In 1969, a meteorite crashed through the sky and landed near the small town of Murchison, Australia. Had shattered into many fragments after its dramatic landing, the interstellar visitor was estimated to weigh over 100 kg (or 220 lb) based on the collected pieces.
Fifty years later, a team of astronomers at the University of Chicago reported that their a surprising finding of the Murchison meteorite: within its fragments, 40 large silicon carbide (SiC) grains are made of interstellar dust that pre-dates the solar system, with the oldest one around 7 billion years old.
The group of researchers determined the ages of the material based on their radiometric analyses of a neon isotope, Ne-21, trapped inside the SiC grains.
Direct dating of stardust was considered almost impossible. The study's corresponding and first author, Philipp Heck, an Associate Professor and a researcher based in the Field Museum of Natural History, attributed a part of their breakthrough to the data sent back from NASA's Voyager 1 probe.
When Voyager 1 entered interstellar space in 2012, it acquired new data on the spectrum of the galactic cosmic ray, which allow the researchers to conduct more accurate direct dating of the meteorite sample.
Heck and colleagues used data on the age of exposure, which measures how long material is exposed to cosmic rays. Cosmic rays contain high-energy particles that can penetrate the nucleus of atoms. Some of these cosmic rays interact with matter to form new elements such as the cosmogenic Ne-21. The longer they are exposed, the more new elements are formed.
They found that these grains about 4 million to 3 billion years before the start of the Solar System (which was about 4.6 billion years ago). These grains represent the oldest datable solid samples available. They are the key to understand the presolar chronology of our galaxy, as well as stars and habitable planetary systems.
Before the current study, the lifetime of interstellar dust can only be estimated using sophisticated theoretical models, which are based on a lot of assumptions and produce results with large uncertainties. That's why the current direct age measurement developed by the Chicago team is so significant.
Scientists suspect that some of the dust may have come from the outflows of dead stars (such as the Egg Nebula) that exist before our solar system. They eventually drift out of its system and become trapped inside meteorites like the Murchison.
This latest discovery is published in the journal Proceedings of the National Academy of Sciences.
Do you know that the the Murchison meteorite is one of most studied meteorite in the history? Check out the video below from ABC Science to learn more about this legendary rock from space.
Murchison meteorite: The rarest of meteorites (ABC Science)