A daring mission to collect dust samples from a kilometer-wide space rock hurtling around the Sun is soon to reach a critical juncture, with mission scientists in Japan preparing to lower their Hayabusa 2 probe to the surface of the asteroid Ryugu. As part of this objective, the team will fire metal bullets into the asteroid's gravely surface, but not without having conducted a dress rehearsal first.
The Hayabusa 2 mission launched in 2014 and began to really close in on its target late last year. As the successor to the Japanese Aerospace Exploration Agency's (JAXA) historic Hayabusa mission, which is the only spacecraft to safely return material from a solar system asteroid to Earth, Hayabusa 2 is designed to perform close examinations of the asteroid Ryugu using a next-generation suite of hardware.
That includes a pair of rovers, which were deployed to the surface in September and sent bouncing across the surface. These robotic hoppers used cameras and sensors to image the surface and gather temperature data, with the intel collected then used to determine the landing spot for the Hayabusa 2 spacecraft. Once it lands, the spacecraft will fire a projectile into the surface to stir up material for collection by its sampling arm.
The scientists had been expecting a fine regolith on the surface of Ryugu, but their observations so far have painted a different picture. Rather than a powdery surface, the hopping robots together with a larger rover have revealed chunky gravel measuring a centimeter across or larger, which called for some further investigations into the safety of the maneuver.
Conveniently, when manufacturing the projector that will be used to blast the surface of the asteroid, the team produced a few spares, along with some extras of the projectiles themselves. This allowed them to work with scientists at the University of Tokyo's to put together an experiment simulating its moment of truth.
The team prepared a large container of artificial gravel made to simulate carbonaceous chondrite meteorite, in the same size and strength scientists now expect to find on the surface. A bullet was then fired at the material inside a vacuum chamber with a high-speed camera used to capture the results.
These exceeded the scientist's expectations, with the simulations indicating that the sampling arm would be able to gather more material than they had anticipated. They found that fragments of gravel crushed on impact smashed into the surrounding gravel and busted it up like a set of billiard balls. They expect the haul to be even greater under the microgravity environment of Ryugu, compared to normal Earth gravity.
Following these precautionary experiments, mission control has now determined it is safe to proceed and today announced that touchdown of Hayabusa 2 is scheduled for this Friday. If everything goes to plan, the spacecraft will spend around 18 months at Ryugu and return its samples to Earth for study in late 2020.
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