In 2008, a stone criss-crossed with tiny diamonds raced through kilometer-thick nitrogen, oxygen and carbon dioxides and heated its exterior as it raced through the thick air. A telescope tracked its progress, watching the asteroid meteor explode. The violent eruption, 23 miles above the ground, sent fragments towards their resting place, dark against the sands of the Nubian desert in Sudan.
The blast and crash were just the last eons of humiliation, from a high pressure starting in a promising planetary start, to a cataclysmic failure, to billions of years of aimless roaming around the solar system.
A new study published in Nature Communications offers a dramatic history of the meteorite's origin today. Based on materials found in diamonds, researchers believe that this could be the remnant of a long-lost planet or planetary embryo; one that was still in its infancy when the chaos of the early solar system destroyed it.
Diamonds are the best friends of a geologist
In this case diamonds are not the most important part of this story. They are just the heavy packing for much more valuable cargo kept inside. While a jeweler may see a piece of rock in a diamond as a blemish, it is valuable to a geologist. Due to their strong crystal structure, diamonds can conserve tiny pieces of material that would otherwise disappear over time under the inexorable changeability of the universe.
Researcher Farhang Nabiei ̵
This visitor was not from Mercury or Mars. The meteorite has been classified as ueilite, a group of meteorites with a mysterious origin, parts of a planetary body or asteroid that do not match any of the rocky bodies that humans have taken today. The researchers already knew that whatever it was, it had probably reached its end in the demolition derby of the early solar system, but the extent of the object (or objects) was still unknown until the inclusions were described. The size of the diamonds is another indication of their deep origin.
"100 microns does not seem to be very big – it's the size of a human hair – but these are much larger diamonds than in converting graphite to a diamond in shock," says Thomas Sharp, a geologist at Arizona State University, which was not involved in the new research, but studied meteorites using similar electron microscopy tools.
"An important piece of the puzzle is that the diamonds are large and zoned, which gives the idea that they have formed deep inside the body (and not in an impact), "said Rebecca Fischer, a planetary scientist at Harvard University who was not involved in the study Email. Fischer points out that the mass composition of the material (an iron-sulfur compound with nickel (Ni) and phosphorus (P)) forms within the diamond only at high pressures. "Fe3S is a well-studied phase that is stable only above 21 GPa. The addition of Ni and P can change the pressure at which it is stable, but the authors argue that this is due to the mass composition they see This might be confirmed in future experimental studies It will also be interesting to further investigate Ureilite diamonds to see if they have captured other high pressure phases in inclusions, which would provide strong support for the authors' interpretation. "Fisher says:
This is further evidence that protoplanets or planetary embryos appeared early in the formation of the solar system when things looked far less populated than they are today. Jupiter and the other gas planets grew rapidly, and their gravitational forces (along with the sun) tended to spin smaller objects. These smaller objects also formed quickly. Previous studies of isotopes found in Martian meteorites indicate that the planet has formed rapidly in the first 2 million years of solar system existence. "The implication was that Mars is a stranded planetary embryo of this size that emerged very early, suggesting that there were planets of this size that formed very early and were involved in the planet formation scenarios," says Meenakshi Wadhwa, director the Center for Meteorite Studies at ASU, which was not involved in the current research.
"Dynamic models have long suggested the presence of many moon- to Mars-sized bodies in the inner solar system at the onset of terrestrial planetary accretion, but they are. It is commonly believed that they were either incorporated into planets or lost by the sun or were ejected from the solar system, for example, "says Fischer. "This is a very interesting proof that we actually have samples from one of these bodies in our meteorite record, the Ureilites."
Planetary scientists are still not sure exactly where the Uranium decaying main body formed or how it was eventually destroyed, but they analyze the samples collected from around the world to try and learn more about to know what came before.
"There have been other classes of meteorites that have been studied. It could have come from a larger parent, but to that extent it has not been quantified," says Wadhwa. Wadhwa explores the chronology of the early solar system by measuring how early crusts arose on planetary embryos (2-4 million years after the formation of the solar system *), and other groups explore how early the dense metal nuclei of early planets had to form the solar system 1 million years old). But finding out how old these objects were was one thing. Estimating how tall they are is another challenge. "I would say that this is the most quantified estimate of a body whose size is no longer available. It is exciting from this perspective." Wadhwa says.
Shock to the System
Computer models detailing the formation of the solar system predict a rapid educational process. From the disk of gas and dust surrounding our star, gas giants swirled rapidly, and soon thereafter more rocky bodies piled up. While today we have only four rocky planets along with a small number of moons and asteroids – in the first 10 million years of the solar system – Nabiei says there may have been dozens of planetary embryos, each of which accumulates as much material as it could.
It was overcrowded, to say the least. And as in any crowded environment, clashes sometimes occurred. These were sometimes creative processes that caused a collapse of our moon. In other cases, they were devastating.
The desert meteorite fragments also testify to this destructive process. The diamonds are relatively large for meteorites – about 10 microns in diameter. The large size of the diamonds has been described in the earlier literature. But recent research by Nabiei and colleagues shows that the diamonds are not just time capsules from the early days of our 4.6-billion-year-old stellar system, but also indicative of some rough interplanetary relationships.
The diamonds were surrounded by graphite layers, which is not unusual. Graphite and diamond are just different forms of the same material, carbon. But due to the orientation of the diamonds Nabiei does not believe that they have formed from the surrounding graphite. Instead, the diamonds were probably partially transformed into graphite during a massive, shocking event, probably the same collision that separated them from their father's body, the unfortunate Planetesimal.
There are many other ureilite samples to test and test to see if they fit into the image of the long-lost planet that has drawn this research for us.
"It raises the question, is there more of these?" Sharp says. "Are there other samples of diamonds that need further characterization to determine if they formed in large bodies as opposed to shock events?"
"We made a picture based on a particular ureilite sample, now we try to look at the other samples and fit them into the picture," says Nabiei. I ask if it's like a puzzle and he laughs and agrees. "At least now we know it's a big puzzle," says Nabiei.
Nabiei looks forward to presenting his work and talking to other researchers about the paper. He said he originally planned to discuss this research at a meeting of the American Geophysical Union last December.
"I was really excited to talk to people and all the scientists there, but it did not happen," Nabiei says. He is Iranian and the recent travel ban meant that he was denied a visa. "I will present it in Paris, but at least for now the US is taboo for us."
Nabiei will continue his research in Switzerland and use tiny fragments to put together some of the gaping holes in the history of our solar system
"We look at inclusions that are a few tens of nanometers in size, and then we talk about planets that have a diameter of thousands of kilometers, "says Nabiei. "It's like two extremes of size, I could never imagine that I could talk about planetary formation microscopy, it's as if we're pushing the boundaries of what we can see."
- Update: In this article the estimates for the formation of the crusts and nuclei of the planetary embryo misrepresented. It is estimated that this process took place 2-4 million years after the birth of the solar system, not 2-4 million years ago. We regret the mistake.