The first touchdown of the spaceship Hayabusa2 on the asteroid Ryugu is scheduled for this week. If successful, the ship shoots a bullet into the rock to collect samples that can be brought to Earth.
The Japanese Aerospace Exploration Agency (JAXA) is just getting ready to land the probe and has modeled the asteroid and bullet here on Earth to practice according to a press release. There was a delay in the scheduled touchdown after the scientists discovered that the composition of the asteroid deviated from their expectations.
According to the publication, Japanese scientists expected a "powdery regolith" on the asteroid. When the rovers of MASCOT and MINERVA-II1 were driven across the surface by Hayabusa2, they found that they were actually covered in centimeter-sized gravel. The team delayed the touchdown of the probe to make sure that the detection mechanism also works with the larger grain size.
In the researchers' tests, a similar 5-gram tantalum bullet was shot in a pebble at 300 meters per second in a vacuum chamber. Fortunately, these tests showed that the bullet breaks and releases enough material of the correct size for Hayabusa2 to collect samples.
The JAXA release notes indicate that the team has performed Earth gravity testing and that under the conditions of the asteroid under weightlessness, more rock is being released.
Hayabusa2 was founded in 2014 to meet with the asteroid Ryugu and to collect samples. Following the troubled but ultimately successful Hayabusa mission, NASA's OSIRIS-REx joins as one of two missions currently exploring asteroids at close range.
If successful, Hayabusa2 will harvest three samples of Ryugu's surface in December 2020 and return it to Earth in a capsule.