Earliest meteorites provide new piece in planetary formation puzzle

Researchers trying to understand how the planets formed have uncovered a new clue by analysing meteorites that are older than the earth.

The research shows that the process which depleted planets and meteorites of so-called volatile elements such as zinc, lead and sodium, must have been one of the first things to happen in our nebula.

The implication of this clue is that ’volatile depletion’ may be an inevitable part of planet formation – a feature not just of our Solar System, but of many other planetary systems too.

The researchers at Imperial College London reached their conclusions after analysing the composition of primitive meteorites, coal-like rocks that are older than the earth and which have barely changed since the Solar System was made up of fine dust and gas.

Their analysis, published today in the Proceedings of the National Academy of Sciences, shows that all the components that make up these rocks are depleted of volatile elements. This means that volatile element depletion must have occurred before the earliest solids had formed.

Dr Phil Bland, from Imperial’s Department of Earth Science and Engineering, who led the research, explains: “Studying meteorites helps us to understand the initial evolution of the early Solar System, its environment, and what the material between stars is made of. Our results answer one of a huge number of questions we have about the processes that converted a nebula of fine dust and gas into planets.”

For planetary scientists, the most valuable meteorites are those that are found immediately after falling to earth, and so are only minimally contaminated by the terrestrial environment. The researchers analysed around half of the approximately 45 primitive meteorite falls in existence around the world.

All of the terrestrial planets in the Solar System as far out as Jupiter, including Earth, are depleted of volatile elements. Researchers have long known that this depletion must have been an early process, but it was unknown whether it occurred at the beginning of the formation of the Solar System, or a few million years later.

Dr Phil Bland is a member of the Impacts and Astromaterials Research Centre (IARC), which combines planetary science researchers from Imperial College London and the Natural History Museum.