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Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings.

ABSTRACT: Saturn's main rings have an energetic particle and gamma ray photon radiation environment produced by ring interactions of galactic cosmic ray (GCR) protons and heavier ions penetrating the planetary dipolar magnetic field. Accurate models of this radiation environment are important for interpretation of Pioneer 11 and Cassini in situ measurements near the rings and for constraints on radiolytic contributions to neutral gas production and ice chemistry. A GEANT (GEometry ANd Tracking) based simulation is used to model flux spectra of protons, electrons, positrons, charged pions, neutrons, and gamma ray photons emitted from GCR interactions with H2O ice spheres approximating the ring material. Dependent on location in the A to D rings within the planetary magnetic field of Saturn, only GCR protons above respective energies of 20 to 72 GeV can reach the rings without being deflected away by the magnetic field. Calculated differential and integral fluxes from our simulations have good agreement with in situ Pioneer-11 measurements in selected energy channels. The charged particle and neutral radiation measurements are sensitive, respectively, to the sizes and areal mass densities of ring bodies. Computed gamma ray emission fluxes are 8% of our calculated limit for detection from the Earth by the Fermi Large Area Telescope. Addition of charged particle sensors and neutron-photon imaging spectrometers to a future Saturn Ring Observer mission would provide valuable information on the ring mass structure. The present paper provides a foundation for modeling of Pioneer 11 and Cassini radiation measurements across the main rings and future measurements of radiation from the rings.

SUBMITTER: Cooper JF

PROVIDER: S-EPMC6351080 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings.

Cooper John F JF Sturner Steven J SJ

Journal of geophysical research. Space physics 20180807 9

Saturn's main rings have an energetic particle and gamma ray photon radiation environment produced by ring interactions of galactic cosmic ray (GCR) protons and heavier ions penetrating the planetary dipolar magnetic field. Accurate models of this radiation environment are important for interpretation of Pioneer 11 and Cassini in situ measurements near the rings and for constraints on radiolytic contributions to neutral gas production and ice chemistry. A GEANT (GEometry ANd Tracking) based simu ...[more]

PMID: 30713823

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Project description:Human deep space and planetary travel is limited by uncertainties regarding the health risks associated with exposure to galactic cosmic radiation (GCR), and in particular the high linear energy transfer (LET), heavy ion component. Here we assessed the impact of two high-LET ions 56Fe and 28Si, and low-LET X rays on genome-wide methylation patterns in human bronchial epithelial cells. We found that all three radiation types induced rapid and stable changes in DNA methylation but at distinct subsets of CpG sites affecting different chromatin compartments. The 56Fe ions induced mostly hypermethylation, and primarily affected sites in open chromatin regions including enhancers, promoters and edges (“shores”) of CpG islands. The 28Si ion-exposure had mixed effects, inducing both hyper and hypomethylation and affecting sites in more repressed heterochromatic environments, whereas X rays induced mostly hypomethylation, primarily at sites in gene bodies and intergenic regions. Significantly, the methylation status of 56Fe ion irradiation sensitive sites, but not those affected by X ray or 28Si ions, could discriminate tumor from normal tissue for human lung adenocarcinomas and squamous cell carcinomas. Thus, high LET radiation exposure leaves a lasting imprint on the epigenome, and affects sites relevant to human lung cancer. The 56Fe ion signature may prove useful in monitoring the cumulative biological impact and associated cancer risks encountered by astronauts in deep space. Genome wide DNA methylation profiling of normal human bronchial epithelial cells irradiated with varying doses of 28Si-ion radiation ( 300 MeV/u at 0, 0.3, 1.0 Gy) , 56Fe-ion radiation (600 MeV/u at 0, 0.1, 0.3, 1.0 Gy) or X rays (320 kV at 0, 1.0 Gy). Triplicate control and irradiated samples were incubated and sampled at 4 timepoints between 2 and 62 days. The Illumina Infinium 450k Human DNA methylation Beadchip was used to obtain DNA methylation profiles across >485,000 CpGs from collected samples. Samples include: 56Fe ions, 4 doses x 4 time points x 3 replicates (4 removed in QC) = 44 samples; 28Si ions = 3 doses x 4 time points x 3 replicates = 36 samples; X ray, 2 doses x 4 time points x 3 replicates (2 removed in QC)= 22 samples.

Dataset Information

Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings.

Publications

Energetic Radiation From Galactic Cosmic Ray Interactions With Saturn's Main Rings.

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