↑Hasegawa, S.; et al. (2008). "Albedo, Size, and Surface Characteristics of Hayabusa-2 Sample-Return Target 162173 1999 JU3 from AKARI". Publications of the Astronomical Society of Japan. 60 (SP2): S399–S405. doi:10.1093/pasj/60.sp2.s399.
Early analysis in 2012 by Thomas G. Müller et al. used data from a number of observatories, and suggested that the asteroid was "almost spherical", a fact that hinders precise conclusions, with retrograde rotation, an effective diameter of 0.85–0.88 kilometers, (0.528 miles) and a geometric albedo of 0.044 to 0.050. They estimated that the grain sizes of its surface materials are between 1 and 10 mm.
Initial images taken by the Hayabusa2 spacecraft on approach at a distance of 700 km (434.9 miles) were released on 14 June 2018. They revealed a diamond shaped body and confirmed its retrograde rotation. Between 17 and 18 June 2018, Hayabusa2 went from 330 km to 240 km (205.05 to 149.1 miles) from Ryugu and captured a series of additional images from the closer approach. Astronomer Brian May created stereoscopic images from data collected a few days later. After a few months of exploration, JAXA scientists concluded that Ryugu is actually a rubble pile with about 50% of its volume being empty space.
The acceleration due to gravity at the equator has been evaluated at about 0.11 mm/s2 (0.00011 m/s2). It rises to 0.15 mm/s2 at the poles. The mass of Ryugu is estimated at about 450 million tons.
Animation of Hayabusa2's orbit from 3 December 2014 to 29 December 2019 Hayabusa2 162173 RyuguEarthSun
The Japan Aerospace Exploration Agency (JAXA) spacecraft Hayabusa2 was launched in December 2014 and successfully arrived at the asteroid on 27 June 2018. It is planned to return material from the asteroid to Earth by December 2020.
The Hayabusa2 mission includes four rovers with various scientific instruments. On 21 September 2018, the first two of these rovers, which hop around the surface of the asteroid, were released from Hayabusa2. This marks the first time a mission has completed a successful landing on a fast-moving asteroid body.
On 3 October 2018, the German-French Mobile Asteroid Surface Scout (MASCOT) lander successfully arrived on Ryugu, 10 days after the MINERVA rovers landed. Its mission was short-lived, however, with only 16 hours available from its batteries.
Hayabusa2 touched down briefly February 22, 2019 on the Ryugu asteroid, fired a bullet into the surface to puff up dust for collection and blasted back to its holding position.
^Photograph of the full disc of 162173 Ryugu by the Optical Navigation Camera – Telescopic (ONC-T) instrument aboard the Hayabusa2 spacecraft. The photograph was taken on 26 June 2018, at a distance of 20 kilometres (12 miles) from the asteroid's surface.