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Hayabusa2's larger than expected crater has deep impact on asteroid age theories

The creation of the artificial crater on the asteroid Ryugu is seen in images taken by a camera deployed from Hayabusa2. The image shows debris emerging from the point of impact 192 seconds after the projectile hit the surface. The bar under the eruption represents a length of 25 meters. Image provided by the U.S. journal Science.

TOKYO -- The crater made on the surface of the asteroid Ryugu by Japanese space probe Hayabusa2 is semicircular and measures around 14.5 meters in diameter, according to data revealed by the Japan Aerospace Exploration Agency (JAXA), Kobe University and others.

The findings, published on March 20 in the electronic edition of the U.S. journal "Science," allowed researchers to estimate that Ryugu's surface formed between millions and tens of millions of years ago, based on how easy it was to make the crater. This would mean that the asteroid Ryugu has a very high chance of being a relatively young celestial object, particularly when considered within the estimated 4.6-billion-year history of our solar system.

The semicircular artificial crater on the asteroid Ryugu which was made by space probe Hayabusa2 is seen outlined in this image provided by JAXA, the University of Tokyo and others.

In April 2019, Hayabusa2 fired a copper impactor into the surface of Ryugu. The area around the point of impact had large rocks, and the copper ball deviated in one direction, causing a semicircular crater with a maximum depth of 2.3 meters.

The crater is seven times larger than any created in tests on Earth ahead of the mission, and its size has exceeded expectations. Although the surface of Ryugu is covered in many stones and rocks measuring from 10 centimeters to several meters across, it's believed that the asteroid's weak gravity -- only around one hundred-thousandth Earth's -- and its more fragile than anticipated surface contributed to the large crater.

Generally, celestial bodies with a lack of large craters on their surface -- meaning that they were hit by few objects -- are hypothesized to be 'young.' Ryugu does have large craters, but because it's now understood that it is an environment in which even small objects can create deep impacts, researchers estimate that the asteroid places on the younger end of its estimated age range of between 6 million and 200 million years.

Masahiko Arakawa, a professor of planetary science at Kobe University, said, "It was very surprising to see that a crater of this size was made. The results will force us to re-evaluate the surface age of other, similar asteroids."

(Japanese original by Tomohiro Ikeda, Science & Environment News Department)

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