The Optical, Spectroscopic, and Infrared Remote Imaging System OSIRIS is the scientific camera system onboard the Rosetta spacecraft (Figure 1). The advanced high performance imaging system will be pivotal for the success of the Rosetta mission. OSIRIS will detect 67P/Churyumov-Gerasimenko from a distance of more than 106 km, characterise the comet shape and volume, its rotational state and find a suitable landing spot for Philae, the Rosetta lander. OSIRIS will observe the nucleus, its activity and surroundings down to a scale of ~2 cm px−1. The observations will begin well before the onset of cometary activity and will extend over months until the comet reaches perihelion. During the rendezvous episode of the Rosetta mission, OSIRIS will provide key information about the nature of cometary nuclei and reveal the physics of cometary activity that leads to the gas and dust coma. OSIRIS comprises a high resolution Narrow Angle Camera (NAC) unit and a Wide Angle Camera (WAC) unit accompanied by three electronics boxes. The NAC is designed to obtain high resolution images of the surface of comet 67P/Churyumov-Gerasimenko through 12 discrete filters over the wavelength range 250–1000 nm at an angular resolution of 18.6 μrad px−1. The WAC is optimised to provide images of the near-nucleus environment in 14 discrete filters at an angular resolution of 101 μrad px−1. The two units use identical shutter, filter wheel, front door, and detector systems. They are operated by a common Data Processing Unit. The OSIRIS instrument has a total mass of 35 kg and is provided by institutes from six European countries.

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OSIRIS – The Scientific Camera System Onboard Rosetta

This paper summarizes the present, preencounter understanding of the physical and chemical processes controlling the inner (r less than 1000 km) region of cometary atmospheres. Special emphasis was attached to compiling a self-consistent set of governing equations. This review is aimed at readers who want to understand the present status of the mantle and coma regions and/or who want to develop new, next generation models which will be needed as the large volume of new observational data will become available in the near future.

Dust and neutral gas modeling of the inner atmospheres of comets

The Halley Multicolour Camera on board ESA’s Giotto spacecraft observed the nucleus of comet P/Halley and its environment and returned more than 2000 images. The observations are summarized, their calibration is described, the status of the analysis and the results are discussed. Topographic features on the nuclear surface and areas of activity are identified. The optical thickness of the dust produced in jet-like features is estimated. The impact and constraints of the observations on cometary nucleus models are discussed.

Comet P/Halley’s nucleus and its activity

Analysis of the data from Giotto’s Dust Impact Detection System experiment (DIDSY) is presented These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14 First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus

The dust distribution within the inner coma of comet P/Halley 1982i: encounter by Giotto's impact detectors.

A taxonomic survey of comet composition 1985-2004 using CCD spectroscopy

Quantitative descriptions of environments near the nucleus of comet P/Halley have been developed to support spacecraft and mission design for the flyby encounters in March, 1986. To summarize these models as they exist just before the encounters, the relevant data from prior Halley apparitions and from recent cometary research are reviewed. Orbital elements, visual magnitudes, and parameter values and analysis for the nucleus, gas and dust are combined to predict Halley's position, production rates, gas and dust distributions, and electromagnetic radiation field for the current perihelion passage. The predicted numerical results have been useful for estimating likely spacecraft effects, such as impact damage and attitude perturbations. Sample applications are cited, including design of a dust shield for spacecraft structure, and threshold and dynamic range selection for flight experiments. It is expected that the comet's activity may be more irregular than these smoothly varying models predict, and that comparison with the flyby data will be instructive.

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S. M. Larson

Papers

The comet Halley dust and gas environment