PTAL – The Planetary Terrestrial Analogues Library for interpreting spectroscopic data

The Planetary Terrestrial Analogues Library (PTAL) project aimed to build and exploit a spectral database for the characterization of the mineralogical and geological evolution of terrestrial planets and small Solar System bodies. The lithological collection of PTAL consists now of 102 terrestrial rock type samples, which form the basis for the spectral library. The PTAL rock types include volcanic, igneous and sedimentary rocks and regoliths from well-studied locations all over the world. The target samples have composition comparable to what is currently known about the Martian global rock type distribution and some samples intend to shed light on the mineralogical properties of the landing area for Mars2020-Perseverance and ESA’s ExoMars (compare Bultel et al., Krzesinska et al., this conference).

The sample characterisation includes mineralogical and chemical analyses with standard commercial and dedicated spacecraft instrumentation (RAMAN, NIR, LIBS) under laboratory conditions (Veneranda et al, 2019; Lantz et al, 2020; Loizeau et al, 2020). The data base also includes detailed field description of the sample sites, coordinates, field photos, the macroscopic appearance of the rock samples and standard geological/petrographic information based on optical thin section studies and XRD (Dypvik et al., in review). 

Our collection of natural field-collected and artificial planetary analogue materials is supplemented by materials, which have been altered in laboratory experiments. These weathering experiments allowed providing spectral information on the formed mineral assemblages and we recommend reinterpretation of previous remote sensing interpretations (Viennet et al. 2017, 2019, Sætre et al. 2019, Bultel et al. 2019).

Being built on naturally occurring, terrestrial, common whole rock samples, in which minerals occur in their natural settings and relations is the biggest strength of this analogue rock collection. It allowed studying possible detection interferences and a comparison of the sensitivity of the different techniques. The collection forms the base for characterization of various alteration pathways manifested in mineralogy and geochemistry of rocks, in order to better understand and explain the alteration and weathering on Mars.

The PTAL spectral library will be made public during this conference. The main aim of the database is to provide sets of whole rock and mineral spectra of rocks that are relevant for rover and satellite missions. The spectra shall aid comparison, identification, quantification and spectral calculation when spectroscopic instruments such as NIR, RAMAN and LIBS operate in planetary missions and/or analysing materials in the field or in the laboratory. The PTAL database will allow users to jointly interpret laboratory results and newly gathered in-situ or remote sensing data using instruments (NIR, LIBS, RAMAN) on board of current and future space missions (e.g., JAXA’s Hayabusa-2, NASA’s Curiosity and Mars2020-Perseverance (Farley et al. 2020) and ESA’s ExoMars-Rosalind Franklin (Vago et al. 2017) rovers).  We will show that the careful characterisation of analogue whole rock samples change the interpretation compared to mineral separate spectra, and allow the assessment of biosignature preservation potential and the presence of organic compounds. We caution that living organisms often contaminate terrestrial rocks, but also organic signatures can be rock compounds incorporated in the rock matrix during multiphase geological processes. The latter comprise on Earth plate tectonics and mountain belt formation, and therefore even if sample spectra may resemble the spectral signature on planetary surfaces, they may not be appropriate  analogues due to their individual evolutionary pathways.   

This database features spectral tools (compare Veneranda et al., this conference) allowing for the spectral data treatment. We have implemented the integration of the database management and algorithms in an end-user platform with graphical interfaces for the use of the data and analysing tools. We will have a demonstration and tutorial (see splinter meetings) and the release of the Planetary Terrestrial Analogues Library to the public during this conference.

Acknowledgements: This project is financed through the European Research Council in the H2020-COMPET-2015 programme (grant 687302).

References: Bultel, Viennet, Poulet, Carter, Werner (2019) Journal of Geophysical Research: Planets 124 DOI: 10.1029/2018JE005845. Dypvik et al (in review) Planetary and Space Science. Farley et al. (2020) Space Sci. Rev. 216, 142. Lantz, Poulet, Loizeau, Riu, Pilorget, Carter, Dypvik, Rull, Werner (2020) Planetary and Space Science 189, 104989. Loizeau, Lequertier, Poulet, Hamm; Pilorget, Meslier-Lourit, Lantz, Werner, Rull, Bibring (2020) Planetary and Space Science 193, 105087. Sætre, Hellevang, Riu, Dypvik, Pilorget, Poulet, Werner (2019) Meteoritics & Planetary Science 1-22. Vago et al. (2017) Astrobiology 17, 471–510. Veneranda, Sáiz, Sanz‐Arranz, Manrique, Lopez‐Reyes, Medina, Dypvik, Werner, Rull (2019) Journal of Raman Spectroscopy 2019, 1–19. Viennet, Bultel, Riu, Werner (2017) Journal of Geophysical Research – Planets 122, 2328–2343. Viennet, Bultel, Werner (2019) Chemical Geology 52, 82-95.