Planetary and Space Science 193 (2020) 105087 Contents lists available at ScienceDirect Planetary and Space Science journal homepage: www.elsevier.com/locate/pss Planetary Terrestrial Analogues Library project: 2. building a laboratory facility for MicrOmega characterization Damien Loizeau a,*, Guillaume Lequertier a, François Poulet a, Vincent Hamm a,Cedric Pilorget a, Lionel Meslier-Lourit a, Cateline Lantz a, Stephanie C. Werner b, Fernando Rull c, Jean-Pierre Bibring a a Universite Paris-Saclay, CNRS, Institut D’astrophysique Spatiale, Batiment^ 121, 91405, Orsay, France b Centre for Earth Evolution and Dynamics, Department for Geosciences, University of Oslo, Oslo, Norway c Department of Condensed Matter Physics, Crystallography and Mineralogy, University of Valladolid, Ave. Francisco Valles, 8, Boecillo, 47151, Spain ARTICLE INFO ABSTRACT Keywords: Multiple spectroscopic techniques have been selected on previous, present and forthcoming missions to explore Planetary analogues planetary surfaces in the Solar System. In particular, forthcoming ESA/Roscosmos and NASA missions to the Spectral library surface of Mars will bring instruments capable of near-infrared (NIR), Raman and Laser Induced Breakdown Space instrument Spectroscopies to analyze the mineralogy and chemistry of rocks. The PTAL (Planetary Terrestrial Analogues Laboratory facility Library) project aims at building a multi-instrument spectral database of a large variety of natural Earth rock samples, including Mars analogues. The NIR hyperspectral microscope MicrOmega was selected to characterize the mineralogy of these analogues within the PTAL project. The instrument model used for the PTAL project is a spare flight model that requires specific care. For the safety of the instrument, and because of the large number of samples in the PTAL library and the requirement to optimize the observational conditions, a dedicated and semi- automated setup was built for the use of the MicrOmega instrument for this project. This paper presents the requirements specified for this setup, the technical solutions that have been selected, their implementation and the performances of the set-up. Sample preparation and operations during sample observations are explained, and a characterization example is presented to briefly illustrate the capabilities of MicrOmega in this set-up. The complete results from the MicrOmega characterizations of the PTAL rock analogues will be presented in a forthcoming paper (Loizeau et al. in prep). 1. Introduction and Raman spectroscopy, and Laser Induced Breakdown Spectroscopy (LIBS), on a large number of natural Earth samples characterized by X- Near InfraRed (NIR) hyperspectral imagers are among the major in- Ray Diffraction (Werner et al., 2018). Those samples have been selected struments of many recent and new payloads of planetary space missions. to represent a variety of geologic contexts with strong analogies to They have the strong advantage of providing mineral and organic in- multiple Martian past aqueous environments. The chosen analysis tech- formation of planetary surfaces with a relatively high speed/high spatial niques represent instruments that will be widely onboard future surface resolution in a non-destructive way. They can be integrated both on exploration missions as best exemplified by the forthcoming ESA/Ex- orbital missions and on surface platforms, to provide surface composi- oMars Rover and NASA/Mars2020 missions that will combine diverse tional information from global surveys to sample microanalyses (e.g. instruments capable of NIR spectroscopy (SuperCam/Mars 2020, ISE- Bibring et al., 2004; Murchie et al., 2007; Pilorget and Bibring, 2013). M/ExoMars, Ma-MISS/ExoMars, MicrOmega/ExoMars), Raman spec- During in situ exploration missions, mineralogical and organic ana- troscopy (SuperCam/Mars 2020, SHERLOC/Mars 2020, RLS/ExoMars), lyses are strongly strengthen by the combination of multiple spectro- and LIBS (SuperCam/Mars 2020) (Wiens et al., 2016; Beegle et al., 2015; scopic and chemical methods including NIR spectroscopy. In this context, Vago et al., 2018). the aim of the PTAL project is to build and exploit a multi-instrument Within the PTAL database, the NIR characterization of the samples is spectral database and joint spectral interpretation tools, including NIR made with both a laboratory point spectrometer of high spectral * Corresponding author. E-mail address: [email protected] (D. Loizeau). https://doi.org/10.1016/j.pss.2020.105087 Received 28 January 2020; Received in revised form 26 August 2020; Accepted 3 September 2020 Available online 10 September 2020 0032-0633/© 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). D. Loizeau et al. Planetary and Space Science 193 (2020) 105087 Table 1 Table 2 MicrOmega FS specifications. Requirements for the set-up. MicrOmega instantaneous 20 μm  20 μm Quantified requirement Origin of the FOV (IFOV) requirement MicrOmega FOV 256  256 IFOV (5  5mm2) Controlled chamber characteristic Spectral range 0.99–3.6 μm þ 4 LEDs (LED1: 595 nm, LED2: 643 Operating MicrOmega À15 CtoÀ20 C Performance nm, LED3: 770 nm and LED4: 885 nm) FS temperature Spectral resolution 20 cm-1 Sample temperature < À5 C Performance Focal distance from the base 28.7 mm Atmosphere Dry atmosphere (no frost or Safety of the of MicrOmega condensation on the instrument or instrument Depth of focus Æ0.1 mm sample) Acquisition duration for one 15 min Operational requirements spectral cube Number of samples per 1-8 or more (depending on sample Automatization analysis size) fl Duration from ambient 1 Hour Duration resolution (detailed in Lantz et al., 2020), and a ight spare of the to optimal conditions MicrOmega ExoMars instrument. MicrOmega is a NIR hyperspectral Accuracy for the sample positioning microscope (Pilorget and Bibring, 2013). MicrOmega illuminates the Horizontally (X, Y) <60 μm  60 μm(3 MicrOmega Automatization field of view with monochromatic light at chosen wavelengths selected pixels) < through an Acousto-Optic Tunable Filter (AOTF) and acquires this way a Vertically (Z) 0.1 mm (MicrOmega depth of Performance focus) series of images at many different wavelengths. Earlier versions of MicrOmega have been selected to characterize Phobos on the Russian PhobosGrunt mission (Pilorget et al., 2011) and the surface of the better performances are achieved at cold temperatures. At these condi- near-Earth asteroid 162,173 Ryugu on the Mascot/Hayabusa-2 lander tions, the background thermal infrared emission of the instrument is mission (Bibring et al., 2017a). The model that is used for the PTAL lower, which increases the Signal to Noise Ratio (SNR) (Riu et al., 2018). project is the spare flight instrument of the MicrOmega model (hereafter In addition, operating the instrument at negative temperatures allows to named MicrOmega FS), whose flight model has been integrated on the simulate the observation conditions on the Martian surface. The thermal ExoMars rover Rosalind Franklin (Bibring et al., 2017b). regulation of the instrument within the PTAL set-up has been thus The use of MicrOmega FS to observe a large number of samples in safe considered as an important aspect of the setup. and efficient conditions required the design of a dedicated set-up. After a For the same reason, it was also chosen to cool-down the samples. short description of the MicrOmega instrument (section 2), the paper Although the systematic subtraction of the “dark” image enables to work describes in detail the choices that were made for the final design of a with samples at ambient temperature, the detector saturation is reached specific set-up for MicrOmega FS (section 3). The operational conditions more rapidly due to the higher thermal emission of the sample. Lowering that were defined for the characterization of the whole PTAL analogue the temperature, and hence the thermal emission of the sample, enables to rock collections are presented in sections 4 & 5. The characterization of acquire data with longer integration time, and hence to increase the SNR. one PTAL mineral sample is then exemplified (section 6), whereas the results of the characterization of the entire PTAL collection using this 2. Technical configuration of the PTAL MicrOmega set-up facility will be presented in a forthcoming paper (Loizeau et al. in prep). 2.1. Requirements 1.1. MicrOmega/ExoMars instrument In addition to the previous requirements related to the performances The MicrOmega instrument for ExoMars (Bibring et al., 2017b)isa of MicrOmega FS, the other major objective of the set-up was to ease and microscope acquiring images with pixels of ~20  20 μm2 over a 256  automatize the characterization of the PTAL samples. This leads to define 256 pixels field of view (~5  5mm2). An AOTF enables to illuminate the several environmental and operational requirements listed in Table 2. field of view (FOV) with monochromatic light in the NIR range from The operational and performance related requirements conduct to ~0.99 to ~3.6 μm with a spectral resolution of 20 cm-1 (equivalent in have both the instrument and the samples in a thermally controlled and wavelength to 2 nm at 1 μm and to 26 nm at 3.6 μm). The cooled detector dry atmosphere to avoid water frost and condensation. The desired ac- acquires the reflected light at each ~300 wavelengths and builds this curacy in the sample positioning implies the use of a precise electroni- way a hyperspectral cube. The NIR observations using the AOTF are cally controlled stage with motions in all three directions. completed with four images illuminated with LEDs (Light Emitting Di- To ensure protection from dust, in compliance with the nature of the odes) centered on wavelengths at about 595, 643, 770 and 885 nm flight model of MicrOmega FS, an additional requirement was made to (Bibring et al., 2017b). The main characteristics are listed in Table 1. set MicrOmega FS in a contained environment with respect to the The spectral range and sampling were selected to enable the identi- samples.