Laboratory spectroscopy study in support of data analysis of OVIRS and OTES instruments on board the OSIRIS-REx mission

NASA OSIRIS-REx sample return mission explored the primitive asteroid 101955 Bennu with the ambitious goal of collect a sample from the surface and return it to Earth. The spacecraft accomplished the first part of its outstanding objective sampling the asteroid surface on 20th October 2020 and, to date, operations are ongoing to prepare the departure from Bennu in March 2021 and the arrival on Earth in September 2023. B-type asteroids, like Bennu, are among the most primitive small bodies in the Solar System and their study is closely related to the formation and the evolution of terrestrial planets. Moreover, Bennu and the other carbonaceous asteroids represent a relevant target for astrobiological study on the origin of life: these small rocky bodies of our Solar System are characterized by presence of hydrated minerals and probably high content of organic material and volatiles. It is therefore evident that these asteroids were probably the vehicle for the arrival of biomolecules to our planet creating the conditions for the birth of first living cell on Earth. By investigating these objects, we push our understanding of the evolution of our planet and origin of life toward new frontiers. This PhD project was developed in the framework of the OSIRIS-REx space mission. The work is characterized by a broad scientific approach improved by the use of both laboratory and remote sensing data analysis from spacecraft instruments. With a multidisciplinary and multi-analysis view I faced with both challenges and advantages of the two techniques. One of the major results obtained in the PhD project concern laboratory investigation of mineral and meteorite spectra in simulated asteroid environment. Specifically temperature dependent effects on mineral and meteorites spectra in mid-infrared region 1500-400 cm-1 (6.6-25 μm) were studied in laboratory at various cryogenic temperatures from 65 K up to 350 K. Several changes were observed mainly in peak intensity, band area and peak position related to the level of hydration and grain sizes. Laboratory findings were directly applied to the analysis of remote sensing data collected by OTES spectrometer on board OSIRIS-REx. As the surface temperature of the asteroid increases from night to day time, some regions show a trend analog to the one observed in laboratory and so linked with high content of hydrated minerals. Contrary, other regions are associated with a lower content of hydrated minerals. For the first time mid-infrared spectroscopic features on a planetary surface show a day- and night-time temperature dependent variation with different magnitudes and trends that are linked to the composition. Further analyses showed that about 15% percentage of Bennu’ surface is dominated by lower content of hydrated minerals placing important constrains to formation of Bennu and its evolutionary models. In detail, different hypothesis about the origin of anhydrous minerals can be formulated: it could come from the interior of differentiated large parent body, it could be thermally shocked during the impact or it could come from the projectile that destroyed Bennu parent body. Laboratory work also included the analysis of UV irradiation of amino acid glycine pure and adsorbed on space relevant minerals that can be likely present on Bennu: serpentines antigorite, olivine forsterite, oxide mineral spinel and iron-sulfide mineral pyrite. In my study, I highlight a smaller efficiency of antigorite and spinel in catalyzing glycine photoreaction with respect to forsterite and pyrite. This kind of information are pivotal to understand the fate of organics on rocky asteroid surfaces. In fact, primitive asteroid Bennu revealed some signatures of organics. Therefore, this analysis will help the scientific community to investigate Bennu surface processing and space weathering. Moreover, with the spacecraft return in 2023, this analysis will provide a base for further detailed investigation on the composition and organic content of the collected sample. Finally, by using infrared spectroscopy analysis, I worked in collaboration with the Science Team on the characterization of the possible candidate sample sites until the selection of the primary target Nightingale, where on 20th October 2020 OSIRIS-REx successfully collected its priceless sample. I investigated the candidate sample sites in order to enhance spectroscopic differences, which were related to presence of pristine and fine material. The primary sample site Nightingale resulted to be scientifically remarkable and characterized by the presence of large amount of fine material as observed during the sample collection. During the three-years PhD project, I also collaborate to the discovery and analysis of exogenous material on the surface of the asteroid. My analysis was used to disentangle the presence of exogenous pyroxene material coming from the vestoid asteroid family with important implication for the dynamical evolution of the asteroid Main Belt. Further activities were made in collaboration with the OSIRIS-REx team, we investigated the spectroscopic behavior of the asteroid surface using statistical multivariate analysis and we evaluated the OH/H2O content of hydrated minerals. Furthermore, we studied several craters in order to understand the impact processing that affected Bennu’ surface obtaining constraints on its evolution. Thanks to the opportunity to be member of the OSIRIS-REX science team, I had the unprecedented chance to investigate the surface of Bennu with amazing resolution. Through several infrared spectroscopic studies, I studied the major features of the surface to unveil the processes that affected the life of Bennu. This asteroid turned out to be an heterogeneous world with an enormous wealth of information that will led us to improve our knowledge on the nature and evolution of carbonaceous asteroids.