A great demolition derby, with a chaotic mess of forming asteroids and planets constantly colliding with each other, took place at the start of the solar system between 7.8 million and 11.7 million years after formation from the sun, according to a new analysis of iron meteorites that were once part of the cores of metallic asteroids.
An international team of researchers has analyzed palladium, silver and platinum isotopes in 18 iron meteorites found on Earth to better understand the evolution of their parent bodies. Metallic asteroids contain dense iron cores and iron meteorites come from these nuclei, blown up by collisions with other asteroids.
Palladium-107 undergoes radioactive decay to silver-107 with a half-life of 6.5 million years. Earlier measurements of the relative abundances of the two isotopes by a mass spectrometer had already suggested that the asteroid the nuclei of which the meteorites were once part cooled rapidly. The question was, when did this rapid cooling occur?
To pinpoint the date, the research team – led by Alison Hunt, senior researcher at ETH Zurich and the National Competence Center for Planetary Research in Switzerland – refined the mass spectrometer process and searched for isotopes of the platinum, a rare metal, which came from cosmic rays impacting meteorites as they traveled through space.
“Our additional measurements of platinum isotope abundance allowed us to correct silver isotope measurements for distortions caused by cosmic irradiation of samples in space,” Hunt said in a statement. statement. “So we were able to date the timing of the collisions more precisely than ever before.”
The dates that Hunt’s team arrived at were between 7.8 million and 11.7 million years after the formation of the solar system – a relatively short period in its history of 4.5 billion years, although the study of other meteorites may lengthen the era.
The finding suggests that the onset solar system was extremely chaotic. Planets wouldn’t even have finished forming, and asteroids and protoplanets would have collided frequently, stripping the silicate mantle from some of the larger asteroids to expose their metallic cores to space and allow them to cool quickly. before further collisions shatter the nuclei. .
“Everything seemed to fall apart at that point,” Hunt said.
Something caused this chaos, and Hunt’s team believes it was largely related to the dissipation of the solar nebula, the cloud of gas that formed the sun. Then the remnants of this cloud settled into a disk around the young star. As the gas cooled, dust and ice condensed in it, which, through a process called accretion, accumulated in the planets, asteroids and comets that we know today.
But the planets had only a finite time to assemble; as the sun lights up gradually, the solar wind began to blow away the remnants of the solar nebula. Young planetary bodies had been brought together by friction with the gas, slowing their orbital speed. Without the gas to hold these planetary bodies, there must have been a period of chaos in which planetary orbits ran amok, resulting in a wave of collisions, before calming down later, the researchers explained.
However, other events around the same time could also have contributed to the chaos, the team noted. The gas giant planets – especially, Jupiter and Saturn – migrated around the early solar system, and their gravitational influence disturbed the orbits of smaller bodies, prompting them to form the asteroid belt and the Kuiper Belt.
One model in particular, known as the “Grand Tack”, claims that Jupiter migrated through the system, as close to the sun as March it’s today, before saturn gravity influenced Jupiter to migrate back to its current position. The Grand Tack model predicts that this event would have taken place about 10 million years in the history of the solar system.
Proving what happened 4.5 billion years ago, however, is the challenge, and this new study suggesting the fate of asteroids that produced iron meteorites provides new evidence of the violence of the solar system primitive.
More information may be revealed when NASA psyche missionwhich launches later this year, will arrive on the metallic asteroid Psyche in 2026.
The research was published online May 23 in the journal natural astronomy.
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