Ir reflectante spectra of Antartic carbonaceous chondrites to better characterize the surfaces of asteroids targetted by sample return missions

Abstract

Undifferentiated carbonaceous asteroids have experienced complex collisional histories, and a significant number are fragments of larger bodies. Meteorites arrived from these asteroids exhibit an amazing reflectance spectra diversity [1-3]. These asteroids are now in the focus of several sample return missions due to the astrobiological relevance of their exploration [4, 5]. In meteorite collections the rocks delivered from these fascinating asteroids are called carbonaceous chondrites (hereafter CCs). Impacts on these asteroids mixed together materials with different compositions and alteration histories. Due to their low bulk densities and porous nature the collisions with other bodies resulted in heavy fragmentation and brecciation of their surfaces. In fact, it is now being recognized that most of the identified CCs in terrestrial collections are breccias characterized by having clasts of different lithologies [6]. Carbonaceous asteroids delivered to the NEO region by dynamic resonances, as the selected targets of Marco Polo-R and Osiris-Rex missions, cannot be considered an exception. They evolved through the Main Belt as a consequence of non-gravitational effects, and in their long journey until becoming a NEO could have experienced space weathering processes changing significantly their reflectance properties. Chemical evidence indicates that the number of carbonaceous asteroids sampled is lower than twenty. Among them, some are represented by ungrouped and extremely rare CCs that are only available thanks to the Antarctic recovery effort made by different teams during the last decades. Due to this we have started a project to increase the number of high resolution reflectance spectra of CCs, with three main goals: 1) To identify the main features that could be used for remote characterization of their parent bodies; 2) To analyze the relevance of grain size in the reflectance spectra and exemplify its influence in regolithcovered carbonaceous asteroids, and 3) To perform experiments to simulate space weathering processes and their influence in the reflectance properties of primitive bodies