Onboard Hayabusa2, NIRS3 observed the Earth and Moon as the spacecraft returned in December for the Earth swing-by. Part of the data obtained is shown in the figure below. NIRS3 is an observational instrument that disperses the light entering its field of view to separate it into different wavelengths (like a prism). The intensity of the light at each wavelength is then measured. The figure displays the spectra collected, chronologically going from left to right. When NIRS3 looks into deep space, we do not see any signal at all. However, when NIRS3 points towards the Earth and Moon, it detects their reflected light. Light from the Moon was detected over the whole wavelength range, but the Earth's reflected light was not detected between wavelengths of 2.5-3.2 µm. This band of wavelengths corresponds to light that is absorbed by water molecules in the Earth's atmosphere. Using this same ability, NIRS3 will investigate the distribution of water-bearing minerals on asteroid surfaces. This test on our wet Earth and dry moon confirms the NIRS3 performance as Hayabusa2 sets off for asteroid Ryugu!
NIRS3 has been developed and operated in cooperation with Japan Aerospace Exploration Agency (JAXA), University of Aizu, Kansei Gakuin University, Tohoku University, Graduate University for Advanced Studies (SOKENDAI), Chiba Institute of Technology, Aichi Toho University, National Institute for Environmental Studies (NIES), National Astronomical Observatory of Japan (NAOJ), National Institute of Polar Research (NIRP), Japan Atomic Energy Agency (JAEA) and Nagoya University.