VIRTIS: the instrument

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:

• Coradini et al, LPI, Vol. 27, 253, VIRTIS Visible Infrared Thermal Imaging Spectrometer for Rosetta Mission, 1996
• Bonsignori, Coradini, Drossart, Arnold, SPIE, 1997
• Coradini et al, Vol. 46, 1291, VIRTIS: An Imaging Spectrometer for the Rosetta Mission (1998). Planetary and Space Science, Volume 46, Issue 9-10, p. 1291-1304.
• Coradini et al. VIRTIS: An Imaging Spectrometer for the Rosetta Mission (2007). Space Science Reviews, Volume 128, Issue 1-4, pp. 529-559.

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

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

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

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.