The asteroids Ryugu and Bennu exhibit the characteristics of the same class of primordial objects

Carbonaceous asteroids are valuable remnants of the formation of the Solar System 4.5 billion years ago. They have partly recorded the processes that governed its early evolution and contributed minerals and chemical compounds that may have been decisive for the evolution of the Earth and the terrestrial planets

The sample returns from asteroid Ryugu by JAXA’s¹ Hayabusa2 mission, followed by those from asteroid Bennu by NASA’s OSIRIS-REx mission, provide for the first time the opportunity to analyse their constituent material in the laboratory without terrestrial alteration. By comparing the samples from these two bodies, the study recently published in Nature Communications demonstrates that Ryugu and Bennu originate from the same class of primordial objects, for which essential properties have now been characterised

These analyses were carried out in the curation laboratory (preservation and analyses) at ISAS² near Tokyo, Japan, where the samples returned from Ryugu - as well as a fraction of the Bennu samples - are stored and protected from any contamination or contact with the terrestrial atmosphere. Within this laboratory is a French instrument, MicrOmega, an infrared hyperspectral microscope designed and developed at the Institut d’Astrophysique Spatiale with the support of CNES. It is jointly operated by teams from the Institut d’Astrophysique Spatiale and the Institute of Space and Astronautical Science (Sagamihara, Japan), who also analyse its results. Coupled with an optical microscope and a mid-infrared point spectrometer, MicrOmega thus contributes to an extensive combined analysis of the samples from the earliest stages of curation.

These analyses showed that the Ryugu and Bennu samples exhibit very similar spectral properties in the near-infrared, down to scales of a few tens of microns. In both cases, a wide variety of diagnostic compounds were detected within the phyllosilicate-rich matrix, notably phosphorus-bearing compounds with high biochemical potential.

Despite certain differences, these results suggest a very similar origin and evolution for the two objects. Their main properties therefore appear to characterise the same class of primordial objects, whose contribution may have been significant in the evolution of Solar System bodies.