OSIRIS imaging system
OSIRIS (the Optical, Spectroscopic, and Infrared Remote Imaging System) is the main imaging system on Rosetta. The programme started in 1994. At this time Nick Thomas was still working at the Max-Planck-Institut für Aeronomie (now MPS) and participated in the definition of the instrument including the required scientific performance.
The system comprises two separate optical systems (a narrow angle camera, NAC, and a wide-angle camera, WAC) which are driven through a common electronics box. Several elements of the two cameras are duplicates of each other. For example, the filter wheels, the mechanical shutters, and the focal planes are identical.
The NAC has a pixel scale of around 18.6 urad/px with a point-spread function of around 1.2 pixels (FWHM) (resolution up to 0.17 m/px). The resolution of the WAC is around five times lower, but with a much larger field of view. The NAC contains a series of moderately wide-band filters (typically 60 nm bandpass) designed to provide high-spatial resolution colours of the surface. The WAC contains a series of filters designed to isolate optical gas emissions with a set of continuum filters available to study the dust and its contamination of signal in the gas lines.
UBE Participation in Planning
As co-investigators on OSIRIS, we were supporting MPS by participating in the planning process. The Rosetta activities at the comet are separated into distinct phases (e.g. lander phase, escort phase, etc.). Within the escort phase, there were several 'fly-bys' where the spacecraft passed very close to the surface for a short time. These fly-bys were done to give us information on the structure of the surface and its evolution as the comet moves towards perihelion. Furthermore, the in-situ instruments (e.g. the mass spectrometer, ROSINA) obtained the highest densities of gas and dust during these fly-bys leading to increased signal to noise and also the likelihood of stronger constraint in inhomogeneous outgassing.
UBE Participation in the Data Analysis
We have analysed a large set of the images acquired (more than 60000 images) and we are still working on it. The main data analysis we have performed are:
- Identification of major surface features and surface evolution of comets ( El-Maarry et al., 2015b; 2018, Giacomini et al., 2016, Sunshine et al., 2016, Thomas et al., 2015a; 2015b)
- Identification of water ice at the surface (Pommerol et al., 2015)
The Hardware Team
Six scientific institutes are represented in the OSIRIS consortium. Each institute assigned a lead scientist to represent them. The institutes and lead scientists at the start of the project were