Much has changed in the 4.5 billion or so years since the Solar System was first coalesced from a disk-shaped cloud of swirling dust and gas.
The matter from which everything is formed has undergone some serious changes – packed into planets, blasted by solar radiation and plasma, altered by interactions with other atoms.
Therefore, the basic components of that primordial disc of early dust are difficult to distinguish. But not, as it happens, completely impossible.
Preserved inside an ancient rock that fell to Earth from space and was found in 2018, an international team of scientists have now identified traces of material that they say must have originated in protoplanetary discwhen the Solar System was young.
It’s a discovery that could give us new insights into the history of the Solar System, and the basic 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 collapsed under its own gravity, spinning, spinning material around it into a disk that fed into the growing star. When the Sun was gone, what was left of that disk formed everything else in the Solar System: the planets, moons, asteroids, comets, and the icy chunks of rock that make up the spherical Oort cloud that is thought to contain it. everything.
That Oort cloud is made up of icy chunks of rock that sometimes enter the inner solar system, orbiting the Sun, shedding gas and dust as they do so. These are long-period comets, with orbits of hundreds to hundreds of thousands of years.
The Oort Cloud, so far from the Sun, is thought to have remained relatively unchanged since the birth of the Solar System, and thus represents 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 closely. Even when cometary fragments containing that primordial material make their long journey through the Solar System to enter Earth’s atmosphere, they melt as they fall.
This brings us to meteorites. Although space is mostly pretty empty, comets and meteorites sometimes collide. When this happens, it is possible for some cometary material to mix into the meteorite, trapped inside as fragments called clasts.
If that meteorite enters Earth’s atmosphere, it will also heat up—but the comet clusters inside may remain shielded and reach the surface intact.
That’s 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 a spectroscopic analysis, the researchers performed a very close analysis of the content of NWA 14250 and the isotopes of the various minerals found in the clasts in it. Minerals in some clasts, the researchers determined, are more likely to be of cometary origin, meaning that meteorites like NWA 14250 could represent a tool for studying the composition of the early Solar System.
But there is more. The clasts, the team found, were very familiar: they resembled clasts found in other meteorites from the outer solar system near Neptune, as well as samples taken from the asteroid Ryugu.
This suggests, the researchers say, that not only is primordial material relatively common (if a little difficult to access), the composition of the protoplanetary disk was relatively uniform during the formation of the Solar System.
“Contrary to current belief, the isotope signature of the comet formation region is ubiquitous among outer Solar System bodies, possibly reflecting an important planetary building block in the outer Solar System,” the researchers write.
“This offers the opportunity to determine the nucleosynthetic fingerprint of the comet formation region and, thus, reveal the accretion history of the solar protoplanetary disk.”
The research was published in Advances in science.