An ancient meteorite reveals the solar system is 4.5682 billion years old, 1.9 million years older than we thought. The difference seems insignificant, but it could mean our solar system was actually born in the blast furnace of a supernova.
In order to determine the age of the solar system, scientists look for meteorites that date back to the beginnings of the solar system. Some of these meteorites have tiny mineral deposits known as calcium-aluminum-rich inclusions, or CAIs. These minerals were trapped and preserved inside the meteorites formed around them. Because CAIs are thought to be among the very first solids to condense out of the nebular gas that birthed the solar system, they provide the oldest possible measurement of the solar system's age.
New analysis of meteorite NWA 2364, which touched down in Morocco in 2004, has revealed a centimeter-wide CAI that is 4.5682 billion years old. Arizona State researchers Meenakshi Wadhwa and Audrey Bouvier arrived at this date by measuring the presence of three different lead isotopes in the CAI, two of which are the product of uranium decay. Because uranium takes billions of years to fully decay into lead, it's possible to measure the levels of decay and figure out an extremely precise age of the sample from the distribution of the isotopes.
That 4.5682 billion year figure is only a tiny fraction older than the previous measurements, but the geochemical tests are precise enough that the researchers are confident that the difference is real. And while a couple million years here or there might seem unimportant in the grand scheme of the solar system's multi-billion year history, it makes a big difference for the initial mixture of elements that made up our solar system.
Of particular interest is the iron isotope iron-60. It has a radioactive half-life of 2.6 million years, which simply means half of a given iron-60 sample decays every 2.6 million years. By extension, if the solar system is about 2 million older than we thought, that means it had nearly double the amount of iron-60 in its initial element distribution. That's a whole lot of iron-60, and there's only one place such an abundance of that isotope could have come from: a supernova explosion.
Wadwha explains how making these tiny distinctions allow us to glean such massive insights about the solar system formed:
"That's the power of geochemistry. You can make very, very precise measurements. Iron-60 is kind of a smoking gun. If present in certain abundances, it can only really be there because of a supernova injection. It gives us a better understanding of the type of environment the solar system evolved in."