A piece of ancient space rock that ended up on Earth is giving scientists the clues they need to understand the cloud of dust from which the Solar System was born.
The rare object is known as Erg Chech 002, and an isotope contained within it suggests a sprinkling of radioactive material from recently exploded stars infused with our Solar System towards the end of its formation.
It's a fascinating glimpse into the solar environment billions of years ago, showing not just how meteorites can serve as time capsules preserving the secrets of the past, but that those secrets can then be used to better understand what we find in other space rocks.
The Sun, like all stars, was born from gas and dust. The solar nebula was a dense cloud floating in space, with a denser region that would collapse under gravity to form a baby star, spooling in more and more material as it spun and grew. Once the Sun had swallowed its fill, the remaining disk of material went into forming the planets.
We have a rough idea what was in the nebula. After all, our own planet, and all the other planets and rocks and dust drifting through the Solar System were made from it. But in many of those places, a lot has changed chemically over the 4.6 billion years or so since the Sun was a mere twinkle in a cloud of dust.
Meteorites and asteroids, by contrast, are thought to represent a relatively pristine sample of the Solar System at the time these objects formed, since they have remained more or less unchanged and unaltered since that time. So we can study them to find out when they formed, and the composition of the material from which they did so.
This brings us back to Erg Chech 002, a meteorite older than Earth and unlike any other. Discovered in 2020 in the Erg Chech sand sea in southwestern Algeria, the stone has an unusual andesitic composition linked with igneous activity, suggesting that the object was once part of a planet early in formation, whose development was arrested early.
One of the elements it contains is a stable isotope of magnesium called magnesium-26. Magnesium-26 is a decay product from a particular radioactive isotope of aluminum, aluminum-26, that is produced during the violent supernova deaths of massive stars.
Aluminum-26 has a relatively short half-life of 717,000 years, but its decay products can be used to infer its past presence in materials, and calculate the age of the objects wherein they are found.
A team of scientists led by cosmochemist Evgenii Krestianinov of the Australian National University in Australia has now used this isotope clock to infer the distribution of aluminum-26 in the solar nebula.
They calculated the age of the meteorite, based on the ratios of its radioactive decay products. Their calculations were consistent with previous calculations of the age of Erg Chech 002 – 4.566 billion years.
Then, the team conducted a comparison with other well-preserved ancient meteorites with a similar rocky composition. They found Erg Chech 002 had significantly more aluminum-26 than other meteorites, a result that they interpreted to mean aluminum-26 was unevenly distributed through our Sun's nebula.
They believe these findings represent a late infall of stellar material into the solar nebula, bringing with it freshly forged radioactive isotopes, including the aluminum-26 that was taken up into the nascent planet from which Erg Chech 002 came.
Previous research suggests that the baby Solar System was inundated with radioactive materials from supernova explosions while the Sun was being born. The work of Krestianinov and his colleagues represents another piece of the puzzle of this curious time in our ancient history.
The research has been published in Nature Communications.