An artist’s impression of the early Solar System as the Solar Nebula begins to disappear, causing asteroids to accelerate and collide. Image credit: Tobias Stierli / Flaeck.

The First Inner Solar System Was Very Chaotic, Research Finds |

Planetary scientists from ETH Zürich and beyond have determined the isotopic compositions of palladium-silver (Pd-Ag) and platinum (Pt) of 13 iron meteorites that formed early in our system’s history solar.

Artist’s impression of the early solar system as the solar nebula begins to disappear, causing asteroids to accelerate and collide. Image credit: Tobias Stierli / Flaeck.

Iron meteorites are thought to represent the once-heated inner parts of planetesimals and are among the oldest bodies in our solar system.

As such, they are survivors of the many dynamic processes that have shaped the architecture of the solar system, including the dissipation of the protoplanetary disk and the runaway growth, migration, and reorganization of giant planets.

“Previous scientific studies have shown that asteroids in the solar system have remained relatively unchanged since their formation billions of years ago,” said lead author Dr Alison Hunt, a researcher at the Institute of Geochemistry. and petrology at ETH Zürich.

“So they are an archive, in which the conditions of the early solar system are preserved.”

“But to unlock this archive, we had to carefully prepare and examine the extraterrestrial material.”

The researchers took 18 samples from 13 different iron meteorites, which were once part of the metallic cores of asteroids.

To perform their analysis, they had to dissolve the samples to be able to isolate Pd, Ag and Pt.

Using a mass spectrometer, they measured the abundances of different isotopes of these elements.

“During the first million years of our solar system, the metallic cores of asteroids were heated by the radioactive decay of isotopes,” they said.

“As they began to cool, a specific Ag isotope produced by radioactive decay began to accumulate.”

“By measuring current Ag isotope ratios in iron meteorites, we were able to determine both when and how quickly the asteroid cores cooled.”

Their results show that the cooling was rapid and likely due to severe collisions with other bodies, which broke through the asteroids’ insulating rocky mantle and exposed their metallic cores to the cold of space.

While the rapid cooling had been indicated by previous studies based on isotopic measurements of Ag, the timing was unclear.

“Our additional measurements of Pt isotope abundance allowed us to correct Ag isotope measurements for distortions caused by cosmic irradiation of samples in space,” said Dr Hunt.

“So we were able to date the timing of the collisions more precisely than ever before.”

“And to our surprise, all of the asteroid nuclei we looked at were exposed almost simultaneously, within 7.8 to 11.7 million years of the formation of the solar system.”

The near-simultaneous collisions of the various asteroids indicated that this period must have been a very unstable phase of the solar system.

“Everything seems to have fallen apart at that point. And we wanted to know why,” Dr Hunt said.

The authors examined different causes by combining their results with those of the most recent and sophisticated computer simulations of the development of the solar system. Together, these sources could narrow the possible explanations.

“The theory that best explained this first energetic phase of the solar system indicated that it was mainly caused by the dissipation of the so-called solar nebula,” said lead author Professor Maria Schönbächler, also from the Institute. of geochemistry and petrology from ETH. Zürich.

“This solar nebula is the remnant of gas that was left behind by the cosmic cloud from which the Sun was born.”

“For a few million years it still circled around the young Sun until it was carried away by winds and solar radiation.”

While the nebula was still there, it slowed down objects orbiting the Sun – the same way air resistance slows down a moving car.

After the nebula disappeared, the lack of gas trail allowed the asteroids to speed up and collide with each other – like bumper cars going into turbo mode.

“Our work illustrates how improvements in laboratory measurement techniques allow us to infer key processes that took place early in the solar system – such as when the solar nebula was likely to depart,” Professor Schönbächler said.

“Planets like Earth were still being born at that time.”

“Ultimately, this can help us better understand how our planets came to be, but also give us insight into others outside our solar system.”

the study was published on May 23, 2022 in the journal natural astronomy.


Hunting AC et al. Dissipation of the solar nebula constrained by impacts and core cooling in planetesimals. Nat Astron, posted on May 23, 2022; doi:10.1038/s41550-022-01675-2

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