The northwest meteorite of Africa 12264 is older than expected
Ben Hoefnagels
Tiny chips of a single meteorite could completely overthrow our understanding of how the solar system has formed, once the space rock has proven to be older than expected.
Previous research suggests that small rocky bodies called protoplanets formed throughout the solar system, but those found beyond the asteroid belt between Mars and Jupiter gathered a little later that those further towards the center – 4.563 billion years ago, against 4.566 billion years for internal protoplanets. It was thought that this difference was that the external bodies had more water and ice, which slowed down the fusion of an inner nucleus.
This gap of three or four million years, although relatively short in cosmological terms, was a commonly accepted part of our cosmological history, but now Ben Rider-Stokes at the open university of Milton Keynes, in the United Kingdom, and his colleagues say he must go there.
It is believed that the formation of the planet implies an accretion, in which dust and gas are gathered by gravity, then differentiation, in which the accreted material warms and bottom, separating into nucleus, coat and crust. These processes have occurred at slightly different times for the inner and external protoplanets of the early solar system, explaining their different history, but now it seems that this is not the case.
The discovery of the team depends on a small meteority called North West Africa 12264, which weighs approximately 50 grams and was bought from a dealer in Morocco in 2018. The researchers received the permission of its owners to analyze tiny shaved particles of the object. They found that the ratio of chrome and oxygen, which varies predictably throughout our solar system, proved that the meteorite came from the outside part.
Its composition has also shown that it was part of a planetary coat – the section between the nucleus and the crust – which makes it the first sample of this type found from the external part of the solar system, although the Protoplanet is no longer existing. “This planet had to be broken in a fairly dramatic way to search this material similar to a coat,” explains Rider-Stokes. “There must have been a very, very large collision.”
But above all, its age as measured by the lead isotopes went against the idea that external protoplants should be younger. “It really took us by surprise because it was extremely old, as if it were some of the oldest materials in the solar system. What he suggests is that the rocky planets have formed in the inner solar system and in the external solar system at the same time, ”explains Rider-Stokes, which could force a rewriting of the models that we use to understand this process.
Sebastiaan Krijt at the University of Exeter, in the United Kingdom, said that the change of events that occurred more than 4 billion years a few million years ago may not be extremely important, but which will actually have a big impact. Understanding the sequence of events that formed our solar system and how the different processes interacted is vital – both for research on our solar system and star systems elsewhere in the universe.
“These formative steps are very short and a million years can make a large and large difference,” explains Krijt. “It is very important to achieve the chronology and to order things well.”
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