Much has changed in the approximately 4.5 billion years since the solar system first emerged from a disk-shaped cloud of swirling dust and gas.
The stuff from which everything is formed has undergone some serious changes: packed into planets, blown up by solar radiation and plasma, changed by interactions with other atoms.
The basic components of that original, early dust disk are therefore difficult to distinguish. But it’s not that it’s completely impossible.
An international team of scientists has preserved an ancient rock that fell to Earth from space and was recovered in 2018. It has now identified traces of material that, they say, must have come from Earth. protoplanetary diskwhen the solar system was still young.
It is a discovery that could give us new insights into the history of the solar system and the fundamental building blocks from which everything around us, here on Earth and around the sun, was born so many centuries ago.
The sun, like all stars, was born in a cloud of dust. A denser knot in the cloud succumbed to its own gravity, spinning and washing the material around it into a disk that fed the growing star. When the sun was done, what was left of that disk formed everything else in the solar system: the planets, the moons, the asteroids, the comets, and the icy chunks of rock that make up the spherical Oort cloud that is thought to encapsulate it. all.
The Oort cloud consists of icy chunks of rock that sometimes find their way into the inner solar system, orbiting the sun and throwing off gas and dust. These are the long-period comets, with orbits of hundreds to hundreds of thousands of years.
So far from the Sun, the Oort Cloud is thought to have remained relatively unchanged since the birth of the solar system, representing the most pristine example of the primordial material that made up the disk that formed the planets.
But this material has been challenging to study accurately. Even as comet fragments containing that primordial material make their long journey through the solar system to enter Earth’s atmosphere, they melt away as they fall.
This brings us to meteorites. Although space is largely quite empty, comets and meteorites sometimes collide. When this happens, it is possible for some cometary material to enter the meteorite and become trapped in it in the form of fragments called clasts.
If that meteorite enters Earth’s atmosphere, it will also be heated – but the cometary clasts within it can remain protected and reach the surface intact.
This is what the team of researchers led by cosmochemist Elishevah van Kooten of the University of Copenhagen discovered in a meteorite called Northwest Africa 14250 (NWA 14250).
Using a scanning electron microscope and spectroscopic analysis, the researchers took a very close look at the contents of NWA 14250 and the isotopes of various minerals found in the clasts therein. The researchers determined that the minerals in some classes are most likely of cometary origin, meaning meteorites like NWA 14250 could be a tool for studying the composition of the early Solar System.
But there’s more. The team found that the clasts were very familiar: they were similar to clasts found in other meteorites from the outer solar system near Neptune, and to samples taken from the asteroid Ryugu.
This suggests, the researchers say, that primordial material is not only relatively common (if a bit difficult to access), but that the composition of the protoplanetary disk was relatively uniform during the formation of the solar system.
“Contrary to current belief, the isotopic signature of the comet-forming region is ubiquitous among bodies in the outer Solar System, possibly reflecting an important planetary building block in the outer Solar System,” the researchers write.
“This provides the opportunity to determine the nucleosynthetic fingerprint of the comet-forming region and thus unravel the accretion history of the Sun’s protoplanetary disk.”
The research was published in Scientific progress.