Tuesday, 20 Apr 2021

Asteroid ‘barely moves’ after being shot with bullet by baffled scientists

An attempt to “bomb” an asteroid with a five-pound copper projectile had a much smaller effect than expected – leading scientists to conclude that asteroids are better at soaking up damage than previously thought.

The results of the 2019 experiment were revealed in a virtual presentation at the Lunar and Planetary Science Conference on 15 March by Gaku Nishiyama at the University of Tokyo.

He described how, on April 5 2019, Japan’s Hayabusa 2 spacecraft fired a single-shot “gun” at asteroid Ryugu, using a 10lb explosive propellant charge.

The “bullet”, a Small Carry-on Impactor, was a 2.5 kg (5.5 lb) copper projectile deigned to leave a fresh crater on the asteroid's surface for scientists to study.

While the bullet left a crater some 33 feet across, scientists also expected its impact to send shockwaves through Ryugu. However its actual effect was far milder.

“Significant boulder movement was expected,” said Nishiyama. “However, such large boulder movement has not been observed.”

Researchers from JAXA, Japan’s equivalent to NASA, have concluded that the ancient asteroid must be very good at absorbing seismic waves – in the region of 100 times more efficient than the Moon.

They speculate that this is because the surface dust on Ryugu is much coarser than moondust, scattering the energy from seismic waves much more efficiently.

However, that leaves the question of what is flattening out Ryugu’s smaller craters. It has no atmosphere, no seismic activity of its own, and now it appears that the space rock can’t be shaken by external impacts.

Images from Hayabusa 2's cameras reveal that Ryugu has fewer small craters on its surface than expected for an asteroid of its size, suggesting that something is moving dust into the craters to fill them in.

Ryugu is thought to date back to the earliest moments of the Solar System’s existence, preserving the chemistry of minerals, ice, and organic compounds that would have existed on the Earth before the emergence of life.

Samples from the asteroid were returned to the Earth in December 2020, and scientists believe the carbon-rich asteroid fragments could provide clues about how water and organic molecules were interacted on the young Earth.

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