149 research outputs found
Microwave emission from granular silicates
Experimental finding is that mass absorption coefficient is independent of frequency but highly dependent on moisture content; effective conductivity increases with frequency, and low tangent is independent of frequency. Computed values of electrical properties are in rough numerical agreement with extrapolated laboratory values on other silicate materials
Calibration of AIS Data Using Ground-based Spectral Reflectance Measurements
Present methods of correcting airborne imaging spectrometer (AIS) data for instrumental and atmospheric effects include the flat- or curved-field correction and a deviation-from-the-average adjustment performed on a line-by-line basis throughout the image. Both methods eliminate the atmospheric absorptions, but remove the possibility of studying the atmosphere for its own sake, or of using the atmospheric information present as a possible basis for theoretical modeling. The method discussed here relies on use of ground-based measurements of the surface spectral reflectance in comparison with scanner data to fix in a least-squares sense parameters in a simplified model of the atmosphere on a wavelength-by-wavelength basis. The model parameters (for optically thin conditions) are interpretable in terms of optical depth and scattering phase function, and thus, in principle, provide an approximate description of the atmosphere as a homogeneous body intervening between the sensor and the ground
Solution of the equation of heat conduction with time dependent sources: Programmed application to planetary thermal history
A computer program (Program SPHERE) solving the inhomogeneous equation of heat conduction with radiation boundary condition on a thermally homogeneous sphere is described. The source terms are taken to be exponential functions of the time. Thermal properties are independent of temperature. The solutions are appropriate to studying certain classes of planetary thermal history. Special application to the moon is discussed
Microwave emission from granular silicates - Determination of the absorption coefficient from plate measurements and the effects of scattering
Microwave mass absorption coefficient in granular silicates from plate measurements and effects of scatterin
Ground Reflectance Measurements from Thematic Mapper Data
Satellite radiance data are measures of solar radiation that has been reflected by the Earth's surface and scattered and absorbed by atmospheric gases and aerosols. Of concern to geologists are the surface reflectance and the degrading effects on surface resolution and albedo contrast introduced by atmospheric phenomena. The objects of this research have been to: (1) provide an empirical relationship between scanner radiance and ground reflectance allowing interpretation of the satellite data in terms of the surface parameter, and (2) assess the precision with which surface spectral reflectance may be recovered from LANDSAT-4 TM data in the presence of perturbing atmospheric and instrumental factors. The approach is field-oriented, and utilizes ground observations of surface spectral reflectance with portable spectrometers and radiometers to develop the required empirical relationships
A study of alteration associated with uranium occurrences in sandstone and its detection by remote sensing methods, volume 2
This document contains tabular and graphic data for volume 1
The Compositional Structure of the Asteroid Belt
The past decade has brought major improvements in large-scale asteroid
discovery and characterization with over half a million known asteroids and
over 100,000 with some measurement of physical characterization. This explosion
of data has allowed us to create a new global picture of the Main Asteroid
Belt. Put in context with meteorite measurements and dynamical models, a new
and more complete picture of Solar System evolution has emerged. The question
has changed from "What was the original compositional gradient of the Asteroid
Belt?" to "What was the original compositional gradient of small bodies across
the entire Solar System?" No longer is the leading theory that two belts of
planetesimals are primordial, but instead those belts were formed and sculpted
through evolutionary processes after Solar System formation. This article
reviews the advancements on the fronts of asteroid compositional
characterization, meteorite measurements, and dynamical theories in the context
of the heliocentric distribution of asteroid compositions seen in the Main Belt
today. This chapter also reviews the major outstanding questions relating to
asteroid compositions and distributions and summarizes the progress and current
state of understanding of these questions to form the big picture of the
formation and evolution of asteroids in the Main Belt. Finally, we briefly
review the relevance of asteroids and their compositions in their greater
context within our Solar System and beyond.Comment: Accepted chapter in Asteroids IV in the Space Science Series to be
published Fall 201
The ancient heritage of water ice in the solar system
Identifying the source of Earth's water is central to understanding the
origins of life-fostering environments and to assessing the prevalence of such
environments in space. Water throughout the solar system exhibits
deuterium-to-hydrogen enrichments, a fossil relic of low-temperature,
ion-derived chemistry within either (i) the parent molecular cloud or (ii) the
solar nebula protoplanetary disk. Utilizing a comprehensive treatment of disk
ionization, we find that ion-driven deuterium pathways are inefficient,
curtailing the disk's deuterated water formation and its viability as the sole
source for the solar system's water. This finding implies that if the solar
system's formation was typical, abundant interstellar ices are available to all
nascent planetary systems.Comment: 33 pages, 7 figures including main text and supplementary materials.
Published in Scienc
Exploring the Origins of Deuterium Enrichments in Solar Nebular Organics
Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues
about their original formation environment. The organic materials in primitive
solar system bodies have generally higher D/H ratios and show greater D/H
variation when compared to D/H in solar system water. We propose this
difference arises at least in part due to 1) the availability of additional
chemical fractionation pathways for organics beyond that for water, and 2) the
higher volatility of key carbon reservoirs compared to oxygen. We test this
hypothesis using detailed disk models, including a sophisticated, new disk
ionization treatment with a low cosmic ray ionization rate, and find that disk
chemistry leads to higher deuterium enrichment in organics compared to water,
helped especially by fractionation via the precursors CHD/CH. We
also find that the D/H ratio in individual species varies significantly
depending on their particular formation pathways. For example, from
AU, CH can reach , while D/H in CHOH
remains locally unaltered. Finally, while the global organic D/H in our models
can reproduce intermediately elevated D/H in the bulk hydrocarbon reservoir,
our models are unable to reproduce the most deuterium-enriched organic
materials in the solar system, and thus our model requires some inheritance
from the cold interstellar medium from which the Sun formed.Comment: 11 pages, 7 figures, accepted for publication in Ap
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