Japan Bombed An Asteroid 300 Million Kilometers Away, Here’s What They Found

Japan's Hayabusa2 spacecraft—which is not returning to Earth with samples of the asteroid—bombed the space rock in 2019. Here's what it found after having created a crater on the surface of the asteroid.

The Japanese national Space Agency (JAXA) made its Hayabusa-2 spacecraft—in orbit around Ryugu—bomb the asteroid orbiting the sun at around 300 Million Kilometers from Earth in order to dig up some material from its surface in order to study it. Ryugu orbits the sun between the orbit of Earth and Mars.

The spacecraft launched a copper “bomb” the size of a tennis ball, creating a crater on the surface of the asteroid.

Now, JAXA has revealed that the bombing of the asteroid revealed stunning details about the space rock, revealed among other things its composition and age.

The impact produced by Hayabusa2’s Small Carry-on Impactor (SCI) created a crater on the surface of Ryugu approximately 10 meters wide. The projectile whose weight was just around two kilograms was fired at a velocity of 2 km/s. The spacecraft launched the SCI on 5 April 2019.

The result was a column of ejected material that was captured by the spacecraft as it flew over the cloud of debris.

The analysis of the debris gathered by the spacecraft, conducted by scientists at Kobe University and published in Science, suggests that Ryugu’s surface is about 8.9 million years old, while other models suggest that the asteroid’s surface could be up to about 158 million years old.

Scientists say that while Ryugu is made of materials up to 4.6 billion years old, the asteroid could have fused with the remains of other broken asteroids only about 10 million years ago, explained  Masahiko Arakawa, lead researcher of the study.

A sequence of images photographed by the Hayabusa2 spacecraft showing the SCI impacting the surface of asteroid Ryugu. Image Credit: JAXA.
Image Credit: JAXA.

Furthermore, scientists suggest that Ryugu’s surface is made of a cohesion-free material, similar to loose sand.

The number and size of craters spotted on asteroids like Ryugu can be used in subsequent studies to determine the age and surface properties of asteroids.

However, these studies require a general understanding of the nature of crater formation – the crater scale laws – which is often derived from laboratory experiments or numerical simulations.

Arakawa and colleagues use observations from the SCI impact experiment to test the crater scale laws and obtain new, unprecedented data from the surface of Ryugu.

They describe the artificial impact crater as semicircular with a raised rim, a central hole, and an asymmetric ejection pattern, perhaps due to the presence of a large buried rock near the point of impact.

The results suggest that the crater grew in the gravity-dominated regime, where the size of the crater is limited by the local gravitational field, a discovery that, according to the authors of the new study, has implications for estimates of the surface age of asteroids.

The Hayabusa2 spacecraft reached the near-Earth asteroid (162173) Ryugu in June 2018, finding that this one-kilometer-long asteroid is covered with boulders with sizes up to approximately 160 meters.

The surface is covered with a regolith layer composed of boulders and granules.

Hayabusa2 is no longer in orbit around asteroid Ryugu. After a successful mission, JAXA ordered the spacecraft to begin its journey back to earth in November 2019. The spacecraft is expected to deliver the material it gathered from the asteroid to scientists on Earth.

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