TopicsFrom a distance of about 700km,
Ryugu's rotation was observed.

Using the ONC-T (Optical Navigation Camera - Telescopic), asteroid Ryugu was photographed continuously from June 14, 2018 at around 21:00 JST through to June 15, 2018 at around 05:10 JST. Figure 1 shows a looped animation of the 52 captured images.

The distance to Ryugu when the images were captured was between about 700 - 650 km. In these photographs, Ryugu is approximately 12 - 13 pixels in diameter. The animation in Figure 1 shows the photographs after image processing has been performed to smooth between the pixels so that the asteroid’s surface looks smooth.

  • (Large image) Figure 1: The rotation of Ryugu is captured in images taken by the ONC-T. The photographs were shot between June 14, 2018 at around 21:00 JST and June 15, 2018 at around 05:10 JST.
    ONC Team: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu and AIST

From this animation, you can see the asteroid surface appears to be strongly angled, and pitted with dents or craters. Also, the axis of rotation looks close to the vertical direction (perpendicular to the ecliptic plane in which the Earth orbits the Sun) in this image. The direction of rotation is retrograde, spinning in the opposite sense to the Earth and Sun, and to the direction of the planetary orbits. This information is very important for exploring the asteroid.

As we see the surface of Ryugu more clearly from now on, we will start to gain a more precise knowledge of the asteroid’s properties.

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(プロジェクトマネージャ 津田雄一)