LESIA Observatoire de Paris-PSL CNRS Sorbonne Université Université de Paris

VIRTIS: the instrument

Thursday 22 October 2020, by Stéphane Erard

VIRTIS stands for Visible and InfraRed Thermal Imaging Spectrometer. This instrument is devoted to the study by remote sensing of the comet 67P/Churyumov-Gerasimenko, by imaging spectroscopy.

The Principal Investigator of VIRTIS is A. Coradini (Istituto di Astrofisica Spaziale, Rome, Italy) and the instrument is built from an international consortium, between Italy, France, and Germany.

A description of the VIRTIS instrument is available in the following publications:

The main objective of VIRTIS is to obtain imaging spectroscopy of the different parts of the comet 67P/Churyumov-Gerasimenko, target of the Rosetta mission, from the UV to the infrared, with emphasis on the IR part. A combination of an imaging spectrometer (VIRTIS-M 0.2 to 5 µm in one channel/2 detectors, at R:200) and aperture spectroscopy (VIRTIS-H 2 to 5 µm, R:1500) will provide an ideal instrument to look simultaneously at spatial variability of nucleus constituents, and fine spectral analysis with separation of ice and mineral contributions.


VIRTIS-M is characterised by a single optical head consisting of a Shafer telescope combined with an Offner imaging spectrometer and by two bidimensional FPAs: the VIS (0.25 - 1 µm) and IR (1-5 µm). A scanning mirror provide a the second spatial dimension of the spectral images. One of the main product of VIRTIS-M will be a global spectral map of 67P/Churyumov-Gerasimenko nucleus, acquired during the mapping phase of the mission.


VIRTIS-H is a high resolution infrared cross-dispersed spectrometer using a prism and a grating. The 2-5 µm spectrum is dispersed in 8 orders on a focal-plane detector array.

VIRTIS-H scientific objectives include coma observations of gas emissions, with rotational separation of lines for H2O and CO, nucleus observations with special interest in separating the 3 µm emissions of PAH and methanol ice, if present.

Optical scheme of Virtis-H
Optical scheme of Virtis-H

Updated 26 January 1999
(crédits : VIRTIS team)

The IRFPA of -M and -H are both housed on bidimensional HgCdTe chips cooled to 70 K by an active cooler in order to reduce dark current. Both spectrometers are cooled down to 135K by means of a radiator, in order to reduce the background level.

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