LINKING PRIMITIVE ASTEROIDS WITH CARBONACEOUS CHONDRITE METEORITES: IMPLICATIONS FOR SPACE MISSIONS TO ASTEROIDS

Telescopic observations of water- and carbon-rich asteroids provide critical constraints on the abundance and distribution of water and organic material in the early Solar System and the significant roles these materials have in the cosmochemical evolution of many diverse Solar System bodies. These “primitive” asteroids, especially those within the C-complex, are widely thought to be linked to CM and CI carbonaceous chondrites. We have observed 45 water-rich asteroids in the 3-μm spectral region, and we are planning to observe 60 more asteroids in the next 3 years using the NASA Infrared Telescope Facility (IRTF) and Gemini North telescopes. Thus far, the investigation has allowed the identification and distribution of at least four 3-μm spectral groups, each of which is presumably related to distinct surface mineralogy.

A supporting study examined spectra of CM and CI carbonaceous chondrites in the laboratory under asteroid-like conditions. In this laboratory study, we identified three spectral groups of CM chondrites (in addition to the CI chondrite Ivuna) on the basis of the 3-μm band center and shape of spectra, showing that distinct parent body aqueous alteration environments experienced by different carbonaceous chondrites can be distinguished using reflectance spectroscopy. Spectral comparisons of meteorites and asteroids have been challenging because meteorite spectra have generally been acquired in ambient terrestrial environments, and hence are contaminated by atmospheric water. However, in our investigation meteorite reflectance spectra were measured under dry conditions (vacuum and elevated temperature) to mimic space conditions and minimize the adsorbed water that affected previous analyses. In this talk we will discuss how 3-μm reflectance spectroscopy is crucial in linking primitive asteroids with carbonaceous chondrites. We will also discuss the implications of this work for the returned carbonaceous samples from asteroids Bennu (OSIRIS-REx target) and Ryugu (Hayabusa2 target).