Calibration and performances of the MicrOmega instrument for the characterization of asteroid Ryugu returned samples

Abstract

MicrOmega, a miniaturized near-infrared hyperspectral microscope, has been selected to characterize in the laboratory the samples returned from Ryugu by the Hayabusa2 mission. MicrOmega has been delivered to the Extraterrestrial Samples Curation Center of the Japanese Aerospace eXploration Agency at the Institute of Space and Astronautical Science in July 2020 and then mounted and calibrated to be ready for the analyses of the samples returned to Earth on December 6, 2020. MicrOmega was designed to analyze the returned samples within a field of view of 5 × 5mm2 and a spatial sampling of 22.5 µm. It acquires 3D near-infrared hyperspectral image-cubes by imaging the sample with monochromatic images sequentially covering the 0.99-3.65 µm spectral range, with a typical spectral sampling of 20cm-1. This paper reports the calibration processes performed to extract scientific data from these MicrOmega image-cubes. The determination of the instrumental response and the spectral calibration is detailed. We meet or exceed the goals of achieving an accuracy of ∼20% for the absolute reflectance level, 1% for the relative wavelength-to-wavelength reflectance, and <5nm for the peak position of the detected absorption features. For the nominal measurements of Ryugu samples with MicrOmega/Curation, the instrument performance also reaches a signal-to-noise ratio of >100 over the entire spectral range. By characterizing the entire collection of the returned samples at the microscopic scale, MicrOmega/Curation offers the potential to provide unprecedented insights into the composition and history of their asteroid parent body.