Chaotic early phase of the solar system

(ORDO NEWS) — Before the formation of the Earth and other planets, the young Sun was surrounded by cosmic gas and dust. Over the millennia, rock fragments of various sizes formed from the dust.

Many of these became the building blocks for subsequent planets. Others did not become part of the planet and continue to orbit the Sun today, for example, in the form of asteroids in the asteroid belt.

Researchers from ETH Zurich and the National Center for Competence in Scientific Research (NCCR) PlanetS, in collaboration with an international team, have analyzed iron samples from the cores of such asteroids that have fallen to Earth as meteorites.

In doing so, they revealed part of their early history during the formation of the planets. Their findings were published in the journal Nature Astronomy.

Witnesses to the early solar system

“Previous scientific studies have shown that asteroids in the solar system have remained relatively unchanged since their formation billions of years ago,” explains lead author of the study, ETH Zurich and NCCR PlanetS scientist Alison Hunt.

“Therefore, they represent an archive in which the conditions of the early solar system have been preserved,” says Hunt.

But to open this archive, the researchers had to carefully prepare and study extraterrestrial material. The team took samples from 18 different iron meteorites that were once part of the metal cores of asteroids.

To carry out the analysis, they had to dissolve the samples in order to isolate the elements palladium, silver and platinum for their detailed analysis. Using a mass spectrometer, they measured the abundance of various isotopes of these elements.

Isotopes are individual atoms of given elements, in this case palladium, silver and platinum, that have the same number of protons in the nucleus but differ in the number of neutrons.

In the first few million years of our solar system’s existence, the metallic cores of asteroids were heated by the radioactive decay of isotopes. When they began to cool, they began to accumulate a special isotope of silver, formed as a result of radioactive decay.

By measuring the current ratio of silver isotopes in iron meteorites, the researchers were able to determine when and how quickly the asteroid cores cooled.

The results showed that the cooling was rapid and most likely due to violent collisions with other bodies that tore apart the asteroids’ insulating rocky mantle and exposed their metal cores to the cold of space. While previous studies based on measurements of silver isotopes had indicated rapid cooling, the timing remained unclear.

“Our additional platinum isotope measurements allowed us to correct silver isotope measurements for distortions caused by cosmic irradiation of samples in space. Thus, we were able to determine the timing of collisions more accurately than ever before,” says Hunt.

“And to our surprise, all the asteroid cores we studied were irradiated almost simultaneously, in the time interval from 7.8 to 11.7 million years after the formation of the solar system,” the researcher says.

The near-simultaneous collisions of various asteroids indicated to the team that this period must have been a very turbulent phase of the solar system. “It seems like everything was falling apart at the time,” says Hunt. “And we wanted to know why,” she adds.

The team looked at various causes, combining their findings with those from the latest, most sophisticated computer simulations of the solar system’s development. Together, these sources were able to narrow down the range of possible explanations.

“The theory that best explained this energetic early phase of the solar system was that it was caused primarily by the dissipation of the so-called solar nebula,” explains study co-author, NCCR PlanetS member and professor of cosmochemistry at ETH Zurich, Maria Schönbechler.

“A solar nebula is a remnant of gas that was left from the cosmic cloud from which the Sun was born. For several million years, it orbited the young Sun until it was blown away by solar winds and radiation,” says Schönbechler.

While the nebula still existed, it slowed down the movement of objects orbiting the Sun, much like air resistance slows down the movement of a car. After the nebula disappeared, the researchers speculate, the lack of gas drag allowed the asteroids to accelerate and collide with each other, like bumper cars put into turbo mode.

“Our work illustrates how improvements in laboratory measurements allow us to infer key processes in the early solar system, such as the probable time of the disappearance of the solar nebula.

At that time, planets like Earth were still in the process of birth. Ultimately this could help us better understand how our own planets were born, as well as give us insight into other planets outside of our solar system,” Schoenbechler concludes.

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