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Solar system’s shape has changed dramatically, scientists say : ScienceAlert

Solar system’s shape has changed dramatically, scientists say : ScienceAlert

The shape of the solar system was once a bit more on the doughy side.

Before it arranged itself into a flattened disk, the distribution of dust and rocks looked more like a doughnut than a pancake. This is the conclusion reached by scientists after studying iron meteorites from the outer parts of our solar system. They found that they can only be explained if the shape of the solar system was once a toroidal core.

This information can help us interpret other emerging planetary systems and determine the order in which they form.

The formation of a planetary system around a star begins in a molecular cloud of gas and dust drifting through space. If a part of the cloud becomes dense enough, it will collapse under its own gravity, spinning around and becoming the seed of a growing baby star. As it spins, material in the surrounding cloud is pulled into a spinning disk that feeds the protostar.

Within that disk, smaller clumps form, becoming protoplanetary seeds that either continue to grow into full planets or, what seems much more common, have their development halted and remain as a smaller object like an asteroid.

We’ve seen these disks around other stars time and time again, with holes carved out by planets slurping up the dust along the way.

But iron meteorites found here in our own solar system tell a different part of the story.

According to a team led by planetary scientist Bidong Zhang of the University of California Los Angeles, the composition of asteroids in the outer solar system requires the cloud of material to be doughnut-shaped, rather than a series of concentric rings in a flat disk. This suggests that the early stages of the system’s merger are toroidal.

The iron meteorites in question – chunks of rock that have made their long journey to Earth from the outer solar system – are richer in refractory metals than those found in the inner solar system. These are metals such as platinum and iridium, the formation of which can only occur in a very hot environment, such as near a forming star.

This is a bit of a tricky problem, because those meteorites didn’t come from the inner solar system, but from the outer one, meaning they must have formed close to the sun and moved outward as the protoplanetary disk expanded. However, according to the modeling conducted by Zhang and his colleagues, these iron objects would not have been able to traverse gaps in a protoplanetary disk.

According to their calculations, the migration would have been easiest if the protoplanetary structure had a toroidal shape. This would have guided the metal-rich objects to the outer edges of the forming solar system.

As the disk cooled and the planets began to form, the inability of the rocks to travel through the openings in the disk acted as a very effective fence, preventing them from migrating back toward the Sun under the influence of gravity.

“When Jupiter formed, a physical gap most likely opened up, trapping the metals iridium and platinum in the outer disk and preventing them from falling into the Sun,” Zhang said.

“These metals were later incorporated into asteroids that formed in the outer disk. This explains why meteorites formed in the outer disk – carbonaceous chondrites and carbonaceous iron meteorites – have much higher iridium and platinum contents than their counterparts in the inner disk.”

It’s amazing what you can learn from a piece of grooved, metallic rock.

The research has been published in the Proceedings of the National Academy of Sciences.