The first operation rehearsal for the first touchdown of Hayabusa2 was performed from September 10 - 12. The spacecraft reached an altitude of about 600 m from the surface of Ryugu and then began to ascend once again. During the operation, the images taken for navigation purposes with the Optical Navigation Camera Wide angle (ONC-W1) were released in real time. The last image captured is shown in Figure 1. This photograph was taken on September 12 at around 12:40 JST at an altitude of 635m from the surface of Ryugu.
In this image, the left-hand side (within the red circle in Figure 1b) appears brightened due to a phenomenon known as the "opposition effect". It is a phenomenon that occurs when the angle formed between the Sun - the celestial body surface - observation point (known as the "phase angle") is close to zero, resulting in the celestial body being illuminated from directly behind the observation point and creating a bright region. In the center of the bright part is a black dot but this is the shadow of Hayabusa2. The sunlight is behind the spacecraft, casting the shadow on the asteroid. It is easier to see that this dot is the shadow of the probe in an animation.
Please visit Hayabusa2 project site for more details.