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Comets considered to be pristine objects contain key information about the early formation of the solar system. Their volatile components can provide clues about the origin and evolution of gases and ices in the comets. Measurements with ROSINA/RTOF at 67P/Churyumov–Gerasimenko have now allowed, for the first time, a direct in situ high-time resolution measurement of the most abundant cometary molecules originating directly from a comet’s nucleus over a long time-period, much longer than any previous measurements at a close distance to a comet between 3.1 and 2.3 au. We determine the local densities of H2O, CO2, and CO, and investigate their variabilities. [ABSTRACT FROM AUTHOR]

We used a dedicated hemispherical energy analyzer to measure energetic and angular distributions of electrons emitted from molybdenum microtips integrated in a 1 cm2 field emitter array designed by the CEA/LETI laboratory. Such cathodes typically deliver about 25 mA at an extraction voltage of 100 V, and are studied in order to replace heated wires as electron sources for space applications. We find that the energy distribution of the beam strongly depends on the extraction voltage, and is therefore expected to vary across the emission lifetime of the device, at a rate depending both on the alteration of the resistive structure with time and on the fate of adsorbed contaminants at the tip surface. A semi-empirical model of the emitters is proposed and used to determine parameters of energetic and angular distributions. The energy dispersion of the beam is found to increase from 2 eV +- 20% up to 9 eV +- 20% eV, for extraction voltages varying from 40 to 100 V. The mean angular dispersion of the beam is found to be 42deg +- 20% when a null electric field is set at the grid extraction surface. [ABSTRACT FROM AUTHOR]