Samples Brought Back From Asteroid Itokawa Reveal ‘Rubble Pile’ Had a Violent Past

Curtin University planetary scientists have shed some light on the evolution of asteroids, which may help prevent future collisions of an incoming ‘rubble pile’ asteroid with Earth.
The scientists studied two incredibly small particles brought back to Earth from the asteroid Itokawa, after they were collected in 2005 from the surface of the 500 metre-wide asteroid, by the Japanese Hayabusa spacecraft.

The capsule and its precious cargo returned to Earth in 2010, landing near Woomera, Australia with only about 1500 asteroid dust particles on board – most of them much smaller than the width of a human hair.

The Geology-published research, Collisional history of asteroid Itokawa, used the Argon-Argon dating technique to investigate when impact crater events happened on Itokawa, offering a glimpse into the asteroid’s impact history.

Lead author of the study, Associate Professor Fred Jourdan from the Department of Applied Geology within the Curtin WA School of Mines, explained Itokawa was no ordinary asteroid, with fly-by pictures taken by Hayabusa prior to sampling in 2005 showing it had a peanut-like shape and resembled a rubble pile of boulders and dust more than solid rock.

“In fact, analyses by Japanese scientists revealed the asteroid had a violent past. Prior to being a rubble pile, Itokawa was part of a much larger asteroid that was destroyed by a collision with another asteroid. Our job was to try to find out when that collision happened,” Dr Jourdan said.

Dr Jourdan explained that the analyses were not without challenges, due to the extremely small size of the particles.

“Using our noble gas mass spectrometer at Curtin University, a revolutionary new machine that we customised for extra-terrestrial samples, we were able to measure tiny amounts of gas and analyse these fragments from Itokawa,” Dr Jourdan said.

“The impact-shocked particle indicated a small-scale collision that occurred 2.1 billion years ago, whereas the other non-shocked particle preserves a very old age, similar to the formation age of the solar system itself.”

According to these results and a series of models, the scientists concluded that asteroids do not always break up due to a single cataclysmic impact. Instead, they can internally fragment due to the medium-sized collisions that constantly batter large asteroids until they shatter from impact.

“The final impact could be seen as ‘the straw that broke the camel’s back’,” Dr Jourdan said.

“Our results tell us that Itokawa was already broken and re-assembled as a rubble pile about 2.1 billion years ago, showing that ‘rubble pile’ asteroids can survive a much longer time in this state than researchers previously thought.

“This is due to their cushion-like nature and the abundance of dust in between the boulders.”

He continued to explain these research results are not only important to understand how our solar system works, but can inform us on the best way to prevent any future collisions of an incoming ‘rubble pile’ asteroid with Earth.

Due to the success of the team’s study, they have been awarded four new particles from Itokawa, and will now look for more information to be unlocked from this asteroid.

Manager of the Curtin Argon-Argon Laboratory Ms Celia Mayers said the team plans to work on samples from the Hayabusa 2 mission, which is on its way to Asteroid Ryugu, and is anticipated to bring back samples in 2020.

“We also recently set up a collaboration with China that plans to bring back samples from the moon in a few years,” Ms Mayers said.

Dr Jourdan and his colleagues at Curtin University conducted their research at the John de Laeter Centre.

Professor Fred Jourdan is available for interview today, please contact the Curtin media team for assistance.

About Curtin University

Curtin University is Western Australia’s largest university, with more than 58,000 students. Of these, over 15,000 are international students. The University’s main campus is in Bentley near the Perth CBD. Curtin has five other campuses across WA, Malaysia and Singapore, with a new campus opening in Dubai in 2018. Curtin also has presence at a number of other global locations.

Curtin is celebrating ’50 Years of Innovation’ in 2017 – the combined history of the Western Australian Institute of Technology (WAIT), which opened its doors to students in 1967 and Curtin University, which opened in 1987. Today, Curtin is estimated to be ranked 180th and in the top one per cent of universities worldwide, and 9 th in Australia in the highly regarded Academic Ranking of World Universities 2017 (ARWU), and features highly in a number of other key world rankings. The University has built a reputation around innovation and an entrepreneurial spirit, being at the forefront of many high-profile research projects in astronomy, biosciences, economics,mining and information technology. It is also recognised globally for its strong connections with industry, and for its commitment to preparing students for jobs of the future. For further information visit curtin.edu.au.