Particles from early solar system found in comet dust

Scientists have discovered that interplanetary dust particles in comets contain leftovers from the early solar system, which may provide a deeper understanding of how the planets were formed.

Researchers from University of Hawaii showed that the initial solids from which the solar system was formed consisted almost entirely of amorphous silicate, carbon and ices.

This dust was mostly destroyed and reworked by processes that led to the formation of planets. Surviving samples of pre-solar dust are most likely to be preserved in comets - small, cold bodies that formed in the outer solar nebula.

In a relatively obscure class of interplanetary dust particles believed to originate from comets, there are tiny glassy grains called GEMS (glass embedded with metal and sulphides) typically only tens to hundreds of nanometres in diameter, less than 1/100th the thickness of human hair.

Using transmission electron microscopy, researchers made maps of the element distributions and discovered that these glassy grains are made up of subgrains that aggregated together in a different environment and prior to the formation of the comet parent body.

This aggregate is encapsulated by carbon of a different type than the carbon that forms a matrix gluing together GEMS and other components of cometary dust.

The types of carbon that rims the subgrains and that forms the matrix in these particles decomposes with even weak heating, suggesting that the GEMS could not have formed in the hot inner solar nebula, and instead formed in a cold, radiation-rich environment, such as the outer solar nebula or pre-solar molecular cloud.

"Our observations suggest that these exotic grains represent surviving pre-solar interstellar dust that formed the very building blocks of planets and stars," said Hope Ishii, from University of Hawaii.

"If we have at our fingertips the starting materials of planet formation from 4.6 billion years ago, that is thrilling and makes possible a deeper understanding of the processes that formed and have since altered them," Ishii added.

The team further plans to search the interiors of additional comet dust particles, especially those that were well-protected during their passage through the Earth's atmosphere.

This will help in increasing the understanding of the distribution of carbon within GEMS and the size distributions of GEMS subgrains.