A visitor from interstellar space
In 1907, a meteorite fell near the town of Camocim in the state of Ceará, Brazil. Unlike the much larger Tunguska event which occurred in Siberia the following year, the Camocim event was a witnessed fall that left behind physical fragments. This space rock is classified as a chondrite, a type of stony meteorite that contains small, spherical mineral grains called chondrules. Chondrites are considered primitive materials, leftovers from the formation of the solar system approximately 4.6 billion years ago. They are built from the dust and grains that existed in the early solar nebula. The Camocim meteorite contains something even older.
Scientific analysis of the fragments revealed the presence of presolar grains. These are tiny, solid particles of minerals like silicon carbide, graphite, and even nanodiamonds that formed before our own Solar System existed. These grains are incredibly rare, making up only a tiny fraction of a meteorite's mass. Their isotopic compositions are very different from materials that formed in our solar system, which allows scientists to identify their ancient, extrasolar origin. These specks of dust condensed in the cooling outflows of long-dead stars, such as red giants or supernovae. They then drifted through interstellar space for millions or billions of years before being caught up in the molecular cloud that would eventually collapse to form our Sun and its planets.