For the past year, space probe Hayabusa2 has pelted asteroid Ryugu with bouncing probes, shot a bullet at it, and taken a bite of it—all for science. But now, the mission has performed its most daring manoeuvre yet: it dropped an explosive on the surface of the asteroid to create a small crater.
If the explosion went as planned—the mission team are yet to confirm the detonation—it will expose some of the asteroid’s subsurface layers that the probe will gather during a later touchdown.
The operation took place on 5 April. First, the probe lowered itself from a parking altitude of 20 kilometres down to 500 metres above the asteroid’s surface. From there it dropped an explosive device. After partially ascending, it then released a second device carrying a camera. The Japan Aerospace Exploration Agency (JAXA) confirmed that the probe had released the device and was safe at 11:56 am Japan time (3:36 am UT).
"We conducted a lot of experiments, but when we did this for real, I was still very nervous," said Osamu Mori, an engineer from JAXA's Institute of Space and Astronautical Science (ISAS) in Sagamihara who was involved in the operation of the impactor, during a live broadcast.
In Ryugu’s extremely weak gravity, the bomb took about 40 minutes to reach the surface. Meanwhile, the spacecraft manoeuvred itself to a safe zone behind the asteroid. That way, when the 9.5 kilograms of explosive charge went off, the debris it kicked up could not harm the probe. The one-use camera device, however, was still hovering above the target, ready to take pictures of the explosion and upload them back to the mother ship via a radio link.Images will confirm whether the charge detonated and created a crater.
Hayabusa2’s mission manager Makoto Yoshikawa, also from ISAS, told Nature in June that the manoeuvre would be “a very risky operation”, but one with big potential payback. The experiment will give astronomers the opportunity to study material under the asteroid's surface, which can shed light on the early Solar System.
In the following weeks, the probe will image the crater from high up. Then at a later date, mission scientists plan to execute the final major step of the mission. They will lower the probe right into the crater and collect a sample. This will be the second sample collected from Ryugu: Hayabusa2 already touched down on 22 February, and collected some of its space dirt after kicking it up with a bullet.
Space agencies have blown craters on Solar System bodies before. In 2005, NASA’s Deep Impact mission released a washing-machine-sized impactor at high speed onto a comet called Tempel 1. And on multiple occasions over the decades, researchers have sent impactors and deliberately crashed probes on the Moon’s surface—including most recently the Lunar Atmosphere and Dust Environment Explorer—and studied the effects.
Hayabusa2 left Earth in late 2014 and arrived at Ryugu in June 2018. In two separate phases in September and October, it then released three small probes onto the surface. The spacecraft is scheduled to head back to Earth before the end of 2019. A year later, a re-entry capsule will take samples down with it so that scientists can study them in their labs.
This article is reproduced with permission and was first published on April 5, 2019.