Ancient Asteroids Reveal The Early Solar System Was More Chaotic Than We Thought
There is no doubt that young solar systems are chaotic places. Cascading collisions defined our young solar system when rocks, boulders, and planetesimals repeatedly collided.
A new study based on pieces of asteroids that crashed into Earth puts a timeline to some of this chaos.
Astronomers know that asteroids have remained essentially unchanged since their formation at the start of the solar system billions of years ago.
They’re like rocky time capsules that hold scientific clues to that important epoch, because differentiated asteroids had mantles that protected their interiors from the weather of space.
But not all asteroids remained whole.
Over time, repeated collisions ripped the insulating mantles from their iron cores, then shattered some of those cores into pieces.
Some of these pieces fell to Earth. Rocks that fell from space were of great interest to people and were a valuable resource in some cases; King Tut was buried with a dagger made from an iron meteorite, and the Inuit of Greenland have made tools from an iron meteorite for centuries.
Scientists are keenly interested in iron meteorites because of the information they contain.
A new study based on iron meteorites – which are fragments of the core of larger asteroids – looked at the isotopes of palladium, silver and platinum. By measuring the amounts of these isotopes, the authors could more tightly restrict the timing of certain events to the early solar system.
The article “Solar nebula dissipation constrained by impacts and core cooling in planetesimals” was published in natural astronomy. The lead author is Alison Hunt from ETH Zurich and the National Center for Research (NCCR) PlanetS.
“Previous scientific studies have shown that asteroids in the solar system have remained relatively unchanged since their formation billions of years ago,” Hunt said. “They therefore constitute an archive in which the conditions of the early solar system are preserved.”
The ancient Egyptians and Inuit knew nothing about elements, isotopes and decay chains, but we did. We understand how different elements decay in chains into other elements, and we know how long it takes.
One of these decay chains is at the heart of this work: the short lifespan 107Pd–107Ag decay system. This chain has a half-life of about 6.5 million years and is used to detect the presence of short-lived nuclides from the early solar system.
The researchers collected samples from 18 different iron meteorites that were once part of the iron cores of asteroids.
Then they isolated the palladium, silver and platinum they contained and used a mass spectrometer to measure the concentrations of different isotopes of the three elements. A particular isotope of silver is essential in this research.
During the first million years of the solar system’s history, decaying radioactive isotopes heated the metallic cores of asteroids. As they cooled and more isotopes decayed, an isotope of silver (107Ag) accumulated in the nuclei. The researchers measured the ratio of 107Ag to other isotopes and determined how fast asteroid nuclei cooled and when.
This is not the first time that researchers have studied asteroids and isotopes in this way. But previous studies did not take into account the effects of galactic cosmic rays (GCR) on isotopic ratios.
GCRs can disrupt the neutron capture process during decay and can decrease the amount of 107Ag and 109Ag. These new results are corrected for GCR interferences by also counting platinum isotopes.
“Our additional measurements of the abundance of platinum isotopes allowed us to correct the measurements of silver isotopes for distortions caused by cosmic irradiation of the samples in space. We were therefore able to date the timing of the collisions more accurately than ever before,” Hunt reported.
“And to our surprise, all of the asteroid nuclei that we looked at were exposed almost simultaneously, within 7.8 to 11.7 million years after the solar system formed,” Hunt said.
A period of 4 million years is short in astronomy. During this brief period, all asteroids measured had their cores exposed, meaning collisions with other objects stripped their mantles. Without the insulating mantle, the cores all cooled simultaneously.
Other studies have shown the cooling to be rapid, but they could not limit the time so clearly.
For the asteroids to have the isotopic ratios found by the team, the solar system had to be a very chaotic place, with a period of frequent collisions that stripped the asteroids’ mantles.
“Everything seems to have fallen apart at that point,” Hunt says. “And we wanted to know why,” she adds.
Why would there be such a chaotic collision period? There are several 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 that time, they could have rearranged the inner solar system, disrupted small bodies like asteroids, and triggered a period of increased collisions. This scenario is called the Nice model.
The other possibility is the gas trail in the solar nebula.
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 too. But the disk changed during the first million years of the solar system.
At first, the gas was dense, which slowed the movement of things like asteroids and planetesimals with a trail of gas. But as the Sun got going, it produced more solar wind and radiation.
The solar nebula was still there, but the solar wind and radiation pushed on it, dissipating it. As it dissipated, it became less dense and there was less drag on objects.
Without the dampening effect of the dense gas, the asteroids accelerated and collided more frequently.
According to Hunt and his colleagues, the reduction in gas drag is responsible.
“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,” explained study co-author Maria Schönbächler.
“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 circled around the young Sun until it was blown away by the winds and solar radiation,” Schönbächler said. said.
“Our work illustrates how improvements in laboratory measurement techniques allow us to infer key processes that took place in the early solar system – such as the probable time when the solar nebula left. Planets like Earth were still being born at Ultimately, this can help us better understand how our own planets came to be, but also give us insight into others outside our solar system,” Schönbächler concluded.
This article was originally published by Universe Today. Read the original article.