Ancient asteroids reveal that the early solar system was more chaotic than we thought

Ancient asteroids reveal that the early solar system was more chaotic than we thought

There is no doubt that young solar systems are chaotic places. Cascade collisions defined our young solar system as rocks, boulders and planetesimals repeatedly collided.

A new study based on pieces of asteroids that crashed into the earth sets a timeline for some of that chaos.

Astronomers know that asteroids have remained largely unchanged since they formed in the early solar system billions of years ago.

They are like rocky time capsules that contain scientific clues from the important era because differentiated asteroids had mantles that protected their interior from space weathering.

But not all asteroids remained intact.

Over time, repeated collisions removed the insulating sheaths from their iron cores and then crushed some of these cores to pieces.

Some of these pieces fell to the ground. Rocks that fell from space were of great interest to humans and were in some cases a valuable resource; King Tut was buried with a dagger made of an iron meteorite, and the Inuit people of Greenland made tools out of an iron meteorite for centuries.

Scientists are very interested in iron meteorites because of the information they contain.

A new study based on iron meteorites – which are fragments from the core of larger asteroids – looked at isotopes of palladium, silver and platinum. By measuring the amounts of these isotopes, the authors were able to limit the timing of certain events in the early solar system more strictly.

The paper “The loss of the solar nebula limited by shocks and nuclear cooling in planetesimals“was published in Nature astronomy. The main authors are Alison Hunt from ETH Zurich and the National Center for Competence in Research (NCCR) PlanetS.

“Previous scientific studies have shown that asteroids in the solar system have remained relatively unchanged since they formed billions of years ago,” Hunt sa. “They are therefore an archive where the conditions for the early solar system are preserved.”

The ancient Egyptians and Inuit knew nothing about elements, isotopes and decay chains, but we do. We understand how different elements decay in chains to other elements, and we know how long it takes.

One of these decay chains is the core of this work: the short-lived 107Pd-107Ag decay system. That chain has a half-life of about 6.5 million years and is used to detect the presence of short-lived ones nuclides from the early solar system.

The researchers collected samples of 18 different iron meteorites that were once part of the asteroids’ iron cores.

Then they isolated palladium, silver and platinum in them and used a mass spectrometer to measure the concentrations of different isotopes of the three elements. A special isotope of silver is crucial in this research.

During the first million years of the solar system’s history, decaying radioactive isotopes heated the metallic nuclei of asteroids. As they cooled and more of the isotopes decayed, an isotope of silver (107Ag) accumulated in the nuclei. The researchers measured the relationship between 107Ag to other isotopes and determined how fast asteroid kernels cooled and when.

This is not the first time scientists have studied asteroids and isotopes in this way. However, previous studies did not take into account the effects of galactic cosmic rays (GCR) on isotope conditions.

GCR can interfere with the neutron capture process during decomposition and can reduce the amount 107Ag and 109Ag. These new results are corrected for GCR interference by also counting platinum isotopes.

“Our additional measurements of platinum isotope occurrences allowed us to correct the silver isotope measurements for distortions caused by cosmic radiation of the samples in space. So we could date the time of the collisions more accurately than ever before,” Hunt reported.

“And to our surprise, all the asteroid cores we studied had been exposed almost simultaneously, within a time frame of 7.8 to 11.7 million years after the formation of the solar system,” Hunt sa.

A time period of 4 million years is short in astronomy. During the short period, all asteroids measured had their nuclei exposed, which means that collisions with other objects removed their mantles. Without the insulating jackets, all the cores were cooled at the same time.

Other studies have shown that cooling was rapid, but they could not limit the time frame as clearly.

In order for the asteroids to have the isotope conditions that the team found, the solar system must be in a very chaotic location, with a period of frequent collisions that removed the mantle from asteroids.

“Everything seems to have broken down by that time,” Hunt said says. “And we wanted to know why,” she adds.

Why would there be a period of such chaotic collisions? There are a couple of possibilities, according to the newspaper.

The first possibility concerns the giant planets of the solar system. If they migrated or were unstable in any way at the time, they could have reorganized the inner solar system, disrupted small bodies such as asteroids, and triggered a period of increased collisions. This scenario is called Nice model.

The second possibility is gas resistance in solnebulosa.

When the sun was a protostar, it was surrounded by a cloud of gas and dust called a solar nebula, just like other stars. The disk contained the asteroids, and the planets would eventually form there as well. But the disk changed during the solar system’s first million years.

At first, the gas was dense, which slowed down the motion of things like asteroids and planetesimals with gas resistance. But when the sun started, it produced more solar wind and radiation.

The solar nebula was still there, but the solar wind and radiation pressed on it and dispersed it. When it disappeared, it became less dense and there was less resistance to objects.

Without the damping effect of dense gas, asteroids accelerated and collided with each other more often.

According to Hunt and her colleagues, the reduction of gas resistance is responsible.

“The theory that best explained this energetic early phase of the solar system indicated that it was mainly caused by the disappearance of the so-called solar nebula”, co-author of the study Maria Schönbächler explained.

“This solar nebula is the remnant of gas left over from the cosmic cloud from which the sun was born. For a few million years it still orbited the young sun until it was blown away by solar winds and radiation,” Schönbächler sa.

“Our work illustrates how improvements in laboratory measurement techniques enable us to draw conclusions about key processes that took place in the early solar system – such as the probable time when the solar nebula had disappeared. Planets like Earth were still being born at that time. Ultimately, this can help us better understand how our own planets were born, but also give us insights about others outside our solar system, “Schönbächler completed.

This article was originally published by The universe today. Read original article.

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