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.

Early Inner Solar System Was Very Chaotic, Study Suggests |

Planetary scientists from ETH Zurich and elsewhere have determined the palladium-silver (Pd-Ag) and platinum (Pt) composition of 13 iron meteorites formed early in our solar system’s history.

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.

Iron meteorites are thought to represent the once-warmed inner parts of planetesimals and are some of the earliest formed bodies in our solar system.

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

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

“But to unlock this archive, we had to thoroughly prepare and research the alien 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 in order to isolate Pd, Ag and Pt.

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

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

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

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

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

Although the rapid cooling had been indicated by previous studies based on Ag isotope measurements, the timing had remained unclear.

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

“This allowed us to date the timing of the collisions more accurately than ever before.”

“And to our surprise, all of the asteroid cores we examined were exposed almost simultaneously, within the span of 7.8 to 11.7 million years after the solar system formed.”

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

“Everything seems to have been beaten up at that time. And we wanted to know why,” said Dr. hunt.

The authors considered several causes by combining their results with those from the latest, most advanced computer simulations of solar system development. Together, these sources could narrow down the possible explanations.

“The theory that best explained this energetic early phase of the solar system indicated that it was mainly caused by the dissipation of the so-called solar nebula,” said senior author Professor Maria Schönbächler, also of the Institute of Geochemistry and Petrology at ETH Zurich. .

“This Solar Nebula is the rest of the gas left over from the cosmic cloud from which the sun was born.”

“For a few million years it still revolved around the young sun until it was blown away by solar winds and radiation.”

While the nebula was still nearby, it slowed down the objects in it orbiting the sun — similar to how air resistance slows down a moving car.

After the nebula cleared, the lack of gas drag caused the asteroids to accelerate and crash into each other — like bumper cars being put into turbo mode.

“Our work illustrates how improvements in laboratory measurement techniques allow us to infer important processes that took place in the early solar system — such as the likely time the solar nebula disappeared,” said Professor Schönbächler.

“Planets like Earth were still in the process of being born back then.”

“Ultimately, this may help us better understand how our planets were born, but also give us insight into others outside our solar system.”

The study was published in the magazine . on May 23, 2022 Natural Astronomy

AC Hunt et al† The dissipation of the Solar Nebula is limited by impacts and nuclear cooling in planetesimals. Nat Astron, published online May 23, 2022; doi: 10.1038/s41550-022-01675-2

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