A dramatic dark spot appears where Hayabusa2 sits on Ryugu asteroid

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The shadow of Hayabusa2 is visible on the surface of the asteroid, as well as the new dark spot on the site of the hit.
Image: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST.

The Japanese spacecraft Hayabusa2 successfully landed on the asteroid Ryugu late last week, blowing up its surface and, hopefully, collecting samples. A new image published by JAXA shows a separate trace on the asteroid where the procedure took place, but the cause of the dark surface function is not immediately clear.

Japan's mission of extracting surface samples of an asteroid and returning them to Earth seems to be performing exceptionally well. The mission's collection phase was unfolded at the end of last week, when the Hayabusa2 probe made its long-awaited descent to the asteroid surface of one kilometer wide, located about 3.2 billion kilometers from the Earth.

To collect samples, the Hayabusa2 probe used a projector – a kind of firearm – to fire a 5-gram tantalum ball into Ryugu's surface at 300 meters per second, or nearly 1,000 feet per second. The debris formed by the impact was then recovered by the sampler cornet of the probe. At least in theory, we will not really know if materials entered the cornet before the probe returned to Earth in December 2020.

A new image released by the JAXA shows a black spot on the sample site. Hayabusa2 took the photo with her optical navigation camera about a minute after touchdown and, while she was returning to her original position about twenty kilometers above the asteroid. The probe took the picture while it was about 25 meters from the sample site. The cause and nature of the dark area are not perfectly clear.

"The color of the area under the probe's shadow differs from that of the environment and was discolored by touchdown," JAXA said in a press release. "At the moment, the reason for the discoloration is unknown, but it could be due to dust that has been blown up by propellants or bullets (projectiles) from the spacecraft."

Both theories make sense, and it could be a combination of both. However, it is unclear whether the impact itself caused the discoloration or whether the probe's activities returned the blackened material from below. Or if it's something else.

Right on Target: The purple circle indicates the target area and the white point indicated by the arrow is the light marker placed on the surface before extraction.
Image: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST.

An annotated image shows the intended touchdown site in purple. The red arrow indicates a target marker previously deployed by the probe; the shining marker served as a landmark to Hayabusa2 as he made his descent. The planners of the JAXA mission hoped to land about 4 to 5 meters from the marker, reports the BBC. Looking at the 6 meter wide target area and dark spots, it looks like Hayabusa2 has nailed the landing site.

An image of the target area (in purple) before the sample extraction. The white X indicates where the marker was finally placed.
Image: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, Aizu University, AIST.

The JAXA also released an image showing the area before touchdown. No discoloration is visible in the photos, which means that the activities of the probe are almost certainly responsible for the new surface.

In the preparatory tests performed on Earth by the JAXA, the considerable impact of the ball could be perceived in slow motion sequences. It is therefore not surprising that the impact on Ryugu, with its minimal gravity, produces such a dramatic surface effect.

Ryugu's work at Hayabusa is not finished yet. Later this year (between April and June), the probe will attempt to extract subsurface materials. To do this, a small explosive device will fall on the asteroid, creating a small crater. Once the dust settles, Hayabusa2 will collapse and attempt to collect samples.

[JAXA, BBC]

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