However, because of the finite extent of the MIRO beam (half power beam width, HPBW ~ 420”), there are cases where one portion of the beam sees the cold space and the other sees the warm nucleus, resulting in mixed spectra features. In general, the MIRO geometry provides two modes of observations, boresight on the nucleus surface (nadir) where the spectra are seen in absorption against the warmer nucleus (compared to the coma), and “limb” where the lines are seen in emission against the background of cold space (cosmic background radiation), see Fig. These line profiles carry information about the variation in expansion velocity, temperature structure (especially for optically thick transition), and density profile along the line of sight (LOS). The CTS provided a high-frequency resolution ( R ~ 1 × 10 7), such that individual spectral line shapes could be accurately determined. This MIRO receiver was also connected to a high-resolution Chirp Transform Spectrometer (CTS Hartogh & Hartmann 1990), tuned to record eight spectral lines of six important species present in the coma (H O, H O, H O, CO, NH 3, and three lines of CH 3OH). The 562 GHz MIRO receiver was designed to be sensitive to radiation at submillimeter wavelengths that are characteristic of molecular emissions due to transitions between rotational states of molecules. It was one of the four remote sensing instruments (the others being OSIRIS, VIRTIS, and ALICE) 1 on board Rosetta that shared the science goal of monitoring the onset of cometary activity and its evolution through the perihelion passage (August 13, 2015). The Microwave Instrument for the Rosetta Orbiter (MIRO) consisted of a 30 cm primary dish followed by two heterodyne receivers operating at center frequencies of 190 and 562 GHz ( Gulkis et al. Open Access funding provided by Max Planck Society. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The results presented here are applicable to remote sensing instruments on board Rosetta. The future possibilities of constraining gas activity distribution on the surface should use 3D codes extracting information from the MIRO spectral line shapes which contain additional information. These results also illustrate why the 1D spherical Haser model can be applied with relative success to analyzing the MIRO data (and generally any Rosetta measurements). This study also suggests that the beam averaged solar incidence angle, local time, and mean normal vectors are not necessarily related to molecules within the MIRO beam. The MIRO instrument cannot discriminate active from inactive regions directly from observations. This is true for the nadir, but a similar conclusion can also be applied to the limb observing geometry.Ĭonclusions. We demonstrate that despite the rather small MIRO field of view there is only a small fraction of molecules that originate from facets within the MIRO beam. We also calculate the ratio of in-beam versus out-of-beam water gas number density. With these parameters we can evaluate the relative contribution of water density originating from facets directly inside the MIRO beam and outside the beam as a function of distance along the MIRO line of sight. This study relies on a detailed 3D nucleus shape model, illumination conditions, and the pointing information of the viewing geometry. This information is crucial to understanding the MIRO derived coma production rates and their relation to the nucleus characteristics, and to understanding the spatial resolution of the measurements. Our aim is to quantify how much water density originates from the facets of the shape model within the field of view of MIRO versus the water contribution from all the other facets. The MIRO instrument’s remote sensing capability is integral to constraining water density, temperature, and velocity fields in the coma of 67P/Churyumov-Gersimenko.Īims. Max-Planck-Institut für Sonnensystemforschung,Į-mail: Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences,ĬAS Center for Excellence in Comparative Planetology, Chinese Academy of Sciences,Ĭontext. Astronomical objects: linking to databases.Including author names using non-Roman alphabets.Suggested resources for more tips on language editing in the sciences Punctuation and style concerns regarding equations, figures, tables, and footnotes
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