SEARCH · Search NASA

Results for “Mass loading”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Interaction of Titan's atmosphere with Saturn's magnetosphere

The Voyager 1 measurements made during the Titan flyby reveal that Saturn's rotating magnetospheric plasma interacts directly with Titan's neutral atmosphere and ionosphere. This results from the lack of an intrinsic magnetic field at Titan. The interaction induces a magnetosphere which deflects the flowing plasma around Titan and forms a plasma wake downstream. Within the tail of the induced magnetosphere, ions of ionospheric origin flow away from Titan. Just outside Titan's magnetosphere, a substantial ion-exosphere forms from an extensive hydrogen-nitrogen exosphere. The exospheric ions are picked up and carried downstream into the wake by the plasma flowing around Titan. Mass loading produced by the addition of exospheric ions slows the wake plasma down considerably in the vicinity of the magnetopause.

Hartle, R. E.↗

NASA NTRS1985

The location of the subsolar bow shock of Venus - Implications for the obstacle shape

The rise in periapsis altitude with time has allowed the Pioneer Venus spacecraft to begin probing the subsolar Venus bow shock. This has allowed the altitude of the subsolar bow shock to be determined by in situ observations for the first time. The observed altitude of 2280 km at the nose together with the previously determined terminator altitude can be used to infer the shape of the obstacle using the gasdynamic model of the solar wind interaction with Venus. When this shape is compared to the measured locations of the Venus ionopause (defined as the point where the magnetosheath magnetic field pressure and ionospheric thermal pressures are equal), it is found that the observed ionopause position is too low to qualify as the obstacle. It is inferred that a layer of the mass loaded plasma in the magnetosheath forms the magnetic barrier.

Russell, C. T.↗

NASA NTRS1986

Plasma fluctuations and large-scale mixing near Comet Giacobini-Zinner

The relationship among plasma densities, flow speeds and directions, and temperatures, at distances within about 100,000 km of Comet Giacobini-Zinner's nucleus, are presently examined in view of lowpass-filtered data from the International Cometary Explorer's electron spectrometer. While the largest amplitude density spikes often have more significant flow changes associated with them, a consistent pattern is not found. Power spectral analyses in and near the sheath/transition regions show that density fluctuation levels are enhanced at all detectable frequencies, consistent with strong density fluctuations on all time scales. Such mechanisms as the amplification of convected ion pickup waves and cometary rays for producing the large plasma variations are discussed. It is suggested that the Rayleigh-Taylor effect-driven mixing mechanism at a mass-loading boundary abut 100,000 km from the nucleus may be operative.

Baker, D. N.↗

NASA NTRS1986

Ion distribution functions in the vicinity of Comet Giacobini-Zinner

Photoionization of neutral molecules in the coma surrounding a comet produces heavy ions which contaminate and mass-load the solar wind. Cometary ion distribution functions in the vicinity of Comet Giacobini-Zinner (GZ) are calculated using a Monte Carlo method. The distribution function calculated behind the shock has both cold (approximately 2 keV) and hot (approximately 40 keV) components.

Cravens, T. E.↗

NASA NTRS1986

Micrometeoroid impact on planetary satellites as a magnetospheric mass source

Proceeding from the observation that planetary satellites are important sources of mass for planetary magnetospheres, it is noted that meteoroid impact vaporization may compete with charged particle sputtering as a supply mechanism. After considering meteoroid-driven vapor sources in the Jovian and Kronian systems, it is concluded that while the larger impact flux values obtained for the outer solar system suggest a role for impact vaporization in the cases of both Jupiter and Saturn, this process will not predominate over sputtering; at the lower end of the impact flux range, however, sputtering everywhere dominates magnetospheric mass loading.

Haff, P. K.↗

NASA NTRS1986

Interactions with planetary ionospheres and atmospheres: A review

The interaction of the solar wind with umnagnetized objects possessing an ionosphere is reviewed. Venus, Mars, Titan, comets (including the artificial comet created by AMPTE) and the unusual interplanetary events interpreted as cometesimals are considered. The role of the interplanetary magnetic field and of mass loading in producing the observed interactions is highlighted. Interpretation to date is based largely on an MHD (fluid) treatment, but results from the first AMPTE barium release and from recordings made at Venus suggest that finite Larmor radius effects introduce asymmetries in the solar wind interaction.

Saunders, Mark A.↗

NASA NTRS1987

A magnetohydrodynamic model of the interaction of the solar wind with the Jovian magnetosphere and a magnetohydrodynamic simulation of the interaction of the solar wind with the out flowing plasma from a comet

A three-dimensional code for a rapidly rotating magnetosphere in which the MHD equations and the Maxwell equations were solved by using the two step Lax Endroff scheme, was developed. Preliminary results were presented at the Fall AGU meeting in San Francisco. The basic simulation model to study the solar wind interactions was adapted to other bodies in addition to Jupiter. Because of the recent comet flybys, a comet was chosen as the first model. The aim was to model the formation of the contact surface and the plasma tail. Later, work was begun on a three-dimensional model which would include the effects of mass loading. This model was designed to study the weak cometary bow shocks observed by the probes to comets Halley and Giacobini-Zinner. The model was successful in reproducing the position and shape of the bow shock which was determined by using observations from the Suisei spacecraft.

Walker, R. J.↗

NASA NTRS1985

Particulate matter in the Venus atmosphere

The paper presents a summary of the data currently available (June 1984) describing the planet-enshrouding particulate matter in the Venus atmosphere. A description and discussion of the state of knowledge of the Venus clouds and hazes precedes the tables and plots. The tabular material includes a precis of upper haze and cloud-top properties, parameters for model-size distributions for particles and particulate layers, and columnar masses and mass loadings.

Ragent, B.↗

NASA NTRS1986

Magnetostrophic balance in planetary dynamos - Predictions for Neptune's magnetosphere

With the purpose of estimating Neptune's magnetic field and its implications for nonthermal Neptune radio emissions, a new scaling law for planetary magnetic fields was developed in terms of externally observable parameters (the planet's mean density, radius, mass, rotation rate, and internal heat source luminosity). From a comparison of theory and observations by Voyager it was concluded that planetary dynamos are two-state systems with either zero intrinsic magnetic field (for planets with low internal heat source) or (for planets with the internal heat source sufficiently strong to drive convection) a magnetic field near the upper bound determined from magnetostrophic balance. It is noted that mass loading of the Neptune magnetosphere by Triton may play an important role in the generation of nonthermal radio emissions.

Curtis, S. A.↗

NASA NTRS1986

Interactions with planetary ionospheres and atmospheres - A review

The interaction of the solar wind with unmagnetized objects possessing an ionosphere is reviewed, with emphasis on recent developments. Venus, Mars, Titan, comets (including the artificial comet created by AMPTE) and the unusual interplanetary events interpreted as cometesimals are considered. The role of the interplanetary magnetic field and of mass loading in producing the observed interactions are highlighted. Interpretation to date is based largely on an MHD (fluid) treatment, but recent results from the first AMPTE barium release and from recordings made at Venus suggest that finite Larmor radius effects introduce asymmetries in the solar wind interaction.

Saunders, Mark A.↗

NASA NTRS1986

Planetary fast neutral emission and effects on solar wind - A cometary exosphere analog

Ion-neutral charge exchange reactions occurring in planetary magnetospheres produce a copious supply of fast neutrals in the form of high-speed magnetospheric neutral winds. Theoretical models of such processes and their subsequent effects on the solar wind are investigated. Source strengths for emission from earth's ring current (10 to the 25th - 10 to the 26th/s), Jupiter's Io plasma torus (1-2 x 10 to the 28th/s), and both the Dione-Tethys torus and the Titan hydrogen torus (10 to the 26th - 10 to the 27th/s) of Saturn are evaluated. The effects of an extensive atomic nitrogen cloud surrounding the orbit of Titan are also considered in connection with the Saturnian aurora. Reionization and pickup of sulfur atoms in the circumplanetary region of Jupiter lead to a small mass-loading effect on the solar wind velocity (less than 10 percent); however, the heat input is substantial, resulting in a large increase in the effective ion temperature (not less than 100 percent). The pickup ion model is also applied tot the generation of electromagnetic ion cyclotron waves in the local neighborhood of the central body. The model suggests the preferential excitation of left-hand-polarized waves in regions where the solar wind-magnetic field angle is large (outer sheath) and right-hand waves in regions where the angle is small (near-tail).

Barbosa, D. D.↗

NASA NTRS1986

Origin of large magnetic fluctuations in the magnetosheath of Venus

The origin of large-amplitude hydromagnetic waves in the Venus magnetosheath downstream of the quasi-parallel bow shock is investigated by means of numerical simulations. It is shown that the most likely source of these waves is the bow shock itself, rather than an instability involving the solar wind and oxygen ions of planetary origin. Pickup of O(+) ions by these waves is also examined and shown to be in agreement with previous test particle calculations. The effect of mass loading on the structure of the shock is also discussed.

Winske, D.↗

NASA NTRS1987

Magnetotails at unmagnetized bodies - Comparison of Comet Giacobini-Zinner and Venus

It is found that the near ionopause environs play a crucial role in the tail formation process at both Venus and G-Z and that draping at the two very different sized bodies occurs on ionopause scale sizes. On the other hand, ion densities, downtail mass fluxes, tailward J x B forces, and lobe betas are factors of about 10,000, 50, 100, and 20 times greater in the G-Z tail than in Venus', while bulk flow speeds and ion temperatures are factors of about 15 and 240 times lower. These large quantitative differences in the properties within the two magnetotails are attributable to the significantly greater upstream mass loading of the solar wind by the extended neutral atmosphere at G-Z (comets in general) compared to the gravitationally bound atmosphere of Venus.

Mccomas, D. J.↗

NASA NTRS1987

Comparative plasma tails of Venus and comets

A review of current models of solar wind flow in the plasma tails of weakly magnetized bodies is presented. Measurements conducted by the Mariner 5 spacecraft, the Veneras 9 and 10, and the PVO orbiters, in the Venus tail, and with the ICE spacecraft in the tail of Comet Giacobini-Zinner, reveal common plasma properties which suggest that similar physical processes are operative. Most notable is the observation of decreased flow velocities and enhanced plasma temperatures in the vicinity of their plasma tails. In Venus, the measured velocity and temperature fields are consistent with the effects of frictional forces between the mass-loaded ionosheath flow and the ionosphere along the (magnetic) polar regions of the ionopause. It is argued that similar conditions exist at a cometary ionopause and that the distribution of magnetic fluxes in a cometary tail is controlled by the entry of plasma fluxes from the (magnetic) polar regions of the comet's ionospheric obstacle. This question is further addressed in connection with the two-step shape of the magnetic profile measured across the tail of the comet. It is suggested that the low intensity outer increases of the magnetic lobes are associated with the draping of the interplanetary magnetic field lines around the comet's ionospheric obstacle, and that the higher intensity increases seen in the inner regions of the magnetic lobes are due to an additional compression of magnetic fluxes produced by the entry of plasma particles into the tail.

Perezdetejada, H.↗

NASA NTRS1987

Solar wind effects on the outer ion coma of Comet Halley

A simple two-dimensional model is developed to examine the composition of the cometary ion coma in the region outside the ionopause which is strongly affected by the solar wind. Two-dimensional ion distributions are obtained assuming a cylindrically symmetric ion coma which accounts for the dynamic effects of the mass-loaded solar wind flow around the cometary ionosphere. The results of this model are discussed in the context of analyzing the GIOTTO ion data.

Flammer, K. R.↗

NASA NTRS1987

Waves in the magnetic field and solar wind flow outside the bow shock at comet P/Halley

The existence of hydromagnetic waves in the mass-loaded solar wind upstream from the bow shock of a comet is well-established both for comet Giacobini-Zinner and for comet Halley. Whereas previous reports have been concerned either with the magnetic field observations or with plasma observations, here observations of the magnetic field with the solar wind proton and alpha particle distributions are combined. This allows the three possible modes of propagation for these waves to be separated. The magnetic component is predominantly transverse to the magnetic field and linearly polarized. The flow vector also has a substantial amount of power parallel to the magnetic field. An examination of the pressure variations shows that slow magnetosonic waves are more common than the fast mode.

Johnstone, A.↗

NASA NTRS1988

A unidimensional model of comet ionosphere structure

The one-dimensional continuity and momentum equations for the plasma formed in the expanding coma of a comet near the sun are studied. An analytic expression for the magnetic field configuration in the presence of outflow, photoionization, dissociative recombination, plasma fluid pressure, and friction between the ions and neutrals is obtained. It is suggested that for a Halley-type comet there will be a region sunward of the nucleus from which the magnetic field is excluded, consistent with Giotto observations. Calculations have been performed for Halley and Giacobini-Zinner type comets, and in the field-free regions it is shown that the dominant terms in the momentum equation balancing the magnetic pressure gradient are the ion neutral friction and the net mass loading momentum gain.

Eviatar, Aharon↗

NASA NTRS1988

A three-dimensional MHD simulation of the interaction of the solar wind with Comet Halley

The interaction between the solar wind and cometary plasmas is simulated using a three-dimensional time-dependent MHD simulation model, and the results are compared with the recent satellite observations of Comet Halley. The model, which includes cometary mass loading, reproduces many of the features observed by the Suisei probe and the Giottot, including the weak bow shock, the enhancement of the magnetic field in front of the contact surface, and the plasma temperature increase across the bow shock (while it decreased near the comet).

Ogino, Tatsuki↗