Asteroid Itokawa was visited by the Earth-collecting spacecraft Hayabusa in 2005. Since the spacecraft returned to Earth in 2010, many research teams have examined the collected space Earth. New findings now show that the asteroid is both older and more durable than previously thought – something that is an important insight for future planetary defense.

The international research team, led from Curtin University in Australia, gained access to three small soil particles. Altogether, Hayabusa returned with 1,500 such, most less than 10 micrometers. The Japanese spacecraft is the first to have collected soil from an asteroid.

The asteroid is old and resilient

Itokawa was discovered in 1998 during the Linear project and is roughly 500 meters wide. The stone was renamed from 1998 SF₃₆ to its current name with the Hayabusa project. The name is a tribute to the Japanese rocket scientist Hideo Itokawa who passed away in 1999.

The asteroid, like most smaller asteroids, is not monolith. This means that it does not consist of one piece of rock, but is a so-called “rubble pile” or “stone pile asteroid” – an accumulation of gravel and boulders held together by gravity.

– We wanted answers to whether rocky asteroids are resistant or whether they break apart at the slightest push, says Associate Professor Nick Timms from Curtin University in a press release about the new study.

According to the researchers, Itokawa formed at least 4.2 billion years ago from a larger monolith asteroid. The fact that Itokawa has survived for so long means that it is very shock absorbent. Comparatively, scientists believe that monolith asteroids of the same size can survive in the solar system’s asteroid belt for a few hundred thousand years.

– In short, we discovered that Itokawa is like a giant “space air cushion” and very difficult to destroy, says Professor Fred Jordan, the main author of the scientific text, in the press release.

The research is important for future planetary defense

The researchers used two different methods to analyze the three particles. Partly a kind of electron microscope with which they could see if the rock had collided with other space rocks. As well as argon-argon dating, a method that uses the decay from Potassium-40 to Argon-40 to determine the age of geological events.

Knowing that Itokawa has survived so long in the solar system indicates that many asteroids should be composite piles of gravel. Any threats heading towards Earth in the future can then be expected to be rocky asteroids. The fact that they are more shock-absorbing than was previously thought, the researchers see as a good sign.

– The good news is that we can use this knowledge to our advantage – if an asteroid is detected too late for a kinetic nudge, we can potentially use a more aggressive approach such as using the shock wave from a nearby nuclear bomb explosion to push the rock-hewn asteroid off course without to destroy it, says Nick Timms in the press release.

A kinetic nudge is exactly what was carried out with Project Dart where a space probe was driven into an asteroid moon to try and throw it off course. That test was conducted to see if asteroid trajectories can be changed well before they reach Earth, all to ward off future space collisions.

Water has been found on both Itokawa and Ryugu

A lot of research has been done on the collected soil particles from Itokawa since 2010. Among other things, a research group, using atomic probe tomography, managed to find water in the dust. Similar results have also been obtained from samples of asteroid Ryugu.

Ryugu was visited by Hayabusa’s successor in 2018 – the spacecraft returned to Earth orbit in 2020 and dropped a capsule containing about 5 grams of asteroid soil. In addition to water, the samples have, among other things amino acids found again. The amino acids were found by scientists who were searching for organic materials.

Hayabusa 2 has had its mission extended following the successful ground retrieval on Ryugu. The spacecraft is now headed for asteroid 1998 KY₂₆ and expected to arrive in 2031. 1998 KY₂₆ rotates very quickly compared to Itokawa and Ryugu, the asteroid has a rotation time of just over ten minutes.

Another similar project is Nasaledda Osiris rex which is currently returning from asteroid Bennu with soil samples. The spacecraft was launched in 2016 and managed to pick up soil from Bennu in October 2020. Osiris-rex will return to Earth in September this year and is expected to bring up to a good kilogram of asteroid soil, the original goal was to collect at least 60 grams.