“Horning in” on an asteroid. Sampler horn will be used to gather up space rock material.
Credit: JAXA/Screengrab/Inside Outer Space


Japan’s Hayabusa2 team reports that the surface of asteroid Ryugu was not what they expected.

Because of this on-the-spot finding, the spacecraft sampler team carried out an experiment to see if Hayabusa2 could still gather material from the asteroid’s surface when they attempt the probe’s touchdown this Friday.

MASCOT en route to asteroid’s surface photographed by an optical navigation camera onboard the Hayabusa2 spacecraft. The ONC-W2 is a camera attached to the side of the spacecraft and is shooting diagonally downward from Hayabusa2. MASCOT appears in the upper edge of the image.
Credit: JAXA, University of Tokyo & collaborators

Final test

Late last year, the sampler team conducted a final test before touchdown, firing an identical bullet to that onboard Hayabusa2 into a simulated soil of the surface of space rock Ryugu. The test evaluated how much sample would be ejected after the bullet’s impact.

Hayabusa2 operators expected the topography of the asteroid would be a powdery fine regolith. That was not found on the surface of Ryugu.

Rather, centimeter-sized or larger gravel was observed by the MASCOT and MINERVA-II1 rovers that landed on the asteroid surface.

Credit: JAXA

 Artificial gravel

“This is quite different from the prediction before launch, so it took time to investigate the safety of the spacecraft during touchdown. Additionally, it was necessary to review whether sample material would still be released from the asteroid surface as originally assumed,” as reported by a new Japan Aerospace Exploration Agency (JAXA) Hayabusa2 twitter posting.

The projector (barrel) and the projectile (bullet) below used in the experiment. As this is a flight spare, the shape and the material are all the same as those of onboard Hayabusa2. Credit: JAXA)

Credit: JAXA

Artificial gravel was prepared in collaboration with Professor Hideaki Miyamoto at the University of Tokyo, Graduate School of Engineering. By simulating properties such as strength, density and composition, Hayabusa2 researchers replicated a carbonaceous chondrite meteorite, which is regarded as fragments of C-type asteroids similar to Ryugu.

The target was formed by stacking up the artificial gravel with a similar size distribution as that observed on the surface of Ryugu based on images from the landers.

Collided like billiards

Experiment results show that the fragments of gravel that were crushed by the bullet were released into the surrounding gravel where they collided like billiards to break up the material.

Target simulating the surface of Ryugu.
Credit: JAXA, University of Tokyo

The resulting sample amount exceeded the initial assumption that would be released from the surface.

While the diameter of the collision site (crater) made by the impact of the projectile is smaller in comparison to that in a fine regolith layer, it was a sufficient size in comparison with the inner diameter of the open tip of the sampler horn, the team reports.

High-speed camera

Although the experiment was carried out in the Earth’s gravity, the images from a high-speed camera revealed that fragments of crushed powdery gravel can pass through the collection horn.

At the target asteroid, under microgravity, even more samples are expected to be introduced into the sampler horn, “meaning that if we land on a terrain similar to the simulated target, we can sample the surface of Ryugu,” the team adds.

“With test results obtained that exceeded expectation,” the twitter posting notes, “the sampler team celebrated for a good new year.”

To view the high-speed camera results, go to:

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