Composition of Low Albedo Solar System surfaces – CLASSY

The general strategy of the project relies on three tasks:

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 reflec- tance 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.

Preliminary results as to February 2019:
- discovery of ammonium salts and aliphatic species at the surface of comet 67P/CG. Implications for the nitrogen budget in comets.
- Correlation between jets and morphology of comets 67P/CG.
- Evidences of lattice swelling by ion irradiation. An alternate mechanism to opaque nanoparticles?
- The NIR spectra of the Ctuhlu organic belt of Pluto: possible effects of ion irradiation and/or high porosity aerosols layer?
- CO as a diluted molecule in N2 at the surface of Pluto as evidenced by experimental measurements on pure CO ice.

- Hong Van HOang has been hired as a PhD student. She will work on Rosetta and New Horizons data at IPAG/LESIA.
- A PhD student will be hired by IAS/UMET on october 2019.
- Irradiation experiments on olivine pursued at Orsay. Structural analysis of samples at ULET.
- Experiments at GANIL in April 2019 for investigating GCR effects on Pluto surface.
- Additional experiments for improving the NH4 abundance at the surface of 67P/CG.
- Investigation of spectralslope/morphology and brigh spots at the surface of 67P/CG (Thèse Hong Van).
- Next meeting of the CLASSY team in june 2019.

3 manuscripts submitted.
2 manuscripts in preparation.

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, and this will will shade 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 meanwhile using them for interpreting the spectral data from the space missions mentioned above. We will study experimentally the effects of the first stages of space weathering (ions irradiation) on the VNIR spectra of dark analogs. We will also conduct experiments that will 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), IAS (Institut d’Astrophysique Spatiale, Orsay), Unite Materiaux et Transformations (UMET, Lille), Laboratoire d’Etudes Spatiales et Instrumentations en Astrophysique (LESIA, Meudon) and Museum National d’Histoire Naturelle (MNHN), and 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 interpretations 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.