In the earliest days of our solar system — before any planets had been cobbled together — the recently formed Sun was circled by cosmic gas and dust. Over time, fragments of rock formed from the dust and many of these orbiting rocks smashed together and some became the gradually larger components of planets-to-be. Others were not part of any planet formation and became asteroids orbiting the Sun, and sometimes falling to Earth as meteorites.
Scientists have found that these asteroids (and their Earth-bound pieces) remained relatively unchanged since their formation billions of years ago.
And so they provide an archive of sorts, in which the conditions of the early solar system are preserved.
Alison Hunt, a planetary scientist at ETH Zurich in Switzerland, led a team that looked at some of that early solar system history and came up with some surprising results.
She and her team at the Swiss National Centre of Competence in Research (NCCR) PlanetS found that almost all of the asteroidal-cores-turned-meteorites they studied had been formed in a short four-million-year period starting almost eight million years the solar system first came into being. A four million-year time span is short in astronomical terms and also unusual in terms of the precision achieved for the dating.
These results, and some inferences about why this period was so chaotic in the early solar system, were reported in Nature Astronomy late last month.
But before we look at why this might have happened, let’s explore a bit about how the team achieved such precise data about when many asteroids were formed.
To access this asteroid/meteorite archive, the researchers had to prepare and examine the extraterrestrial material from iron meteorites that had fallen to Earth. Once part of the metallic cores of asteroids, samples from 18 different iron meteorites were used in the analysis.
The researchers first had to dissolve the samples to be able to isolate the elements palladium, silver and platinum — the key to their efforts.
Using a mass spectrometer they measured abundances of different and identifiable isotopes of these elements, and with their results they could put tighter constraints on the timing of events in the early solar system.