Rubble pile asteroids are hard to destroy

Rubble pile asteroids: Potato-shaped asteroid with small pebbles hovering all over it.
Rubble pile asteroids, such as the asteroid Itokawa, are not made from one large rock but from countless small pieces. This is an artist’s concept of Itokawa’s gravitationally bound rubble pile based on a 3D model of the asteroid. Image via Kevin Gill/ Doug Ellison/ NASA-JPL/ Curtin University.

While some asteroids are giant chunks of rock chipped off from larger bodies in collisions, many asteroids are just rubble piles. Rubble pile asteroids are gravitational collections of numerous boulders, rocks and pebbles. And, as researchers from Curtin University announced on January 24, 2023, unlike asteroids made of one large piece that last for a few million years, the rubble pile asteroids have been around for billions of years. In fact, they’ve been around since the beginning of our solar system. So that means these asteroids are hard to destroy, and that has important implications for the safety of our planet.

The scientists published their peer-reviewed results in the Proceedings of the National Academy of Sciences on January 23, 2023.

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Rubble pile asteroids are forever

Lead author Fred Jourdan, of Curtin University and director of the Western Australian Argon Isotope Facility, studied the rubble pile asteroid Itokawa. This 1,640-foot-long (500-meter-long) collection of space rocks lies about 1.25 million miles (2 million km) from Earth. It is about the size of the Sydney Harbour Bridge. Itokawa was the target of the Japanese Space Agency’s Hayabusa 1 probe.

Jourdan’s team of international scientists studied three of Itokawa’s dust particles that Hayabusa 1 returned to Earth. They made some intriguing discoveries. First, they found that Itokawa was hard to destroy and resistant to collision. And second, they said that Itokawa is almost as old as the solar system itself. Jourdan explained:

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. The survival time of monolithic asteroids the size of Itokawa is predicted to be only several hundreds of thousands of years in the asteroid belt.

But rubble piles are a different story. Jourdan continued:

The huge impact that destroyed Itokawa’s monolithic parent asteroid and formed Itokawa happened at least 4.2 billion years ago. We attribute such an astonishingly long survival time for an asteroid the size of Itokawa to the shock-absorbent nature of rubble pile material. In short, we found that Itokawa is like a giant space cushion and very hard to destroy.

Studying asteroid dust particles

One of the techniques the team used to study these precious dust particles is electron backscattered diffraction. This technique can measure if a meteor impact has shocked the rock.

A second method they used was argon-argon dating. This method allows measuring argon isotopes of a single grain of rock, which can date when asteroid impacts occurred.

Discovering the age of Itokawa helped the scientists understand how long similar asteroids survive and how many there might be in our solar system.

Helping protect Earth from collisions

Co-author Nick Timms of Curtin University explained how their studies added to their knowledge of these asteroids. Previously, scientists didn’t know the durability and lifespan of rubble pile asteroids. This unknown element meant that scientists had holes in their knowledge of how to protect Earth against a rubble pile hurtling toward Earth. Timms said:

We set out to answer whether rubble pile asteroids are resistant to shocks or whether they fragment at the slightest knock. 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.

Fortunately, this knowledge means we can prepare. Timms continued:

The good news is that we can also use this information to our advantage. If scientists detect an asteroid 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.

It’s comforting to know we have one more tool in our arsenal for protecting Earth in the long term.

Bottom line: Scientists discovered that rubble pile asteroids have been around since the beginning of the solar system and are very hard to destroy.

Source: Rubble pile asteroids are forever

Via Curtin University

January 26, 2023

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