At a glance, meteorites might only be marginally more interesting than regular old rocks, but look closely and they can tell us stories of ancient stars and long-lost planets. One of these stories has now been uncovered in a piece of space rock retrieved from Antarctica, containing grains from a stellar explosion that predates the Sun.

Cosmologically speaking the Sun is a relative youngster, at only about 4.6 billion years old. Entire generations of stars have been born, lived and died before the Sun came along, and they helped to seed the universe with materials that form new stars and planets. Grains of dust from that era rarely survive until the present day, but when they do they can tell us a lot about those ancient objects.

"As actual dust from stars, such presolar grains give us insight into the building blocks from which our solar system formed," says Pierre Haenecour, lead author of the new study. "They also provide us with a direct snapshot of the conditions in a star at the time when this grain was formed."

Now researchers have found a particularly strange presolar grain inside a primitive, chondritic meteorite. Using ion and electron microscopy, the team analyzed the grain, known as LAP-149, down to the atomic level. Mostly made up of graphite, the grain was found to have extremely high levels of a carbon isotope called 13C, and the researchers concluded that it originated in a nova.

The grain LAP-149 (inset) is mostly made of graphite with an oxygen-rich silicate inclusion, which is the first such combination ever found to have originated in a nova Heather Roper/University of Arizona

A nova is the explosion given off by a white dwarf in a binary star system. If the two get too close, the white dwarf can start chowing down on material from its partner star, eventually reigniting and burping out new chemical elements in a huge blast.

"The carbon isotopic compositions in anything we have ever sampled that came from any planet or body in our solar system varies typically by a factor on the order of 50," says Haenecour. "The 13C we found in LAP-149 is enriched more than 50,000-fold. These results provide further laboratory evidence that both carbon- and oxygen-rich grains from novae contributed to the building blocks of our solar system."

But the grain is even stranger still. The analysis also revealed a high-oxygen, silicate impurity embedded inside, which had never been seen in this kind of grain before.

"Our find provides us with a glimpse into a process we could never witness on Earth," says Haenecour. "It tells us about how dust grains form and move around inside as they are expelled by the nova. We now know that carbonaceous and silicate dust grains can form in the same nova ejecta, and they get transported across chemically distinct clumps of dust within the ejecta, something that was predicted by models of novae but never found in a specimen."

The team wasn't able to figure out the exact age of LAP-149 because the sample was too small, but larger objects of a similar nature could help answer that question.

This isn't the first time unusual inclusions in a meteorite have revealed intriguing stories. Recently, scientists discovered a piece of an asteroid that had eaten the seed of a comet. The Hypatia stone may also predate the Sun, while tiny blue crystals in another space rock reveal our star's rowdy younger years.

The research was published in the journal Nature Astronomy.

Source: University of Arizona