Refractory species in the neutral gas coma of comet 67P/Churyumov-Gerasimenko
Abstract
For more than 2 years the European Space Agency's Rosetta mission carried out a close inspection of comet 67P/Churyumov-Gerasimenko. Among the payload instruments was ROSINA - DFMS, the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis - Double Focusing Mass Spectrometer (Balsiger et al. 2007). DFMS was dedicated to measure the relative and absolute abundances of the neutral gas species present in the coma. DFMS had a mass resolution that was sufficiently high to separate refractory elements from organic molecules. When the comet was at a heliocentric distance of 3 au before perihelion, DFMS detected the refractory elements sodium, silicon, potassium, and calcium, which were most likely sputtered off the comet's surface by impacting solar wind ions (Wurz et al., 2015). However, recent analysis of the DFMS data revealed the presence of not only these elements, but also iron, in atomic form also close to perihelion (Rubin et al., 2021). During that time, the comet was much more active, with a substantial atmosphere preventing the solar wind from reaching both the surface of the comet and the dust grains in the coma near Rosetta (Behar et al., 2017). Our observations are in line with recent observations of refractory iron and nickel in the gas phase around more than 20 comets (Manfroid et al., 2021). ROSINA DFMS failed to detect suitable parents or fragments for these refractory elements. Therefore, these refractory elements are released directly in their atomic form from small coma grains and not from a distributed source of larger molecules. In this presentation we will summarize these recent findings in the coma of comet 67P/Churyumov-Gerasimenko and discuss their implications.
References Balsiger et al., ROSINA - Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, Sp. Sci. Rev., 128(1), 745-801, 02/2007 Behar et al., The birth and growth of a solar wind cavity around a comet - Rosetta Observations, Mon. Not. R. Astron. Soc., 469, S396-S403, 03/2017 Manfroid et al., Iron and nickel atoms in cometary atmospheres even far from the Sun, Nature, 593, 372-374, 05/2021 Rubin et al., Refractory elements in the gas phase for comet 67P/Churyumov-Gerasimenko, Astron. Astrophys., Astron. Astrophys., 658, A87, 12/2021 Wurz et al., Solar Wind Sputtering of Dust on the Surface of 67P/Churyumov-Gerasimenko, Astron. & Astrophys., 583, A22, 10/2015- Publication:
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44th COSPAR Scientific Assembly. Held 16-24 July
- Pub Date:
- July 2022
- Bibcode:
- 2022cosp...44..265R