Hayabusa 2 touches and collects an asteroid sample



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The Japanese spacecraft Hayabusa 2 landed on Ryugu, the asteroid in orbit since last summer, and took a sample of its surface.

Practice makes perfect.

Last week, Hayabusa 2 plunged to take a sample of the surface of the asteroid 162173 Ryugu, diving like a peregrine falcon. Everything went smoothly as expected: by the time the sample cone came in contact, a tantalum ball was drawn to the surface, sweeping the material containing an asteroid that was projected in the cornet. Then the spaceship flew away. Hayabusa 2 has now sealed the sample collection compartment and preserved the sample for its return to Earth in December 2020.

Descent to Ryugu

Hayabusa 2 took this photo with his optical navigation camera at 180 meters before engaging in his final descent to take a sample of the Ryugu asteroid.
JAXA / Tokyo Univ. / Kochi Univ. / Rikkyo Univ. / Nagoya Univ. / Chiba Institute of Technology / Meiji University. / Aizu Univ. / AIST

Everything seems so easy, but this facility did not happen without a lot of work and worry. Thirteen years ago, Hayabusa's predecessor, Hayabusa 2, suffered damage during his two sampling attempts and the shotgun mechanism did not work. It took extraordinary creativity and perseverance on the part of Hayabusa's engineers to bring the spacecraft back to Earth, and the sample capsule it sent back contained only a few micrograms of dust. The memory of these struggles weighed heavily on those who worked on Hayabusa 2, one of whom pointed out that the successful sample capture was a "revenge" for Hayabusa's murders.

Grab sample

Finding the right place to taste Ryugu was more difficult than expected. Itokawa had large "ponds", relatively smooth deposits of dust and pebbles. Hayabusa sampled one. But when Hayabusa 2 arrived in Ryugu on June 27, 2018, no such pond was visible: the asteroid was uniformly rocky.

The team had to develop new selection criteria for sampling sites because no Ryugu sites met the criteria they had defined before launch. Scientists have defined two extremely narrow landing sites on which they must navigate between potentially damaging rocks. The team tried to go down to these sites twice. Back on Earth, they checked whether the firing mechanism would release enough material from a rocky surface; it seemed, then they proceeded, and everything worked perfectly – probably.

After the touchdown

Hayabusa 2 took this photo of Ryugu on February 22 as the Space Shuttle began to climb immediately after his brief touchdown. One can see the shadow of Hayabusa 2, as well as a dark spot where spacecraft propellers are hunting for lighter materials on the surface of Ryugu.
JAXA / Tokyo Univ. / Kochi Univ. / Rikkyo Univ. / Nagoya Univ. / Chiba Institute of Technology / Meiji University. / Aizu Univ. / AIST

We will not know for sure how successful the sampling was until Hayabusa 2 returned to Earth. The spacecraft has no way of measuring how much material is introduced into the chamber. However, all spacecraft telemetry, descent velocity profile, and rise to temperature changes within the sample horn are compatible with successful sampling.

And after?

Hayabusa 2 could actually take two more samples, placing them in two other collection compartments in the sample return capsule. At present, the mission must decide whether obtaining the additional sample would be worth the extra risk.

Hayabusa 2 also has a (literally) flashy experience to achieve. It has a small deployable cab impactor (SCI), a mainly copper spacecraft containing explosives that can create an artificial crater on the surface of Ryugu. Hayabusa 2's will house the explosion behind the mass of the asteroid, but it would be a shame to unleash a firework without seeing it explode. Thus, Hayabusa 2 also has a deployable camera, DCAM3, which it will launch soon after the deployment of SCI to (hopefully) get views of the formation of the crater. If the experiment succeeds, the team will follow by collecting material from the crater. Being able to directly compare materials from the altered surface of the asteroid to its relatively pristine interior would be a boon to scientists, who often have to determine bulk composition from remote observations of the surface of asteroids.

Hayabusa 2 must wait until planetary alignment begins to return to Earth. It will therefore remain close to Ryugu until November or December. His return will take about a year. After dropping the sample in the Australian desert on December 7, 2020, the spacecraft could possibly continue an extended mission, flying over another asteroid. Hopefully the sample capsule will contain a lot of asteroids, which Japan will share with researchers and laboratories around the world.

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