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On the light-absorbing surface layer of cometary nuclei: I. Radiative transfer
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Astronomy and Space Physics.
2002 (English)In: Icarus, ISSN 0019-1035, Vol. 156, no 1, 223-248 p.Article in journal (Refereed) Published
Abstract [en]

A small but increasing volume of observations of cometary nuclei has

accumulated during the last two decades. This development is accelerating

with upcoming space missions such as Stardust, Contour, and Rosetta. In

response to the growing need for a theoretical understanding of optical

properties of cometary nuclei, we have calculated synthetic reflectance

spectra in the 0.2-2.0 micrometer wavelength region, photometric

colors in the Johnson-Kron-Cousins UBVRI system, and visual geometric

albedos, for a large number of porous ice-dust mixtures with different

composition, regolith grain sizes and grain morphologies, such as

core-mantle grains, dense clusters of such grains, and large irregular

particles with internal scatterers. The calculations are based on Mie theory,

the Discrete Dipole Approximation, Hapke theory, and a numerical solution

of the equation of radiative transfer in particulate media. In addition,

wavelength-integrated directional-hemispherical albedos and flux attenuation profiles in the

regolith as functions of depth, have been calculated in order to improve the

energy budget and treatment of energy boundary conditions in thermal models

of cometary nuclei.

Our results are compared with spectra and colors of observed cometary nuclei.

Our main conclusions are that only regolith consisting of relatively large

core-mantle grains, or clusters of smaller core-mantle grains, are capable

of reproducing the red colors seen in comets; that ice-dust mixtures

actually can be darker than ice-free regolith under certain circumstances;

and that solar radiation sometimes penetrates to a depth that is comparable

to the region in which diurnal temperature variations occur.

Place, publisher, year, edition, pages
2002. Vol. 156, no 1, 223-248 p.
Keyword [en]
comets, surfaces, radiative transfer
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:uu:diva-15042DOI: doi:10.1006/icar.2001.6760OAI: oai:DiVA.org:uu-15042DiVA: diva2:42813
Available from: 2008-02-04 Created: 2008-02-04 Last updated: 2011-01-13

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