a further space weathering process setting the time scales for long term exposure of different regolith layers to the ion irradiation. Sputtering and ionization of impact ejecta grains may provide a substantial feedback of pickup ions for multiple cycles of heliosheath acceleration and icy body interaction. Thus the space weathering interactions are potentially of interest not only for effects on sensible surface composition of the icy bodies but also for evolution of the heliosheath plasma energetic ion, and neutral emission environment.

Cooper, John F.↗

NASA NTRS2005

Modelling the Neutral Atmosphere and Plasma Environment of Saturn

The first year of this contract has resulted in two publications with the P.I. and co-I Jurac as lead authors and two publications where these team members are co-authors. These papers discuss modeling work undertaken in preparation for Cassini; the goal was to summarize our current best knowledge of the ion and neutrals sources and distributions. One of the major goals of this project is to improve models of the plasma and neutral environment near Saturn. The paper "A self-consistent model of plasma and neutrals at Saturn: Neutral cloud morphology" [Jurac and Richardson, 20051 presents results on the neutral clouds near Saturn using a model which for the first times treats the ions and neutrals self-consistently. We also for the first time include a directly sputtered H source. The Voyager and HST observations are used as model constraints. The neutral source is adjusted to give a good match to the HST observations of OH. For this initial run the ion parameters from Richardson et al. are used; charge exchange with ions is a major neutral loss process. The neutral profile derived from the model is then used in a model of plasma transport and chemistry (with the plasma diffusion rate the only free parameter). This model gives new values of the ion composition which are then fed back into the neutral model. This iteration continues until the values converge.

Richardson, John D.↗

NASA NTRS2003

Modeling the Extended Neutral Atmosphere and Plasma Environment near Saturn

In the three years of this study we have published five papers in refereed journals. We have first examined satellite sources and their contribution to the observed neutral cloud. Based on the total calculated satellite sources and the spatial distribution of sputtered H20, we concluded that they cannot produce observed OH cloud. The E-ring contribution has been also studied in detail.In order to produce observed OH cloud we suggested that the E-ring might be the dominant source in inner Saturnian magnetosphere. We proposed a possible resupply mechanism which is needed to keep both E-ring and OH cloud in the present state: collisions between E-ring grains and remains of a disrupted satellite near Enceladus Lagrangian points. In this scenario a large amount of material, ranging from a few micrometers to hundred of meters, which is optically invisible at present, is likely to exist there. The fourth paper compares the magnetosheaths of the outer planets. A surprising result is that the hot proton component comprises about 40% of the total density, much larger than predicted by shock theory. Gas dynamic models of the boundaries show that the magnetospheres of Jupiter and Saturn are flattened at the poles. The last paper was published in GRL and is the first based of the model of neutrals developed as a main goal of this grant and which is now operational.This Monte Carlo collision code self- consistently determines the neutral distribution. from the rings and satellites until they are lost by ionization, by collisions with rings, moons, or Saturn, or by escape from Saturn. Our model is unique in that it includes the effects of plasma chemistry and both plasma-neutral and neutral neutral collisions to determine the dynamical evolution of the water group neutrals in Saturn's magnetosphere. The lifetimes of the neutrals against loss to photoionization, charge exchange, electron dissociation and electron impact dissociation are based on the model given by (Richardson et al. 1998) and vary with position in the magnetosphere. The dominant neutral dissociation channels H20->OH+H, H20-> O+H2, and OH->O+H2 are considered.

Richardson, John D.↗

NASA NTRS2002

Investigation of Solar Wind Correlations and Solar Wind Modifications Near Earth by Multi-Spacecraft Observations: IMP 8, WIND and INTERBALL-1

The foundation of this Project is use of the opportunity available during the ISTP (International Solar-Terrestrial Physics) era to compare solar wind measurements obtained simultaneously by three spacecraft - IMP 8, WIND and INTERBALL-1 at wide-separated points. Using these data allows us to study three important topics: (1) the size and dynamics of near-Earth mid-scale (with dimension about 1-10 million km) and small-scale (with dimension about 10-100 thousand km) solar wind structures; (2) the reliability of the common assumption that solar wind conditions at the upstream Lagrangian (L1) point accurately predict the conditions affecting Earth's magnetosphere; (3) modification of the solar wind plasma and magnetic field in the regions near the Earth magnetosphere, the foreshock and the magnetosheath. Our Project was dedicated to these problems. Our research has made substantial contributions to the field and has lead others to undertake similar work.

Paularena, Karolen I.↗

NASA NTRS1995

An extended plasma model for Saturn

The Saturn magnetosphere model of Richardson and Sittler (1990) is extended to include the outer magnetosphere. The inner magnetospheric portion of this model is updated based on a recent reanalysis of the plasma data near the Voyager 2 ring plane crossing. The result is an axially symmetric model of the plasma parameters which is designed to provide accurate input for models needing either in situ or line-of-sight data and to be a useful tool for Cassini planning.

Richardson, John D.↗

NASA NTRS1995

Radial evolution of the solar wind from IMP 8 to Voyager 2

Voyager 2 and Interplanetary Monitoring Platform (IMP) 8 data from 1977 through 1994 are presented and compared. Radial velocity and temperature structures remain intact over the distance from 1 to 43 AU, but density structures do not. Temperature and velocity changes are correlated and nearly in phase at 1 AU, but in the outer heliosphere temperature changes lead velocity changes by tens of days. Solar cycle variations are detected by both spacecraft, with minima in flux density and dynamic pressure near solar maxima. Differences between Voyager 2 and IMP 8 observations near the solar minimum in 1986-1987 are attributed to latitudinal gradients in solar wind properties. Solar rotation variations are often present even at 40 AU. The Voyager 2 temperature profile is best fit with a R(exp -0.49 +/- 0.01) decrease, much less steep than an adiabatic profile.

Richardson, John D.↗

NASA NTRS1994

The magnetosheath of Neptune: Models and observations

This paper gives a complete overview of the plasma and magnetic field in the magnetosheath of Neptune. A more sophisticated method is used to reanalyze the plasma data. This method provides better values of plasma density, velocity, and temperature in the magnetosheath both inbound and outbound from the planet than published previously. The data are compared to results obtained from a gasdynamic model of low around a planetary magnetosphere. Agreement of theory and data is good for some parameters and poor for others. We show that some discrepancies between the model predictions and observations may be due to changes in the solar wind parameters. The model results and data are used to check the hypothesis that Voyager encountered the high-latitude plasma mantle downstream from Neptune. The deviations of the data from the model results in this region are consistent with those expected for a mantle crossing, with the exception of the plasma temperature which decreases in one crossing and increases in the other. This may indicate that our knowledge of the nature of the mantle-magnetosheath boundary is not complete.

Richardson, John D.↗

NASA NTRS1994

Solar wind oscillations with a 1.3 year period

The Interplanetary Monitoring Platform 8 (IMP-8) and Voyager 2 spacecraft have recently detected a very strong modulation in the solar wind speed with an approximately 1.3 year period. Combined with evidence from long-term auroral and magnetometer studies, this suggests that fundamental changes in the Sun occur on a roughly 1.3 year time scale.

Richardson, John D.↗

NASA NTRS1993

Modeling the Europa plasma torus

The existence of a torus of plasma generated by sputtering from Jupiter's satellite Europa has long been suspected but never yet convincingly demonstrated. Temperature profiles from Voyager plasma observations indicate the presence of hot, possibly freshly picked-up ions in the general vicinity of the orbit of Europa, which may be interpreted as evidence for a local plasma torus. Studies of ion partitioning in the outer regions of the Io torus reveal that the oxygen to sulfur mixing ratio varies with radial distance; this may indicates that oxygen-rich matter is injected from a non-Io source, most probably Europa. We have constructed a quantitative model of a plasma torus near the orbit of Europa which takes into account plasma input from the Io torus, sputtering from the surface of Europa, a great number of ionization and charge exchange processes, and plasma loss by diffusive transport. When the transport time is chosen so that the model's total number density in consistent with the observed total plasma density, the contribution from Europa is found to be significant although not dominant. The model predicts in detail the ion composition, charge states, and the relative fractions of hot Europa-generated and (presumed) cold Io-generated ions. The results are generally consistent with observations from Voyager and can in principle (subject to limitations of data coverage) be confirmed in more detail by Ulysses.

Schreier, Ron↗

NASA NTRS1993

A quantitative model of plasma in Neptune's magnetosphere

A model encompassing plasma transport and energy processes is applied to Neptune's magnetosphere. Starting with profiles of the neutral densities and the electron temperature, the model calculates the plasma density and ion temperature profiles. Good agreement between model results and observations is obtained for a neutral source of 5 x 10 exp 25/s if the diffusion coefficient is 10 exp -8 L3R(N)/2s, plasma is lost at a rate 1/3 that of the strong diffusion rate, and plasma subcorotates in the region outside Triton.

Richardson, John D.↗

NASA NTRS1992

A new model for plasma transport and chemistry at Saturn

A model of plasma transport and chemistry is described which calculates the evolution of a plasma population in latitude and radial distance. This model is applied to the magnetosphere of Saturn, where it is used to fit the density profile of the heavy ions assuming both satellite and ring sources of plasma. Use of an extended source region is found to significantly alter the resulting plasma profile. Water ions cannot fit the observed density profile inside L = 6 even with a large ring source. Oxygen ions can fit the density profile throughout the region inside L = 12 given a suitable profile of neutral hydrogen; a suitable profile contains up to 5 H/cu cm outside L = 4 with the number increasing inside this. Preferred values of K are 1-3 x 10 exp -10 R(S)2/s, but any value K less than 10 exp -9 R(S)2/s can be accommodated. The temperature profile is shown to favor models invoking in situ plasma formation and loss as opposed to models where transport is important.

Richardson, John D.↗

NASA NTRS1992

Detailed analysis of low energy plasma data under the Voyager Uranus data analysis program

Research effort included the PLS data analysis program where modifications to the data fitting procedure and elimination of possible noise and electron contamination were made. The analysis code corrections were used in checking the Neptune data gathered during the Voyager 2 encounter and for analyzing selected plasma spectra from the warm Io torus. A major task accomplished was the summary of Uranus-related research in the U.S. National Report to the International Union of Geodesy and Geophysics for the 1987 - 1990 quadrennium. A limited amount of work was accomplished on assessing the Pedersen conductivity of the ionosphere and comparing it with inferred values from shielding by the Uranian ring current. Under this grant there has been a great deal of effort expended on identifying and classifying plasma waves and oscillations in the magnetosheath and solar wind downstream from Uranus. Large amplitude oscillations in plasma parameters are found in the magnetosheath, with density changes of up to a factor of ten occurring on times scales of minutes. New algorithms developed for analyzing the inbound bow shock crossing of Neptune will probably be applied to a more detailed analysis of the Uranus shock in the near future.

Mcnutt, Ralph L., Jr.↗

NASA NTRS1991

Voyager 2 electron observations in the magnetosphere of Neptune

This paper describes electron data obtained during the Neptune encounter by the Voyager 2 plasma science experiment. The densities and temperatures of low-energy (10-5950 eV) electrons and the electrostatic potential of the spacecraft near Neptune are derived. The data indicate that the escape of charged particles from Triton and the local ionization of atoms in the neutral torus originating from Triton are the major plasma sources. It is inferred that this neutral torus of hydrogen atoms has a density of about 300/cu cm and an inner boundary at 8 R(N). The data near Neptune exhibit signatures suggesting that both precipitation into Neptune's atmosphere and ring absorption are important plasma loss mechanisms. Plasma transport in the magnetosphere appears to be very fast; the diffusion coefficient is 1 x 10 exp -7 L exp 3 R(N) exp 2/sec.

Zhang, Ming↗

NASA NTRS1990

Atomic and molecular hydrogen from Titan in the Kronian magnetosphere

The question of the neutral gas and plasma population in the region of the Kronian magnetosphere, outside the plasma mantle and inside the magnetopause, dominated by the efflux of Titan's atmosphere is considered. A model that has been used successfully to describe the inner magnetosphere is applied to this region under constraints derived from the plasma science and ultraviolet spectrometer experiments on Voyager. It is shown that it is not possible to reconcile the results of these two experiments simultaneously with the values of the atomic and molecular source strengths of the atmosphere of Titan extant in the literature. The possible sources of the discrepancy are delineated.

Eviatar, Aharon↗

NASA NTRS1990

Water group plasma in the magnetosphere of Saturn

The paper deals with the question of the composition and spatial distribution of water group plasma in the magnetosphere of Saturn. It is suggested that the problem of the coexistence of neutral atomic hydrogen and such a plasma can be resolved if the dominant ion is taken to be H2O(+) or H3O(+). It is also suggested that this ion may provide a means of radiative cooling of the inner magnetosphere plasma which is possibly easier to realize than transport of nitrogen from Titan. As a source for this plasma in the region inward of the icy satellites, the ring atmosphere is suggested. The depleted plasma density in the domain between the Dione-Tethys torus and the ring plane crossing of Voyager may provide an explanation for the survival of the E-ring. Data are presented which indicate that H2O(+) or H3O(+) is also a favored candidate in the outer magnetosphere and that it can diffuse without loss through the hot electron gas.

Eviatar, Aharon↗