Space dust reveals Earth-killer asteroids tough to destroy

Good luck blowing up a pile of rubble. Boffins suggest we'll need to create a diversion instead

An asteroid named Itokawa that's been identified as potentially hazardous to Earth would be difficult to destroy, according to new research analyzing dust particles collected from the ancient rock.

Measuring 330 metres across, Itokawa is the first-ever asteroid to be sampled in a space mission. Japan's Aerospace Exploration Agency launched its Hayabusa 1 probe in 2003 to study Itokawa, and managed to return about a milligram of stuff taken from the asteroid's surface to Earth seven years later.

Now, an international team of researchers led by Curtin University, Australia, has studied three dust particles from the sample to estimate Itokawa's age and disposition. Argon dating revealed the asteroid is older than 4.2 billion years, and has been described as having a cushion-like structure. The team discovered Itokawa is older and tougher than previously thought. 

"Unlike monolithic asteroids, Itokawa is not a single lump of rock, but belongs to the rubble pile family which means it's entirely made of loose boulders and rocks, with almost half of it being empty space," Fred Jourdan, lead author of the research published in the in the Proceedings of the National Academy of Sciences and a geochemistry professor at Curtin University, said in a statement.

The gaps make rubble pile asteroids good at absorbing the shock from collisions. "We found that Itokawa is like a giant space cushion, and very hard to destroy," Jourdan added. Itokawa was originally formed from a monolithic ancient asteroid that fractured into pieces after a violent collision. Bits of leftover rock and dust coalesced into a rubble pile under gravitational forces to create Itokawa.

"Now that we have found they can survive in the solar system for almost its entire history, they must be more abundant in the asteroid belt than previously thought, so there is more chance that if a big asteroid is hurtling toward Earth, it will be a rubble pile," said Nick Timms, co-author of the paper and geology professor also from Curtin University.

He believes that studying these types of space rocks in more detail will help space agencies around the world develop strategies to prevent potential collisions. Since Itokawa would be difficult to destroy, creating a diversion may be a better way to steer it away from Earth.

"The good news is that we can also use this information to our advantage – if an asteroid is detected too late for a kinetic push, we can then potentially use a more aggressive approach like using the shockwave of a close-by nuclear blast to push a rubble-pile asteroid off course without destroying it," he said.

Last year, NASA demonstrated it was possible to knock an asteroid and change its orbit using kinetic impact in its DART mission. Lindley Johnson, NASA's Planetary Defense Officer, who helped lead the DART mission, previously told The Register that a potentially hazardous asteroid needs to be nudged about 8,000 miles to safely move it beyond the radius of Earth and outside of the danger zone. "That can easily be accomplished a year or two in advance," he said.

"We want to study more particles because each particle seems to tell its own unique story so we're excited to have access to four more particles that we're studying now," Jourdan told The Register.

"The second aspect is that we would recommend a space mission that would do exactly like DART but with a much more aggressive approach so maybe not a full nuclear explosion but which would still pack some serious explosive to see if what we predict with our study and what some numerical models predict as well is true. I think it's a good idea to test hypothesis like that when it's not really needed and not at the last moment when an asteroid is about to hit us. We are [also] very excited by the Osiris-Rex sample return mission which is going to bring back particle from rubble pile Asteroid Bennu, if all goes well, 23rd September 2023 this year. We can't wait to get our hands on some of these samples to see if Bennu formed as long ago as Itokawa," he concluded. ®