Abstract
We present the analysis of ≈100 molecular maps of the coma of comet 67P/Churyumov-Gerasimenko that were obtained with the MIRO submillimeter radiotelescope on board the Rosetta spacecraft. From the spectral line mapping of H216O, H218O, H217O, CH3OH, NH3, and CO and some fixed nadir pointings, we retrieved the outgassing pattern and total production rates for these species. The analysis covers the period from July 2014, inbound to perihelion, to June 2016, outbound, and heliocentric distancesrh= 1.24–3.65 AU. A steep evolution of the outgassing rates with heliocentric distance is observed, typically inrh−16, with significant differences between molecules (e.g. steeper variation for H2O post-perihelion than for methanol). As a consequence, the abundances relative to water in the coma vary. The CH3OH and CO abundances increase after perihelion, while the NH3abundance peaks around perihelion and then decreases. Outgassing patterns have been modeled as 2D Gaussian jets. The width of these jets is maximum around the equinoxes when the bulk of the outgassing is located near the equator. From July 2014 to February 2015, the outgassing is mostly restricted to a narrower jet (full width at half-maximum ≈80°) originating from high northern latitudes, while around perihelion, most of the gaseous production comes from the southernmost regions ( − 80 ± 5° cometocentric latitude) and forms a 100°–130° (full width at half-maximum) wide fan. We find a peak production of water of 0.8 × 1028molec. s−1, 2.5 times lower than measured by the ROSINA experiment, and place an upper limit to a 50% additional production that could come from the sublimation of icy grains. We estimate the total loss of ices during this perihelion passage to be 4.18 ± 0.18 × 109kg. We derive a dust-to-gas ratio in the lost material of 0.7–2.3 (including all sources of errors) based on the nucleus mass loss of 10.5 ± 3.4 × 109kg estimated by the RSI experiment. We also obtain an estimate of the H218O/H217O ratio of 5.6 ± 0.8.
Highlights
Comets are the most pristine remnants of the formation of the solar system 4.6 billion years ago
The Microwave Instrument for the Rosetta Orbiter (MIRO) is a submillimeter radiometer equipped with two continuum channels at 188 and 562 GHz and a high spectral resolution (44 kHz) heterodyne spectrometer working in frequency-switching mode (Gulkis et al 2007)
The maps of the various molecular lines obtained with the MIRO spectrometer contain 3D information on the outgassing pattern: 2D spatial information in the plane of the sky, plus Doppler velocity information
Summary
Comets are the most pristine remnants of the formation of the solar system 4.6 billion years ago. Understanding their composition and the sublimation process of their ices as they heat up approaching the Sun was one of the main objectives of the Rosetta mission of the European Space Agency to comet 67P/Churyumov-Gerasimenko (67P). 67P from a 5–1400 km distance until 30.5 September 2016, when Rosetta terminated its operations at the surface of the comet, at 3.83 AU from the Sun (Accomazzo et al 2016, 2017). The Microwave Instrument for the Rosetta Orbiter (MIRO) is a submillimeter radiometer equipped with two continuum channels at 188 and 562 GHz and a high spectral resolution (44 kHz) heterodyne spectrometer working in frequency-switching mode (Gulkis et al 2007). Four molecules were targeted through their rotational lines in the 548–579 GHz range: tHHio122n7OOo, fCwtHhere3eOmoHabi,sneCrisvOoe,tdoaptnoicdhsaNpneHdcl3iee. stI.hnFeoafrdredmqiteuitoehnnatnltyoolo,Hcthc126ureOrer,ilnHign12e8ssOawtuaernardeobserved to measure the rotational temperature
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