A chunk of a meteorite found in the desert sands of Algeria could be a piece of a baby planet that never made it.
According to an in-depth analysis of the rock’s composition and age, the meteorite known as Erg Chech 002 is not only older than Earth, it is volcanically formed – suggesting that it could once have been part of the crust of an object that known as a protoplanet. .
As such, it is a rare opportunity to study the early stages of planet formation and learn about conditions in the earliest days of the solar system, when the planets we know and love were still forming .
EC 002 was found just in May last year, several chunks of rock with a combined weight of 32 kilograms (70 pounds) in the Erg Chech Sand Sea in southwestern Algeria. It was quickly identified as unusual; instead of the chondritic composition of most recovered meteorites – which form when bits of dust and rock stick together – the texture was coagulating, with inclusions of pyroxene crystals.
It was therefore classified as an achondrite, a meteorite made of what appears to be volcanic material, formed on a body that has fused internally to distinguish the crust’s core – a protoplanet, one of the middle stages of planet formation.
Of the tens of thousands of meteorites identified, only a few thousand – 3,179, according to the Meteoritical Bulletin Database – are achondrites.
Most of these achondrites come from one of two parent bodies and are basaltic in composition. This means that they cannot tell us much about the diversity of protoplanets in the early solar system.
EC 002, on the other hand, is not basalt, but a type of volcanic rock known as andesite, a team of scientists led by geochemist Jean-Alix Barrat from the University of Western Brittany in France has identified.
Of all the meteorites we’ve found so far, even among achondrites, that makes EC 002 extremely rare – and opens a new way for understanding planet formation.
According to the team’s analysis, the rock is oldThe radioactive decay of aluminum and magnesium isotopes suggests that these two minerals crystallized about 4.565 billion years ago, in a parent body that grew 4.566 billion years ago. For context, the Earth is 4.54 billion years old.
“This meteorite is the oldest magmatic rock analyzed to date and sheds light on the formation of the primordial crusts that covered the oldest protoplanets,” the researchers wrote in their paper.
Unlike basalt, which is created by the rapid cooling of lava rich in magnesium and iron, andesite consists mainly of sodium-rich silicates and forms – at least on Earth – in subduction zones, where the edge of a tectonic plate is pressed underneath. another.
Although it is rarely found in meteorites, the recent discovery of andesite in meteorites in Antarctica and Mauritania has prompted scientists to investigate how it may occur. Experimental evidence suggests it may arise from the melting 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 features of EC 002 – that is, the way it interacts with light – with the spectral features of asteroids, they couldn’t find anything in the solar system that matched the meteorite.
Remains of the Andesite crust are not only rare in the meteorite record; they are also rare in the asteroid belt. Which begs the question: If the formation process was so simple and common, where on earth did all the differentiated protoplanets end up?
The same place where most of the material in the solar system ended up, probably: they were either pulverized or incorporated into larger rocky bodies; or maybe a combination of both.
Because EC 002 is slightly older than Earth, it’s even possible that its protoplanetary siblings helped build Earth from a knot of denser material in the dust cloud that orbited the baby sun.
While we have a pretty good handle on the way baby planets are born, which grow over millions of years as clumps of rocks and dust stick together, the details of the process are a little more mysterious.
EC 002 provides a spectacular opportunity to refine our understanding of how our home system evolved from the dust.
The research is published in PNAS