Distributed source of glycine in 67P/ Churyumov Gerasimenko
Katia HadraouiHervé CottinStavro IvanovskiPascal ZapfK. AltweggY. BénilanN. BiverVincenzo Della CorteN. FrayS. MerouaneA. RotundiVladimir Zakharov
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The European Space Agency spacecraft Rosetta accompanied the Jupiter-family comet 67P/Churyumov-Gerasimenko for over 2 yr along its trajectory through the inner solar system. Between 2014 and 2016, it performed almost continuous in situ measurements of the comet’s gaseous atmosphere in close proximity to its nucleus. In this study, the 16 O/ 18 O ratio of H 2 O in the coma of 67P/Churyumov-Gerasimenko, as measured by the ROSINA DFMS mass spectrometer onboard Rosetta, was determined from the ratio of H 2 16 O/H 2 18 O and 16 OH/ 18 OH. The value of 445 ± 35 represents an ~11% enrichment of 18 O compared with the terrestrial ratio of 498.7 ± 0.1. This cometary value is consistent with the comet containing primordial water, in accordance with leading self-shielding models. These models predict primordial water to be between 5 and 20% enriched in heavier oxygen isotopes compared to terrestrial water.
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In 2014 September, as Rosetta transitioned to close bound orbits at 30 km from comet 67P/Churyumov–Gerasimenko, the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) data showed large systematic fluctuations in both the spacecraft potential and the collected currents. We analyse the potential bias sweeps from RPC-LAP, from which we extract three sets of parameters: (1) knee potential, that we relate to the spacecraft potential, (2) the ion attraction current, which is composed of the photoelectron emission current from the probe as well as contributions from local ions, secondary emission, and low-energy electrons, and (3) an electron current whose variation is, in turn, an estimate of the electron density variation. We study the evolution of these parameters between 4 and 3.2 au in heliocentric and cometocentric frames. We find on September 9 a transition into a high-density plasma region characterized by increased knee potential fluctuations and plasma currents to the probe. In conjunction with previous studies, the early cometary plasma can be seen as composed of two regions: an outer region characterized by solar wind plasma, and small quantities of pick-up ions, and an inner region with enhanced plasma densities. This conclusion is in agreement with other RPC instruments such as RPC-MAG, RPC-IES and RPC-ICA, and numerical simulations.
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