# 3D analysis of spatial resolution of MIRO/Rosetta measurements at 67P/CG

## TL;DR

This study quantifies the spatial resolution of MIRO measurements at 67P/CG, showing that most water molecules originate outside the MIRO beam and highlighting the importance of 3D modeling for accurate data interpretation.

## Contribution

The paper provides a detailed 3D analysis of MIRO's spatial resolution, demonstrating the limited contribution of in-beam molecules and supporting the use of 1D models for data analysis.

## Key findings

- Most water molecules originate outside the MIRO beam.
- Small fraction of molecules come from within the MIRO beam.
- 3D modeling enhances interpretation of MIRO spectral data.

## Abstract

The MIRO instrument's remote sensing capability is integral in constraining water density, temperature and velocity fields in the coma of 67P/Churyumov-Gersimenko. Our aim is to quantify the contribution to the water density from all facets inside and outside the field-of-view (FOV) of MIRO, in both, nadir and limb geometries. This information is crucial for understanding the MIRO derived coma production rates and their relation to the nucleus characteristics, and inherent spatial resolution of the data. This study relies on a detailed 3D nucleus shape model, illumination conditions and the pointing information of the viewing geometry. With these parameters, we can evaluate the relative contribution of water density originating from facets directly inside the MIRO beam as well outside of the beam as a function of distance along the MIRO line-of-sight. We also calculate the ratio of in-beam versus out-of-beam number density. 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. This is true for nadir, but also translated into the limb observing geometry. The MIRO instrument cannot discriminate active from non-active regions directly from observations. This study also suggests that the beam averaged solar incidence angle, local time and mean normal vectors are not necessary related to molecules within the MIRO beam. These results also illustrate why the 1D spherical Haser model can be applied with relative success for analyzing the MIRO data (and generally any Rosetta measurements). 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. The presented results are in fact applicable to all relevant instruments onboard Rosetta.