Engineering topics

Brin, G. D.

Publications and source records attributed to Brin, G. D..

3 records

NASA NTRS1979

Dust release and mantle development in comets

A model of dust release and dust mantle development by cometary nuclei is developed to explain the brightness asymmetry observed in comets before and after perihelion. Assuming that the cometary nucleus consists of a uniform mixture of dust and volatile ices and taking into account the differential mass spectrum of the dust and the effect of nuclear gravity, it is shown that the factor which determines whether a comet will be brighter before or after perihelion is the mass ratio of dust to volatiles in the nucleus. If this ratio is greater than about two, the comet will be brighter on the inward path and not lose its mantle near perihelion. Applying the model to comet Halley (dust to volatiles ratio presumed to be less than two), it is predicted that the comet remains without a mantle until it reaches a heliocentric distance of 2.035 AU after perihelion and loses its mantle suddenly at a distance of about 1.45 AU on the inward path, causing it to be brighter after perihelion. Predictions of monochromatic brightness are found to be in fair agreement with total observed brightnesses.

Brin, G. D.↗

NASA NTRS1978

On the monochromatic brightness variations of comets

The nonsteady development of the multispecies atmosphere of a long-period comet approaching the sun is modeled, and the associated monochromatic brightness variations are discussed in terms of the varying abundances of the atmospheric species. A simple homogeneous clathrate structure, 85% of which is H2O, provides the representation for the cometary nucleus. Monochromatic brightness variations of the emission bands due to OH, CN and C2 are found to follow the law proposed by Levin (1943) for small heliocentric distance where a quasi-steady approximation is valid. However, the large time-scales of residence for emitting species leads to a breakdown of Levin's law at large heliocentric distances.

Mendis, D. A.↗

NASA NTRS1977

Monochromatic brightness variations of comets. II - Core-mantle model

A class of comets, of which Comet Kohoutek (1973f) is typical, show total as well as monochromatic brightness asymmetries about perihelion. They are fainter after perihelion than before at the same heliocentric distance. A model of the cometary nucleus consisting of a growing nonvolatile dust mantle surrounding a volatile icy core is used to discuss this phenomenon. Numerical results are obtained for Comet Kohoutek (1973f). It is found that dust mantles of thickness in the range of 10-75 cm can be grown by perihelion passage for various values of the thermal conductivity of the dust if there is no substantial dust blow-off by the sublimating volatiles. The thermal conductivity of the dust mantle is quite small and is dominated by 'radiative conductivity' for heliocentric distances less than about 2 AU. Since the radiative conductivity is larger for larger grain size, the thickest mantle corresponds to coarsest matrix. The production rate of the 'parent-molecules' as well as the monochromatic brightness of their 'daughter' products increases less steeply than in the mantleless case, as the comet approaches perihelion.

Mendis, D. A.↗