Sample Return Science
Sample return is the best method for in-depth study of extraterrestrial materials since the site they originated were explored by remote sensing and/or by the surface lander, or by "mulci-scale" observations.
Hayabusa is the first sample return mission from an asteroid, the S-type asteroid 25143 Itokawa (1998SF36). Hayabusa visited and explored there for 3 months in 2005, and return sample from there in 2010. Although the amount of sample is tiny, the historical sample return brought us many great scientific results.
Hayabusa2 is the second sample return mission from an asteroid, theC-type asteroid 162173 Ryugu (1999JU3). Hayabusa2 visited and explored there from June 2018 to Nov 2019, including the remote sensing, two surface lander experiments, one impactor experiment, and two touchdowns for sample collection, and returned sample from there to earth in Dec 2020. The return sample (5.4g) is now in initial description for future detailed analyses.
Infrared Hyperspectral Microscopy for Sample Description
Initial description of return sample is the first step for in-depth study of the sample return mission in the ISAS Extraterrestrial Sample Curation Center (ESCuC). One of the method is near-infrared hyperspectral microscopy using an AOTF-based MicrOmega developed by IAS (France) to characterize the sample in 22 µm per pixel, of the area of 5 x 5 mm square, in the wavelength range of 0.99 to 3.65 µm. This instrumnet allows us to detect silicates, philosilicates (aqueously altered silicate minerals), carbonates, organics, ices, sulfates, and other minerals within the sample.
Thermal Imaging of Planetary Surfaces
Hayabusa2 TIR performed the first-ever one-rotation global thermal imaging of an asteroid, the C-type asteroid 162173 Ryugu, and derived the thermal inerita and roughness map from the diurnal temperature profiles. We discovered that the surface is covered with boulders and rocks with lower thermal inerita (typically 300 ± 100 J m-2K-1s-0.5 or tiu) compared with that of typical charbonaceous chondrites (600-1000 tiu), indicating highly porous material. (Okada+, Nature 2020; Shimaki+, Icarus 2020). This value is consistent with that of in situ measurements by MARA on MASCOT lander (Grott+, Nature Astron. 2019) and with that of ground observations (Mueller, A&A 2017).
We also discovered colder boulders "Cold Spots" and hotter areas "Hot Spots" compared with their surroundings during the low altitude observations (Okada+, Nature 2020; Sakatani+, Nature Astron. 2021). This diversity indicates the variation of the degree of alteration inside of the parent body or before the formation of the parent body, or remnant fragments of impacted bodies to the parent body (Tatsumi+, Nature Astronon, 2021).
Future Instrumentation for Planetary Exploration
Thermal Infrared Multiband Imaging is being developed to be onboard in the ESA Hera mission to explore the asteroid Didymos binary system, through thermal imaging for thermophysical properties and through multi-band thermal infrared imaging for compositional mapping. This methodology is also applicable for thermal infrared microscopy of extraterrestrial return sample with the exchange of optics.
Other InstrumentsDevelopment of new instrument for future missions and sample return, such as thmermal IR microscope, multi-turn time-of-flight mass spectrometer.
