Before the formation of the Earth and other planets, the Sun’s rays were still surrounded by cosmic gas and dust. During the millennium, stone fragments of various sizes were formed in the dust. Many of these became elements of modern planetary construction. Some have never been part of the planet and still revolve around the Sun today, such as asteroids in an asteroid belt.
Researchers from ETH Zurich and the National Research Center (NCCR) PlanetS, in collaboration with an international team, analyzed metal samples from the context of such asteroids that live on Earth as meteorites. In doing so, they revealed a portion of their early history at the time when the planets were built. Their findings were published in the journal Nature Astronomy.
Witnesses to the first solar system
“Previous scientific studies have shown that the planets of the solar system have remained unchanged from their design, billions of years ago,” explains leads author and researcher at ETH Zurich and NCCR PlanetS, Alison Hunt explains. “They are, therefore, a historical archive, in which the conditions of the original solar system are preserved,” Hunt said.
But to unveil this archive, researchers had to prepare well and explore extraterrestrial objects. The team took samples of 18 different iron meteorites, once part of asteroid metal particles. To perform their analysis, they needed to disperse the pieces to distinguish the elements of Palladium, Silver, and Platinum for further research. With the help of a mass spectrometer, they measured the mass of the different isotopes of these elements. Isotopes of other atoms of a given element, Palladium, Silver, and Platinum, all share the number of protons in their nuclei but differ in the number of neutrons.
During our solar system’s first few million years, metallic asteroid cores are burned by radioactive decay as they begin to cool off, and some silver isotope produced by radioactive decay accumulates. By measuring modern isotope measurements of silver inside metal meteorites, researchers could determine when asteroid cores cooled and how fast.
The results showed that cooling was rapid and possibly due to severe collisions with other bodies, which tore off a protective layer containing asteroids and put their metal in the freezer space. While rapid cooling was shown in previous studies based on silver isotope measurements, the timing was unclear.