Much has changed in the 4.5 billion years since the Solar System first coalesced from a disk-like cloud of swirling dust and gas.
The matter from which everything was made has undergone serious changes – packed into planets, battered by sunlight and plasma, altered by interactions with other atoms.
The basic components of this initial, early dust disk are therefore difficult to discern. But no, as it happens, completely impossible.
Preserved inside an ancient rock that fell to Earth from space and was recovered in 2018, an international team of scientists has now identified traces of material they say must have come from protoplanetary diskwhen the solar system was young.
It’s a discovery that can 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 many eons ago.
The sun, like all stars, was born in a cloud of dust. The denser knot in the cloud collapsed under its own gravity, spinning and coiling material around itself into a disk that fed into the growing star. When the Sun ended, what was left of the disk formed everything else in the Solar System: planets, moons, asteroids, comets, and the icy chunks of rock that make up the spherical Oort cloud that is thought to encapsulate it. All.
This Oort Cloud consists of icy chunks of rock that sometimes penetrate the inner Solar System, orbiting the Sun and releasing gas and dust in the process. 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 earliest example of the primordial material that made up the planet-forming disk.
But careful study of this material was challenging. Even as cometary fragments containing this primordial material make their long journey through the Solar System to enter Earth’s atmosphere, they dissipate as they fall.
This brings us to meteorites. Although space is mostly pretty empty, comets and meteorites sometimes collide. When this happens, it’s possible that some cometary material, trapped inside as fragments called clasts, can become mixed into the meteorite.
If this meteorite enters Earth’s atmosphere, it will also be heated – but the cometary clusters contained within may remain protected and reach the surface intact.
That’s what a team of researchers led by astrochemist 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 scientists performed a very detailed analysis of the contents of NWA 14250 and the isotopes of the various minerals found in the clasts within them. The scientists found that the minerals in some of the clasts are most likely of cometary origin, meaning meteorites like NWA 14250 could provide a tool for studying the composition of the early solar system.
But there is more to it. The team found that the clasts 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 the primordial material relatively common (if somewhat difficult to access), but 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 outer Solar System bodies and likely reflects an important planetary building block in the outer Solar System,” the researchers write.
“This provides an opportunity to determine the nucleosynthetic fingerprint of the comet-forming region and hence reveal the accretion history of the solar protoplanetary disk.”
The research was published in Scientific advances.