Statistics – Applications
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30s.541m&link_type=abstract
Meteoritics, vol. 30, no. 5, page 541
Statistics
Applications
Comets, Composition, Gamma-Rays, Cosmogenic, Numerical-Simulations, Monte Carlo
Scientific paper
In the last three decades, measurements have been obtained from both spaceflight programs and meteorite studies that allow certain constraints to be imposed on the theoretical models for the origin and evolution of the solar system. One of the key questions involved in the understanding of this evolution is: what was the composition of the primitive solar nebula? It is believed that comets and asteroids may contain some of the most primitive material remaining in our solar system today. The exploration of comets and asteroids must be largely carried out by remote sensing. The gamma rays escaping from their surfaces can be used for mapping the elemental composition of the surface's top few tens of centimeters [1,2]. Elements that can be mapped using gamma-ray spectroscopy include all major, many minor and some trace ones. The expected fluxes of gamma rays at the surface of a comet are calculated for various assumed chemical compositions of comets and for some specific models of comet's nucleus. In order to predict the expected gamma-ray fluxes, the neutron spatial and energy distributions were calculated using the LAHET Code System (LCS) [3] for the simulation of cosmic-ray interactions with a target body. LCS is a system of general-purpose Monte Carlo computer codes that treat the relevant physical processes of particle production and transport. This code system and its applications to the planetary studies is described in more detail in [4]. An isotropic irradiation of a sphere with radius 2 km, the assumed radius of the comet's nucleus, by 4.8 protons/cm2/s, corresponding to the GCR primary particle spectrum averaged over a typical solar cycle, was simulated. The composition was assumed to be a mixture of rock with the elemental composition of carbonaceous chondrites and ice made of H2O, CO2 and HCN. The rock to ice ratio was varied from 3 to 0.33, which span a wide range of cometary nucleus composition models. Using the calculated neutron fluxes, we determined the intensities of the strongest gamma-ray lines produced in the cometary nucleus via nonelastic-scattering and neutron-capture reactions. Precise theoretical modeling of gamma-ray fluxes is necessary for interpretation of the measured gamma-ray fluxes, such as from Rosetta, to completely characterize the comet's elemental composition. Knowing the dependences of gamma-ray fluxes on the chemical composition of comet, we will be able to characterize the rocky component even if it is different from known meteorite types. Calculated fluxes of gamma rays produced in nonelastic scattering reactions were used also to investigate measuring some isotopic ratios and possibly detecting isotopic anomalies. We know that comets are made of silicate dust and various ices, but the ratio of ices to rock is model dependent. Our calculations show that the abundance of H, C, N, O, and major elements present in the rock can be measured independently. This will allows us to determine both the rock to ice ratio and the composition of the ice component with little ambiguity. The interferences occurring in the determination of the contents of important elements, such as carbon, were studied in detail. In summary, our simulations of gamma rays escaping from cometary surfaces indicate that the analysis of gamma-ray spectra provide fairly accurate information about the chemical composition of the comet's surface. References: [1] Reedy R. C. et al. (1973) JGR, 78, 5847-5860. [2] Boynton W. V. et al. (1992) JGR, 97, 7081-7698. [3] Prael R. E. and Lichtenstein H. (1989) Los Alamos Report LA-UR-89-3014. [4] Masarik J. and Reedy R. C. (1994) GCA, 58, 5307-5317.
Brückner James
Masarik Jozef
No associations
LandOfFree
Simulation of Gamma-Ray Production in Comets and Their Utilization for Chemical Composition Investigation does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Simulation of Gamma-Ray Production in Comets and Their Utilization for Chemical Composition Investigation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Simulation of Gamma-Ray Production in Comets and Their Utilization for Chemical Composition Investigation will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-831057