Let’s face it presolar grains are neat. Tiny particles from stars that lived and died before our Solar System was born. The story of how these mysterious microscopic minerals were first identified, isolated and extracted from meteorites must surely be one of the great scientific detective stories of the late twentieth century. And clearly it remains a fascinating area of research.
Recently a paper with some astonishing results was published in PNAS, Proceedings of the National Academy of Sciences to give it its full name. A team led by Philipp Heck of the University of Chicago dated 40 large* presolar silicon carbide grains from the Murchison meteorite and found that some had ages indicating that they predated our Solar System by as much as 3,000 million years. Since our Solar System is generally accepted to be nearly 4,600 million years old that could make some of the grains 7,600 million years old or more (the error bars on these dates are fairly large). If that conclusion wasn’t astonishing enough, there’s more!
The grains dated in this study likely formed in the outflows of asymptotic giant branch stars, that’s AGB stars to the cognoscenti. AGBs are pretty much at the end of their lives having been on the main sequence for a fair old time. When they get to the AGB stage such ageing stars shed huge amounts of material into the interstellar medium. There it would have wafted around for a while before being trapped into the collapsing gas and dust from which our own Solar System formed. Philipp Heck and co-authors suggest that most of these grains were probably only free floating in space for a few hundred million years. They estimate that their source AGB stars themselves sprang into life about 7,000 million years ago during a period of enhanced stellar formation.
So, last week at BPSC we were all chatting about these results. They had been featured on the BBC website and I had received several emails from friends asking me if I had heard about these amazing findings. Being able to date grains that existed before our Solar System formed is a major scientific achievement. They might be small, but these tiny minerals certainly have an amazing story to tell. The great Stephen Hawking once said: “Look up at the stars and not down at your feet. Try to make sense of what you see, and wonder about what makes the universe exist. Be curious.” This study certainly lives up to that ambition.
*Well not so large really. They have diameters of about one hundredth of a millimetre!
Upper image: The town of Murchison, Victoria, Australia where on 28th September 1969 the important Murchison meteorite fell to Earth. Photo credit: ABC Science: Fiona Pepper