Scientists found that diamonds found in a meteorite that exploded over the Nubian desert in Sudan a decade ago formed inside a "lost planet" that once surrounded the sun in the early solar system.
Microscopic analyzes of the small diamond meteorites revealed that they contain compounds that occur under intense pressure, suggesting that diamonds formed well below the surface of a planet.
In this case, it was calculated that the mysterious world was somewhere between Mercury and Mars in size.
Astronomers have hypothesized that dozens of budding planets, varying in size from the moon to Mars, formed in the first 10 million years of the solar system, but were separated and repacked in collisions violent ones that finally created the terrestrial planets that orbit the sun today.
If the latest findings are confirmed, the Almata Sitta meteorite will be the only known remnant of one of these lost planets long ago. The material will give scientists a unique window into the cosmic conditions that prevailed in the deep history of the solar system.
"The simulations have suggested that the primitive solar system had dozens of these embryonic planets that collided with each other to form the terrestrial planets, but having evidence of one of them? I did not expect that," said Farhang Nabiei, who studied pieces of the meteorite at the Federal Institute of Technology in Lausanne, Switzerland.
Philippe Gillet, lead author of the study, said: "We are doing archeology, looking to the past and trying to decipher the history of the solar system."
The Almata Sitta meteorite was the first to be tracked by telescopes when it accelerated towards Earth and exploded over the Nubian desert in 2008. The event sparked a recovery effort at the University of Khartoum, which collected 480 pieces of the meteorite that equals 4 kg of damaged material.
Early inspections of the meteorite revealed that it is a ureilite, an unusual composition that does not coincide with other space rocks known to have come from the moon or Mars. The finding led some scientists to speculate that it might have had a more exotic origin .
That suspicion grew when researchers noticed small diamonds in the meteorite material. While other meteorites are known to contain diamond crystals, these are usually much smaller. Typical meteorite diamonds are only a few millionths of a millimeter and are thought to form in collisions with other space rocks that send short but intense shock waves through the carbon-rich asteroids.
In 2015, Swiss laboratory researchers teamed up with Japanese scientists to argue that diamonds in the Almata Sitta meteorite, which are up to 100 micrometers long, were much larger than could be formed in collisions with other asteroids. They speculated at that time that the meteorite could have come from a lost planet, but they sought more evidence to reinforce their theory.
Writing in the journal Nature Communications, the Swiss team now describes new analyzes that show that diamonds in the meteorite contain spots of an iron-sulfur compound that are thought to form at pressures in excess of 20 gigapascals. They conclude that diamonds were formed with specks within them, deep in the surface of an unknown world.
"We're probably looking at an object that was one of the first planets that surrounded the sun before crashing into each other to create the real planets we have today," Gillet said.
James Wittke, who directs the meteorite laboratory at Northern Arizona University, said the scientists' conclusions were reasonable. "We think there were probably many more fathers in the early solar system, which have been destroyed since then, so a destroyed body since the size of Mercury is reasonable," he said. "One as large as Mars seems a bit surprising, but this article presents the best, and perhaps only, kind of evidence to determine the size of these major bodies"