Abstract

Our Solar System is the only planetary system that can be thoroughly explored by spacecrafts and by the analysis of planetary samples in the laboratory. It provides a unique glance at the mechanisms leading to stars and planets formation, a vision that is complementary to that derived from remote observations of nascent planetary systems. Chemical, dynamical and chronological information is trapped in the more primitive bodies that escaped extensive planetary evolution, as asteroids, comets and Kuiper Belt Objects (KBOs). The composition of these so-called small bodies then constitutes a major and outstanding issue.

VNIR spectro-photometry allows for systematic surveys and therefore provides a global appraisal of the compositional diversity of the small body population as a whole. However, the composition of dark small bodies remains poorly known and presently, a number of fundamental issues are still pending :

• What composition is associated with each taxonomic spectral class ?
• Does space weathering play a role in the definition of taxonomic spectral classes ?
• How are they linked with available cosmomaterials ?

The interpretation of VNIR spectra is the angular stone of all these issues and the central objective of CLASSY. Our proposal arises in the general context of a wealth of data collected by the space missions ROSETTA, DAWN and NEW HORIZONS. We benefit from high quality and high spatial resolution multi-angular VNIR observations with unprecedented photometric accuracy. The interpretation of these data will lead to major results on the composition of a comet (67P/CG), the type C asteroid Ceres and KBO 2017 MU 69, shading new light on the interpretation of the taxonomic spectral classes in term of composition, and on the asteroid-comet continuum. However, this interpretation requires experimental data that have not been measured so far.

CLASSY aims at conducting these experiments and interpreting the spectral data from the space missions mentionned above. We will study experimentally the effects of the first stages of space weathering (ions irradiation) on the VNIR spectra of dark analogs, and investigate the composition and textural parameters that control VNIR spectra through multi-angular radio-spectro-goniometric measurements on sub-micrometric organics-minerals assemblages.

The CLASSY consortium is multidisciplinary and includes 5 laboratories :

• Institut de Planetologie et d’Astrophysique de Grenoble (IPAG, Grenoble): P. Beck, L. Bonal, O. Brissaud, L. Flandinet, O. Poch, E. Quirico, B. Schmitt
  
• IAS (Institut d’Astrophysique Spatiale, Orsay): A. Aleon-Toppani, D. Baklouti, R. Brunetto, C. Lantz and Z. Djouadi.
  
• Unite Materiaux et Transformations (UMET, Lille): F. De la Pena, C. Depecker, C. Le Guillou, H. Leroux
  
• Laboratoire d’Etudes Spatiales et Instrumentations en Astrophysique (LESIA, Meudon): A. Barucci, S. Erard, S. Fornasier, F. Merlin
  
• Museum National d’Histoire Naturelle (MNHN): M. Roskosz
  

CLASSY gathers a broad range of fields as Planetary and Space sciences, Surface sciences, Material Sciences, Meteoritics, Mineralogy, Irradiation physics and Data science. Most of researchers belonging to this consortium have been used to collaborate together, and they share many common publications. CLASSY offers the opportunity to strengthen these collaborations, and to provide innovative in- terpretations and breakthrough of data collected by space missions of primary interest. It will also form a internationally competitive team that will apply for grains that will be returned back to Earth by the Hayabusa 2 and Osiris-Rex missions.

Task 1: Ion irradiation experiments that aim at investigating the first stage of space weathering, as the effects of solar wind irradiation on dark surfaces analogs and carbonaceous chondrites. The samples will be characterized with microanalytical techniques, before and after irradiation, and their spectral properties characterized as well.

Task 2:  Multi-angular reflectance experiments that aim at studying the spectral reflectance properties of dark small bodies analogs and carbonaceous chondrites, and irradiated samples as well (Task 1). High signal-to-noise ratio and multi-angular bi-directional reflec- tance data will be collected with a unique home-made instrument designed and built at IPAG. Submicrometric fine-grained porous analogs will be produced through dedicated protocoles.

Task 3: Interpretation of spectral data of dark small bodies based on Tasks 1 and 2, in particular those collected by the space missions Rosetta, Dawn and New Horizons, for which multi-angular and extensive independent constraints on surface composition are available.