Meteorites can be cosmic time capsules, containing a bit of what the universe had in it before the Solar System formed. Recently, scientists discovered grains that could be up to 7 billion years old. Now, a new study on a different meteorite reports the discovery of more grains that predate the Solar System. What’s very exciting is that these presolar grains are found where they shouldn’t be. The results are reported in Nature Astronomy.
The sample analyzed was found in the Allende meteorite. This meteorite has calcium-aluminum-rich inclusions, which are some of the oldest objects ever formed in the Solar System. One of them, called the Curious Marie inclusion, is where a team of researchers from Washington University in St. Louis spotted the presolar grains.
"What is surprising is the fact that presolar grains are present," team leader Professor Olga Pravdivtseva said in a statement. "Following our current understanding of Solar System formation, presolar grains could not survive in the environment where these inclusions are formed."
These calcium-aluminum inclusions form at high temperatures. Temperatures were so high when the Sun formed that fragile presolar grains made of silicon carbide (SiC) should have been broken up by the intense heat. But in this meteorite, they weren’t, suggesting that there might be more than one way for these inclusions to form.
"The fact that SiC is present in refractory inclusions tells us about the environment in the solar nebula at the condensation of the first solid materials," added Pravdivtseva. "The fact that SiC was not completely destroyed in Curious Marie can help us to understand this environment a little bit better. Many refractory inclusions were melted and lost all textural evidence of their condensation. But not all."
This is not the first attempt to find SiC presolar grains in inclusions but it is the first time it has been found. The parent body, the Allende meteorite, is the largest carbonaceous chondrite meteorite ever found on our planet. It fell over the Mexican State of Chihuahua in 1969 and over 2 tons of meteorite fragments were discovered. The piece analyzed is from the collection of the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Chicago Field Museum.