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Results for “protoplanetary”

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.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Protoplanetary core formation by rain-out of minerals

Models of giant protoplanets computed by DeCampli and Cameron (1979) show that Fe and other minerals in the planet interior are in a liquid state during one of the stages of protoplanet evolution. A model of coalescence of liquid drops was developed using the 'stochastic' collection equation of Slattery (1978); the growth times to droplets was much shorter than the period during which the drops are in a liquid state. Brownian collection quickly coalesced the tiny droplets to a radius of 0.005 cm; gravitational collection was required to form droplets of radii greater than 0.005 cm.

Slattery, W. L.↗
NASA NTRS1988

Interactions of planetesimals with protoplanetary atmospheres

The 'core instability' mechanism presently postulated for the interaction of planetesimals with the envelopes of growing giant planets involves core growth through the accretion of solid bodies in the solar nebula; the core thereby becomes more effective in the gravitational attraction of gas from the surrounding nebula into an envelope, until a runaway accretion stage is reached. Two-body trajectory curves of planetesimals through this envelope are computed which demonstrate the depth of penetration and the cross-sections for capture of icy and rocky planetesimals.

Podolak, Morris↗
NASA NTRS1988

Generation of dynamo magnetic fields in protoplanetary and other astrophysical accretion disks

A computational method for treating the generation of dynamo magnetic fields in astrophysical disks is presented. The numerical difficulty of handling the boundary condition at infinity in the cylindrical disk geometry is overcome by embedding the disk in a spherical computational space and matching the solutions to analytically tractable spherical functions in the surrounding space. The lowest lying dynamo normal modes for a 'thick' astrophysical disk are calculated. The generated modes found are all oscillatory and spatially localized. Tha potential implications of the results for the properties of dynamo magnetic fields in real astrophysical disks are discussed.

Stepinski, T. F.↗
NASA NTRS1991

Magnetohydrodynamic puzzles in the protoplanetary nebula

The following subject areas are covered: (1) magnetization of meteorites; (2) the possible origin of a nebular magnetic field; (3) the possibility of magnetic flares; (4) external manifestations; (5) dynamical effects of the magnetic fields; and (6) the problem of ionization.

Levy, Eugene H.↗
NASA NTRS1993

The evolution of protoplanetary disks

Accretion disks evolve by transferring angular momentum outwards, which allows mass to flow inwards onto the central object. The radial structure and time-dependent behavior of low-mass, Keplerian, viscous disks is analyzed. Potential mechanisms for the angular momentum transport in disks are reviewed. An evolutionary model of a low mass disk around a pulsar is presented.

Ruden, Steven P.↗
NASA NTRS1994

Investigations of the dynamical evolution of protoplanetary nebulae

The spectral energy distributions (SED's) of all the known Class I (protostellar) sources in the Taurus molecular cloud were modelled. The Tereby, Shu, & Cassen (1984, TSC) density distribution for a rotating, infalling envelope was adopted. The radiative equilibrium temperature distribution from the spherical average of the TSC density distribution was calculated. The resulting spherically-symmetric temperature distribution then provides the source function to obtain the emergent spectrum at a given inclination angle i from the formal solution of the transfer equation, using the exact density (opacity) distribution. Results showed that the SED's of the protostar candidates in Taurus can be reproduced with TSC models having infall rates close to the values predicted by the theory of isothermal cloud collapse. Flat Spectrum T Tauri Stars were studied. The mid- to far-infrared fluxes of 'flat spectrum' T Tauri stars can be explained by radiative equilibrium emission from infalling dusty envelopes. This explanation indicated that models employing 'active' disks, in which the temperature distribution is a parameterized power law, should be invoked with caution. Infall also naturally explains the scattered light nebulae detected around many flat-spectrum sources. Results showed that the SED's of the protostar candidates in Taurus can be reproduced with TSC models having infall rates close to the values predicted by the theory of isothermal cloud collapse. Flattened infalling envelope models are also being studied.

Hartmann, Lee W.↗
NASA NTRS1994

Turbulent diffusion and concentration of chondrules in the protoplanetary nebula

Turbulence is known to possess structure on many scales. The largest or integral scale L is usually taken to be the largest dimension of the system. Two different turbulent regimes are likely to be of importance. Early stage convective turbulence in a hot nebula probably extends over the entire nebula scale height, and probably has typical eddy frequency comparable to the orbit frequency. At a later stage, midplane shear layer turbulence can be driven by the presence of a differently rotating, densely settled particle layer, with different length and timescales.

Cuzzi, J. N.↗