A piece of meteorite found in the sands of the Algerian desert could be a piece of a planet baby that has never reached it.
According to an in-depth analysis of the composition and age of the rock, the meteorite known as Erg Chech 002 is not only older than Earth, but formed volcanically, suggesting that it may have been part of the crust of an object known as a protoplanet. .
As such, it represents a rare opportunity to study the early stages of planet formation and learn more about the conditions of the early days of the solar system, when the planets we know and love today were still forming.
EC 002 was found in May last year several pieces of rock with a combined weight of 32 kilograms (70 pounds) in the sandy sea of Erg Chech, southwestern Algeria. It was identified fairly quickly as unusual; instead of the chondritic composition of most recovered meteorites, which form when pieces of dust and rock join together, their texture was igneous, with inclusions of pyroxene crystals.
Therefore, it was classified as acondrite, a meteorite made of what appears to be volcanic material, originating in a body that has undergone an internal fusion to differentiate the crust core: a protoplanet, one of the middle stages of formation. of the planet.
Of the tens of thousands of meteorites identified, only a few thousand (3,179, according to the weather report database) are acondrites.
Most of these chondrites come from one of the two parent bodies and have a basaltic composition. This means that they cannot tell us much about the diversity of protoplanets at the beginning of the solar system.
EC 002, on the other hand, is not basaltic, but a type of volcanic rock known as andesite, has been determined by a team of scientists led by geochemist Jean-Alix Barrat of the University of Western Brittany in France.
Of all the meteorites we have encountered so far, even among the chondrites, it makes EC 002 extremely rare and opens a new pathway to understanding the formation of the planet.
According to the team’s analysis, the rock is old. The radioactive decay of the isotopes of aluminum and magnesium suggests that these two minerals crystallized about 4.565 million years ago, in a parent body that accumulated 4.566 million years ago. By context, the Earth is 4.54 billion years old.
“This meteorite is the oldest igneous rock analyzed so far and sheds light on the formation of the primordial crusts that covered the oldest protoplanets,” the researchers wrote in their article.
Unlike basalt, which is formed from the rapid cooling of lava rich in magnesium and iron, andesite is composed primarily of sodium-rich silicates, and at least on Earth it is formed in subduction zones, where the edge of a tectonic plate is pushed below. another.
Although rarely found in meteorites, the recent discovery of andesite in meteorites found in Antarctica and Mauritania prompted scientists to investigate how it could occur. Experimental evidence suggests that it can be formed from the fusion of chondritic material.
Because chondritic bodies are so common in the solar system, it is possible that the formation of protoplanets with andesite crusts was also common. However, when the team compared the spectral characteristics of EC 002, that is, its way of interacting with light, with the spectral characteristics of asteroids, they could not find anything in the Solar System that matched the meteorite.
Remains of andesitic crust are not only rare in the meteorite record; they are also rare in the asteroid belt. What raises the question: if the formation process was so simple and common, where did it come from in all the differentiated protoplanets?
Probably in the same place where most of the material in the solar system ended up: either pulverized or incorporated into larger rocky bodies; or, perhaps, a combination of both.
Because CE 002 is slightly older than Earth, it is even possible that its protoplanetary siblings helped build the Earth from a knot of denser material in the cloud of dust orbiting the baby Sun.
While we have pretty decent control over how baby planets are born, which grow over millions of years as groups of rocks and dust come together, the details of the process are a little more mysterious.
EC 002 represents a spectacular opportunity to fine-tune our understanding of how our home system came out of the dust.
The research has been published in PNAS.