The asteroid belt could be just one big crucible of space rocks

The asteroid belt, a ring of rubble between Mars and Jupiter, has sometimes been thought of as abandoned remnants from the beginning of the solar system. But new research published in the journal Nature shows that the belt was actually formed during an unruly later era, when the planets themselves were in motion.

For decades, astronomers thought the belt was formed from the same cloud of dust and rock that formed our planets. This theory was based on sightings of a few asteroids in the 1980s. Astronomers have seen many more asteroids since then.

“There have been some very large surveys over the last decade that have expanded our understanding from a few thousand asteroids to hundreds of thousands of asteroids,” said Francesca DeMeo, an astronomer at the Harvard Smithsonian Center for Astrophysics.

When DeMeo and his co-author, Benoit Carry from the Paris Observatory, looked at all these new asteroids, they found something surprising. Many of the rocks seemed to come from somewhere outside the asteroid belt.

“What we see today in the asteroid belt is a kind of melting pot of asteroids that formed in different places in the solar system,” DeMeo explains.

The duo’s analysis upset old visions of the belt. “It’s really nice work,” says Kevin Walsh, theorist at the Southwest Research Institute. “They did a terrific job.”

But if asteroids came from everywhere, how did the belt come together?

The answer, Walsh says, could be planets. New theories suggest that in the beginning, our planets weren’t in pretty orbits. At the start of the solar system, 4.5 billion years ago, the nebula of dust and rock that formed the planets also dragged them by gravity. Later, says Walsh, the planets themselves may have been sent off in new directions.

Each time they left their ordered orbits, the planets passed through a cloud of asteroids. And as they moved, they shook those rocks, like flakes in a snow globe. According to this view, many asteroids “have been launched into the asteroid belt and have been implanted there,” says Walsh.

/ NASA/JPL/Institute of Space Sciences


Jupiter jostled planets and asteroids… like a boss.

Richard Binzel, planetary scientist at MIT, says that according to this view, planets are much more active than previous models suggested.

“They scatter asteroids, they throw them up, down, sideways. Some [asteroids] leave the solar system; some will crash in the sun,” he says.

These were quite large planetary deviations. Mars might have veered very close to Earth. And the largest planet in the solar system, Jupiter, may have dipped near Mars’ current position.

“Jupiter kind of ruled the roost and was kind of the big bully of the neighborhood,” Binzel says. “And as Jupiter migrated, he pushed and pulled and pulled everything else with him.”

In fact, Jupiter may have had a big impact – literally – here on Earth. The tilting of Jupiter in the inner solar system threw many asteroids towards us. Our planet has been beaten. Francesca DeMeo says the effect of this bombardment could have been profound.

“It could have caused some of the asteroids to hit Earth but deliver water at the same time, which could be why we have oceans on Earth and why Earth can support life,” he says. she. “But it can also cause destruction, where if you have too many asteroids raining down when life has already formed, then that’s a destructive force.”

Questions like whether asteroids brought life to Earth, or extinguished it, are yet to be answered. But this new survey of asteroids seems to confirm that giving birth to a solar system is more chaotic and dangerous than previously thought.

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