The asteroid belt could bear the scars of migrating planets

The distribution of rocks in the asteroid belt has preserved traces of the migration of giant planets billions of years ago, a new simulation suggests (Illustration: D Minton/R Malhotra)

Today’s asteroid belt may have been shaped by a tumultuous time in the early solar system when Jupiter and Saturn spun out of their original orbits, according to a new simulation. Ultimately, the work could help refine a picture of how fast the planets moved and where they started.

Recent studies have suggested that many objects in the solar system were reworked nearly 4 billion years ago. Jupiter, Saturn, Uranus and Neptune are believed to have originated close to each other before gravitational interactions with extensive rocky debris altered their trajectories.

Their movement then caused rocky debris to scatter like skittles, potentially explaining what hit the Earth, Moon and Mars with so many craters around 3.8 billion years ago.

However, this same rearrangement could explain the appearance of the main asteroid belt between Mars and Jupiter.

Several grooves in the belt appear to be void of asteroids. Called Kirkwood gaps, they are thought to be cleared of debris by Jupiter’s gravity, causing all objects in orbit to move chaotically. Saturn’s moons have produced similar gaps in the planet’s rings.

David Minton and Renu Malhotra at the University of Arizona in Tucson wanted to reproduce the asteroid belt and its gaps in a computer simulation.

Position change

Using the current orbits of the giant planets Jupiter, Saturn, Uranus and Neptune, the team was able to roughly reproduce the observed distribution of asteroids over a simulated period of around 4 billion years.

But they were much luckier when they started with the best estimates of the locations of giant planets early in the solar system’s history. It is believed that the four planets started relatively close to each other. Then Jupiter moved inward while Saturn, Uranus and Neptune moved outward.

“We are able to produce an asteroid belt that looks much more like the observed asteroid belt than a model that only uses the giant planets in their current positions,” Minton says.

Erosion Belt

In this version of the simulation, two of the spaces in the belt showed a distinct signature: a sharp inner edge and a smudged and relatively empty outer edge.

This is what we would expect if Jupiter dug the holes during its migration to the Sun. In this case, the inner edges of the gaps represent where Jupiter stopped in its migration, Minton explains. Such a “profile” of deviation is closer to the observed distribution of asteroids than the team’s other simulation using the planets’ current orbits, he adds.

Saturn’s outward migration also appears to have left its mark on the asteroid belt. But in Saturn’s case, it was on the inner edge of the whole belt – not the gaps. At the inner edge of the belt, asteroids were lost as their orbits were destabilized by the natural oscillation of Saturn’s orbit over time. This erosion continued as Saturn moved outward, so the inner edge of the belt is determined by the ringed planet’s current orbit.

Migration speed

In the simulation, the belt lost 62% of its original asteroid population due to the migration of giant planets. But some estimate that the real asteroid belt has actually lost 90-95% of its asteroids.

The slower the migration of planets, the more asteroids will be lost due to gravitational interactions with them. “If the planets moved too slowly, you wouldn’t have an asteroid belt,” Minton said. new scientist.

By refining the model, astronomers could get a better idea of ​​how long the migration takes and where the planets originated, he adds.

And if chased asteroids are responsible for the late heavy bombardment that hit the Earth, Moon and Mars 3.8 billion years ago, belt modeling could also help determine how long the explosion lasted.

Journal reference: Nature (flight 457, page 1109)

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