Virtis: An Imaging Spectrometer for the Rosetta Mission

Abstract

International audienceThe VIRTIS (Visual IR Thermal Imaging Spectrometer) experiment has been one of the most successful experiments built in Europe for Planetary Exploration. VIRTIS, developed in cooperation among Italy, France and Germany, has been already selected as a key experiment for 3 planetary missions: the ESA-Rosetta and Venus Express and NASA-Dawn. VIRTIS on board Rosetta and Venus Express are already producing high quality data: as far as Rosetta is concerned, the Earth-Moon system has been successfully observed during the Earth Swing-By manouver (March 2005) and furthermore, VIRTIS will collect data when Rosetta flies by Mars in February 2007 at a distance of about 200 kilometres from the planet. Data from the Rosetta mission will result in a comparison – using the same combination of sophisticated experiments – of targets that are poorly differentiated and are representative of the composition of different environment of the primordial solar system. Comets and asteroids, in fact, are in close relationship with the planetesimals, which formed from the solar nebula 4.6 billion years ago. The Rosetta mission payload is designed to obtain this information combining in situ analysis of comet material, obtained by the small lander Philae, and by a long lasting and detailed remote sensing of the comet, obtained by instrument on board the orbiting Spacecraft. The combination of remote sensing and in situ measurements will increase the scientific return of the mission. In fact, the “in situ” measurements will provide “ground-truth” for the remote sensing information, and, in turn, the locally collected data will be interpreted in the appropriate context provided by the remote sensing investigation. VIRTIS is part of the scientific payload of the Rosetta Orbiter and will detect and characterise the evolution of specific signatures – such as the typical spectral bands of minerals and molecules – arising from surface components and from materials dispersed in the coma. The identification of spectral features is a primary goal of the Rosetta mission as it will allow identification of the nature of the main constituent of the comets. Moreover, the surface thermal evolution during comet approach to sun will be also studied

Properties of the dust in the coma of 67P/Churyumov-Gerasimenko observed with VIRTIS- M

“…The data set covers 11.8 h, almost a complete rotation period of 67P/CG. The slit extends horizontally for 256 pixels (∼4.5 km) and is scanned vertically for 66 lines (∼1.15 km) using the scanning mirror of the instrument (Coradini et al 2007). …”

“…Coupled to VIRTIS-M is a bore-sighted higher resolution pointing echelle spectrometer, VIRTIS-H, with a numerical resolution of about 2000 and a field of view (FOV) of 500 × 1500 μrad. For a complete description of the VIRTIS instrument, see Coradini et al (2007).…”

“…In the VIS channel, however, a considerable amount of instrumental scattered light and stray light from higher orders of the IR channel, which share the convex grating mirror in the Offner spectrometer (see Filacchione 2006;Coradini et al 2007), limits the useful range to about 400-800 μm, and even in this interval, there may be issues. We note that there is a considerable amount of colour information that can be obtained from the VIRTIS data so that the present analysis must be considered preliminary.…”

“…Since 2014 August, the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) (Coradini et al 2007) on board the Rosetta spacecraft performed continuous observations of the inner coma of the Rosetta spacecraft target 67P/CG. VIRTIS is composed of a high spectral resolution channel (VIRTIS-H) and two channels devoted to spectral mapping (VIRTIS-M), covering the spectral range of 0.22-1.04 μm (VIS) and 0.95-5.06 μm (IR), both with 432 spectral bands.…”

The MicrOmega Investigation Onboard Hayabusa2

“…The 3D data cubes (x, y, λ) are compressed onboard via the Langevin and Forni (2000) algorithm before transmission to the ground. This algorithm is based on wavelet transform and has been used successfully for OMEGA/MEx (Bibring et al 2004) and VIRTIS/Rosetta (Coradini et al 2007). Since image acquisition can be requested in any order, the 2D (x, y) images are reorganized from the lowest to the highest wavelength before compression.…”