Jason DavisMay 03, 2019

Here’s an Update on Hayabusa2’s Crater-Creating Explosion

We already knew that Hayabusa2 successfully fired a copper plate into asteroid Ryugu, and that the spacecraft found the resulting crater on 25 April. Now, thanks to a newly translated JAXA press briefing, English speakers have a few more details about how the ambitious operation went.

Hayabusa2: Japan's mission to Ryugu and other asteroids

Japan's Hayabusa2 spacecraft returned a sample from asteroid Ryugu to Earth in December 2020.

Hayabusa2 imaged its explosive-packed SCI experiment after deployment on 5 April with both thermal and optical cameras. JAXA says SCI separated from Hayabusa2 at about 20 centimeters per second, fell towards Ryugu for 40 minutes, and detonated about 300 meters above the surface. A detail I found particularly fascinating was that due to Ryugu's 7.6-hour rotation period, Hayabusa2 had to drop SCI about 30 degrees east of its target region! 

Hayabusa2 SCI deployment
Hayabusa2 SCI deployment This animation shows Hayabusa2 deploying its SCI explosives package 500 meters above Ryugu on 4 April 2019. The frames were captured every 2 seconds by Hayabusa2's Thermal Infrared Imager and have been sped up.Image: JAXA / Edited by Jason Davis

After deploying SCI, Hayabusa2 fled behind Ryugu to avoid any debris from either the explosive device itself or material flying off the surface. The spacecraft was about 1 kilometer to the west and 3.5 kilometers behind Ryugu when detonation occured. DCAM3, the small camera Hayabusa2 left behind to watch the explosion and relay pictures, worked exactly as planned. Its analog camera worked for 20 minutes and captured 500 images before the battery ran out, while the digital camera worked for 3 hours and 20 minutes.

Compare this image from the digital camera with a 2017 rendering of what scientists thought it might look like. Not bad:

Hayabusa2 SCI impact (DCAM3 digital camera)
Hayabusa2 SCI impact (DCAM3 digital camera) Hayabusa2's deployable DCAM3 digital camera caught this view of debris spreading from Ryugu approximately 3 seconds after the SCI experiment detonated on 5 April 2019.Image: JAXA
Hayabusa2 simulated DCAM3 view
Hayabusa2 simulated DCAM3 view A simulated view of what DCAM3 might see during the Hayabusa2 SCI experiment.Image: Saiki et. al (2017)

After the SCI detonation, Hayabusa2 flew on a long, looping track that took it more than 100 kilometers from Ryugu. JAXA confirmed the spacecraft returned to its 20-kilometer home position on 20 April, and on 23 April it began descending to a height of just 1.6 kilometers to search for the crater it made. The crater ended up being easy to find!

Hayabusa2 SCI impact before and after
Hayabusa2 SCI impact before and after This animation shows a 20-meter wide crater created on Ryugu after Hayabusa2's SCI experiment struck the surface with a copper impactor on 5 April 2019. The before and after pictures were taken on 22 March and 25 April 2019. The images were captured using the spacecraft's Optical Navigation Camera - Telescopic.Image: JAXA, The University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, The University of Aizu, AIST

The area affected by the blast is roughly 20 meters wide—much bigger than JAXA scientists expected it to be. "We did not expect such a big alternation so a lively debate has been initiated in the project!" the Hayabusa2 Twitter account reported.

JAXA is now considering whether to collect a second sample for return to Earth, either from the newly created crater or a different location. That sample collection wouldn't happen until June or later. The spacecraft is set to leave Ryugu in November or December 2019, and return to Earth in late 2020.

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