Roger V. Yelle

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The Cassini Ion Neutral Mass Spectrometer (INMS) has obtained the first in situ composition measurements of the neutral densities of molecular nitrogen, methane, molecular hydrogen, argon, and a host of stable carbon-nitrile compounds in Titan's upper atmosphere. INMS in situ mass spectrometry has also provided evidence for atmospheric waves in the upper(More)
Data acquired by the Ion Neutral Mass Spectrometer (INMS) on the Cassini spacecraft during its close encounter with Titan on 26 October 2004 reveal the structure of its upper atmosphere. Altitude profiles of N2, CH4, and H2, inferred from INMS measurements, determine the temperature, vertical mixing rate, and escape flux from the upper atmosphere. The mean(More)
The Cassini spacecraft passed within 168.2 kilometers of the surface above the southern hemisphere at 19:55:22 universal time coordinated on 14 July 2005 during its closest approach to Enceladus. Before and after this time, a substantial atmospheric plume and coma were observed, detectable in the Ion and Neutral Mass Spectrometer (INMS) data set out to a(More)
[1] We present a study of the formation and distribution of benzene (C6H6) on Titan. Analysis of the Cassini Mass Spectrometer (INMS) measurements of benzene densities on 12 Titan passes shows that the benzene signal exhibits an unusual time dependence, peaking 20 s after closest approach, rather than at closest approach. We show that this behavior can be(More)
The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength(More)
Spectroscopy of Io's Pele plume against Jupiter by the Hubble Space Telescope in October 1999 revealed absorption due to S2 gas, with a column density of 1.0 +/- 0.2 x 10(16) per square centimeter, and probably also SO(2) gas with a column density of 7 +/- 3 x 10(16) per square centimeter. This SO2/S2 ratio (3 to 12) is expected from equilibration with(More)
Titan’s atmosphere is unique because dissociation of N2 and CH4, the primary atmospheric constituents, provides the H, C, and N atoms necessary for the synthesis of complex organic molecules. The first steps in the synthesis of organic molecules occur in the upper atmosphere where energetic photons and electrons dissociate N2 and CH 4. We determine the(More)
[1] Measurements of the mole fractions of CH4 and Ar by the Ion Neutral Mass Spectrometer on the Cassini orbiter are analyzed to determine the rate of vertical mixing in Titan’s atmosphere and the escape flux of CH4. Analysis of the Ar data indicates an eddy mixing rate of 2–5 10 cm s , an order of magnitude smaller than previously determined from analysis(More)
Results from the occultation of the sun by Neptune imply a temperature of 750 +/- 150 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane, acetylene, and ethane at lower levels. The ultraviolet spectrum of the sunlit atmosphere of Neptune resembles the spectra of the(More)