Artist impressions show Hayabusa2 releasing the Small Carry-on Impactor (left) and the projectile hitting the asteroid, with an observation camera in the foreground and Hayabusa2 in the distance, behind the asteroid (right).
JAXA
By Dennis Normile
Japan’s Hayabusa2 mission continued its unprecedented explorations today by apparently creating an artificial crater in an asteroid, a space exploration first. Officials confirmed that the operation to fire a projectile into asteroid Ryugu went smoothly, though as of early evening Japan time they were still trying to confirm whether a crater had actually been formed. If so, its exact location and size will have to be confirmed later.
Developed by the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Science in Sagamihara, Hayabusa2 was launched in December 2014 and traveled 3.2 billion kilometers through space before reaching its home position 20 kilometers away from Ryugu, a diamond-shaped asteroid about 1 kilometer by 900 meters in size orbiting between Earth and Mars.
The mission’s objective is to collect samples both from Ryugu’s surface and its interior and return them to Earth for analyses that should yield information on the materials that existed in the early solar system and give clues about the formation and evolution of planets. The samples might also provide evidence for the theory that asteroids and comets are one source of Earth’s water and its amino acids, the building blocks of life. Scientists are particularly eager to get material from beneath the surface that has not been affected by eons of space weathering.
In February, Hayabusa2 briefly landed on Ryugu and fired a tantalum pellet into the surface that likely knocked about 10 grams of rock fragments into a collection horn. Getting subsurface material is more of a challenge. Landing on and drilling into the asteroid was logistically impractical, mission planners concluded. They also rejected using explosives to blast a crater, as that would contaminate the samples. They settled on shooting a nonexplosive, 2-kilogram copper projectile into Ryugu from space, by detonating explosives on a tiny, 14-kilogram spacecraft dubbed the Small Carry-on Impactor (SCI).
Earlier today, Hayabusa2 descended to 500 meters above the asteroid and released the SCI. The mothership moved away laterally and about 19 minutes later released another tiny satellite carrying two cameras to record the projectile’s impact. The craft then continued to the far side of Ryugu to be shielded from any debris from the SCI explosion and from the crater.
The SCI carried 9.5 kilograms of a plastic explosive packed into a conical chamber capped at the base by a saucer-shaped plate of copper. A timer on the SCI was set to give Hayabusa2 40 minutes to reach safety before triggering the explosive. The force of the explosion was expected to punch the copper plate into a bullet-nosed missile about the size of a baseball that would hit the asteroid traveling at about 2000 meters per second. The resulting crater could be several meters in diameter, depending on the characteristics of the asteroid’s rock.
Images and data from Hayabusa2 indicate the separation of SCI and the camera to observe the impact went smoothly, mission manager Makoto Yoshikawa reported at an afternoon press briefing. Further data from the spacecraft indicate that it was not hit by any debris and is operating normally as it moves to its home station 20 kilometers from the asteroid. As of late Friday evening Japan time, mission officials were analyzing images from the deployed camera to confirm whether the crater was created.
Mission controllers will wait until the week of 22 April for debris to settle and then send Hayabusa2 back to examine the crater remotely. If they can identify a suitable site, they will then land Hayabusa2 in or near the crater to collect samples. The craft could make a third touchdown to collect more samples from the surface. If all goes well, Hayabusa2 will return its treasures to Earth in 2020.
Source: Science Mag