Overview of initial remote-sensing observations of asteroid Ryugu by Hayabusa2
Abstract
Hayabusa2 is the second sample return mission from an asteroid after Hayabusa mission. The target asteroid is (162173) Ryugu, which is a C-type asteroid. The main science objective is to investigate organic matters and water at the beginning of the solar system. The technological purpose is to maturate the new technology developed by Hayabusa and to develop other new technology for space missions. Hayabusa2, which was launched December 3, 2014, arrived at Ryugu on June 27, 2018. Ryugu is a top-shaped asteroid about 900m in diameter. The shape is rather unexpected because the spin period of Ryugu is not so short as those of top-shaped asteroids known previously. The remote sensing observations were done from the distance of 20km at first by the four instruments, ONC (Optical Navigation Camera), LIDAR (Laser Altimeter), NIRS3 (Near Infrared Spectrometer), and TIR (Thermal Infrared Imager). Up to now (end of July), we found that Ryugu has sharp ridge along its equator, and that there are about 50 crater candidates. The largest one is about 300m in diameter. The surface is covered by numerous boulders. The largest one is located near the one of the poles and the size is about 130m. We also found by the observation of TIR that the surface temperature is different between the north hemisphere and the south hemisphere, which shows the seasonal difference. The visible and infrared spectra were obtained by ONC-T (with 7 filters) and NIRS3. The visible spectrum is very flat and its variations are very small. But we observed small variation in both albedo and spectral slope on Ryugu. As for the near infrared spectrum by NIRS3, it showed homogeneous and featureless spectra between 1.8 and 3.2 microns, which indicates lack of hydrated minerals in the entire surface. These features are very interesting from the science point of view and it is very important to decide where to touchdown and where to release the lander (MASCOT) and the rovers (MINERVA-II). The landing site selections will be done in August by considering these remote sensing observation data, shape model, and gravity measurements. The lander and rover releases will be done in September and October 2018, and the 1st touchdown will be done in October.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5050101Y