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R.E. Johnson

Publications and source records attributed to R.E. Johnson.

7 recordsLinked to original sources
USGS2008

Simulation of Na D emission near Europa during eclipse

The Cassini imaging science subsystem observed Europa in eclipse during Cassini's Jupiter flyby. The disk-resolved observations revealed a spatially nonuniform emission in the wavelength range of 200-1050 nm (clear filters). By building on observations and simulations of Europa's Na atmosphere and torus we find that electron-excited Na in Europa's tenuous atmosphere can account for the observed emission if the Na is ejected preferentially from Europa's dark terrain. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗
USGS1999

Hydrogen peroxide on the surface of Europa

Spatially resolved infrared and ultraviolet wavelength spectra of Europa's leading, anti-jovian quadrant observed from the Galileo spacecraft show absorption features resulting from hydrogen peroxide. Comparisons with laboratory measurements indicate surface hydrogen peroxide concentrations of about 0.13 percent, by number, relative to water ice. The inferred abundance is consistent with radiolytic production of hydrogen peroxide by intense energetic particle bombardment and demonstrates that Europa's surface chemistry is dominated by radiolysis.

Science↗
USGS1996

O2 on ganymede: Spectral characteristics and plasma formation mechanisms

Weak absorption features in the visible reflectance spectrum of Jupiter's satellite Ganymede have been correlated to those observed in the spectrum of molecular oxygen. We examine the spectral characteristics of these absorption features in all phases of O 2 and conclude that the molecular oxygen is most likely present at densities similar to the liquid or solid γ-phase. The contribution of O 2 to spectral features observed on Ganymede in the near-infrared wavelength region affects the previous estimates of photon pathlength in ice. The concentration of the visible absorption features on the trailing hemisphere of Ganymede suggests an origin due to bombardment by magnetospheric ions. We derive an approximate O 2 formation rate from this mechanism and consider the state of O 2 within the surface.

Geophysical Research Letters↗
USGS1967

Residues in fish, wildlife, and estuaries. Indicator species near top of food chain chosen for assessment of pesticide base levels in fish and wildlife--clams, oysters, and sediment in estuarine environment

Federal efforts to determine pesticide levels in fish and wildlife are being carried out by the Bureau of Sport Fisheries and Wildlife, U. S. Department of the Interior. Monitoring estuarine pesticide levels in clams, oysters, and sediments is a joint endeavor of the Bureau of Commercial Fisheries, U. S. Department of the Interior, and the Water Supply and Sea Resources Program of the National Center for Urban and Industrial Health, Public Health Service, U. S. Department of Health, Education, and Welfare.

Pesticides Monitoring Journal↗